Overview of unpolarized structure function measurements at high x Roy J. Holt Jefferson Lab 13 October 2010

Argonne National Laboratory 2 Outline  Introduction and Motivation  New generation of experiments and tools –The proton structure function –The neutron structure function –The strange quark distribution and Drell-Yan  Concluding statement We are providing benchmark data for hadron structure.

Argonne National Laboratory 3 W p u (x,k T,r ) Wigner distributions d 2 k T d 3 r PDFs f 1 u (x),.. h 1 u (x)‏ d 2 k T dr z d3rd3r Form Factors G E (Q 2 ), G M (Q 2 )‏ dxd 2 k T dr z & FT 3 Four Pillars of Hadron Structure GPDs TMD PDFs f 1 u (x,k T ),.. h 1 u (x,k T )‏ 3 D See X. Jiang, K. Hafidi, A. Accardi See Z.-E. Meziani, J. Blumlein, J. Soffer

Argonne National Laboratory 4 Parton model Quark charge Prob. of q in proton Structure function leptonic hadronic What is the internal landscape of the hadron? NSAC 2007 –Benchmark: Spatial, spin, flavor and gluonic structure Partonic structure of the nucleon fraction of the proton’s momentum carried by the struck quark

Argonne National Laboratory 5 Large x is essential for particle physics  Parton distributions at large x are important input into simulations of hadronic background at colliders, eg the LHC. –High x at low Q 2 evolves into low x at high Q 2. –Small uncertainties at high x are amplified.  HERA anomaly: (1996): excess of neutral and charged current events at Q 2 > 10,000 GeV 2 –Leptoquarks???? –~0.5% added to u(x) at x > 0.75 S. Kuhlmann et al, PLB 409 (1997) Lake of Geneva Large Hadron Collider Airport CMS ATLAS LHCb ALICE

Argonne National Laboratory 6 W production at the LHC  W production at the LHC is sensitive to the d/u ratio  W’s and Z will be “standard candles” at the LHC J.-L.Lai et al, hep-ph 14 Jul 2010

Argonne National Laboratory 7 Proton structure function Plot credit: A. Accardi (See J. Owens, S. Alekhin, A. Guffanti, D. Renner, V. Radescu) DIS from proton gives good sensitivity to u, but not to d

Argonne National Laboratory 8 Why are proton structure function data still interesting?  New data at very high x can reveal information about: –Target mass corrections –High twist effects –Soft gluon resummation –Order in  s –Quark-hadron duality –Hadronic models  Recent data from JLab – more to follow after JLab 12 GeV Upgrade and Drell-Yan experiments CTEQ6X, A. Accardi et al, PR D81 (2010) (See J. Owens, S. Alkhin, T. Hobbs, M. Glatzmaier, S. Kulagin, A. Accardi, W. Melnitchouk, S. Malace, F. Steffens, S.-H. Lee, S. Liuti, E. Christy)

Argonne National Laboratory 9 Why is high x so difficult?  W > 2 GeV eg. if x =0.9, then Q 2 = 27 GeV 2 Practical limit at JLab12: x = 0.8

Argonne National Laboratory 10 The proton structure function  JLab E , S. Malace et al  Utilize resonance region  Invoke duality Upgraded JLab has unique capability to define the valence region Plot credit: S. Malace, JLab PAC36 DOE milestone HP14 (2018)

Argonne National Laboratory 11 Proton structure function at an EIC  MEIC simulation  E e = 4 GeV, E p = 60 GeV  Luminosity ~ 3 x  1 year of running (26 weeks) at 50% efficiency, or 230 fb -1 Alberto Accardi, Nuclear Chromodynamics with an EIC Argonne, April 2010 With C. Keppel and R. Ent An EIC is a powerful probe of the valence region.

Argonne National Laboratory 12 The Neutron Structure Function  Proton structure function:  Neutron structure function (isospin symmetry):  Ratio:  Nachtmann inequality:  Focus on high x: Parton model ->

Argonne National Laboratory 13 Uncertainty in the d(x)/u(x) ratio  Q 2 > 4 GeV 2  W > 3.5 GeV  x < 0.7

Argonne National Laboratory 14 Structure Function Ratio Problem  Convolution model –Fermi motion and binding, covariant deuteron wave function, off-shell effects Melnitchouk and Thomas (1996)  Nuclear density model: –EMC effect for deuteron scales with nuclear density. Frankfurt and Strikman (1988) Fermi smearing Smearing + binding Nuclear density model (See I. Cloet)

Argonne National Laboratory 15 Models of the structure function  SU(6)-symmetric wave function of the proton in the quark model (spin up): –u and d quarks identical, N and  would be degenerate in mass. –In this model: d/u = 1/2, F 2 n /F 2 p = 2/3.  SU(6) symmetry is broken: N-  Mass Splitting –Mechanism produces mass splitting between S=1 and S=0 diquark spectator. –symmetric states are raised, antisymmetric states are lowered (~300 MeV). –S=1 suppressed => d/u = 0, F 2 n /F 2 p = 1/4, for x -> 1  pQCD: helicity conservation (q  p) => d/u =2/(9+1) = 1/5, F 2 n /F 2 p = 3/7 for x -> 1.

