Contents 2

J-PARC E19 Collaboration 3

Pentaquark search 4 Genuine exotic hadron (uudds bar ) M = ~1540 MeV/c 2 (decay    KN) Situation is still controversial... Pentaquark   Historical background   pentaquark was first predicted by Diakonov et al. in SPring8/LEPS group reported the evidence for   in Dozen experimental groups published supporting evidence for the  , followed by a number of experiments with no evidence.

Physics Motivation Distinctive feature of  + pentaquark – Need some mechanism to suppress decay. 5 Meson-Baryon molecule Diquark structure (Need quark rearrangement for KN decay) R.Jaffe, F.Wilczek (2003)

Our Approach ( J-PARC E19 ) 1.Pion induced reaction – Complementary to photo-production (LEPS/CLAS). – Expect sizable production cross section. => High statistics 6   + p → K  +  + 2.High resolution missing mass spectroscopy – K1.8 beam line & SKS =  M < 2 MeV (FWHM) 2.6  KEK-PS E522 Miwa et al., PLB 635, 72.  M ~ 13.4 MeV (FWHM)  M ~ 13.4 MeV (FWHM) Previous experiment

Our Approach ( J-PARC E19 ) 1.Pion induced reaction – Complementary to photo-production (LEPS/CLAS). – Expect sizable production cross section. => High statistics 7   + p → K  +  + 2.High resolution missing mass spectroscopy – K1.8 beam line & SKS =  M < 2 MeV (FWHM)

Experimental setup 8   beam 1.92/2.00 GeV/c Dedicated to the ( ,K) reaction spectroscopy

History of E19 9 This presentation Shirotori et al., PRL 109, (2012).   Peak was not observed. We concluded that E522 bump was not the signal by 10 times higher sensitivity.

Note on   decay width 10 PV Fs 500MeV PV Fc 1800MeV sqrt(s) [MeV]  [  b] J p =1/2 +,   = 1MeV Theoretical calculations : T. Hyodo et al., PRC 72, (2005), PTP 128, 523 (2012). p lab =2.0 GeV/c p lab = 1.92 GeV/c Higher beam momentum provides higher sensitivity.  2.0 GeV/c ( = Max. of K1.8 B.L.) Even if no peak, stronger constraint on the   decay width will be obtained. s-channel dominance    ∝ g 2 KN  ∝ 

Result of the E19-2nd run 11

SKS spectrometer 12 K K Scattered particle M 2   p p M 2 [GeV 2 ]  SKS system : p K PID counters – Timing counter – Aerogel Cherenkov (K/  ) : n=1.05 – Lucite Cherenkov (K/p) : n=1.49 Tracking – MWDCs : 3 mm pitch – DCs : 10 mm pitch, 2m×1m size Good momentum reconstruction and PID !! We can separate only K very clearly. Example of analysis 1

Vertex-Z Vertex-(X vs Y) Vertex Reconstruction 13 LH2 Target cell  67.8 × 120 mm  K Target cell is clearly identified !! Consistent with horizontally oblate beam shape. window Beam LH2 target Empty target (scaled) Example of analysis 2

Consistency check with previous exp. 14   + p → K + +  1.37 GeV/c Missing mass resolution:  M  = 1.92 MeV (FWHM) – Equivalent to the 1st run. Cf.) 1.86±0.08 E19-1st   Missing Mass  M = 1.92 ±0.05 MeV   + p → K + +  1.37 GeV/c  E19-2 nd Preliminary  M  = 1.74 MeV (FWHM)

15   + p → K + +  1.37 GeV/c Missing mass resolution:  M  = 1.92 MeV (FWHM) – Equivalent to the 1st run. Cf.) 1.86±0.08 E19-1st   Differential Cross Section Preliminary Differential cross section – Almost consistent with 1st run and reference data. – Good understanding of efficiencies and acceptance.   + p → K + +  1.37 GeV/c Consistency Check  OK Consistency check with previous exp.  M  = 1.74 MeV (FWHM)

E19-2 nd Preliminary Analysis Result of E19-2nd run No peak structure was observed. Upper limit on differential cross section averaged from 2 to 15 deg: < 0.28  1.50 – 1.57 GeV/c 2 16   + p → K  + p  = 2.0 GeV/c An example of fitting GeV/c 2 Fitting results of each mass and Upper limit (90%C.L.)

