Baryon spectroscopy at CLAS and CLAS 12 Ken

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

Missing baryon resonances With D 13 Without D 13 After Cx, Cy from CLAS, revised as most likely P 13. Eur Phys J A 34 (07) 243 Mart & Benhold, Phys. Rev. C 61 012201(R) (1999) • 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 • Really missing or undetected since weak coupling to these channels • Try other channels. Eg. K photoproduction • Eg. Cross sections show some hints of new D 13. • Better to look at angular distributions and polarization observables.

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 πN recoil targ ☻ KY γ γ targ recoil ☻☻☻ ☻☻☻ ☻☻☻ I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B 95 347 (1975). circ polarized photons longitudinally polarized target linearly polarized photons transversely polarized target Complete, and over-determined

Continuous Electron Beam Accelerator Facility LINAC Jefferson Lab C Injector A B C Experimental Halls E: 0. 75 – 6 Ge. V Imax: 200 m. A RF: 1499 MHz Duty Cycle: 100% s(E)/E: 2. 5 x 10 -5 Polarization: 80% Simultaneous distribution to 3 experimental Halls

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

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

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

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

1 st pol. observables in K photoproduction on p at CLAS. P, Cx and Cz R. Bradford et al. , Phys. Rev. C 75, 035205 (2007). → L fully polarised

g 8 b, July 2005 Lin. polarized photon energy range: 1. 3 – 2. 1 Ge. V preliminary results: 0 p, Mike Dugger, ASU SAID Beam Asymmetry Σ CLAS data • • Very high statistics. Good agreement with previous measurement. We have P well determined – expect <5% systematic error in P. ~10 Me. V Eg bins, and will extend up to 2. 1 Ge. V Similar for +n, hp, h’p

g 8 b preliminary results - +L and +S 0 Craig Paterson, Glasgow gp -> +L -> +pp- gp -> +S 0 -> +Lg -> +pp-g Single polarization observables S Photon asymmetry P Recoil polarization (induced pol. along y) T Target asymmetry Double polarization observables Ox Polarization transfer along x Oz Polarization transfer along z L S 0 figure by R. Schumacher, CMU

g 8 b preliminary results - +L Results compared with previous results from LEPS • 6, 100 Me. V Energy bins • 1550 -> 2050 Me. V • More bins for our data Increase the angular coverage to backward angles EL IM IN A R Y LEPS also recently have some consistent, new points at backward angles. Hicks et al. , PRC 76, 042201(R) (2007). PR •

g 8 b preliminary results - +L Ox/Oz extracted from fit to 2 d asymmetry T Target asymmetry from 2 d asymmetry (not shown) P Recoil pol. from acceptance corrected proton dist. G 8 summary Several analyses at advanced stage. Only a small sample presented here +L , +S 0 : Single (P, T, S ) and double (Ox, Oz) polarization observables p 0 p, p+n, hp, h’p, wp, p+p-p : polarization photon beam asymmetry, S …. several publications expected next year g 8 b GRAAL CLAS J. W. C. Mc. Nabb, et al. (CLAS) Phys. Rev. C 69, 042201(R) (2004).

g 9 FROST – FROzen Spin Target (butanol = C 4 H 9 OH) Meson photoproduction with linearly and circularly polarized photons on polarized target E 02 -112: E 03 -105/E 04 -102: E 05 -012: E 06 -013: γp→KY (K+Λ, K+Σ 0, K 0Σ+) γp→π0 p, π+n γp→ηp γp→π+π-p Racetrack coils for transverse polarization g 9 a running conditions November 3, 2007– February 12, 2008 Longitudianally polarized target Circularly and linearly polarized photon beam 0. 5 -2. 4 Ge. V Trigger: at least one charged particle in CLAS Target Pol > 80%, Relaxation time > 1600 hrs – better that design goals g 9 b March – July 2010 Transversely polarized target

g 9 FROST sample analysis of gp +n Steffen Strauch, University of South Carolina CH 2 IN 12 C IM butanol A R Y CH 2 EL 12 C PR butanol

Measurements on n (Deuterium) target • G 10. • 1 st Unpolarized photons on Deuterium measurement of σ for the γ n → K+ Σ- Edwin Munevar, GWU • Detect p- n, K+ PR EL IM IN A R Y Sergio Anefalos Pereira, INFN. Phys. Lett. B 688 (2010) 289 -293 • Σ from p- n inv. mass • CLAS Data ▲ LEPS _____ Gent RPR model • Circularly and linearly polarized photons on n (g 13, Deuterium target) • γ n → K+ Σ- analysis for polarization observables underway. Edwin Munevar, GWU

Measurements on n (Deuterium) target • G 13 PR EL IM IN A R Y Linearly polarized photons on n (Deuterium) • Measurement of S for γ n → - p Daria Sokhan, Edinburgh

Measurements on n (Deuterium) target PR EL IM IN A R Y G 13 1 st measurement of Beam Asymmetry gn (p) -> K 0 s L 0 (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

