Γ* The study of hadron structure using single pion electroproduction off the proton in CLAS Why single pion production electroproduction ? Because single.

γ* The study of hadron structure using single pion electroproduction off the proton in CLAS Why single pion production electroproduction ? Because single and double pion production are the two largest contributors to the total photo- and electroproduction cross sections off protons in the resonance region. The final states produced in these two exclusive channels have considerable hadronic interactions, so called the final state interactions. (FSI) FSI may be determined using the experimental data with hadronic probes. Colloquium Kijun Park Feb. 25, 2011

Colloquium @ College of William and Mary 02/25/2011 K. Park
Universe Jefferson lab accelerator provides high energetic currently up to 6GeVand high polarized around 70% continuous electron beam to three different experimental Halls simultaneously. College of William and Mary 02/25/ K. Park

Earth Jefferson lab accelerator provides high energetic currently up to 6GeVand high polarized around 70% continuous electron beam to three different experimental Halls simultaneously. College of William and Mary 02/25/ K. Park

Including Human Life Jefferson lab accelerator provides high energetic currently up to 6GeVand high polarized around 70% continuous electron beam to three different experimental Halls simultaneously. College of William and Mary 02/25/ K. Park

Over 98% of the mass of visible matters nucleons Jefferson lab accelerator provides high energetic currently up to 6GeVand high polarized around 70% continuous electron beam to three different experimental Halls simultaneously. College of William and Mary 02/25/ K. Park

In terms of scale …. College of William and Mary 02/25/ K. Park

In terms of composition … Nucleons protons, neutrons Hypersons Baryons(fermions) L, S, W,… composite fermions contain three valence quarks or antiquarks. Pentaquarks Hadrons q+ , X--, ??? particle strongly interacting composite particles Mesons(bosons) Pseudoscalar composite bosons Contain one valence quark and one antiquark. pions, kaons, h, D, B, … Vector Atomic nuclei J/y, r, w, f, K*… consist of protons and neutrons. Atoms consists of a small, heavy nucleus surrounded by a relatively large, light cloud of electrons Hadrons Main article: Hadron Hadrons are defined as strongly interacting composite particles. Hadrons are either: Composite fermions, in which case they are called baryons. Composite bosons, in which case they are called mesons. Quark models, first proposed in 1964 independently by Murray Gell-Mann and George Zweig (who called quarks "aces"), describe the known hadrons as composed of valence quarks and/or antiquarks, tightly bound by the color force, which is mediated by gluons. A "sea" of virtual quark-antiquark pairs is also present in each hadron. strongly interacting composite particles Atomic nuclei Atomic nuclei consist of protons and neutrons. Each type of nucleus contains a specific number of protons and a specific number of neutrons, and is called a nuclide or isotope. Nuclear reactions can change one nuclide into another. See table of nuclides for a complete list of isotopes. Atoms Atoms are the smallest neutral particles into which matter can be divided by chemical reactions. An atom consists of a small, heavy nucleus surrounded by a relatively large, light cloud of electrons. Each type of atom corresponds to a specific chemical element. To date, 118 elements have been discovered, while only the first 112 have received official names. Refer to the periodic table for an overview. The atomic nucleus consists of protons and neutrons. Protons and neutrons are, in turn, made of quarks. Molecules Molecules are the smallest particles into which a non-elemental substance can be divided while maintaining the physical properties of the substance. Each type of molecule corresponds to a specific chemical compound. Molecules are a composite of two or more atoms. See list of compounds for a list of molecules. Molecules the smallest particles into which a non-elemental substance College of William and Mary 02/25/ K. Park

particle College of William and Mary 02/25/ K. Park

Experiments Where/what/how can we measure ?
Why single pion production electroproduction ? Because single and double pion production are the two largest contributors to the total photo- and electroproduction cross sections off protons in the resonance region. The final states produced in these two exclusive channels have considerable hadronic interactions, so called the final state interactions. (FSI) FSI may be determined using the experimental data with hadronic probes. Experiments College of William and Mary 02/25/ K. Park

Jefferson lab accelerator provides high energetic currently up to 6GeVand high polarized around 70% continuous electron beam to three different experimental Halls simultaneously. College of William and Mary 02/25/ K. Park

CEBAF Large Acceptance Spectrometers A B C Jefferson lab accelerator provides high energetic currently up to 6GeVand high polarized around 70% continuous electron beam to three different experimental Halls simultaneously. College of William and Mary 02/25/ K. Park

Emax GeV Imax mA Duty Factor 100% sE/E Beam P ~ 85% Eg(tagged) ~ GeV CEBAF Large Acceptance Spectrometers A B C Jefferson lab accelerator provides high energetic currently up to 6GeVand high polarized around 70% continuous electron beam to three different experimental Halls simultaneously. College of William and Mary 02/25/ K. Park

The CLAS Collaboration =41 institutions 11 countries Arizona State University, Tempe, AZ University Bari, Bari, Italy University of California, Los Angeles, CA California State University, Dominguez Hills, CA Carnegie Mellon University, Pittsburgh, PA Catholic University of America CEA-Saclay, Gif-sur-Yvette, France Christopher Newport University, Newport News, VA University of Connecticut, Storrs, CT Edinburgh University, Edinburgh, UK University Ferrara, Ferrara, Italy Florida International University, Miami, FL Florida State University, Tallahassee, FL George Washington University, Washington, DC University of Glasgow, Glasgow, UK Old Dominion University, Norfolk, VA Rensselaer Polytechnic Institute, Troy, NY Rice University, Houston, TX University of Richmond, Richmond, VA University of Rome Tor Vergata, Italy University of South Carolina, Columbia, SC Thomas Jefferson National Accelerator Facility, Newport News, VA Union College, Schenectady, NY Virginia Polytechnic Institute, Blacksburg, VA University of Virginia, Charlottesville, VA College of William and Mary, Williamsburg, VA Yerevan Institute of Physics, Yerevan, Armenia Brazil, Germany, Morocco and Ukraine, , have individuals or groups involved with CLAS, but with no formal collaboration at this stage. University of Grenoble, Grenoble, France Idaho State University, Pocatello, Idaho INFN, Laboratori Nazionali di Frascati, Frascati, Italy INFN, Sezione di Genova, Genova, Italy Institut de Physique Nucléaire, Orsay, France ITEP, Moscow, Russia James Madison University, Harrisonburg, VA Kyungpook University, Daegu, South Korea University of Massachusetts, Amherst, MA Moscow State University, Moscow, Russia University of New Hampshire, Durham, NH Norfolk State University, Norfolk, VA Ohio University, Athens, OH College of William and Mary 02/25/ K. Park

Outlook Introduction Transition Form resonances Scaling DIS Exclusive Hard Process in DIS Summary College of William and Mary 02/25/ K. Park

Electromagnetic Probe
Why are you using e.m. probe for hadron structure study ? Why single pion production electroproduction ? Because single and double pion production are the two largest contributors to the total photo- and electroproduction cross sections off protons in the resonance region. The final states produced in these two exclusive channels have considerable hadronic interactions, so called the final state interactions. (FSI) FSI may be determined using the experimental data with hadronic probes. Electromagnetic Probe College of William and Mary 02/25/ K. Park

