Ξ and Ω Spectroscopy at Jefferson Lab

Transcription

1 Ξ and Ω Spectroscopy at Jefferson Lab Lei Guo Florida International Univeristy For the CLAS and GlueX Collaboration Supported by DOE 1

2 Ξ and Ω Spectroscopy at Jefferson Lab Motivation Ω - cross section measurement of γp Ω - K + K + K 0 and study of production mechanism (ΔS=-3) Cascade physics Excited cascade resonances (J P, missing states) Polarization measurement of Ξ - Testing various lattice QCD and hadronic models Existing photoproduction data Future experiments at CLAS12 and GlueX 2

3 The baryon decuplet J=3/2 Motivation: The Baryon Ground States in the Quark Model The baryon octet J=1/2 n S 0 p Σ Λ -1 Σ 0 Σ + I 3 Q Ξ -2 Ξ 0 N(Ω)=N(Δ*) N(Ξ)=N(N*)+N(Δ*) 3

4 Motivation: History of Ω - (sss) Baryon First measurement of J(Ω ) at SLAC: Ξ c 0 Ω Κ +, Ω Λ Κ J=3/2 J=5/2 J(Ω )=3/2, if J(Ξ c0 )=1/2 Barnes et al, PRL 12:204, Κ p Κ 0 K + Ω 1964, Aubert et al, PRL.97:112001,

5 Motivation: photoproduction mechanism of the very strangest baryon: Ω What is so strange about Ω - photoproduction? Mechanism totally unknown None of the constituent quark (s) is Backward Ω - from the target (ΔS=-3) V. Shklyar (Effective Lagragian) Different models predicts opposite angular preferences Cross section predictions are consistent: σ ~1nb at GlueX/CLAS12 energy range Forward Ω - A. Afanasev (VMD) 5

6 Motivation: Excited (PDG***) Ω/Ξ Baryons (half a century later) (J) P M(MeV) Γ(MeV) Ω(2250)?? 2250 Ξ(1530) (3/2) Ξ(1690) (1/2?)? 1690 <30 Ξ(1820) (-3/2?) Ξ(1950) (?)? Ξ(2030) (>=5/2)? Very few Ω/Ξ baryons have been identified in the last 50 years Even fewer have their quantum numbers determined Little is know about the production mechanism Photon beam could be a powerful alternative to Kaon beams 6

7 Motivation: Where are all the Ξ resonances Width (MeV) N Δ Λ Σ Ξ Cascades are narrower?: Number of strange quarks Ξπ decay suppressed for the lighter states Mass (GeV) easier to identify?, but more difficult to produce

8 Motivation: LQCD prediction for the S=-1 Hyperon Spectra Λ Flabor Structure of the excited baryon spectra from lattice QCD Σ 8 F 10 F Number of states compatible with QM predictions: Just as many missing states! S=-1 Hyperons can be also probed via the ΞK channel! R. Edwards et al. Flavor structure of the excited baryon spectra from lattice QCD,PRD 87, (2013) 8

9 Motivation: LQCD prediction for the Ξ and Ω spectra Ξ Ω 8 F 10 F Lattice QCD and CQM and consistent in terms of the number of missing states! 9

10 Existing Data(CLAS G11, 2004) Ground states are seen cleanly at CLAS Differential and total cross sections are extracted Comparison with model predictions suggest intermediate hyperons 10

11 Existing Data(CLAS G12, 2008) 2 Events/10MeV/c Ξ 0 M: ± : ± N: 2648 ± 132 S/B ratio: γ p K + K + π - (Ξ 0 ) MM(K K ) (GeV/c ) MM(K + K + K - ) (GeV/c 2 ) Ξ 0 /Λ/Σ decay chain not detected (can not determine J P ) Limited by beam energy, excited γ p K + K + (Ξ ) states unlikely in CLAS Expected total number of Ω - : CLAS/g12 data Need CLAS12 and GlueX!!! Λ Σ 0 E γ : GeV γ p K + K + K - (Λ/Σ) 11

