1. Argonne March 2, 2005 1 Curtis A. Meyer Pentaquarks: An Experimental Overview Based, in part, on work carried out with Alex Dzierba and Adam Szczepaniak Before 2003 …. searches for flavor exotic baryons showed no evidence for such states. Since 2003 …. Hadronic Physics has been very interesting. 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 hep-ex/0412077

2. Argonne March 2, 2005 2 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). Spectacular Development 2003: T. Nakano et al.  n ! K + K - n on a Carbon target. Phys. Rev. Lett. 91, 012002, (2003)  + ! K + n The Dam Breaks ….

3. Argonne March 2, 2005 3 LEPS CLAS SAPHIR COSY DIANA JINR SVD ZEUS HERMES NA49 H1 PRL 91 (2003) 012002  C 12 ! K - K + n ++ ++ K+nK+n ++ K+nK+n PRL 91 (2003) 252001, PRL 92 (2004) 032001  d! K + K - np  p!  + K - K + n ++ K+nK+n Phys.Lett B572 (2003) 127  p! K 0 S K + n Phys.Lett.B595 (2004) 127 ++ K0SpK0Sp K0SpK0Sp pp!  + K 0 S p Positive Sightings Phys.Atom.Nucl.66(2003)1715 hep-ex/0401024 BC at CERN & FNAL hep-ex/0309042 Phys.Lett.B585(2004) 213 Phys.Lett.B592(2004)7 PRL 92(2004)042003 Phys.Lett.B588(2004)17 ++ ++ ++ ++ ++ 55 0c0c K0SpK0Sp K0SpK0Sp K0SpK0Sp K0SpK0Sp K0SpK0Sp K + Xe! K 0 S X’ p+C 3 H 8 ! K 0 S pX pA! pK 0 S X  A! K 0 S pX ep! e’pK 0 S X (quasi-real photoproduction) ep! e’pK 0 S X pp!  X ep! e’pD* - X Experiment Reaction searched publication ++ 55 0c0c Claim Decay (Table by Alex Dzierba)  D *- p

4. Argonne March 2, 2005 4 4.6  4.8  5.2  7.8  4.4  6.7  ~5  4.6  5.6  4.3  The Data Reported Significance  5 - -  5 0 0c0c 4.2  ~5.5 

5. Argonne March 2, 2005 5 A narrow structure whose width is less than experimental resolution Summary of Results ++ Old data constrain   <1MeV  5 --  5 0 c0c0 Na49: Mass: 1862 MeV Width < Resolution H1: Mass : 3100 MeV Width ~10 MeV Charge Exchange

6. Argonne March 2, 2005 6 Statistics Experiment Signal Background Significance Publ.  1  2  3 Spring8 19 17 4.6  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 18 9 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 ** An improved analysis shows a less significant peak! && Shown to be charge exchange 55 cc

7. Argonne March 2, 2005 7 Zeus Result Phys. Lett. B591 (2004) 7. (U.Karshon, Pentaquark-04) Fragmentation, Q 2 >20GeV 2 Observe:  + mass=1.521 GeV width=6.1 MeV 230 Events on 1080 Background No Signal for:  5,  0 c Mass=1465 Width=15 368 Events ?? ~6000  ~200  (1520) 230  + K S p is not manifestly Exotic. It could be a  Interesting Result fragmentation is a good source of  + !

8. Argonne March 2, 2005 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 - 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) ,  Highly unconstrained final states Unknown Backgrounds Many Cuts to pull out the signal

9. Argonne March 2, 2005 9 CLAS  d ! K + K - p (n) miss 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 and either the a 2 (1320) or f 2 (1270) is sharper. Published Fit NOT AN OFFICIAL CLAS RESULT Disturbing Effect on the  + ! ++ Reaction is unknown

10. Argonne March 2, 2005 10 COSY pp!  +  +  + ! K S p K S !  +  -  + ! n  + 2 Hits in the first hodoscope  + & p 4 Hits in the 2 nd and 3 rd 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   p  KSKS ++

11. Argonne March 2, 2005 11 Negative Reports CDFALEPH HyperCPDELPHI SELEXL3 FOCUSWA89 E690ZEUS BESHERA-B BELLESPHINX BaBarPHENIX COMPASS ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ 55 55 55 55 55 55 55 55 55 c0c0 c0c0 c0c0 c0c0 c0c0 hep-ex/0408025,0410024 (  +,K +,p)Cu ! PX hep-ex/0410027 ( ,p,  )p! PX Quark Confinement 2004  p! PX DPF 2004 pp! PX QNP2004 - PRD 70 (2004) 012004 e + e - ! J/  (  (2S) KN! PX hep-ex/0411005 e + e - !  (4S) hep-ex/0408064 Hadronic Z decays Submitted to Phys. Lett. B Hadronic Z decays hep-ex/0410080 hep-ex/0410029  - N! PX ep! PX hep-ex/0407026 pA! PX Accepted in PRL pC(N)!  K X hep-ex/0407026 AuAu! PX nuc-ex/0404001 (Table by Alex Dzierba) LASS hep-ex/0412031 K + p! K + n  + ++