Why excitations of the nucleon ?
Investigation tool for Nucleon where : ground state nucleon Elastic Scattering Deep Inelastic Scattering Resonance Excitation : quark-gluon short dist. : internal structure of ground & excited state Nucleons/baryons are complex enough to Foundation of Quark model “reveal physics hidden from us in mesons” The hadrons constitute most of the visible matter. The contribution of the current quark masses into total baryon mass is very small; most of the hadron mass comes from strong interactions. Investigation of the spectrum and the internal structure of the hadrons provides information about the underlying strong interactions. One of the really interesting physics topics is to investigate the strong interactions in the confinement regime. 1. Elastic Scattering Target stays intact and Q2/(2m_p (E’-E0)= 1 holds. A good tool to study the ground state of the nucleon 2. Deep Inelastic Scattering Energy transfer is large, target is broken apart. A good tool to study the quark-gluon content of the nucleon at small distances. 3. Resonance excitation The target is excited into a single bound system. Allows us to study the internal structure of the ground and the excited states, and very useful for the exclusive reactions. ... baryons were at the foundation of the development of the quark model by Gell-Mann and Zweig. And a hidden quantum number, later called "color", was introduced by Greenberg to explain why the Delta++ resonance, which is represents the largest cross section in pi+-proton scattering, could even exist. The colorless quark model would not allow its excitation. Key : Nπ decay channels of the intermediate excited states. This analysis covers not only Δ(1232) but high resonance states. Study of Resonance to understand Nucleon Structure Most Studies for NΔ(1232) and NN*(1535) using pπ0, pρ channels States with I=1/2 couple more to the nπ+ than pπ0 Cross Section & Asymmetry gives us information on resonances in excited states In mathematics, an abelian group, also called a commutative group, is a group such that for all a and b in G. In other words, the order of elements in a product doesn't matter. Such groups are generally easier to understand, although large infinite abelian groups remain a subject of current research. Groups that are not commutative are called non-abelian (rather than non-commutative). Abelian groups are named after Niels Henrik Abel. Gell-Mann & Zweig - Quark Model O. Greenberg - The D++ problem/color College of William and Mary 02/25/ K. Park

Transition Form Factors
How we can describe the electroproduction of an excited state ? Why single pion production electroproduction ? Because single and double pion production are the two largest contributors to the total photo- and electroproduction cross sections off protons in the resonance region. The final states produced in these two exclusive channels have considerable hadronic interactions, so called the final state interactions. (FSI) FSI may be determined using the experimental data with hadronic probes. Transition Form Factors College of William and Mary 02/25/ K. Park

Why E.M. probes for study of hadron structure ? π,r, ... Probe resolution B=N,N*,D* N low high (GeV) Q2=6 GeV2 Why do we use electromagnetic probes to study hadron structure? I think the answer is that the e.m. probe allows us to efficiently address the central question of hadron physics: What are the relevant degrees of freedom at varying distance scales? To simply illustrate this I show here the quark propagator mass calculated in LQCD, Dyson Schwinger, and other approaches as a function of the momentum transfer. In the e.m. probe we can vary the resolution and momentum transfer. In doing so, we probe the effective degrees of freedom in the nucleon from meson-nucleon, to constituent quarks, to elementary partons. The study of nucleon resonance transitions provides a testing ground for our understanding of these effective degrees of freedom. College of William and Mary 02/25/ K. Park 20

Why E.M. probes for study of hadron structure ? π,r, ... Probe resolution B=N,N*,D* N The study of nucleon resonance transitions provides a testing ground for our understanding of these effective D.o.F low high (GeV) Q2=6 GeV2 Q2=12 GeV2 Access to the essence of non-perturbative strong interactions Why do we use electromagnetic probes to study hadron structure? I think the answer is that the e.m. probe allows us to efficiently address the central question of hadron physics: What are the relevant degrees of freedom at varying distance scales? To simply illustrate this I show here the quark propagator mass calculated in LQCD, Dyson Schwinger, and other approaches as a function of the momentum transfer. In the e.m. probe we can vary the resolution and momentum transfer. In doing so, we probe the effective degrees of freedom in the nucleon from meson-nucleon, to constituent quarks, to elementary partons. The study of nucleon resonance transitions provides a testing ground for our understanding of these effective degrees of freedom. generation of > 97% of nucleon mass enhance capability to map out QCD b function in constituent regime College of William and Mary 02/25/ K. Park 21

SU(6)xO(3) Classification of Baryons
Lowest Baryon Supermultiplets SU(6)xO(3) Symmetry Particle Data Group Using the SU(6) x O(3) classification scheme of the symmetric CQM, known states can be sorted into super multiplets of energy and orbital angular momentum of the 3-quark system. The examples shown are the ones which I will discuss. Then there are the well known empty boxes which are states that SU(6) symmetry predicts but haven’t been identified in experimental analysis, and there are questions about the underlying degrees-of-freedom of some of the well known states such as the Roper and S11. Studying the transition from the ground state will allow us to make more definite statement about the nature of these states. SU(6) : describe the symmetry properties of the spin-flavor wave function O(3) : the symmetry group for orbital angular momentum of the 3quarks system According to their symmetry properties, principal energy levels N, and orbital angular momentum L, the 3quark states can be associated with supermultiplets. In the models the quarks are not in spherically symmetric configuration but rather in a diquark-quark configuration with reduced number of degrees of freedom. => Electroproduction of nucleon resonances should be a very sensitive tool to distinguish between these alternative configuration. College of William and Mary 02/25/ K. Park 22

Lowest Baryon Supermultiplets SU(6)xO(3) Symmetry Particle Data Group D13(1520) S11(1535) D33(1700) Using the SU(6) x O(3) classification scheme of the symmetric CQM, known states can be sorted into super multiplets of energy and orbital angular momentum of the 3-quark system. The examples shown are the ones which I will discuss. Then there are the well known empty boxes which are states that SU(6) symmetry predicts but haven’t been identified in experimental analysis, and there are questions about the underlying degrees-of-freedom of some of the well known states such as the Roper and S11. Studying the transition from the ground state will allow us to make more definite statement about the nature of these states. SU(6) : describe the symmetry properties of the spin-flavor wave function O(3) : the symmetry group for orbital angular momentum of the 3quarks system According to their symmetry properties, principal energy levels N, and orbital angular momentum L, the 3quark states can be associated with supermultiplets. In the models the quarks are not in spherically symmetric configuration but rather in a diquark-quark configuration with reduced number of degrees of freedom. => Electroproduction of nucleon resonances should be a very sensitive tool to distinguish between these alternative configuration. P33(1232) P11(1440) College of William and Mary 02/25/ K. Park 23

