A Search for the LHCb Charmed Pentaquark using Photoproduction of J/ - PowerPoint PPT Presentation


 A Search for the LHCb Charmed “Pentaquark” using Photoproduction of J/ ψ at Threshold in Hall C at Jefferson Lab Sylvester Joosten sylvester.joosten@temple.edu on behalf of the spokespeople Eugene Chudakov Mark Jones Sylvester Joosten Zein-Eddine Meziani Michael Paolone PAC 44, July 26, 2016

The LHCb charmed “pentaquark” P c is a hot topic Since the CERN press release from July 14, 2015… 221 citations in a year! Discovery inspired large number of theoretical work, touching our community and beyond 2

Discovery of the LHCb charmed “pentaquark” P c Λ b → K − pJ/ Ψ Aaij, R, et. al (LHCb) PRL 115-7 (2015) Λ b → Λ ∗ J/ Ψ → ( K − p ) J/ Ψ 2 P c states needed to Λ b → K − P c → K − ( pJ/ Ψ ) describe results narrow: P c (4450) (12 σ ) narrow : P c (4450) wide : P c (4380) wide: P c (4390) (9 σ ) spin/parity either: 5/2+, 3/2- 
 (most likely!) 5/2-, 3/2+ 3/2-, 5/2+ 3

charmed “pentaquark” in photo-production Common explanations: LHCb: 2 new charmed “pentaquark” ( P c ) states alternative: kinematic enhancements through anomalous triangle singularity (ATS) Lui X-H, et al., PLB 757 (2016), p231 
 (and references therein) Photo-production ideal tool to distinguish between both explanations if P c real states, also created in photo-production kinematic enhancement through ATS not possible in Wang Q., et al., PRD 92-3 (2015) 034022-7 
 photo-production (and references therein) P c (4450) translates to narrow peak around E γ = 10 GeV JLab is the ideal laboratory for the measurement, due to luminosity, resolution and energy reach at threshold! 4

J/ ψ photo-production: what do we know? e − Cross section well constrained above c 100 GeV γ J/ Ψ c Almost no data near-threshold Resolution of the existing e + P’ measurements too low P t -channel 2 of the 3 lowest points unpublished! Brodsky S J, et al., PLB 498-1 (2001), p23 3 3 10 10 [nb] [nb] Cornell 75 σ σ SLAC 75 2 2 10 10 SLAC 76 (Unpub.) Cornell 75 2-gluon fit 10 10 SLAC 75 SLAC 76 (Unpublished) CERN NA14 1 1 FNAL E401 FNAL E687 * H1 Combined ( ) γ 1 − 1 − 10 10 * ZEUS Combined ( ) γ P c ? * LHCb 2014 ( ) γ 2 2 − − 10 10 3 5 6 2 4 10 15 20 10 10 10 10 10 10 5 5 E [GeV] E [GeV] γ γ

Resonant J/ ψ production through P c decay γ γ J/ ψ J/ ψ Cross section depends on coupling to ( J/ ψ , p ) channel P c P c J/ ψ angular distribution s − channel u − channel P’ P depends on P c spin/parity P’ P s-channel u -channel (a) (b) 3% coupling Arbitrary Units 1 4 [nb] t-channel J/ Ψ Cornell 75 P 5/2+ σ c SLAC 76 (Unpublished) 0.8 P 3/2- c 3 t-channel (2-gluon) P 5/2- c P 5/2+ (3% coupling) c P 3/2+ c 0.6 P 3/2- (3% coupling) c sum 2 0.4 1 0.2 0 1 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1 0 − − − − − 8 8.5 9 9.5 10 10.5 11 11.5 12 cos( ) θ E [GeV] d σ γ ( γ p → P c → J/ ψ p ) Leverage cos( θ ) dependence to d cos θ J/ ψ maximize S/B at low coupling! Wang Q., et al., PRD 92-3 (2015) 034022-7 6

Proposed Experiment in Hall C Run with 2 settings: Setup similar to E-05-101(WACS) 50 μ A electron beam at 10.7 GeV ”SIGNAL” Setting (9 days): (or 11 GeV) minimizes accidentals and 9% copper radiator maximizes signal/background : HMS: 34 o , 3.25 GeV electrons 15cm liquid hydrogen target SHMS: 13 o , 4.5 GeV positrons total 10% RL + e ”BACKGROUND” Setting: 
 S2Y LGC 4 S2X A1 (2 days): precise determination of HGC S1XS1Y C4F10 Cerenkov DC2 1 2 DC1 AGC the t -channel background Argon/Neon Cerenkov 2 D 1 S M H 3 S Q Q HMS: 20 o , 4.75 GeV electrons Q HB positron in SHMS 9% Cu Radiator SHMS: 20 o , 4.25 GeV positrons To beamdump Incident beam Detector Stacks: Hydrogen Standard Detector Package, Q target Tracking/ Timing: Q HMS Q 1. Drift Chambers Radiator Well Understood 2. Hodoscopes D 1 Particle ID: 3. Gas erenkov 2 3 4. Lead Glass Calorimeter Bottom line: 
 4 2 - e can run SOON and FAST electron in HMS 7

Maximizing the sensitivity Use HMS and SHMS to maximize P c “SIGNAL” Setting signal over t -channel background Arbitrary Units 4 t-channel J/ Ψ P 5/2+ c P 3/2- c 3 P c (4450) 5/2+ P 5/2- positron in c P 3/2+ c SHMS 2 1 0 1 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1 − − − − − cos( ) θ electron in t -channel HMS 8

