Hyperon production and polarization with CLAS at JLab

Hyperon production and polarization with CLAS at JLab Sergio Anefalos Pereira Laboratori Nazionali di Frascati (for the CLAS Collaboration)

Introduction A major goal of hadron physics is to probe the structure of the nucleon and its excited states. ◦ The N* spectrum is a direct reflection of the underlying degrees of freedom of the nucleon. Symmetric Constituent Quark Models predict a higher number of excited states S. Anefalos Pereira Quark and flux-Tube Models predict increased number of states April 13 - DIS 2011 Quark-Diquark models predict fewer states 2

Missing Resonances 1. Quark models predict many more baryons that have been observed, “missing” resonances; 2. Many baryon resonances are predicted studying the channels with π, but very few were established; Löhring, Metsch, Petry, EPJ A 10, 395(2001) The CLAS program is designed to obtain accurate electromagnetic production cross section and spin observables over a broad kinematic range. Strangeness production is an important part of this program. S. Anefalos Pereira April 13 - DIS 2011 3

Why studying KY ? ü To resolve the question of “missing” resonances • have information about the structure of the nucleon • Couplings of nucleon resonances to KY final states will differ from the πN, ηN and ππN final states. ü Self-analyzing weak decay of hyperons allows recoil polarization measurements with high statistics: • polarization observables are crucial to extract elementary amplitudes high discriminating power against various models • one can have access to all observables (not possible with channels) S. Anefalos Pereira April 13 - DIS 2011 4

JLab Accelerator CEBAF • • Continuous Electron Beam Energy 0. 8 -5. 7 Ge. V 200 A, polarization 85% Simultaneous delivery to 3 Halls CLAS S. Anefalos Pereira April 13 - DIS 2011 5

Hall B: Cebaf Large Acceptance Spectrometer beam Torus magnet 6 superconducting coils Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers Liquid D 2 (H 2)target + start counter; e minitorus • Broad angular coverage (8° 140° in LAB frame) • Charged particle momentum resolution ~0. 5% forward dir Drift chambers argon/CO 2 gas, 35, 000 cells CLAS is designed to measure exclusive reactions with multi-particle final states Time-of-flight counters plastic scintillators, 684 photomultipliers Gas Cherenkov counters e/ separation, 216 PMTs S. Anefalos Pereira April 13 - DIS 2011 6

Define the Spin Observables (unpolarized target) K+ proton S. Anefalos Pereira April 13 - DIS 2011 7

Define the Spin Observables (unpolarized target) K+ proton S. Anefalos Pereira April 13 - DIS 2011 8

Define the Spin Observables (unpolarized target) K+ proton S. Anefalos Pereira April 13 - DIS 2011 9

Polarization observables in pseudoscalar meson production 4 Complex amplitudes: 16 real polarization observables. Complete measurement from 8 carefully chosen observables. Only hyperon can provide recoil polarization N recoil targ KY γ γ targ recoil B T R I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B 95 347 (1975). linearly polarized photons circ polarized photons S. Anefalos Pereira longitudinally polarized target transversely polarized target April 13 - DIS 2011 complete and over-determined 10

16 Pseudoscalar Meson Photoproduction Observables For + p K+ : Single Polarization Beam & Target Beam & Recoil Target & Recoil S. Anefalos Pereira R. Bradford et al. Phys. Rev. C 73 035202 (2006), M. E. Mc. Cracken et. al. , PRC 81, 025201 (2010) C. Paterson et al. (Glasgow), to be published { J. Mc. Nabb et al. Phys Rev C 69 042201 (2004) { { { FROST (g 9 a) under analysis FROST (g 9 b) under analysis C. Paterson et al. (Glasgow), to be published R. Bradford et al. Phys. Rev. C 75 035205 (2007), M. E. Mc. Cracken et. al. , PRC 81, 025201 (2010) FROST (g 9 b) under analysis FROST (g 9 a) under analysis April 13 - DIS 2011 11 11

Photoproduction on neutrons (deuteron target) neutron channels are almost unexplored add constraints in the resonance extractions. study Final State Interaction: § Compare bound proton and free proton results § Study YN interactions S. Anefalos Pereira April 13 - DIS 2011 12

Neutron experiments @ CLAS Unpolarized (g 10) Final data set with several published papers n Target: 24 cm liquid deuterium n Data taking: March 13 - May 16, 2004 n E( ): 0. 75 -3. 58 Ge. V n Integrated luminosity: ~ 50 pb− 1 γn (p) → K+ Σ – (p) neutron cross sections Polarized (g 13) data process ongoing § Target: 40 cm liquid deuterium § Data taking: October 2006 – June 2007 § Circular polarized beam n (p) K 0 (p) § E = 0. 4 – 2. 5 Ge. V n (p) K 0 0 (p) neutron cross sections and spin observables § Linear polarized beam § E = 1. 1 - 2. 3 Ge. V n (p) K+ (p) − 1 § Integrated luminosity: ~ 90 pb n (p) K+* (p) n (p) K+* * (p) neutron cross sections and beam asymmetry S. Anefalos Pereira April 13 - DIS 2011 13

