Baryon spectroscopy at CLAS and CLAS12 Baryons’10, Dec 2010, Osaka, Japan Ken Livingston, University of Glasgow, Scotland For the CLAS collaboration Hadron spectroscopy at CLAS The N* programme CLAS 12 Summary Hadron spectroscopy at CLAS The N* programme CLAS 12 Summary Study of nucleon resonances: Measurement of the transition form factors Search for missing states Strangeness production  and  production Cascade spectroscopy Search for “unconventional states” high statistics search of pentaquark states search for hybrid mesons > 100 analyses in progress

Missing baryon resonances Clear indication of resonances in γp cross section for many channels Constituent quark models predict many resonances, but several missing Mostly from πN scattering and single π photoproduction Eg. Cross sections show some hints of new D 13. Better to look at angular distributions and polarization observables. Really missing or undetected since weak coupling to these channels Try other channels. Eg. K photoproduction With D 13 Without D 13 Mart & Benhold, Phys. Rev. C (R) (1999) After Cx, Cy from CLAS, revised as most likely P13. Eur Phys J A34 (07) 243

Polarization observables in pseudoscalar meson production 4 Complex amplitudes: 16 real polarization observables. Complete measurement from 8 carefully chosen observables. πN has high statistics but in KY recoil is self-analysing I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B (1975). πNπNKY recoil targ γγ targ recoil ☻☻☻ ☻ linearly polarized photons ☻☻☻ longitudinally polarized target ☻☻☻ transversely polarized target circ polarized photons ☻☻☻ Complete, and over-determined

A B C Continuous Electron Beam Accelerator Facility  E: 0.75 –6 GeV  I max : 200A  RF: 1499 MHz  Duty Cycle:  100%  (E)/E: 2.5x10 -5  Polarization: 80%  Simultaneous distribution to 3 experimental Halls Injector LINAC Experimental Halls Jefferson Lab

CEBAF Large Acceptance Spectrometer Cherenkov Counter e/ separation, 256 PMTs Time of Flight Plastic Scintillator, 684 PMTs Drift Chamber 35,000 cells Target +  start counter e mini-torus Electromagnetic Calorimeter lead/plastic scintillator, 1296 PMTs Torus Magnet 6 Superconductive Coils

Tagged photons at CLAS Tagged bremsstrahlung photons up to 6GeV. Timing resolution < 1 beam bucket. Circularly polarized up to ~80% now standard Linearly polarized coherent bremsstrahlung up to >90%.

Polarization observables at CLAS  + N →  m Linear Polarisation Circular polarisation Nucleon recoil polarimiter x → Y  Hyperons are “self analysing” Transverse polarized nucleon targets p n 2011 Longitudinally polarized nucleon targets p n 2011

Polarization observables - a simple example,  Systematics of detector acceptance cancel out. “Only” need to know P lin, the degree of linear polarization.

1 st pol. observables in K photoproduction on p at CLAS. P, C x and C z →  fully polarised R. Bradford et al., Phys. Rev. C 75, (2007).

g8b, July 2005 Lin. polarized photon energy range: 1.3 – 2.1 GeV preliminary results:   p, Mike Dugger, ASU CLAS dataSAID Very high statistics. Good agreement with previous measurement. We have P well determined – expect <5% systematic error in P. ~10MeV Eg bins, and will extend up to 2.1GeV Similar for   n  p,  ’p Beam Asymmetry Σ

g8b preliminary results -    and     Craig Paterson, Glasgow  p     p    p         p      Single polarization observables  Photon asymmetry P Recoil polarization (induced pol. along y) T Target asymmetry Double polarization observables O x Polarization transfer along x O z Polarization transfer along z figure by R.Schumacher, CMU

g8b preliminary results -    Results compared with previous results from LEPS 6, 100MeV Energy bins > 2050MeV More bins for our data Increase the angular coverage to backward angles LEPS also recently have some consistent, new points at backward angles. Hicks et al., PRC 76, (R) (2007). PRELIMINARY

g8b preliminary results -    O x /O z extracted from fit to 2d asymmetry T Target asymmetry from 2d asymmetry (not shown) P Recoil pol. from acceptance corrected proton dist. g8b GRAAL CLAS J.W.C. McNabb, et al. (CLAS) Phys. Rev. C 69, (R) (2004). P Recoil pol. G8 summary Several analyses at advanced stage. Only a small sample presented here        Single (P,T,  ) and double (O x,O z ) polarization observables   p   n  p,  ’p,  p     p : polarization photon beam asymmetry,  …. several publications expected next year