Search for baryon states in γp➝pω➝pπ+π-(π0) p • Spin density matrix elements in bins. Preliminary ΔW = 10 Σ for γ p§→ω The CLAS data are used as input to a Me. V, Oh, for et W al = 1. 7– 2. 4 Ge. V in blue - blue shades. Patrick Collins, ASU single channel event-based, energy • Previous world data in red. independent partial wave analysis (the Paris first ever for baryons). Sarantsev, et al § 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)/G 17(219 0) M. Williams, et al. (CLAS) , Phys. Rev. C 80: 065208, 2009 M. Williams, et al. (CLAS) , Phys. Rev. C 80: 065209, 2009

Construction of the new Hall D 12 Ge. V CEBAF Upgrade of the arc magnets CHL-2 Upgrade of the instrumentation of the existing Halls Beam Power: 1 MW Beam Current: 90 µA Max Pass energy: 2. 2 Ge. V Max Enery Hall A-C: 10. 9 Ge. V Max Energy Hall D: 12 Ge. V

Spectroscopy with CLAS 12 The construction of Low Q Tagging Facility or Forward Tagger has been proposed to continue the spectroscopy program with CLAS 12 using quasi-real photoproduction • electron scattering at “ 0” degrees (Low. Q, 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 CLAS 12 Pi. D for final states with strangeness • Complementary to GLUEX Coh. Brem. photon beam • Parasitic running • • < 6 Ge. V • • 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 W-) Compton scattering Meson polarizabilities Large -t physics T-GPDs Meson Spectroscopy at CLAS and CLAS 12, Carlos Salgado SP 2, Wed 14. 00

Summary q CLAS has large hadron spectroscopy programme q q Huge effort on N*, missing baryon resonances q Complete measurements on p and n soon (KL, KS) q Single and double pol observables on many other channels CLAS 12 q A forward tagger offers a whole new hardon spectrosopy programme Some related CLAS talks to be give here: Meson Spectroscopy at CLAS and CLAS 12, Carlos Salgado SP 2, Wed 14. 00 K*L and K*S photoproduction at CLAS, Ken Hicks EM 1, Tues 17. 45 Extraction of Multipole Amplitudes from Over-Complete Experiments in Meson Photoproduction, A. Sandorfi MO Thurs 10. 10

Extra slides

K production on n. Deuterium target How good a “free” neutron target is Deuterium ? G 13. Compare photon asymmetry of gp (n) -> +L 0 (n) with gp -> +L 0 (free and bound p) Y EL IM IN A R × Free ● Quasi free PR photon asymmetry S gp (n) -> +L 0 (n) Russell Johnstone, Glasgow Cosqcm (-1. 0 - +1. 0) Each plot is 200 Me. V photon energy bin 1100 -2150 Me. V S 0 L 0 Free and quasi-free proton Quasi free neutron good approx. to free, here.

K production on n. Deuterium target G 13 gn (p) -> K 0 s L 0 (p) Neil Hassall, Glasgow gn (p) -> K 0 s S 0 (p)

K production on n. Deuterium target G 13 1 st measurement of Beam Asymmetry gn (p) -> K 0 s L 0 (p) PR EL IM IN A R Y Neil Hassall, Glasgow Single, and double polarization observables in progress

Recoil polarimetry possibilities ? n(q, f) =no(q){1+A(q)[Pycos(f)–Pxsin(f)] - How to do this for 4 detector x and y (transverse) components of nucleon polarisation Nucleon polarimeter for CB@MAMI, D. Watts, Edinburgh q Graphite g 8 b data. p g Start counter K. Livingston + p → + n with (n, p) scatter (detect +p) q n p+ Mx( p→ ++X) Angle between Pncalc and Ppmeasured

CLAS coherent bremsstrahlung facility • Tagging spectrometer with high rate, good energy and timing resolution • High quality, thin diamond (Glasgow) • Tight photon beam collimation (ISU) • Polarimetry P en hot er on gy • High precision goniometer (GWU) P >>90% Peak 90% pol. “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

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

g 8 b preliminary results - K+L +L Photon Asymmetry, S, extracted from cos(2 f) fit to azimuthal kaon distribution Fits shown for 1 energy bin 340 (20 E, 17 q) kinematic bins Almost full angular coverage

g 8 b preliminary results - K+S 0 Results compared with previous results from GRAAL PR EL IM IN A R Y 7, 50 Me. V Energy bins 1175 -> 1475 Me. V Good agreement with previous results

g 8 b preliminary results - K+S 0 Results compared with previous results from LEPS 6, 100 Me. V Energy bins 1550 -> 2050 Me. V More bins for our data!!! PR EL IM IN A R Y Increase the angular coverage to backward angles

Polarimetry: from pair (e+, e-) production H. Schmieden, Bonn • Well described by QED, but experimentally difficult – small opening angle e+ • Pair production simulations by Kharkov group e • Polarimeter built and tested at Sping 8, recently tested at Jlab Peak > 90% pol. PRELIMINARY K. Livingston, Glasgow • 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. J. Santoro, CUA

Polarimetry: from hadronic reaction R. Beck, Mainz -> Bonn 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 Recent preliminary results from JLab (g 8 b) • Proton target • Back to back charge particles in Start Counter • Atomic or hardonic ? • Asymmetry from ~20 mins DAQ data • Constant with E from 1. 3 Ge. V – 1. 9 Ge. V