* There are questions about underlying degrees-of-freedom of some well known state like P11, S11, D13 Lowest Baryon Supermultiplets SU(6)xO(3) Symmetry Particle Data Group * Study of transition from ground state allows make more definite statement about the nature D13(1520) S11(1535) D33(1700) Missing States? Using the SU(6) x O(3) classification scheme of the symmetric CQM, known states can be sorted into super multiplets of energy and orbital angular momentum of the 3-quark system. The examples shown are the ones which I will discuss. Then there are the well known empty boxes which are states that SU(6) symmetry predicts but haven’t been identified in experimental analysis, and there are questions about the underlying degrees-of-freedom of some of the well known states such as the Roper and S11. Studying the transition from the ground state will allow us to make more definite statement about the nature of these states. SU(6) : describe the symmetry properties of the spin-flavor wave function O(3) : the symmetry group for orbital angular momentum of the 3quarks system According to their symmetry properties, principal energy levels N, and orbital angular momentum L, the 3quark states can be associated with supermultiplets. In the models the quarks are not in spherically symmetric configuration but rather in a diquark-quark configuration with reduced number of degrees of freedom. => Electroproduction of nucleon resonances should be a very sensitive tool to distinguish between these alternative configuration. P33(1232) P11(1440) College of William and Mary 02/25/ K. Park 24

Why excitations of the nucleon ? Nucleons represent the real world, they must be at the center of any discussion on “why the world is the way it is” The contribution of the current quark masses into total baryon mass is very small Most of the hadron mass comes from strong fields. The hadrons constitute most of the visible matter. The contribution of the current quark masses into total baryon mass is very small; most of the hadron mass comes from strong interactions. Investigation of the spectrum and the internal structure of the hadrons provides information about the underlying strong interactions. One of the really interesting physics topics is to investigate the strong interactions in the confinement regime. 1. Elastic Scattering Target stays intact and Q2/(2m_p (E’-E0)= 1 holds. A good tool to study the ground state of the nucleon 2. Deep Inelastic Scattering Energy transfer is large, target is broken apart. A good tool to study the quark-gluon content of the nucleon at small distances. 3. Resonance excitation The target is excited into a single bound system. Allows us to study the internal structure of the ground and the excited states, and very useful for the exclusive reactions. ... baryons were at the foundation of the development of the quark model by Gell-Mann and Zweig. And a hidden quantum number, later called "color", was introduced by Greenberg to explain why the Delta++ resonance, which is represents the largest cross section in pi+-proton scattering, could even exist. The colorless quark model would not allow its excitation. Key : Nπ decay channels of the intermediate excited states. This analysis covers not only Δ(1232) but high resonance states. Study of Resonance to understand Nucleon Structure Most Studies for NΔ(1232) and NN*(1535) using pπ0, pρ channels States with I=1/2 couple more to the nπ+ than pπ0 Cross Section & Asymmetry gives us information on resonances in excited states In mathematics, an abelian group, also called a commutative group, is a group such that for all a and b in G. In other words, the order of elements in a product doesn't matter. Such groups are generally easier to understand, although large infinite abelian groups remain a subject of current research. Groups that are not commutative are called non-abelian (rather than non-commutative). Abelian groups are named after Niels Henrik Abel. College of William and Mary 02/25/ K. Park

Electroproduction Amplitudes photocoupling amplitudes → A1/2, A3/2 and S1/2 Pion electroproduction multipole amplitude → El, Ml and Sl . l : the orbital angular momentum in Nπ system. ± sign : spin of proton couples to the orbital momentum. p g* N N* Electroproduction of hadronic final states via s-channel resonance decay. A: transverse coupling S : scalar coupling respect to the total helicity of the gammaN system. The electroproduction of an excited state can be described in terms of 3 photocoupling amplitudes A1/2, A3/2 and S1/2 . We still need to learn a lot more about the light quark baryon spectrum. It has been studied mostly with pion probes. However, there may be many states that do not coupleto pions, especially higher mass state, while possibly coupling to photons. The spectrum can tell us about the underlying symmetry properties due to different quark-gluon configurations, or interaction mechanism At different photon virtualities we probe how the relevant dof change as a function of the distance scale. The quantities of interest are the helicity amplitudes A1/2,... as a function of Q2. Since both photon and nucleon carry spin, we probe the spin structure in the regime of strong QCD. Our main tool in resonance studies is meson production. However, mesons are not only produced via resonance decays. In order to understand the full production mechanism in terms of resonant and non-resonant amplitudes we need to further develop, what one may call the Standard Model of meson production. Finally, N* electroexcitation allows us to better understand the observed connections between the nucleon resonance region and the deeply inelastic regime. A1/2, A3/2,S1/2 El, Ml ,Sl College of William and Mary 02/25/ K. Park

Electroproduction Amplitudes Light quark baryon spectrum (mostly pion probes) Many high mass states couple to possibly photon instead of pion Diff. photon virtuality can probe how relevant D.o.F change as distance scale Both photon, nucleon carry spin → probe the spin strucure in QCD p g* N N* Electroproduction of hadronic final states via s-channel resonance decay. A: transverse coupling S : scalar coupling respect to the total helicity of the gammaN system. The electroproduction of an excited state can be described in terms of 3 photocoupling amplitudes A1/2, A3/2 and S1/2 . We still need to learn a lot more about the light quark baryon spectrum. It has been studied mostly with pion probes. However, there may be many states that do not coupleto pions, especially higher mass state, while possibly coupling to photons. The spectrum can tell us about the underlying symmetry properties due to different quark-gluon configurations, or interaction mechanism At different photon virtualities we probe how the relevant dof change as a function of the distance scale. The quantities of interest are the helicity amplitudes A1/2,... as a function of Q2. Since both photon and nucleon carry spin, we probe the spin structure in the regime of strong QCD. Our main tool in resonance studies is meson production. However, mesons are not only produced via resonance decays. In order to understand the full production mechanism in terms of resonant and non-resonant amplitudes we need to further develop, what one may call the Standard Model of meson production. Finally, N* electroexcitation allows us to better understand the observed connections between the nucleon resonance region and the deeply inelastic regime. A1/2, A3/2,S1/2 El, Ml ,Sl College of William and Mary 02/25/ K. Park

Thomas Jefferson National Accelerator Facility CEBAF Large Acceptance Spectrometers e- e- CLAS consist of 4 detector systems such as DC, CC, TOF, EC Torus Magnet : superconductivity to make different curvature for charged particles And DC for particle’s tracking information which can provide its 3momentum information Then time-of-flight measure by TOF scintillator to dertmine the particle’s mass combine with 3momentum. π+ College of William and Mary 02/25/ K. Park

Why it is interesting ? Diagrams contributing into nπ+ electroproduction Study of Resonance to understand Nucleon Structure Most Studies for NΔ(1232) and NN*(1535) using pπ0, pρ channels States with I=1/2 couple more to the nπ+ than pπ0 Cross Section & Asymmetry gives us information on resonances in excited states College of William and Mary 02/25/ K. Park

Cross section & Asymetry Single pion electroproduction Cross Section Asymmetry Physics motivation College of William and Mary 02/25/ K. Park

