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Pentaquarks:

Pentaquarks:. An Experimental Overview. Curtis A. Meyer. Based, in part, on work carried out with Alex Dzierba and Adam Szczepaniak. Outline Overview of the positive evidence data, statistics, specific results Overview of the negative results The  and c The +

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Pentaquarks:

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  1. Pentaquarks: An Experimental Overview Curtis A. Meyer Based, in part, on work carried out with Alex Dzierba and Adam Szczepaniak Outline Overview of the positive evidence data, statistics, specific results Overview of the negative results The  and c The + Issues with some of the data Summary & Conclusions Before 2003 …. searches for flavor exotic baryons showed no evidence for such states. Since 2003 …. Hadronic Physics has been very interesting. hep-ex/0412077

  2. Spectacular Development +! K+n 1997: Diakonov, Petrov and Polykov use a chiral soliton model to predict a decuplet of pentaquark baryons. The lightest has S=+1 and a mass of 1530 MeV and expected to be narrow. Zeit. Phys. A359, 305 (1997). 2003: T. Nakano et al. n ! K+K-n on a Carbon target. Phys. Rev. Lett. 91, 012002, (2003) The Dam Breaks ….

  3. Positive Sightings + Reaction searched Claim Decay 0c Experiment 5 publication + pA! pK0SX + C12! K-K+n LEPS SVD K+n K0Sp hep-ex/0401024 PRL 91 (2003) 012002 + + d! K+K- np p!+K-K+n A! K0SpX  CLAS BC at CERN & FNAL hep-ex/0309042 K0Sp K+n PRL 91 (2003) 252001, PRL 92 (2004) 032001 ep! e’pK0SX + + p! K0SK+n HERMES SAPHIR (quasi-real photoproduction) K+n K0Sp Phys.Lett.B585(2004) 213 Phys.Lett B572 (2003) 127 + + ep! e’pK0SX pp!+K0Sp ZEUS COSY K0Sp K0Sp Phys.Lett.B595 (2004) 127 Phys.Lett.B592(2004)7 5 + pp! X K+Xe! K0SX’ DIANA NA49  K0Sp Phys.Atom.Nucl.66(2003)1715 PRL 92(2004)042003 0c + p+C3H8! K0SpX ep! e’pD*-X JINR H1 D*-p K0Sp Phys.Lett.B588(2004)17 hep-ex/0401024 (Table by Alex Dzierba)

  4. The Data Reported Significance 4.8 5.2 4.6 7.8 5- -50 4.2 ~5 4.4 6.7 0c 4.6 ~5 ~5.5 4.3 5.6

  5. Summary of Results + 5--50 Na49: Mass: 1862 MeV Width < Resolution Charge Exchange c0 H1: Mass : 3100 MeV Width ~10 MeV A narrow structure whose width is less than experimental resolution Old data constrain <1MeV

  6. Statistics Experiment Signal Background Significance Publ.123 Spring8 19 17 4.6 4.6 3.2 2.6 Spring8 56 162 4.4 3.8 2.9 SPAHIR 55 56 4.8 7.3 5.2 4.3 CLAS (d)** 43 54 5.2 5.9 4.4 3.5 CLAS (p) 41 35 7.8 6.9 4.7 3.9 DIANA && 29 44 4.4 4.4 3.4 2.7  189 6.7 6.0 3.5 3.0 HERMES 51 150 4.3-6.2 4.2 3.6 2.7 COSY 57 95 4-6 5.9 4.7 3.7 ZEUS 230 1080 4.6 7.0 6.4 4.7 SVD 41 87 5.6 4.4 3.6 2.8 NOMAD 33 59 4.3 4.3 3.4 2.7 NA49 38 43 4.2 5.8 4.2 3.4 NA49 69 75 5.8 8.0 5.8 4.7 H1 50.6 51.7 5-6 7.0 5.0 4.1 5 c ** An improved analysis shows a less significant peak! &&Shown to be charge exchange

  7. Zeus Result Fragmentation, Q2>20GeV2 Interesting Result ~6000  ~200 (1520) 230 + fragmentation is a good source of +! KS p is not manifestly Exotic. It could be a  Phys. Lett. B591 (2004) 7. Mass=1465 Width=15 368 Events ? Observe: + mass=1.521 GeV width=6.1 MeV 230 Events on 1080 Background No Signal for: 5 , 0c (U.Karshon, Pentaquark-04)