Background: Bethe-Heitler pair production γ p → e + e − p k k l + l + l - Not an issue! l - Estimated using p p p’ p’ calculations from Pauk and Vanderhaeghen 1 [nb] Constant background 
 σ < 10% of the t -channel J/ ψ Can be exactly calculated 1 − 10 Cornell 75 and controlled for SLAC 76 (Unpublished) Interference negligible at t-channel (2-gluon) Bethe-Heitler the P c (4450) peak 2 − 10 Pauk V and Vanderhaeghen M, PRL 115(22) (2015) 221804 8 8.5 9 9.5 10 10.5 11 11.5 12 E [GeV] γ 9

Background: lepto-production problem: 50 μ A electron beam travels through target! solution: only quasi-real photons ( Q 2 ~ 0.01 GeV 2 ) play a role! virtual photon flux drops with Q 2 higher Q 2 means lower W 2 for fixed ν and t -channel cross section drops for lower W 2 phase space drops rapidly for lower W 2 acceptance drops with Q 2 6 − 10 × ] Acceptance 2 4 xsec [nb/GeV 2 e p (Q > 0.01) Setting "SIGNAL" 0.001 3 2 0.0005 1 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 2 2 2 2 Q [GeV ] Q [GeV ] Quasi-real photons ENHANCE the count rate 10

Background: single e ± and π ± tracks electron rate estimated using CTEQ5, cross checked with F1F209 positron rate estimated using EPC combined with a background program from E94-010 coincidence rate < 10 -5 Hz (50ns trigger window) pion rates estimated using Wiser Assuming a pion rejection > 10 3 from the Cherenkov + Calorimeter, coincidence rate ~ 10 -5 Hz Accidental Rate < 10 -2 x Signal Rate NEGLIGIBLE! 11

Acceptance ”SIGNAL” Setting: acceptance edges far removed from P c peak position ”BACKGROUND” Setting : acceptance centered to the left of the P c peak position “SIGNAL” Setting “BACKGROUND” Setting 3 3 − − 10 10 × × Acceptance Acceptance 0.6 t-channel J/ t-channel J/ Ψ Ψ 0.03 P 5/2+ P 5/2+ c c 0.4 0.02 0.2 0.01 0 0 8 8.5 9 9.5 10 10.5 11 8 8.5 9 9.5 10 10.5 11 E [GeV] E [GeV] γ γ Good Acceptance over the full width of the resonance 12

Projected results for “SIGNAL” Setting assuming 5% coupling (value favored by existing photo-production data) Wang Q., et al., PRD 92-3 (2015) 034022-7 t -channel: 120 events 9 days of beam time at 50 μ A 5/2+: 881 events 5/2+ peak dominates the spectrum 3/2-: 266 events Counts Counts t-channel J/ t-channel J/ Ψ Ψ P 3/2- (5.0% coupling) P 3/2- (5.0% coupling) c c 200 P 5/2+ (5.0% coupling) P 5/2+ (5.0% coupling) c c sum sum 200 9 day estimate 9 day estimate 150 100 100 50 0 0 6 5 4 3 2 1 0 1 2 9 9.5 10 10.5 11 11.5 12 − − − − − − 2 E [GeV] t [GeV ] γ Only 9 days! Significance > 20 σ ! 13

Projected results for “BACKGROUND” Setting 2 days of beam time at 50 μ A able to separate 5/2+ from t -channel at low E γ will provide first-hand information about t -channel production near threshold t -channel: 682 events assuming 5% coupling (value favored by existing 5/2+: 204 events 3/2-: 26 events photo-production data) 150 Counts Counts 300 t-channel J/ t-channel J/ Ψ Ψ P 3/2- (5.0% coupling) P 3/2- (5.0% coupling) c c P 5/2+ (5.0% coupling) P 5/2+ (5.0% coupling) c c sum sum 100 200 2 day estimate 2 day estimate 50 100 0 0 6 5 4 3 2 1 0 1 2 9 9.5 10 10.5 11 11.5 12 − − − − − − 2 E [GeV] t [GeV ] γ Only 2 days! 14

Sensitivity for Discovery sensitivity calculated using a Δ -log-likelihood formalism 5 standard deviation level of sensitivity starting from 1.3% coupling! Projection for 1.3% coupling ] σ Counts Sensitivity [n t-channel J/ Ψ P 3/2- (1.3% coupling) 10 c P 5/2+ (1.3% coupling) c 20 sum 9 day estimate 10 Projected Sensitivity 5 limit σ 1 0 1 1.5 2 2.5 3 9 9.5 10 10.5 11 11.5 12 coupling [%] E [GeV] γ 15

Impact on the world data for J/ ψ production [nb] "SIGNAL" Setting (9 days) "BACKGROUND" Setting (2 days) σ 3 Cornell 75 SLAC 76 (Unpublished) J/ with P (5% coupling) ψ c 2 1 0 8 8.5 9 9.5 10 10.5 11 11.5 12 E [GeV] γ 16

Run Plan Total Beam Time Request: 11 days (264h), 10.7 GeV (or 11 GeV), 50 μ A, Hall C Run Plan: 1. t -channel “BACKGROUND”: 40 hours 2. radiator out: 8 hours (longer if needed) 3. main “SIGNAL” measurement: 216 hours 11 days, 
 standard equipment! 17

Summary High impact result will either confirm P c resonance, or strongly exclude its existence Strong sensitivity to the coupling down to 1.3% Will provide knowledge about J/ ψ production (absolute cross section!) near threshold Helps future experimental endeavors at CLAS12 and SoLID Only need 11 days Straightforward experiment, able to run early with a standard Hall C package 18

Collaboration 19

APPENDIX BACKUP SLIDES