D(1232) Resonance g M1 e e / P(938) J=1/2 Δ(1232) J=3/2 e e / Spin J=3/2 , Isospin I=3/2. From angular momentum and parity conservation γN  Δ transition can be induced by E2, M1 and C2 multipoles. SU(6)xO(3) symmetric quark model describes γN  Δ transition as a single quark spin flip. The N-Delta has been measured for more than 30 years. But only in the past decade have the experimental and analysis tools become accurate enough to determine. One of the first observed baryon resonances. Spin J=3/2 and isospin I=3/2. From angular momentum and parity conservation γN  Δ transition can be induced by E2, M1 and C2 multipoles. SU(6)xO(3) symmetric quark model describes γN  Δ transition as a single quark spin flip. If SU(6)xO(3) spatial wave functions are pure L=0, then γN  Δ transition can only be induced by j=1 photons, i.e. only M1+ allowed. D-waves in the wave function will allow for E1+ and S1+ contributions. More sophisticated models allow for explicit pion degrees of freedom (pion cloud). pion cloud can also introduce E1+ and S1+ contributions. REM , RSM College of William and Mary 02/25/ K. Park

Multipole Ratios – before 2001 REM RSM This shows the data on the electric quadrupole of magnetic dipole ratio and the scalar quadrupole to magnetic dipole ratio. The colored points are mostly from the seventies and exhibit large systematic discrepancies. The more recent data indicate that REM is small and negative, -2% to -3%, and has a weak Q2 dependence, while RSM may have a stronger Q2 dependence if one ignores this point. Today, the emphasis is on control of systematics. While in spectrometer experiments the kinematics needs to be adjusted many times during a measurement CLAS measures all kinematics simultaneously. College of William and Mary 02/25/ K. Park

Transition to the 2nd Resonance Region Measure Q2 dependence of Transition F.F. Poorly understood in nrCQMs. 1) lower mass, 2) wrong sign of photo-coupling Other models: - Light front kinematics (relativity) - Hybrid baryon with gluonic excitation |q3G> - Quark core with large meson cloud |q3m> - Nucleon-sigma molecule |Nσ> - Dynamically generated Nπ resonance P11(1440) Hard form factor (slow fall off with Q2) Not a quark resonance, but KΣ dynamical system? S11(1535) In the so-called 2nd resonance region we have 3 nucleon states, the famous Roper, the S11 and D13. Each one of them has distinctive features that makes them important to study. The Roper is poorly understood in CQM. The mass is much too low and the photocoupling amplitude has the wrong sign. Alternative models have been developed that use LC kinematics, describe the state as a hybrid, …. The S11 exhibits a hard form factor. It has also been described as a dynamical K-Sigma system. The D13 is predicted in QM’s to rapidly change its helicity structure from 3/2 to ½ dominance. Indications of this have been seen, but no systematic study has been done. P11(1440) = [56,0+] Quark and bag model predict higher mass (several x100MeV) than observed mass recent qLQCD simulations show even a much larger mass for first excited state of the nucleon wrong mass ordering between P11(1440) and S11(1535) states Non-relativistic CQMs cannot explain sign of photocoupling amplitude A1/2 (S. Capstick, I. Aznauryan) Change of helicity structure with increasing Q2 from λ=3/2 dominance to λ=1/2 dominance, predicted in nrCQMs, pQCD. D13(1520) College of William and Mary 02/25/ K. Park 33

Roper Resonance : P11(1440) Cano-Gonzalez Capstick Simula CQM : N=2 radially excited state(Close, Capstick, Simula). Hard Quark core and a Vector Meson cloud (Cano-Gonzalez). q3G ( Li-Burkert). Li-Burkert Close Capstick Roper signature has been clearly seen in πN and γN reactions. The low mass of P11(1440) has always been a mystery. CQM considers it as an N=2 radially excited state(Close, Capstick, Simula). Roper can also be a system consisting of a hard quark core and a vector meson cloud (Cano-Gonzalez). Suggested (Li-Burkert) that Roper can be a hybrid states with an explicit gluonic degree of freedom (q3G). Recently there were suggestions that P11(1440) is a pentaquark state. Various Q2 dependences for transition form-factors are predicted by different models. Simula Cano-Gonzalez Li-Burkert Close College of William and Mary 02/25/ K. Park

Roper Resonance : P11(1440) ????? CQM : N=2 radially excited state(Close, Capstick, Simula). Hard Quark core and a Vector Meson cloud (Cano-Gonzalez). q3G ( Li-Burkert). Experimental data is crucial !! ????? Roper signature has been clearly seen in πN and γN reactions. The low mass of P11(1440) has always been a mystery. CQM considers it as an N=2 radially excited state(Close, Capstick, Simula). Roper can also be a system consisting of a hard quark core and a vector meson cloud (Cano-Gonzalez). Suggested (Li-Burkert) that Roper can be a hybrid states with an explicit gluonic degree of freedom (q3G). Recently there were suggestions that P11(1440) is a pentaquark state. Various Q2 dependences for transition form-factors are predicted by different models. College of William and Mary 02/25/ K. Park

UIM and DR fit at low and high Q2 Number of data points >50,000 Ee = 1.515, 1.645, 5.754GeV K.Park et al., (CLAS) Phys. Rev. C 77, , (2008). Observable Q2 # of data points 0.40 0.65 3,530 3,818 2,308 1,716 33,000 956 805 918 812 3,300 0.375 0.750 172 412 Low Q2 : Aznauryan et al., PRC 71, , (2005). PRC 72, , (2005). high Q2 for Roper : Aznauryan et al., and CLAS collaboration arXiv, 0804,0447 (2008). Low Q2 : I. Aznauryan et al., PRC 71, , (2005)., PRC 72, , (2005). High Q2 on Roper : I. Aznauryan et al., (CLAS), arXiv: College of William and Mary 02/25/ K. Park

Q2 dependence of N-D transition amplitudes Magnetic Dipole Form Factor Quadrupole Ratios CLAS Hall A Hall C MAMI Pion cloud REM QM CLAS Hall A Hall C MAMI Pascalutsa, Vanderhaeghen Sato, Lee RSM 0.2 No sign for onset of asymptotic behavior, REM→+100%, RSM→ const. REM remains negative and small, RSM increases in magnitude with Q2. Meson-baryon contributions needed to describe multipole amplitudes College of William and Mary 02/25/ K. Park

Multipole Ratios – before 2001 Precise multipole ratios: δREM, δRSM < % REM remains small and negative at -2% to -3.5% from 0 ≤ Q2 ≤ 6 GeV2. No trend towards asymptotic behavior. Helicity conservation - REM→+100 (%). RSM negative and increase in magnitude. Helicity conservation – RSM → constant Dynamical models allow description of multipole ratios in large Q2 range. REM < 0 favors oblate shape of Δ and prolate shape of the proton at large distances. REM REM<0 RSM At high Q2 REM remains small at a few % and negative in contradiction to the predicted asymptotic behavior of REM -> +100% . Similar, RSM rises in magnitude but also shows no signs of becoming constant. These are challenges to theory. If we zoom in on the lower Q2 part Oblate : 구체가 편평한…편원… Prolate : 편장한 …폭이 퍼진… R_EM < 0 : Oblate R-EM > 0 : prolate REM>0 College of William and Mary 02/25/ K. Park 38