12 Existing Data:Cross section results γ p K + K + (Ξ ) γ p K + K + (Ξ (1530)) These CLAS g11 results were sufficient for rate estimation; G12 cross sections being reviewed: Ξ* cross section upper limit ~1nb; Need CLAS12 and GlueX!!! 12

13 Spin-Parity Determination of Ξ* Spin can be measured by angular distributions (PWA) Parity measurement challenge: Minami ambiguity Ξ* Y (1/2 + ) + M 1 (0 - ): two solutions J P Double Moment Analysis (DMA) Y (1/2 + ) B (1/2 + ) + M 2 (0 - ) Double moments: H(lmLM)= Σ D L Mm (θ 1, φ 1 ) Dl m0 (θ 2, φ 2 ) DMA: 1 J + 2 H ( 11LM) = P(! 1) 2J + 1 2L( L+ 1) H (10LM) Linear dependence gives simple, multiple tests for J, P for any odd L 2J and M L 13

14 Example: Parity Measurement of Ξ(1820) Ξ(1820) CERN-SPS Ξ-Be reaction ImH(11LM) Needs corroboration " Biagi et al., Z.Phys.C34, 175 (1987) M(!K 0 )(GeV / c 2 ) 3 " Ξ(1820) 2 counts: ~50 Need to detect whole decay chain ImH(10LM) CLAS12 estimate: ~12k Ξ(1820) with complete decay chain at CLAS12 (80 beam days) 14

15 Existing data: Ξ induced polarization in photoproduction Very clean signals: Ξ - Λ Background γ K + π 0 p Y* K + Ξ - First time measurement! (Bono Ph.D Thesis, 2014) 15

16 Existing data(clasg12): Ξ Polarization in photoproduction Results VS prediction: Limited by statistics R~0.3 VS R~1 for Λ results Unable to distinguish models Future data expects orders of magnitude more statistics GlueX CLAS12: Very Strange Experiment 16

17 Future: Very Strange Experiment at CLAS12 with Forward Tagger Calorimeter Tracker HTCC Moller cup Scintillation Hodoscope Moller Shield GEMC implementation Ee : GeV θe : 2.5o-4.5o Q2: GeV2 Eγ: GeV Pγ: 10-85% 17

18 Future: CLAS12 Expected Particle Rate Detected particles Measured Decays Overall Efficiency Rate/hr Ω K + K + K 0 ~3.9% ~3.6 ~7k Ω K + K + K 0 K - Ω ~0.5% ~0.5 ~1k Total Detected Ξ K + K + π - Ξ ~9.3% ~440 ~0.9M Ξ (1530) K + K + π - Ξ (1530) ~7.4% ~140 ~270K Ξ (1820) K + K + K - p Ξ (1820)Λ ~0.63% ~6 ~12K Assuming half field and 80 beam days Vertex Efficiency/Branching Ratio included 18

19 2 Events/10MeV/c Future: CLAS12 Ξ Polarization and Ξ - (1820) Spin-Parity Measurement Ξ - polarization measurement: (should be E γ dependent)! p! K + K + " #! K + K + " # ($) Ξ - (1820) double moments! p! K + K + " # (1820) " # (1820)! K # ($! " # p) Expected M(ΛK - ) spectrum Ξ (1820) Pythia background MM(K K ) (GeV/c ) - P Ξ Im(H(113M)) Expected P Ξ vs E γ E γ =8.25 GeV P Ξ -=0.1 P Ξ -=0.3 cosθ Expected double moments (L=3) * Ξ Im(H(103M)) (statistical uncertainty only) 19 -

