Pentaquarks: An Experimental Overview. Curtis A. Meyer. Before searches for flavor exotic baryons showed no evidence for such states.

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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 Before searches for flavor exotic baryons showed no evidence for such states. Since Hadronic Physics has been very interesting. Pentaquarks 1

2 Spectacular Development 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). K + n 2003: T. Nakano et al. γ n K + K - n on a Carbon target. Phys. Rev. Lett. 91, , (2003) The Dam Breaks. Pentaquarks 2

3 Positive Sightings Experiment Reaction searched publication Claim Decay Ξ 5 Θ 0 c LEPS CLAS SAPHIR COSY DIANA JINR γ C 12 K - K + n PRL 91 (2003) γ d K + K - np γ p π + K - K + n PRL 91 (2003) , PRL 92 (2004) γ p K 0 S K+ n Phys.Lett B572 (2003) 127 pp Σ + K 0 S p Phys.Lett.B595 (2004) 127 K + Xe K 0 S X Phys.Atom.Nucl.66(2003)1715 p+c 3 H 8 K 0 S px hep-ex/ SVD pa pk 0 S X K + n K 0 S p hep-ex/ ν A K 0 S px ν BC at CERN & FNAL K + n hep-ex/ K 0 S p K + n K 0 S p K 0 S p K 0 S p HERMES ZEUS NA49 H1 ep e pk 0 S X (quasi-real photoproduction) Phys.Lett.B585(2004) 213 ep e pk 0 S X Phys.Lett.B592(2004)7 pp Ξπ X PRL 92(2004) ep e pd* - X Phys.Lett.B588(2004)17 K 0 S p K 0 S p Ξ 5 Θ 0 c Pentaquarks (Table by Alex Dzierba) 3

4 The Data Reported Significance 4.6σ 4.8σ 5.2σ 7.8σ 5.2σ 4.4σ 6.7σ ~5σ Ξ 5 -- Ξ σ ~5σ 4.6σ 5.6σ 4.3σ ~5.5σ Θ 0 c Pentaquarks 4

5 Summary of Results Ξ 5 -- Ξ 5 0 Na49: Mass: 1862 MeV Width < Resolution Θ c 0 H1: Mass : 3100 MeV Width ~10 MeV A narrow structure whose width is less than experimental resolution Old data constrain Γ Θ <1MeV Pentaquarks 5

6 Statistics Experiment Signal Background Significance Publ. ξ 1 ξ 2 ξ 3 Spring σ Spring SPAHIR σ CLAS (d) σ CLAS (p) σ DIANA σ ν σ HERMES σ COSY σ ZEUS σ SVD σ NOMAD σ NA σ NA σ H σ Pentaquarks 6

7 Zeus Result Phys. Lett. B591 (2004) 7. Interesting Result Fragmentation, Q 2 >20GeV 2 Mass=1465 Width= Events ~6000 Λ ~200 Λ(1520) 230 fragmentation is a good source of! What does Λπ look like? (many Σ Λπ) Σ? Observe: mass=1.521 GeV width=6.1 MeV 230 Events on 1080 Background No Signal for: Ξ 5, Θ 0 c Pentaquarks 7 (U.Karshon, Pentaquark-04)

8 Negative Reports CDF HyperCP SELEX FOCUS E690 BES BELLE BaBar COMPASS ALEPH Hadronic Z decays Θ 0 c Θ 0 hep-ex/ , c Ξ 5 Submitted to Phys. Lett. B Ξ 5 (π +,K +,p)cu PX Hadronic Z decays hep-ex/ (π,p,σ)p PX Quark Confinement 2004 DELPHI L3 WA89 ZEUS HERA-B PHENIX hep-ex/ hep-ex/ γ p PX Σ - N PX hep-ex/ Ξ Θ c 0 5 hep-ex/ Ξ 5 pp PX QNP ep PX Ξ 5 hep-ex/ Ξ 5 e + e - J/ψ (ψ(2s) pa PX PRD 70 (2004) PRL 93 (2004) KN PX SPHINX pc(n) θ K X hep-ep/ Θ 0 c EPJ A21 (2004) 455 e + e - Υ (4S) AuAu PX hep-ex/ Ξ 5 J.Phys.G 30 (2004) S1201 Ξ 5 Θ c 0 Ξ 5 Pentaquarks 8 (Table by Alex Dzierba)