Fit to p+ diff. cross sections, Structure functions DR DR w/o P11 UIM DR UIM College of William and Mary 02/25/ K. Park

P11(1440) CQM Comparison at low and high Q2 K.Park et al., (CLAS) Phys. Rev. C 77, , (2008). I. G. Aznauryan, V. Burkert, K.Park et al., (CLAS) Phys. Rev. C 78, , (2008). 1.Weber, PR C41(1990) Capstick..PRD51(1995)3598 3.Simula…PL B397 (1997)13 4.Riska..PRC69(2004)035212 5.Aznauryan, PRC76(2007)025212 6.Cano PL B431(1998)270 Non-relativistic CQ Models do not reproduce sign of A1/2 at Q2=0, and show no zero-crossing. Relativistic CQ Models (LC) give correct sign and show zero-crossing but miss strength at Q2=0. In the Roper case the first systematic analyses was done in a combined analysis of pi+ and pi0 data, and of p-pi+-pi- data from CLAS that showed the rapid drop of A1/2 followed by a zero-crossing, while S1/2 is large and positive. The pion analyese were done using both UIM and Dispersion relations which gave consistent results. nrQCM cannot incorrect sign and no zero crossing. CQM on LC have correct sign and zero cross sing but lack strength at photon point, which maybe due to pion effects. These effect should be less important at higher Q2. → go to higher Q2 to reduce effects of meson contributions. College of William and Mary 02/25/ K. Park 40

P11(1440) Transition high Q2, Hybrid State ? g Analysis with Unitary Isobar Model (UIM) Fixed-t Dispersion Relations (DR) q3 G Nπ, pπ+π- DR UIM nπ+ In a nonrelativistic approximation A1/2(Q2) and S1/2(Q2) behave like the γ*NΔ(1232) amplitudes. nπ+ pπ0 Include > 35,000 data points in fits. Suppression of S1/2 has its origin in the form of vertex γq→qG. It is practically independent of relativistic effects Z.P. Li, V. Burkert, Zh. Li, PRD46 (1992) 70 The analysis with the UIM model results in the following behavior. A large positive amplitude A1/2 peaking near 2 GeV2 followed by a smooth falloff. The UIM and DR analyses give consistent results. previous data College of William and Mary 02/25/ K. Park 41

Legendre moments of Np for low and high Q2 I. G. Aznauryan, V. Burkert, K.Park et al., (CLAS) Phys. Rev. C 78, , (2008). Nπ Nππ Nπ, Nππ LCQM Q3G D0 L+T D2 L+T D0 LT’ pπ0 nπ+ DR UIM Q2=0.4 GeV2 Sign change observed at same Q2 Magnitudes of A1/2 and S1/2 consistent in the two channels. High Q2 behavior consistent with dominant radial excitation of nucleon. Rules out gluonic excitation College of William and Mary 02/25/ K. Park

Helicity Amplitudes P11(1440) L. Tiator and M. Vanderhaeghen, Phys. Lett. B 672, 344 (2009) P11(1440) Light (dark) regions: positive (negative) charge densities proton(PT) and P11 are in LF helicity +½ state.. proton and P11 polarized along x-axis with opposite spin projections. ρ0 bx (fm) by (fm) ρT bx (fm) by (fm) Meson-Baryon Dressing absolute meson-baryon cloud amplitudes (EBAC) In a quark picture, the proton→ N(1440)P11 transition is dominated by up quarks in a central region of radius ~0.4 fm, and by down quarks in an outer band up to 0.8 fm. quark core contributions (constituent quark models) College of William and Mary 02/25/ K. Park

Negative Parity States in 2nd N* Region * It will be submitted to Phys. Rev. D soon Hard form Factor (slow fall off vs. Q2) Not a quark resonance, but a dynamically generated resonance of coupled channel, e.g, πN, ηp, ΚΣ, ΚΛ S11(1535) D13(1520) Change of helicity structure with increasing Q2 from λ=3/2 dominance to λ=1/2 dominance as predicted in CQMs, pQCD nrCQM Prediction from the 1970’s !! College of William and Mary 02/25/ K. Park

Helicity Amplitudes S11(1535) H. Denizli et al., (CLAS) Phys. Rev. C 76, , (2007). I. G. Aznauryan, V. Burkert, K.Park et al., (CLAS) Phys. Rev. C 80, , (2009). LC SR LCQM CLAS 2007 CLAS 2002 previous results Analysis of pη assumes S1/2=0 CLAS pη CLAS nπ+ HallC pη Branching ratios βNπ = βNη = 0.45 Eta channel does not have P11 interference nut pion channel has strong interference with P11. This allows us to extract the S1/2 from pion channel. Therefore, pion channel is crutial to be studied. A1/2 (Q2) from Nπ and pη are consistent First extraction of S1/2(Q2) amplitude. College of William and Mary 02/25/ K. Park

Helicity Amplitudes D13(1520) I. G. Aznauryan, V. Burkert, K.Park et al., (CLAS) Phys. Rev. C 80, , (2009). nπ+ pπ0 Nπ, pπ+π- PDG pπ0 First data set that allows determination of S1/2(Q2) Clear evidence of helicity switch from λ=3/2 dominance at Q2=0 to λ=1/2 dominance at high Q2 => This is a stringent prediction of the CQM. @ nrCQM This graph show the resulting D13 transition amplitudes. The right graph shows the A3/2 amplitude which is dominant at the photon point but drops rapidly with Q2. The A1/2 amplitude, which is small at Q2=0, rises in magnitude and becomes dominant Q2> 1 GeV2. Such behavior is predicted in the VQM, which in its simplest version (only spin and orbit flip single quark transitions) predicts for the ratio of A1/2 and A3/2. At high Q2 A1/2 is predicted to become dominant. A1/2 = helicity conserving amplitude A3/2 = helicity non-conserving amplitude. CQMs and pQCD Ahel → +1 at Q2→∞ College of William and Mary 02/25/ K. Park

Transition charge density fo D13(1520) P bx (fm) by (fm) Proton and N(1520)D13 polarized along x-axis with opposite spin projections Nearly full charge separation perpendicular to polarization vector in transverse space. ρT by (fm) ρ0 bx (fm) Proton and N(1520)D13 are in LF helicity +½ state, transition is dominated by negative charge near center (details sensitive to large Q2 extrapolation), and by positive charge in a region up to 1.3 fm. Very strong quadrupole pattern extending to large radius. College of William and Mary 02/25/ K. Park

Resonance scaling behavior I. G. Aznauryan, V. Burkert, K.Park et al., (CLAS) Phys. Rev. C 80, , (2009). η Resonance transition amplitudes should scale asymptotically as: Q3A1/2 → const. Data appear to reach a plateau, but conclusive tests of scaling require higher Q2. π S11 P11 D13 College of William and Mary 02/25/ K. Park