20 Ξ - Measurement: Future: CLAS12 Ξ and Ξ(1530) cross section measurements! p! K + K + " #! K + K + " # ($)! p! K + K + (" # ) Ξ - (1530) Measurement! p! K + K + " # (1530)! K + K + " # (" 0 )! p! K + K + (" # (1530)) Simulation assumed no angular dependence: Measurement in backward angle (CM) should have smaller uncertainty than shown due to larger expected cross section dσ/dcosθ (nb) dσ/dcosθ (nb) d! c.m d cos"! " d! c.m d cos"! " (1530) - Ξ cos(θ c.m ) cos(θ c.m - Ξ (1530) ) 20

21 (nb) - Future: CLAS12 Ω Mass Spectrum and Cross Sections Ω - Measurement: When four kaons detected, spectra is expected to be background FREE! p! K + K + K 0 (" # )! p! K + K + K 0 K # ($) Expected Cross section Measurements (Assuming no energy or angular dependence) σ Ω Important to understand the production mechanism E γ (GeV) Counts Constrain! mass "=0.005 GeV Unconstrained "=0.030 GeV 0 Detect K+K+K K- cos( ) c.m. M(ΛK - ) E (GeV) MM(K + K + K 0 ) 21

22 Future: GlueX: Expected yields of Ξ states GlueX Proposal on Decays to Strange Final States (Jlab PAC39, 40 and 42) GlueX an ideal place to search for excited cascades: More uniform acceptance than CLAS12 Gound states more challenging Due to the fast Kaon, and slow pion from excited cascades decay Excited states could be more favorable: Slower kaon and faster pion Expected for some cascade states at GlueX (Assuming σ Ξ-(1320) ~15nb, and σ Ξ-(1530) ~2nb) Ξ - (1320) : ~800,000 Ξ (1530): ~100,000 K+K+K-Λ final state: ~90,0000 (Pythia) GlueX/CLAS12 mesurements are complimentary 22

23 Future:K 0 L Workshop on Physics with Neutral Kaon Beam at Jlab : Newport News, VA 2016 (arxiv: ) beams at Hall D? K 0 L beam created from photon beam on a Be target in Hall D ΔL ~ 16m (From Be to LH2 targets) ~2000 /sec (x10 higher than LASS experiment at SLAC Opportunities for X and W spectroscopy with KL beams Cascade production: ~10 4 Ξ*/month K L 0 p! K + " 0(*) ;K +! + " #(*) Omega production: K L 0 p! K + K + " #(*) ~10 2 Ω*/month 23

24 The Very Strange Collaboration A. Afanasev 1,2, M. Amaryan 3), Ya.I. Azimov 4), N. Baltzell 5), M. Battaglieri 6), V. Baturin 2),W. Boeglin 7), J. Bono 7), B.Briscoe 8) V. Burkert 2), S. Capstick 9), D. Carman 2), A. Celentano 6), V. Crede 9), R. De Vita 6), M. Dugger 10,*), G. Fedotov 11), G. Gavalian 3) J. Goetz 12,*), L. Guo 7, **), D. Glazier 13), H. Haberzettl 8), S. Hasegava 14), K. Hicks 15), D. Ireland 16), P. Khetarpal 7), F. Klein 17), A. Kubarovsky 18), V. Kubarovsky 2), M. Kunkel 3), K. Livingston 16), H. Lu 19), P. Markowitz 7), P. Mattione 19), V. Mokeev 2), K. Nakayama 20), Y. Oh 21), M. Osipenko 6), M. Paolone 22), E. Pasyuk 2,*), J. Price 23), B. Raue 7), M. Ripani 6), B. Ritchie 10), W. Roberts 9), F. Sabatie 24), H. Sako 14), C. Salgado 25), S. Sato 14), K. Shirotori 14), V. Shklyar 26), S. Stepanyan 2), I. Strakovsky 8,*), M. Taiuti 6), N. Walford 17), D. Watts 13, *), D. Weygand 2), R. Workman 8), V. Ziegler2, *) 1) Hampton University, USA 2) Thomas Jefferson National Accelerator Facility, USA 3) Old Dominion University, USA 4) Petersburg Nuclear Physics Institute,, Russia 5) Argonne National Laboratory, USA 6) INFN Genova, Italy 7) Florida International University, USA 8) The George Washington University, USA 9) Florida State University, USA 10) Arizona State University, USA 11 ) University of South Carolina, USA 12) University of California at Los Angeles, USA 13) Edinburgh University, United Kingdom 14) Japan Atomic Energy Agency, Japan 15) Ohio University, USA 16) University of Glasgow, United Kingdom 17) Catholic University of America, USA 18) Rensselaer Polytechnic Institute, USA 19) Carneige Mellon University, USA 20) University of Georgia, USA 21) Kyungpook National University, Republic of Korea 22) Temple University, USA 23) California State University, Dominguez Hills, USA 24) CEA-Saclay, France 25) Norfolk State University,, USA 26) Giessen UniversityGermany 24