Meson photoproduction with linearly and circularly polarized photons on polarized target E02-112: γp→KY (K + Λ, K + Σ 0, K 0 Σ + )‏ E03-105/E04-102: γp→π 0 p, π + n E05-012: γp→ηp E06-013: γp→π + π - p g9a running conditions November 3, 2007– February 12, 2008 Longitudianally polarized target Circularly and linearly polarized photon beam GeV Trigger: at least one charged particle in CLAS Target Pol > 80%, Relaxation time > 1600hrs – better that design goals g9 FROST – FROzen Spin Target (butanol = C 4 H 9 OH) g9b March – July 2010 Transversely polarized target Racetrack coils for transverse polarization

butanol 12 CCH 2 g9 FROST sample analysis of gp  + n butanol 12 CCH 2 Steffen Strauch, University of South Carolina PRELIMINARY

G10. Unpolarized photons on Deuterium 1 st measurement of σ for the γ n → K + Σ - Measurements on n (Deuterium) target Detect  - n, K + Σ from  - n inv. mass Circularly and linearly polarized photons on n (g13, Deuterium target) γ n → K + Σ - analysis for polarization observables underway. Edwin Munevar, GWU Sergio Anefalos Pereira, INFN. Phys. Lett. B 688 (2010) CLAS Data ▲ LEPS _____ Gent RPR model Edwin Munevar, GWU PRELIMINARY

Measurements on n (Deuterium) target G13 Linearly polarized photons on n (Deuterium) Measurement of  for γ n →  - p Daria Sokhan, Edinburgh PRELIMINARY

G13 1 st measurement of Beam Asymmetry  n (p)   s    p  Neil Hassall, Glasgow Single, and double polarization observables in progress Measurements on n (Deuterium) target

HDIce Solid Deuterium-Hydride (HD) – a new class of polarized target Spin can be moved between H and D with RF transitions All material can be polarized with almost no background Run in Spring 2011

Spin density matrix elements in bins ΔW = 10 MeV, for W = 1.7–2.4 GeV in blue - blue shades. Previous world data in red. Search for baryon states in γp ➝ pω ➝ pπ + π - (π 0 ) M. Williams, et al. (CLAS), Phys.Rev.C80:065208,2009 M. Williams, et al. (CLAS), Phys.Rev.C80:065209,2009 F 15 (2000)/G 17 (219 0)  The CLAS data are used as input to a single channel event-based, energy independent partial wave analysis (the first ever for baryons).  ω production is dominated by the well known F 15 (1680), D 13 (1700) and G 17 (2190), and a predicted “missing” F 15 (2000). Preliminary Σ for γ p →ω p Oh, et al Patrick Collins, ASU Paris Sarantsev, et al

CHL-2 Upgrade of the arc magnets 12 GeV CEBAF Construction of the new Hall D Beam Power: 1MW Beam Current: 90 µA Max Pass energy: 2.2 GeV Max Enery Hall A-C: 10.9 GeV Max Energy Hall D: 12 GeV Upgrade of the instrumentation of the existing Halls

< 6 GeV Spectroscopy with CLAS12 The construction of Low Q Tagging Facility or Forward Tagger has been proposed to continue the spectroscopy program with CLAS12 using quasi-real photoproduction electron scattering at “0” degrees (LowQ, post-target tagging): low-Q 2 virtual photon  real photon photons tagged by detecting the scattered electron quasi-real photons are linearly polarized and the polarization can be determined event by event high luminosity on thin (gas)- targets can exploit CLAS12 PiD for final states with strangeness Complementary to GLUEX Coh. Brem. photon beam Parasitic running A new physics programme Meson spectroscopy –Spectroscopy on H target and search for exotics –Spectroscopy on 4 He and other gas targets Hadron spectroscopy –Heavy mass baryon resonances (Cascades and  - ) Compton scattering Meson polarizabilities Large -t physics T-GPDs Forward Tagger Meson Spectroscopy at CLAS and CLAS12, Carlos Salgado SP2, Wed 14.00