Multipole amplitudes for g*p np+ P11(1440) P11(1440) At Q2= GeV2, resonance behavior is seen in these amplitudes more clearly than Q2=0 Imaginary Real Im Re(DR) Re(UIM) DR and UIM give close results for real parts of multiple amplitudes College of William and Mary 02/25/ K. Park

what we can learn from measurements … Amplitude determined up to 4.5GeV2 using two different analysis approaches (DR, UIM) Sign change of A1/2 Gluonic excitation ruled out due to Q2 dependence of both amplitudes High Q2 behavior consistent with radial excitation of the nucleon as in CQM P11(1440) Amplitude measured in nπ+ channel, for the first time Hard A1/2 form factor confirmed First measurement of S1/2 , sign inconsistent with CQM S11(1535) Rapid switch of helicity structure from A3/2 dominance to A1/2 dominance at Q2 > 0.6GeV2 D13(1520) College of William and Mary 02/25/ K. Park

Impact of Roper A1/2, S1/2 data on Model Comparison of MAID 08 and JLab analysis A1/2 L. Tiator MAID 07 And new Maid analysis with K. Park data MAID 08 S1/2 S1/2 College of William and Mary 02/25/ K. Park 52

Impact of D13(1520) A3/2, A1/2 data on Model Get more reliable estimation of systematics from the good agreement for A3/2 and S1/2 determination among various resonance extractions SAID model ? Resonance fit done over a narrow range in W but for all Q2 College of William and Mary 02/25/ K. Park

Deep Inelastic Scattering Region
Why DIS is interested ? Forward scattering Our main tool in resonance studies is meson production. However, mesons are not only produced via resonance decays. In order to understand the full production mechanism in terms of resonant and non-resonant amplitudes we need to further develop, what one may call the Standard Model of meson production. Therefore, N* electroexcitation allows us to better understand the observed connections between the nucleon resonance region and the deeply inelastic regime. Deep Inelastic Scattering Region College of William and Mary 02/25/ K. Park

Theoretical Motivation Instead of remarking the physics motivation, I would like to bring the hand-bag diagram of DVCS and DVMP in GPD College of William and Mary 02/25/ K. Park

Theoretical Motivation Pert. hard part soft part Successful factorization GPD : Successful factorization between hard part and soft part at Q2->infinit, Xbj=Q2/(Q2+W2), t << fixed region @ Q2 ∞ , t << fixed College of William and Mary 02/25/ K. Park

Why is it interesting ? Photoproduction !! t-channel scaling behavior at large angle Generalized scaling law appears at above resonance region and large angle(θ=90o) L.Y. Zhu, PRL 91, (2003) Non-pertubative transition between pion and baryon in backward angle In the scaling regime, above resonances, Cross section will be composited by scaling parameter s with powering of the number of consistuents quarks in initial and final states. Very naively speaking, angle dependent cross section shows the unique scaling behavior in its (forward, middle, backward angle) region Investigation of Transition Distribution Amplitude J.P. Lansberg, B. Pire, PRD75, (2007) College of William and Mary 02/25/ K. Park

Analysis W>2GeV cut Only for 9 xbj bins CRS with low t ACC Preliminary CRS with high t ACC Point out why we need high t channel. Previously scaling law has been observed with photon prodution data. Since we cab extend high t region which allows us to access the scaling regime but electroproction data, which means we can have additional physics information can achieve in terms of Q2 College of William and Mary 02/25/ K. Park

Deep Inelastic Scattering Region
Why DIS is interested ? Backward scattering Our main tool in resonance studies is meson production. However, mesons are not only produced via resonance decays. In order to understand the full production mechanism in terms of resonant and non-resonant amplitudes we need to further develop, what one may call the Standard Model of meson production. Therefore, N* electroexcitation allows us to better understand the observed connections between the nucleon resonance region and the deeply inelastic regime. Deep Inelastic Scattering Region College of William and Mary 02/25/ K. Park

Theoretical Motivation What about u <<, DVCS ? Pert. Pert. hard part ??? soft part Non-pert. Part does not describe the Hadron  Hadron transition IF u <<, DVCS (PRD71 (2005)) -> non-pert. Part does not describe H-> H transition by GPD Rather than Hadron->gamma, Baryon -> meson transition ??? Need a Transition DA (TDAs) College of William and Mary 02/25/ K. Park

Theoretical Motivation Non-pertubative transition between pion and baryon in backward angle Investigation of Transition Distribution Amplitude B. Pire, L. Szymanowski PRD71, (2005) Pert. Pert. Mesonic TDA pp  g*p0 @ GSI pp  g*g t << @ GSI pp  J/p0 @ GSI e+e- B-factories g*g  r+p- GSI (PANDA collaboration) =>FAIR Rather than Hadron->gamma, Amplitude = Correlation between meson →g transition Large Q2 would provide hard scale with pert. expansion College of William and Mary 02/25/ K. Park

Theoretical Motivation Non-pertubative transition between pion and baryon in backward angle Investigation of Transition Distribution Amplitude J.P. Lansberg, B. Pire, PRD75, (2007) Pert. Pert. Pert. Baryonic TDA e’p+ n u << , t CLAS e’ph, e’ppo @ CLAS w at 180o @ Hall-C JLAB 12GeV g*p  pJ/ @ COMPASS Rather than Baryon -> meson transition GPD can not describe Non-perturbative part Baryon →π transition Amplitude = Meson almost stay at rest in the target(baryon) rest frame College of William and Mary 02/25/ K. Park

Preliminary cross section Blue square : data with stat. err. only Red triangle : fit with cos2f Preliminary Definitely we can observe the 2phi-modulation in cross sections. Q2 needs to be larger than 4GeV2 for the TDA mechanism to possibly dominate[B.Pire], and a study of this mechanism therefore, need data at larger Q2, which should definitely be available at the 12GeV program Average Chi2 ~ 1.74 except last Q2 bin College of William and Mary 02/25/ K. Park

σT+εσL σT+εσL Preliminary structure functions Preliminary J.P. Lansberg, B. Pire, PRD75, (2007) But p0 – calculation for x=0.8, q=180o Structure functions has been extraced with theoretical prediction. However, prediction is based on pi0 case for Xi=0.8 and theta* =180deg. College of William and Mary 02/25/ K. Park

Summary & Plans ? Overall Summary College of William and Mary 02/25/ K. Park

Polarization data to improve resonance separation New data on Q2 dependence of higher mass states An extensive program is underway with polarized photon beams and polarized target to search for new baryon states (CLAS) Large effort underway at EBAC to develop the coupled channel analysis of these and other data Proposal for a transition form factor program at high Q2 for the Jlab 12 GeV upgrade with CLAS12 We measured the differential cross section with extended –t region Hard exclusive process of meson in the backward angle opens a new window in the understand of hadronic physics in the framework of the collinear-factorization approach of QCD. Measurement of cross sections and asymmetries are crucial to develop a realistic model for the TDAs. EBAC : the Excited Baryon Analysis Center Transition matrix elements (off-diagonal) , if double-polarization (long-trans) College of William and Mary 02/25/ K. Park