25 Summary Ω/Ξ baryons are underexplored CLAS12/GlueX is well suited to study Ω/Ξ physics CLAS12 Very Strange Experiment with Forward Tagger GlueX and possible K L beam in Hall D Ω : cross section can be measured production mechanism can be investigated (Missing) Excited cascade resonances: Spin-Parity could be determined Ξ(1320) polarization: insight to the production mechanisms Intimately related to intermediate hyperons 25

26 Backup Slides 26

27 Cross Sections: Rate Estimation Assuming σ(ω - )~ 0.3nb (Afanasev, Roberts, Shklyar) σ(ξ - )~15nb (Oh, Nakayama, et al.) SLAC inclusive: 117nb@20GeV σ(ξ - (1820/1690)): around 1-5nb (Oh et al) Luminosity: cm -2 s -1 FT acceptance: 2.5~4.5 o (θ) Ω - rate: 90/hr 0.5~5.0GeV (E e ) Ξ- rate: 3.6k/hr Ξ (1690)/Ξ (1820): k/hr CLAS12 acceptance not yet accounted for σ(ξ - ) σ(ω - ) Eγ<4.8GeV Hadronic translation Roberts 1 Roberts 2 Shklyar 27

28 Excited Cascade Production (Prediction) σ (nb) Eγ(GeV) Eγ(GeV) K. Nakayama, Y. Oh, and H. Haberzettl results obtained using parameters obtained from PRC74, (2006) Predictions for the Ξ(1820) IS consistent with CLAS data: signal would have been insignificant 28

29 Expected Results: Mass Splitting Measurements Ξ - Measurement:! p! K + K + " #! K + K + " # ($)! p! K + K + (" # ) Ξ 0 Measurement! p! K + K + " (# 0 ) CLAS! p! K + K 0 (# 0 )! K + " + " (# 0 ) Measurements feasible in multiple channels to reduce systematic uncertainty Calibration can be tuned using other well CLAS12/Simulation know states (Λ, Σ, K s, etc)! stat (M Expected statistical uncertainty:! " " M! 0 ) < 0.1MeV 29

30 Energy Dependence of the Ξ - Cross Sections dσ/dm(ξκ) dσ/dcosθ Ξ - (nb) σ Ξ (Ε γ ) Ε γ =2.9GeV Ε γ =3.8GeV cosθ - Ξ dσ(nb/gev) Nakayama et al. predicts plateauing behavior at higher beam energies PRC 74, (2006) PRC83, (2011) Model only included limited number of intermediate hyperons The Ξ - cross section could continue to increase at higher E γ Angular distributions expected to change with E 30 γ

31 Simulation and Background Estimation (Ω ) Main source: Hadronic background Pythia Simulation: γ p p+anything S/B ratio 1:10 Λ cut and vertex cut γ p K + K + K 0 K - (Λ) Data almost background free if vertex cut is included γ p K + K + K 0 (Ω ) Ω MM(K + K + π + π ) (GeV) Pythia bg Pythia bg +vertex cut Pythia background Ω 100 Vertex resolution:1.0mm Detached vertex cut: 5mm M(K - Λ) (GeV) (5-10% loss of data) 31