γ n(p) → K+ Σ (p) cross sections CLAS 2010 LEPS 2006 Regge-3 model • first “complete” look at hyperon production off neutron • deuteron target (spectator proton) FSI ~ 10% • Ghent model with K+ and K*(892) with no resonances S. Anefalos Pereira et. al. , Phys. Lett. B 688 (2010) S. Anefalos Pereira April 13 - DIS 2011 14

γ n(p) → K+ Σ (p) cross sections CLAS 2010 LEPS 2006 Regge-3 model • first “complete” look at hyperon production off u- channel neutron • Hint of contribution for • deuteron target higher energies proton) (back angle(spectator rise) FSI ~ 10% • Ghent model with K+ and K*(892) with no resonances S. Anefalos Pereira et. al. , Phys. Lett. B 688 (2010) S. Anefalos Pereira April 13 - DIS 2011 15

G 13 preliminary beam asymmetry results n K 0 (Neil Hassal, Glasgow) Y 1. 5 Ge. V 1. 7 Ge. V 1. 9 Ge. V PR EL IM IN A R 1. 3 Ge. V 2. 1 Ge. V K MAID - P 11, P 13, S 11, D 13 K corrected MAID - no D 13 S. Anefalos Pereira April 13 - DIS 2011 2. 3 Ge. V 16

G 13 preliminary beam asymmetry results n K 0 PR EL IM IN A R Y (Neil Hassal, Glasgow) K MAID - P 11, P 13, P 31, S 11, S 31 MAID – P 11, P 13, S 11, S 31 MAID – S 11, P 13 S. Anefalos Pereira April 13 - DIS 2011 MAID - P 11, P 13, P 31, S 11 17

Edwin Munevar, GWU PR EL IM IN A R Y Measurements on n (Deuterium) target • Circularly and linearly polarized photons on n (g 13, Deuterium target) • γ n → K+ Σ- analysis for polarization observables underway. Edwin Munevar, GWU S. Anefalos Pereira April 13 - DIS 2011 18

Rescattering study with G 13 1. 3 – 1. 5 Ge. V Indicates that quasi-free neutron is a good approximation to a free neutron 1. 5 – 1. 7 Ge. V 1. 9 – 2. 1 Ge. V EL 1. 7 – 1. 9 Ge. V IM IN A R Y 1. 1 – 1. 3 Ge. V PR photon asymmetry ratio (free / quasi-free p) p (n) > K+ 0 (n) Russell Johnstone, Glasgow (comparing H 2 (g 8) and D 2 (g 13) data) 0 0 Cosqcm (-1. 0 to +1. 0) Free and quasi-free proton Quasi free neutron good approx. to free S. Anefalos Pereira April 13 - DIS 2011 19

Summary • KY photoproduction offer kinematic and analysis advantages in N* physics; • CLAS detector provides very precise measurements in a broad kinematic range; • Published CLAS KY results on proton ( , P, Cx, Cz) and more observables to be published soon (Ox, Oz, G, E, Lx, Lz); • Neutron channels are almost unexplored; • Deuteron target can be used to study FSI, comparing bound and free proton, as well as YN interactions; • Cross sections results on the neutron in a wide photon energy and angular range has been obtained with CLAS with g 10 experiment. Analysis with g 13 data are ongoing and more will come with HD-Ice. S. Anefalos Pereira April 13 - DIS 2011 20

Backup slides S. Anefalos Pereira April 13 - DIS 2011 21

FROST FRozen Spin Target (C 4 H 9 OH – polarized butanol) with longitudinal and transverse polarization Polarization Result Design +82% -85% (80%) 1/e relaxation time 2800 h (+) (500 h) 1600 h (-) Entire repolarization procedure takes under 6 hours Take data for 5 -6 days Excellent reliability! S. Anefalos Pereira April 13 - DIS 2011 22

HD-Ice target for polarised neutrons v Designed to run with both photon and electron beams v New polarized target (H D ) v Under construction! v 04/20 to 05/05/2011 production running 05/05 to 05/12/2011 electron beam test run S. Anefalos Pereira April 13 - DIS 2011 23

Photoproduction on protons • Unpolarized cross sections • Single beam polarization • Recoil polarization • Double polarization (Beam and Recoil) – Circular polarized beam – Linear polarized beam S. Anefalos Pereira April 13 - DIS 2011 24

p K+ Total Cross Sections CLAS 06 SAPHIR 04 SAPHIR 98 � ABBHM • Two bump structure seen • CLAS/SAPHIR disagreement Missing resonance? R. Bradford et al. Phys. Rev. C 73 035202 (2006) S. Anefalos Pereira April 13 - DIS 2011 25