Thomas Jefferson National Accelerator Facility GeV CEBAF Large Acceptance Spectrometers A B D 12GeV Upgrade Enhanced Detectors CLAS consist of 4 detector systems such as DC, CC, TOF, EC C College of William and Mary 02/25/ K. Park

New Capabilities in Halls A, B, & C, and a New Hall D
9 GeV tagged polarized photons and a 4 hermetic detector D Super High Momentum Spectrometer (SHMS) at high luminosity and forward angles C CLAS12 with new detectors and higher luminosity (1035 /cm2-s) B High Resolution Spectrometer (HRS) Pair, and specialized large installation experiments A

9 GeV tagged polarized photons and a 4 hermetic detector D Super High Momentum Spectrometer (SHMS) at high luminosity and forward angles C Thank you for your attention CLAS12 with new detectors and higher luminosity (1035 /cm2-s) B High Resolution Spectrometer (HRS) Pair, and specialized large installation experiments A College of William and Mary 02/25/ K. Park

BACKUP SLIDES

Backward angle constraint Kinematical variables GPD can not describe Non-perturbative part Baryon →π transition - J.P. Lansberg, B. Pire, PRD75, (2007) Pert. Pert. Pert. There are three main physical and phenomenological motivations. As first motivation, First evidence of resonance around 2GeV had been shown in gamma p data. And some how flattening distribution of higher mass region. Preliminary G10 data showed that enhancement of 2GeV of W region clearly. Secondly, Especially backward region processing is so unique and interesting. GPD can describe the hard part process but not soft part(non-perturbative part) in the t-channel. Backward can make constraint of t-channel which means u-channel contribution dominant. In that case, one can expects transition between hadron and meson in the soft part. (physics wide, 무엇을 탐구하나 ?) Thirdly, Resonance contribution in the u-channel (isospin ½ or 3/2 relatred baryon trajectory). Energy independent scaled cross section (ds/du) proper to exp(u) or exp(3u). These three motivations are strongly correlated to high mass and backward angle region but they are independently physics analysis topic. We tried to approach to these motivation with present data (e1-6 data : electro-production). We have one more advantageous physics observable than photo-production data. College of William and Mary 02/25/ K. Park

Assign Systematic and Model Uncertainties Background Contributions : UIM-background built from nucleon exchanges in s- and u-channel, and t-channel exchanges of π, ρ, ω mesons. Born terms in UIM and DR depend on proton, neutron, and pion form factors. For UIM the form factors of ρ and ω enter as well. Use available parameterizations of measured nucleon and pion form factors. -For GEn use parameterization that accounts for all measured values up to 1.45GeV2; assign 50% uncertainty for extrapolation into the range 1.7 <Q2 < 4.2GeV2 -For G(ρ(ω)->πγ) = GD, supported by QCD SR and quark model, assign 50% uncertainty. Quadratic summing of all uncertainties defined as systematic error I. Background contributions UIM-background built from nucleon exchanges in s- and u-channel, and t-channel exchanges of pi, rho, omega mesons. Born terms in UIM and DR depend on proton, neutron, and pion form factors. For UIM the form factors of rho and omega enter as well. Use available parameterizations of measured nucleon and pion form factors. -for Gen use parameterization that accounts for all measured values up to 1.45GeV2; assign 50% uncertainty for extrapolation into the range 1.7 <Q2 < 4.2GeV2 -for G_(rho(omega)->pi gamma) = GD, supported by QCD SR and quark model, assign 50% uncertainty. Quadratic summing of all uncertainties defined as systematic error I. College of William and Mary 02/25/ K. Park

Assign Systematic and Model Uncertainties (cont’d) Resonance Contributions : Fit (a) : all resonant amplitudes are fitted Fit (b) : assume SQTM for transverse amplitudes of resonances in [70,1] supermultiplet (connected by symmetry to S11(1535) and D13(1520)), and their longitudinal couplings=0. Use uncertainties from averaging procedure of fit(a) and fot(b) as systematic uncertainty II. Model Contributions : Average results from UIM and DR and use deviations as model uncertainties III. Resonance contribution, cont’d Fit (a) : all resonant amplitudes are fitted Fit (b) : assume SQTM for transverse amplitudes of resonances in [70,1] supermultiplet (connected by symmetry to S11(1535) and D13(1520)), and their longitudinal couplings=0. Use uncertainties from averaging procedure of fit(a) and fot(b) as systematic uncertainty II. Model contribution : Average results from UIM and DR and use deviations as model uncertainties III. Complete systematic uncertainties : * Square root of quadratic sum of uncertainties I,II, III. Complete Systematic Uncertainties Square root of quadratic sum of uncertainties I,II, III. College of William and Mary 02/25/ K. Park

Legendre Moments Δ disappears rapidly with Q2 Other structures and features remain strong Delta disappears rapidly with Q2, other structures and features remain strong College of William and Mary 02/25/ K. Park

Quark Model Fundamental particle of hadrons. Interaction : Eight gluon fields in QCD : SU(3) Complicate picture in long distances QCD Presence of Color tensor forces spin-spin interaction Simplified other degrees of freedom (pions) may be needed In the constituent quark model the nucleon consists of 3 “fat” ~300 MeV constituent quarks in a confining potential. Presence of Color tensor forces, such as spin-spin interaction, which can break the spherical symmetry of the ground state. May be too simplified, other degrees of freedom, such as pions, may be needed. College of William and Mary 02/25/ K. Park

Fixed-t Dispersion Relations for invariant Ball amplitudes (Devenish & Lyth) γ*p→Nπ Dispersion relations for 6 invariant Ball amplitudes: Unsubtracted Dispersion Relations (i=1,2,4,5,6) Subtracted Dispersion Relation College of William and Mary 02/25/ K. Park

Analysis: Some points which are specific to high Q2
From the analysis of the data at different Q2 = GeV , we have obtained consistent results for fsub(t,Q2) fsub(t,Q2) has relatively flat behavior, in contrast with π contribution: College of William and Mary 02/25/ K. Park

Analysis: some points which are specific to high Q2 (continued)
The background of UIM we use at large Q2 consists of the Born term and t-channel ρ and ω contributions At high Q2, a question can arise if there are additional t-channel contributions, which due to the gauge invariance, do not contribute at Q2=0, e.g. π(1300), π(1670), scalar dipole transitions for h1 (1170), b1(1235), a1(1260) … Such contributions are excluded by the data. College of William and Mary 02/25/ K. Park

Analysis (continued) Fitted parameters: amplitudes corresponding to: P33(1232), P11(1440) , D13(1520) , S11(1535) F15 (1680) Amplitudes of other resonances, in particular those with masses around 1700 MeV, were parameterized according to the SQTM or the results of analyses of previous data Including these amplitudes into the fitting procedure did not change the results College of William and Mary 02/25/ K. Park