  8. LEPS • C ! K+ K- X Assume that the reaction is  n !+ K- Calculate Missing Mass( n ! K- X ) d ! K+K-X Assume  n !+K- Highly unconstrained final states Unknown Backgrounds Many Cuts to pull out the signal Cuts to remove: ! K+K- (1520)! p K- d ! K+K- d Missing Mass( d, KK X) is a neutron Fermi Momentum Corrections Backgrounds: KKN phase space (1020) ,

  9. CLAS Fit + Published d ! K+K- p (n) miss Reaction is unknown Independent analysis of the data: energy loss corrections from target 1C-Kinematic fit to final state Flat confidence level Known resonances get sharper and have the right mass: (1520) (1020) Evidence for higher mass , S ‘ s and either the a2(1320) or f2(1270) is sharper. Disturbing Effect on the + ! NOT AN OFFICIAL CLAS RESULT

  10. COSY  KS p  pp!++ +! KS p KS!+- +! n + +  2 Hits in the first hodoscope + & p 4 Hits in the 2nd and 3rd planes +-+ p (2-plane hodoscopes so ambiguous) No Particle Identification, No Momentum Measurement, No charge measurement. Pure Geometry and a zero constraint fit to the reaction

  11. Negative Reports Hadronic Z decays + + c0 c0 hep-ex/0408025,0410024 5 5 Submitted to Phys. Lett. B Hadronic Z decays (+,K+,p)Cu ! PX + + hep-ex/0410027 hep-ex/0410080 + + (,p,)p! PX Quark Confinement 2004 hep-ex/0410080 + -N! PX p! PX c0 5 5 DPF 2004 hep-ex/0410029 + pp! PX ep! PX c0 5 5 hep-ex/0407026 QNP2004 - pA! PX e+e-! J/ ((2S) + + 5 PRD 70 (2004) 012004 Accepted in PRL + + KN! PX pC(N)! K X c0 hep-ex/0411005 hep-ex/0407026 e+e-!U (4S) + + AuAu! PX hep-ex/0408064 5 nuc-ex/0404001 + + K+p! K+ n + LASS hep-ex/0412031 5 (Table by Alex Dzierba)

  12. The --(1861)

  13. NA49 5(1860) fixed target experiment at CERN - spectrometer 158 GeV/c proton beam width is below detector resolution

  14. Null Results 5(1860) HERA-B

  15. Null Result 5(1860) ALEPH and ZEUS also null result CDF FOCUS

  16. The 0c(3100)

  17. H1 at HERA

  18. Null Results ZEUS CDF FOCUS

  19. The +(1540)

  20. Bubble Chamber No signals in the Dalitz Plots (Taken from the PDG, 2004)

  21. Scattering Data K+n P-wave Phase Shifts 1MeV wide resonance at 1540

  22. Negative Results HERA-B pC! pK0SX SPHINX e+e-! (p K0)X ALEPH BaBar (1520) K*(892) +? CDF HyperCP +(1540) BELLE (1520) pKS

  23. SPHINX 70 GeV p on Carbon Targets The detector is sensitive to charged particles and the direction of neutrons and KL by hits in the BCAL. p + N ! p K+ K- N p + N ! p KS KL N p + N ! p KS KS N p + N ! n K+ KS N p + N ! p KL KL N p + N ! n K+ KLN Detect (1520) in p K-, n KS No  in either p Ks or n K+ Don’t See ~16000 (1520) nK+ pKL pKS Monte Carlo

  24. Belle e+e- with an interesting twist Look at the pKS pK- and pK+ final states whose primary Vertex is from material in the detector (1520) pK- pKS 16000 (1520)! K- p Exclude:  N !(1520) K-p !(1520) Signal comes from KN!(1520)X No signal in KS p It is very hard to produce the + In K+N interactions, but it falls apart into this just fine.

  25. SELEX 0.1% of Data (1520) No + 2,800,000 Mass (KS p) Mass (K-p) Mass (KS p) 600Gev Beams (-,-,p,+ ) (67%,14%,18%, 1%) Very significant charmed baryon results.