Summary  CLAS has large hadron spectroscopy programme  Huge effort on N*, missing baryon resonances  Complete measurements on p and n soon (K , K  )  Single and double pol observables on many other channels  CLAS 12  A forward tagger offers a whole new hardon spectrosopy programme Some related CLAS talks to be give here: Meson Spectroscopy at CLAS and CLAS12, Carlos Salgado SP2, Wed K*  and K*  photoproduction at CLAS, Ken Hicks EM1, Tues Extraction of Multipole Amplitudes from Over-Complete Experiments in Meson Photoproduction, A. Sandorfi MO Thurs 10.10

 p (n)      n  Russell Johnstone, Glasgow K production on n. Deuterium target PRELIMINARY photon asymmetry  How good a “free” neutron target is Deuterium ? G13. Compare photon asymmetry of  p (n)      n  with  p      (free and bound p)   × Free ● Quasi free Free and quasi-free proton Quasi free neutron good approx. to free, here. Cos  cm ( ) Each plot is 200MeV photon energy bin MeV

G13  n (p)   s     p  n (p)   s    p  Neil Hassall, Glasgow K production on n. Deuterium target

PRELIMINARY G13 1 st measurement of Beam Asymmetry  n (p)   s     p  Neil Hassall, Glasgow Single, and double polarization observables in progress

Recoil polarimetry possibilities ? g8b data  + p →  + n with (n,p) scatter (detect  + p) M x (  p→  + +X)  ++ n p  Start counter K.Livingston Angle between P n calc and P p measured  x and y (transverse) components of nucleon polarisation n(  ) =n o (  ){1+A(  )[P y cos(  )–P x sin(  )] - How to do this for 4  detector Nucleon polarimeter for D. Watts, Edinburgh Graphite

Tagging spectrometer with high rate, good energy and timing resolution High precision goniometer (GWU) High quality, thin diamond (Glasgow) Tight photon beam collimation (ISU) Polarimetry “A device called a goniometer tilts the diamond, much like a lady turning her hand to admire the sparkle of a new ring.” - JLAB On Target Magazine Peak > 90% pol. CLAS coherent bremsstrahlung facility Photon energy P > 90%

Measurements with photon beam profile detector D. Glazier, Glasgow 1 st Measurement of 2D photon enhancement for coherent bremsstrahlung (MAMI,Mainz) paper in preparation Good agreement with coherent bremstrahlung calculations Improvements in incoherent component, collimation + multiple scattering. No evidence of high energy photons from quasi channeling. Investigation of 2D strip detector for polarimetry Coherent peak at 300Mev, MAMI electron beam energy 855MeV below peakcoherent peakabove peak

   Photon Asymmetry, , extracted from cos(2  ) fit to azimuthal kaon distribution Fits shown for 1 energy bin 340 (20E, 17  ) kinematic bins Almost full angular coverage g8b preliminary results -   

g8b preliminary results -     Results compared with previous results from GRAAL 7, 50MeV Energy bins > 1475MeV Good agreement with previous results PRELIMINARY

Results compared with previous results from LEPS 6, 100MeV Energy bins > 2050MeV More bins for our data!!! Increase the angular coverage to backward angles PRELIMINARY g8b preliminary results -    

Pair production simulations by Kharkov group Polarimeter built and tested at Sping8, recently tested at Jlab e+e-e+e- Polarimeter to be based on Jlab design Microstrip detectors, or pixel detectors (Atlas group) Bonn student completed 10 months exchange in Glasgow now to be full time in Bonn. Polarimetry: from pair (e +,e - ) production H.Schmieden, Bonn Well described by QED, but experimentally difficult – small opening angle PRELIMINARY J.Santoro, CUA Peak > 90% pol. K.Livingston, Glasgow

Use reaction with a known photon asymmetry Can be high statistics Very good relative monitor of polarization Combined beam, target polarization. Non-indpendent – depends on specific expt Need very good systematics or calibration Awaiting MAMI polarized target and polarised photon beam in 2 nd half of 2007 Polarimetry: from hadronic reaction R. Beck, Mainz -> Bonn Recent preliminary results from JLab (g8b)‏ Proton target Back to back charge particles in Start Counter Atomic or hardonic ? Asymmetry from ~20mins DAQ data Constant with E from 1.3GeV – 1.9GeV