Differential cross section of p K+ full line: full model with additional S 11, P 13 and D 13 resonances dotted line: no S 11 resonance dot-dashed line: no P 13 resonance dashed line: no D 13 resonance Coupled-channel approach by Julia-Diaz et al. (PRC 73, 055204) Alternative approaches propose other contributions for the resonance-like structure at 1. 9 Ge. V: • D 13 (Bennhold & Mart) • P 13 (Nikanov et al. ) • P 11 (Ghent model) • KKN bound state (Martinez Torres et al. ) new predicted bound state with a mix of a 0(980)N and f 0(980)N S. Anefalos Pereira April 13 - DIS 2011 26

K d /dcos c. m. ( b) Differential cross section of p K+ CLAS Mc. Cracken 2010 CLAS Bradford 2006 SAPHIR 2004 1. 6 1. 8 2. 0 2. 2 2. 4 2. 6 2. 8 M. E. Mc. Cracken et. al. , S (Ge. V) PRC 81, 025201 (2010) n n broader energy range, better statistics, good agreement between CLAS 2006 (Bradford et al. ) and new CLAS 2010 data set. Different data set, different trigger, different analysis chain S. Anefalos Pereira April 13 - DIS 2011 27

Differential cross section of p K+ 1. 62 Ge. V 2. 84 Ge. V S. Anefalos Pereira April 13 - DIS 2011 28

Total cross section of p K+ 0 CLAS 06 SAPHIR 04 SAPHIR 98 � ABBHM • Single-bump: resonance-like structure near 1. 9 Ge. V – N* & D resonances • Better agreement with SAPHIR than R. Bradford et al. Phys. Rev. C 73 035202 (2006) S. Anefalos Pereira April 13 - DIS 2011 29

Differential cross section of p K+ 0 CLAS 10 CLAS 06 SAPHIR 04 B. Dey et. al. ar. Xiv: 1006. 0374 v 2 [nucl-ex] submitted to Phys. Rev. C n n broader energy range, better statistics, good agreement between CLAS 2006 (Bradford et al. ) and new CLAS 2010 data set. Different data set, different trigger, different analysis chain S. Anefalos Pereira April 13 - DIS 2011 30

Photoproduction on protons • Unpolarized cross sections • Single beam polarization • Recoil polarization • Double polarization (Beam and Recoil) – Circular polarized beam – Linear polarized beam S. Anefalos Pereira April 13 - DIS 2011 31

CLAS g 8 b improved results - K+ IN IM EL PR • • Increase the angular coverage to backward angles A R Y linearly polarized photon asymmetry Wider range Improved precision Good agreement among CLAS, GRAAL and LEPS Results for p K+ 0 coming as well S. Anefalos Pereira April 13 - DIS 2011 32

CLAS g 8 b improved results - K+ linearly polarized photon asymmetry RY A MIN I L E PR • • Wider range Improved precision Good agreement among CLAS, GRAAL and LEPS Results for p K+ 0 coming as well S. Anefalos Pereira April 13 - DIS 2011 33

CLAS g 8 b improved results - K+ IN IM EL PR • • Increase the angular coverage to backward angles A R Y linearly polarized photon asymmetry Wider range Improved precision Good agreement among CLAS, GRAAL and LEPS Results for p K+ 0 coming as well S. Anefalos Pereira April 13 - DIS 2011 34

CLAS g 8 b improved results - K+ linearly polarized photon asymmetry Increase the angular coverage to backward angles RY A MIN I L E PR • • Wider range Improved precision Good agreement among CLAS, GRAAL and LEPS Results for p K+ 0 coming as well S. Anefalos Pereira April 13 - DIS 2011 35

CLAS g 8 b improved results - K+ linearly polarized photon asymmetry Increase the angular coverage to backward angles RY A MIN I L E PR • • Wider range Improved precision Good agreement among CLAS, GRAAL and LEPS Results for p K+ 0 coming as well S. Anefalos Pereira April 13 - DIS 2011 36