Argonne National Laboratory 16 Structure Function Ratio Reviews: N. Isgur, PRD 59 (1999), S Brodsky et al NP B441 (1995), W. Melnitchouk and A. Thomas PL B377 (1996) 11, R.J. Holt and C. D. Roberts, arXiv: [nucl-th], I. Cloet et al, Few Body Syst. 46 (2009) 1. DOE milestone HP14 (2018) SU(6) symmetry pQCD 0 + qq only DSE: 0 + & 1 + qq

Argonne National Laboratory 17 Extractions with modern deuteron wave functions J. Arrington et al, J. Phys. G 36 (2009) Lorentz invariant convolution relation Light front with null plane kinematics The ratio at high x has a strong dependence on deuteron structure. A. Accardi, et al., arXiv: More p/d data at JLab 12 GeV E J. Arrington, A. Daniel, D. Gaskell PAC 36: recommended approval (See F. Olness, S. Kumano, A. Daniel, S. Kulagin, J. Arrington)

Argonne National Laboratory 18 Tagged Neutron in the Deuteron – BONUS + CLAS12 PAC36: “recommended approval” JLab E , S. Bueltmann, H. Fenker, M. Christy, C. Keppel et al See S. Bueltmann, M. Sargsian, S. Kulagin

Argonne National Laboratory 19 Nuclear Physicists’ Approach to F 2n  Problem: –The deuteron experiments present extraction complications.  Nuclear physicists’ solution: Add another nucleon.  3 H/ 3 He ratio: minimizes nuclear physics uncertainties I. Afnan et al., Phys. Lett. B493, 36 (2000); Phys. Rev. C68, (2003) E. Pace, G Salme, S. Scopetta, A. Kievsky, Phys. Rev. C64, (2001) M. Sargsian, S. Simula, M. Strikman, Phys. Rev. C66, (2002) No DIS data exist for the triton!

Argonne National Laboratory 20 Tritium target at JLab?? Tritium Target Task Force E. J. Beise (U. of Maryland) B. Brajuskovic (Argonne) R. J. Holt (Argonne) W. Korsch (U. of Kentucky) A. T. Katramatou (Kent State U.) D. Meekins (JLab) T. O’Connor (Argonne) G. G. Petratos (Kent State U.) R. Ransome (Rutgers U.) P. Solvignon (JLab) B. Wojtsekhowski (JLab) JLab Review: June 3, > “No show stopper” E G. Petratos et al PAC 36: recommended conditional approval See G. Petratos

Argonne National Laboratory 21 Parity Violating Deep Inelastic Scattering Proton target only PAC35 “recommended approval” Requires special spectrometer P. Souder – SoLID JLab E (See P. Souder, T. Hobbs, M. Glatzmaier)

Argonne National Laboratory 22 Deep inelastic neutrino scattering from the proton  Charge current neutrino/antineutrino scattering MINOS high energy tune: 2 years LH2 target MINER A: J. Morfin   d W+W+   u W-W- (See J. Morfin, R. Petti)

Argonne National Laboratory 23 Deuteron structure function at an EIC  E e = 8 GeV, E N = 30 GeV  Luminosity ~ 3.5 x  One year of running (26 wk) at 50% efficiency, or 35 fb -1  Detect ~30 GeV proton “Super BoNuS” Alberto Accardi, Nuclear Chromodynamics with an EIC Argonne, April 2010 With C. Keppel and R. Ent

Argonne National Laboratory 24 The strange quark distribution function Strange quark distribution - HERMES New data: COMPASS II at CERN, JLab with12 GeV, MINER A at FNAL Far future: EIC-> also charm distribution, gluonic Sivers effect; LHeC -> beauty distribution A. Airapetian et al, PLB 666 (2008) 446

Argonne National Laboratory 25 Projections for strange quarks COMPASS-II JLAB E K. Hafidi et al.

Argonne National Laboratory 26 What about Drell-Yan experiments?  Pion structure function shape at very high x ??  Azimuthal asymmetry for the proton Boer-Mulders vs. pQCD?  High x distribution functions 4u + d soft gluon resummation issues?  The kaon structure function should be measured See J.-C. Peng, P. Reimer  COMPASS-II, FNAL E906 SeaQuest, FAIR, J-PARC Settled by soft gluon resummation – Aicher, Schaeffer, Vogelsang, hep-ph/

Argonne National Laboratory 27 Concluding statement  Understanding hadrons will be one of nuclear physics’ greatest contributions to science  New 21 st century tools have positioned us well for the next decade: –JLab 12 GeV, CERN COMPASS-II, FNAL MINER A, FNAL E906, RHIC, J-PARC, FAIR, petascale computing.  Far future: EIC, exascale computing –Continue to develop and assess the high x case for the EIC  We are camped on one of the most interesting frontiers in science

Argonne National Laboratory 28 Drell-Yan azimuthal asymmetry R. J. Holt and C. D. Roberts, arXiv: [nucl-th] FNAL E906 SeaQuest

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