P11 contribution to Legendre Moments for Peaks in Delta, D13, S11 region, broad enhancement from P11 Broad structure from 1.2 to 1.5GeV due to s-p interference terms Dip in Delta region S11-D13 interference Peaks in Δ, D13, S11 region, broad enhancement from P11 Broad structure from 1.2 to 1.5GeV due to s-p interference terms Dip in Delta region S11-DP11 interference College of William and Mary 02/25/ K. Park

Theoretical Motivation Baryonic TDA The kinematics imposes the exchange of 3 quarks in the u -channel Factorization in the generalized Bjorken limit: The object factorized from the hard part is a Transition Distribution Amplitude Interpretation at the amplitude Amplitude of probability to find a meson within the proton College of William and Mary 02/25/ K. Park

Theoretical Motivation TDA and DA are very similar except gamma5 in vector and axial structures. These are canceled out in chiral limit which is xi->1, Delta_T2 ->0, Q2 >> W => In this case, V, A, and T are only functions of x_i Where x_i is the light-cone momentum fraction carried by participant quarks. p is the light –cone projection of P College of William and Mary 02/25/ K. Park

Kinematical variables One of the good chance to access the phi-dependent cross section check is related to TDA at backward angle. Here I show the handbag diagram to describe the TDA mechanism. First of all, note that definition of Delta2 and Transition amplitude can be function of x, Xi, Delta2, For this analysis, we focused on the backward angle, which can achieve the constraint by ratio between transverse component of Delta2 and Q2. Here Delta2T is function of xi and u and Xi is function of x in xbj limit. Kinematic angle region constraint by Transverse momentum transfer square College of William and Mary 02/25/ K. Park

Theoretical expectation Prediction is based on pi0 case. College of William and Mary 02/25/ K. Park

CLAS and reaction channel Kinematical variables Unpol. CRS w/ one-photon exchange approx. Kinematic observables and definition in analysis College of William and Mary 02/25/ K. Park

Analysis 1 E1-6 data outlook No (s-) resonance access (= no event below 2GeV of W) No missing mass cut Kinematic coverage in our data College of William and Mary 02/25/ K. Park

Analysis 1 Particle identification Requirement W>2GeV Kinematic coverage in our data Once we required W>2GeV, we have to deal with PID between protons and pions due to the finite detector resolution. College of William and Mary 02/25/ K. Park

Analysis 1 Particle identification Requirement W>2GeV cosq* <0.0 DT2 <0.5GeV 2 Kinematic coverage in our data However, fortunately enough, once we require the backward angle by constraint angle and transverse pion momentum. PID is no longer issue. As we see the clear separation between pions and protons. College of William and Mary 02/25/ K. Park

Analysis 1 Particle identification Requirement W>2GeV cosq* <0.0 DT2 <0.5GeV 2 TOF mass 3sigma cut Kinematic coverage in our data On top of this advantage, we applied the TOF mass cut with 3sigma College of William and Mary 02/25/ K. Park

Analysis 1 Particle identification Requirement W>2GeV cosq* <0.0 DT2 <0.5GeV 2 TOF mass 3sigma cut b : 2sigma cut Kinematic coverage in our data And 2sigma of beta cut for better Particle identification. College of William and Mary 02/25/ K. Park

Analysis 1 t Impact of D T2 cut u Dependence of Delta_T2 cut in terms of |u| and |t| vs. cos\theta* In this analysis, it is very important key how to define the well separated “u” and “t”. Remember, TDA required events only in the region of high “W” and small “u” and large “t” These plot might be instructive~! Here we see the kinematic coverage changes (especially u and t channel) in terms of cos\theta* with various Delta_T2 cut from 1.0GeV2 to 0.5GeV2. Here you see t and u as function of cos\theta* with Delta_T2 cut accordingly. And left side two plots are showing the missing mass spectrum for Q2=2.05 and 2.92GeV2 with different Delta_T2 cuts Ultimate Delta_T2 < 0.5GeV2 cut make approximately 5% event surviving from no cut. Blue bullets : D_T2 < 0.5GeV2 cut Red hist : D_T2 < 1.0GeV2 cut cos q* College of William and Mary 02/25/ K. Park

Analysis 2 Yield obtain after BG subtraction Black bullets : exp. Data before BG subtraction Red bullets : exp. Data before BG subtraction Blue solid lines : nominal MMx 3 s cut Here are more examples in logarithm scale for different 9 phi-angles. Some examples of missing mass spectrum before/after BG subtraction in terms of ph-bin. For Q2=3.48GeV2 College of William and Mary 02/25/ K. Park

Analysis 3 MC simulation Kinematic coverage from MC and binning that we made College of William and Mary 02/25/ K. Park

Analysis 4 MC simulation GPP + Pion momentum correction Blue bullets : exp. Data after BG subtraction Red hist. : GPP + w/o (left) & with (right) correction applied MC Missing mass spectrum comparison between data and MC with some momentum correction after GPP Momentum correction (constant momentum (-15MeV) subtraction~!! Usually adding extra momentum to compansate narrower mmx resolution) for MC only “positive pion under maximum magnetic field MC simulation” - tested with K-Lambda, piN with high and mid B field. In the GPP, Pion which has the smallest mass with carrying lower momentum and out-banding in particular … College of William and Mary 02/25/ K. Park

Analysis 5 Comparison I Two event generators were tested cos q cut was applied on top of DT2 cut GSIM DATA Comparison between data and MC in terms of angles and Delta_T2 vs. cos\theta College of William and Mary 02/25/ K. Park

Analysis 6 Acceptances Some examples of acceptances overall Q2 bins with appropriate cuts W>2GeV MMx cut cosq* <0.0 DT2 <0.5GeV 2 College of William and Mary 02/25/ K. Park

Summary Hard exclusive process of meson in the backward angle opens a new window in the understand of hadronic physics in the framework of the collinear-factorization approach of QCD. Measurement of cross sections and asymmetries are crucial to develop a realistic model for the TDAs. Careful study has been performed by communicating with theory group (kinematic binning, corrections, acceptance(GENEV/FSGEN), cuts, etc.) We measured the differential cross sections on backward angle in the kinematic range of W > 2GeV, high “t” and low “u”. We extracted the structure functions from differential cross sections, s TT has a similar amplitude of s LT s T+ e s L is ~2x larger than s TT and s LT . Open questions ? College of William and Mary 02/25/ K. Park

Γ* The study of hadron structure using single pion electroproduction off the proton in CLAS Why single pion production electroproduction ? Because single.

Similar presentations

Presentation on theme: "Γ* The study of hadron structure using single pion electroproduction off the proton in CLAS Why single pion production electroproduction ? Because single."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Γ* The study of hadron structure using single pion electroproduction off the proton in CLAS Why single pion production electroproduction ? Because single.

Similar presentations

Presentation on theme: "Γ* The study of hadron structure using single pion electroproduction off the proton in CLAS Why single pion production electroproduction ? Because single."— Presentation transcript:

Similar presentations

About project

Feedback