Upper limit on decay width MeV for ½+ 3.7 MeV for ½ MeV for ½+ 3.7 MeV for ½- g KN  Considering about theoretical uncertainty (coupling scheme and form factor), we chose the most conservative case as the upper limit.   ∝ g 2 KN  ∝  T. Hyodo et al., PTP 128, 523 (2012). Upper Limit on   for J P 

Summary J-PARC E19 is a pentaquark   search experiment with high statistics and high resolution. –   p → K   + reaction – J-PARC K1.8 B.S. and SKS New result of E19-2 nd run was presented. – Consistency with the 1 st run was checked.  O.K. –   missing mass resolution of 1.74 MeV was evaluated. – No peak structure was observed in MM spectrum. – Upper limit for   production cross section was obtained to be 0.28  1.50 – 1.57 GeV/c 2 – This corresponds to upper limit on   decay width of 0.61 and 3.7 MeV for J P = ½+ and ½-, respectively. 18

BACKUPS 19

1st run result of E19 No prominent peak structure No prominent peak structure < 0.26  b/sr Upper limit: < 0.26  1.51  1.55 GeV/c 2 20   + p → K  GeV/c E19-1st data background (sim.) s-channel dominance   ∝ g 2 KN  ∝   Upper limit of decay width 0.72 MeV for ½+ 3.1 MeV for ½ MeV for ½+ 3.1 MeV for ½- Shirotori et al., PRL 109, (2012).

Comparison with background simulation 21 Simulation with measured cross section using angular distributions  production : uniform (S-wave)  (1520) : ∝ 1+cos 2  cm  (D-wa ve ) BG reactions    p →  n→K  K  n  = 30±8  b)    p →  (1520) K  →K  K  p  = 21±5  b)    p →K  K  n    p →K  K  p  ~25  b) O. I. Dahl et al. Phys. Rev. B 163, 1377 (1967). (Bubble chamber data)

Cut condition :     < 15 deg Vertex-(X 2 +Y 2 ) < 25 2 mm < Vertex-Z < 60 mm 0.15 < m 2 < 0.4 GeV 2  2 cut : Local tracking  2 < 20 (BcOut  2 < 10) SKS, K18 tracking  2 < 30 22

23 Previous experiments at KEK-PS E522 :   p → K   1.92 GeV/c E559 :   p →    1.20 GeV/c K. Miwa et al., PLB 635, 72 (2006). K. Miwa et al., PRC 77, (2008). 2.6  Bump structure (2.6  )  Not enough to claim the existence Upper limit:  < 3.9  b (90% C.L.) Bump structure (2.6  )  Not enough to claim the existence Upper limit:  < 3.9  b (90% C.L.) No peak structure Upper limit:  < 3.5  b/sr (90% C.L.) No peak structure Upper limit:  < 3.5  b/sr (90% C.L.)   -induced   -induced Prev. Exp GeV

Positive Results (~2005) LEPSDIANACLAS-d HERMES ITEP COSY-TOF ZEUS SVD SAPHIR CLAS-p 4.3  3.4  3.2  5.1  3.6  4.9  3.6  4~5  4.7  4.4  24 [CAUTION] Significances ware recalculated by significance = S/√(S+B) or S/dS

Positive Results (updated) LEPS DIANA HERMES ITEP ZEUS SVD CLAS-p 5.5  5.1  3.6  4.9  3.6  4~6  5.8  25 CLAS-d < 0.3 nb COSY-TOF < 0.15  b Some confirmed their evidence, but others did not... Some confirmed their evidence, but others did not... [CAUTION] Significances ware recalculated by significance = S/√(S+B) or S/dS

Negative Results 26 FOCUS BABAR SPHINX CDF BES BELLE LEP HERA-B HyperCP PHENIX (   ) 

27 J-PARC Hadron facility High-p K1.1BR K1.8BR K1.8 Primary proton beam T1 target KL

GC BH1 BC1 BC2 K1.8 Beam Spectrometer SKS Spectrometer MS2 Q10 Q11 Q12 Q13 D4 SDC3 SDC4 TOF LC AC1 AC2 SDC2 SDC1 BC4 BC3 BH2 Target 2009 Oct 28

2011 Sep. Injection angle : 30  15 deg. Higher-momentum acceptance. Higher-momentum acceptance. For future experiments. For future experiments. Injection angle : 30  15 deg. Higher-momentum acceptance. Higher-momentum acceptance. For future experiments. For future experiments. Rotation of SKS 29 Recovery from the earthquake

Setup difference of 1 st and 2 nd run 30 E19-1 st run (2010)E19-2 nd run (2012) 30 deg. injection 15 deg. injection