  26. CDF Resonance Min. Bias Jet>20GeV (1520) 3276§ 327 4915§ 702 K*+ 15695§ 775 35769§ 1390 + 18§ 56 -56§ 100 90% CL + <89 <76 +KS pK- + cc p KS + cc

  27. The Numbers Experiment(1520)  Lc ____________________________________ E690 5000 ALEPH 2800 CDF 3300 16000 BaBar 10000000 100000 HERA-B 5000 3000 50000 SPHINX 5500 23700 12000 HYPERCP COMPASS BELLE 15520 SELEX 2,800,000 ____________________________________ (1530) D D* ________________________________________________________ E690 15000 ALEPH 3350 200 25000 CDF 36000 1000 3000000 536000 BaBar 258000 17000 HERA-B 18000 ZEUS 2600 160 WA89 676000 FOCUS 84000 36000 Experiment s b (1520)  ____________________________________________ Spring 8 19 17 25 Spring 8 56 162 180 SAPHIR 55 56 530 CLAS(d) 43 54 212 126 CLAS(p) 41 35 DIANA 29 44 1152  19 8 HERMES 51 150 850 COSY 57 95 ZEUS 230 1080 5700* 193 SVD 35 93 260 NOMAD 33 59 ________________________________________ s b  D* ________________________________________ NA49 38 43 1640 H1 50 52 3000 ________________________________________ Positive Results Some Negative Results * Estimate from cross section

  28. Low Energy Experiments Kinematic Reflections a2(1320)! K+K- +(1540) Produce a spin-2 or spin-3 resonance that decays to K+K- . Have non-uniform populations of |m|=0,1,2,… Produces a broad enhancement near 1.5 (1020) a2(1320)/f2(1270) CLAS f2(1270) Mass(+-)

  29. Kinematic Reflection? The CLAS  d ! p n K+K- Data Mass (K+n) Mass (K+K-) Mass (K-n) Solid lines are predicted using K+K- resonances Kinematic Fit (Dzierba, et al.)

  30. Statistical Fluctuation You need to understand your background to claim a new discovery! Chance of the Background Fluctuating into the observed signal CLAS Published Simple Physics Background Naïve Background Dzierba Background

  31. Games Use Dzierba Background Generate 40 random spectra 3 are Fake 1 is CLAS

  32. Severe Cuts Mass (K- K+ n) Mass (K+ n) CLAS: Phys. Rev. Lett. 92, 032001,(2004) After Cuts Mass (K+ n) p!+K+K-(n) missing Uncut Spectrum Design cuts to remove diagrams (b), (c) and (d) j t!-j < 0.28 GeV2 cos *K+ < 0.6

  33. Monte Carlo Study p ! a2/f2 a2 or f2! K+K- Y12 j YML( cos, ) j2 Raw j t!-j < 0.28 GeV2 and cos *K+ < 0.6 (Alex Dzierba)

  34. Ghost Tracks Mass(+-) + p Mass(pKS) - (p>2GeV/c)! p- Select KS “Create a +” It is easy to manufacture narrow peaks in the data near 1.5GeV that appear to decay to p KS . (M. Longo QNP 2004)

  35. 5 Pentaquark c Pentaquark One low statistics report by H1 Five negative results. Null results in both the same and different production mechanisms. Factor of 10 to 1000 times for data in known resonances. Possible ghost track in D* Decay X 5(1860) One low statistics report by NA49 Nine negative results. Null results in both similar and different production mechanisms. 1-2 orders of magnitude more data in known resonances. X c(3100)

  36. + Pentaquark 11 low-statistics reports near 1500 MeV Low-energy reports suffer from some combination of the following: (a) Fermi motion effects. (b) Severe cuts whose effects may not have been adequately studied. (c) Insufficiently constrained reactions. (d) Kinematic reflections. 15 new high-statistics searches in a number of reactions with excellent resolution that have come up empty. Bubble chamber data from decades ago show no evidence. KN scattering data severely limit this The Zeus result is interesting. It suggests that fragmentation is a good way to produce the +. KS p is not strangeness exotic Not really consistent with ALEPH, BaBar, BELLE, CDF, … What does H1 have to say on this?

  37. PDG 2004

  38. Conclusions 2004 Pentaquark Stock Value Jun. Dec. Jan. The possible existence of pentaquarks is still very much an experimental question, and the data do not look very convincing. If they exist, they not only have exotic quantum numbers, but very exotic production and decay modes. I hope that the issue can be settled soon – but I am not buying stock.

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