9 NA49 Ξ 5 (1860) fixed target experiment at CERN - spectrometer 158 GeV/c proton beam width is below detector resolution Pentaquarks 9

10 Null Results Ξ 5 (1860) HERA-B Pentaquarks 10

11 Null Result Ξ 5 (1860) ALEPH and ZEUS also null result CDF FOCUS Pentaquarks 11

12 H1 at t HERA Pentaquarks 12

13 Null Results ZEUS CDF FOCUS Pentaquarks 13

14 Negative Results (1540) HERA-B pc pk 0 S X SPHINX BELLE Λ(1520) pk S ALEPH e + e - (p K 0 )X BaBar HyperCP Λ(1520) K * (892) CDF? Pentaquarks 14

15 Bubble Chamber No signals in the Dalitz Plots Pentaquarks (Taken from the PDG, 2004) 15

16 Scattering Data K + n P-wave Phase Shifts 1MeV wide resonance at 1540 Pentaquarks 16

17 The Numbers Positive Results Some Negative Results Experiment s b Λ Λ(1520) φ Spring Spring SAPHIR CLAS(d) CLAS(p) DIANA ν 19 8 HERMES COSY ZEUS * 193 SVD NOMAD s b Ξ D* NA H * Estimate from cross section Experiment Λ Λ(1520) φ E ALEPH 2800 CDF BaBar HERA-B SPHINX HYPERCP COMPASS BELLE Ξ Ξ(1530) D D * E ALEPH CDF BaBar HERA-B ZEUS WA FOCUS Pentaquarks 17

18 Low Energy Experiments 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 Kinematic Reflections a 2 (1320) K + K - φ(1020) a 2 (1320) (1540) CLAS Pentaquarks 18

19 Kinematic Reflection? The CLAS γ d p n K + K - Data Mass (K - n) Mass (K + K - ) Mass (K + n) Solid lines are predicted using K + K - resonances Pentaquarks (Dzierba, et al.) 19

20 Statistical Fluctuation CLAS Published Simple Physics Background You need to understand your background to claim a new discovery! Naïve Background Dzierba Background Chance of the Background Fluctuating into the observed signal Pentaquarks 20

21 Games Use Dzierba Background Generate 40 random spectra 3 are Fake 1 is CLAS Pentaquarks 21

22 Severe Cuts γ p π + K + K - (n) missing Mass (K + n) Uncut Spectrum Mass (K + n) Mass (K - K + n) Design cuts to remove diagrams (b), (c) and (d) t γ π - < 0.28 GeV 2 cos θ * K + < 0.6 After Cuts Pentaquarks 22 CLAS: Phys. Rev. Lett. 92, ,(2004)

23 Monte Carlo Study γ p a 2 /f 2 a 2 or f 2 K + K - Y M L( cosθ, φ) 2 Y 1 2 Raw t γ π - < 0.28 GeV 2 and cos θ * K + < 0.6 Pentaquarks 23 (Alex Dzierba)

24 Ghost Tracks Λ (p>2gev/c) pπ - + p π - Mass(π + π - ) Select KS It is easy to manufacture narrow peaks in the data near 1.5GeV that appear to decay to p K S. Mass(pK S ) Create a Θ+ Pentaquarks 24 (M. Longo QNP 2004)

25 Ξ 5 Pentaquark One low statistics report by NA49 RIP Nine negative results. Null results in both similar and different production mechanisms. 1-2 orders of magnitude more data in known resonances. Θ c Pentaquark One low statistics report by H1 RIP Five negative results. Null results in both the same and different production mechanisms. Factor of 10 to 1000 times for data in known resonances. Pentaquarks 25

26 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. Not really consistent with ALEPH, BaBar, BELLE, CDF, What does H1 have to say on this? Pentaquarks 26

27 PDG 2004 Pentaquarks 27

28 Conclusions 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. Pentaquark Stock Value 2004 Jan. Jun. Dec. I hope that the issue can be settled soon but I am not buying stock. Pentaquarks 28