Photoproduction on protons • Unpolarized cross sections • Single beam polarization • Recoil polarization • Double polarization (Beam and Recoil) – Circular polarized beam – Linear polarized beam S. Anefalos Pereira April 13 - DIS 2011 37

p K+ Hyperon Recoil Polarization GENT Regge model GLV Kaon-MAID R. Bradford et al. , Phys. Rev. C 75, 035205 (2007). S. Anefalos Pereira April 13 - DIS 2011 38

p K+ Hyperon Recoil Polarization CLAS Mc. Cracken 2010 SAPHIR 2004 CLAS Mc. Nabb 2004 GRAAL 2007 n n n S. Anefalos Pereira April 13 - DIS 2011 Wider range Improved precision More detailed structure now visible! CLAS PWA in progress Good agreement among CLAS, SAPHIR and GRAAL 39

p K+ Hyperon Recoil Polarization CLAS Mc. Cracken 2010 SAPHIR 2004 CLAS Mc. Nabb 2004 GRAAL 2007 n n n S. Anefalos Pereira April 13 - DIS 2011 Wider range Improved precision More detailed structure now visible! CLAS PWA in progress Good agreement among CLAS, SAPHIR and GRAAL 40

p K+ 0 Hyperon Recoil Polarization n n S. Anefalos Pereira April 13 - DIS 2011 Wider range Improved precision More detailed structure now visible! CLAS PWA in progress Good agreement among CLAS, SAPHIR and GRAAL 41

p K+ 0 Hyperon Recoil Polarization n n S. Anefalos Pereira April 13 - DIS 2011 Wider range Improved precision More detailed structure now visible! CLAS PWA in progress in three angular bins (0. 3, 0. 5 and 0. 7) there are few isolated discrepancies between CLAS data that is not clear yet. Studies underway. 42

Photoproduction on protons • Unpolarized cross sections • Single beam polarization • Recoil polarization • Double polarization (Beam and Recoil) – Circular polarized beam – Linear polarized beam S. Anefalos Pereira April 13 - DIS 2011 43

R. Bradford et al. , Phys. Rev. C 75, 035205 (2007). Results: Cz for K+ Very large transfer along z Poor performance by pre-2007 models Kaon-MAID Julia-Diaz, Lee, Saghai, Tabakin Sarantsev and Nikonov S. Anefalos Pereira April 13 - DIS 2011 Guidal, Laget, Vanderhaeghen Shklyar, Lenske, and Mosel Janssen, Ryckebusch Corthals, Ryckebusch, and Van Cauteren 44

R. Bradford et al. , Phys. Rev. C 75, 035205 (2007). Results: Cx for + K Poor performance by pre-2007 models Kaon-MAID Julia-Diaz, Lee, Saghai, Tabakin Sarantsev and Nikonov S. Anefalos Pereira April 13 - DIS 2011 Guidal, Laget, Vanderhaeghen Shklyar, Lenske, and Mosel Janssen, Ryckebusch Corthals, Ryckebusch, and Van Cauteren 45

Effect of including CLAS data in models cz cx p K+ • • multipole model • Nikanov et al’. ’s refit of Bonn-Gachina multicoupled- channel isobar model mix includes: S 11 -wave, P 13(1720), P 13(1900), P 11(1840) P 13(1900) is not found in quark-diquark models. Kaon-MAID the CLAS data is very important to constraint theoretic models Cx. Cz without N*(1900)P 13 Cx. Cz with N*(1900)P 13 V. A. Nikanov et al. , Phys Lett. B 662, 246 (2008). see also: A. V. Anisovich et al. , Eur. Phys J. A 25 427 (2005). S. Anefalos Pereira E. Santopinto Phys Rev. C 72, 022201(R), (2005) April 13 - DIS 2011 46

Total polarization for the “Fully Polarized ” Confirmed by GRAAL: A. Lleres et al. Eur. Phys. J. A 39, 149 (2009) - No model predicted this CLAS result. - For 0 channel no full polarization has been observed – RΣ 0 = 0. 82 0. 03 S. Anefalos Pereira April 13 - DIS 2011 47

Photoproduction on protons • Unpolarized cross sections • Single beam polarization • Recoil polarization • Double polarization (Beam and Recoil) – Circular polarized beam – Linear polarized beam S. Anefalos Pereira April 13 - DIS 2011 48

p K+ (g 8 b) Beam-Recoil Ox and Oz 1 0 -1 Kaon. MAID; RPR 2 -Regge only; RPR 2 -core; RPR 2 -w/D 13 Strong differences to the model predictions. These data will improve model capability. S. Anefalos Pereira April 13 - DIS 2011 49

p K+ (g 8 b) Beam-Recoil Ox and Oz 1 0 -1 Kaon. MAID; RPR 2 -Regge only; RPR 2 -core; RPR 2 -w/D 13 Strong differences to the model predictions. These data will improve model capability. S. Anefalos Pereira April 13 - DIS 2011 50

p K+ (g 8 b) Beam-Recoil Ox and Oz 1 0 -1 Kaon. MAID; RPR 2 -Regge only; RPR 2 -core; RPR 2 -w/D 13 Strong differences to the model predictions. These data will improve model capability. S. Anefalos Pereira April 13 - DIS 2011 51