12. Argonne March 2, 2005 12 The  -- (1861)

13. Argonne March 2, 2005 13 width is below detector resolution fixed target experiment at CERN - spectrometer 158 GeV/c proton beam fixed target experiment at CERN - spectrometer 158 GeV/c proton beam NA49  5 (1860)

14. Argonne March 2, 2005 14 HERA-B Null Results  5 (1860)

15. Argonne March 2, 2005 15 CDF FOCUS ALEPH and ZEUS also null result Null Result  5 (1860)

16. Argonne March 2, 2005 16 The  0 c (3100)

17. Argonne March 2, 2005 17 at HERA H1

18. Argonne March 2, 2005 18 CDF FOCUS ZEUS Null Results

19. Argonne March 2, 2005 19 The  + (1540)

20. Argonne March 2, 2005 20 Bubble Chamber No signals in the Dalitz Plots (Taken from the PDG, 2004)

21. Argonne March 2, 2005 21 Scattering Data K + n P-wave Phase Shifts 1MeV wide resonance at 1540

22. Argonne March 2, 2005 22 BELLE HyperCP Negative Results  + (1540) CDF  1520) K * (892) +?+? ALEPH BaBar e + e - ! ( p K 0 )X HERA-B pC! pK 0 S X  1520) pK S SPHINX

23. Argonne March 2, 2005 23 SPHINX 70 GeV p on Carbon Targets The detector is sensitive to charged particles and the direction of neutrons and K L by hits in the BCAL. p + N ! p K + K - N p + N ! p K S K L N p + N ! p K S K S N p + N ! n K + K S N p + N ! p K L K L N p + N ! n K + K L N Detect Don’t See  1520) in p K -, n K S ~16000  (1520) No  in either p K s or n K + nK+ pK L pK S Monte Carlo

24. Argonne March 2, 2005 24 Belle  1520) pK S e + e - with an interesting twist Look at the pK S pK - and pK + final states whose primary Vertex is from material in the detector 16000  (1520)! K - p Exclude:  N !  (1520) K - p !  (1520) Signal comes from KN!  (1520)X pK - No signal in K S p It is very hard to produce the  + In K + N interactions, but it falls apart into this just fine.

25. Argonne March 2, 2005 25 SELEX 600Gev Beams (  -,  -,p,  + ) Mass (K - p)  1520) 2,800,000 Mass (K S p) 0.1% of Data Mass (K S p) No  + (67%,14%,18%, 1%) Very significant charmed baryon results.

26. Argonne March 2, 2005 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 pK - + cc +KS+KS p K S + cc

27. Argonne March 2, 2005 27 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 ________________________________________ Experiment   (1520)  c ____________________________________ 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 The Numbers Positive Results Some Negative Results * Estimate from cross section

28. Argonne March 2, 2005 28 Low Energy Experiments Kinematic Reflections  + (1540) a 2 (1320)! K + K - 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 a 2 (1320)/f 2 (1270)  1020) CLAS Mass(  +  - ) f 2 (1270 )

29. Argonne March 2, 2005 29 Mass (K - n) Mass (K + K - ) Mass (K + n) Kinematic Reflection? (Dzierba, et al.) The CLAS  d ! p n K + K - Data Solid lines are predicted using K + K - resonances Kinematic Fit

30. Argonne March 2, 2005 30 Statistical Fluctuation CLAS Published Naïve Background Simple Physics Background Dzierba Background Chance of the Background Fluctuating into the observed signal You need to understand your background to claim a new discovery!

31. Argonne March 2, 2005 31 Use Dzierba Background Generate 40 random spectra 3 are Fake 1 is CLAS Games

32. Argonne March 2, 2005 32 Severe Cuts  p!  + K + K - (n) missing CLAS: Phys. Rev. Lett. 92, 032001,(2004) Design cuts to remove diagrams (b), (c) and (d) j t  !  - j < 0.28 GeV 2 cos  * K + < 0.6 Mass (K + n) Uncut Spectrum Mass (K + n) Mass (K - K + n) After Cuts

33. Argonne March 2, 2005 33 j t  !  - j < 0.28 GeV 2 and cos  * K + < 0.6 Raw Monte Carlo Study (Alex Dzierba) a 2 or f 2 ! K + K - j Y M L ( cos ,  ) j 2  p !  a 2 /f 2 Y12Y12

34. Argonne March 2, 2005 34 Ghost Tracks  (p>2GeV/c)! p  - -- p ++ Mass(  +  - ) Select K S Mass(pK S ) “Create a  + ” It is easy to manufacture narrow peaks in the data near 1.5GeV that appear to decay to p K S. (M. Longo QNP 2004)

35. Argonne March 2, 2005 35  5 Pentaquark 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.  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  5 (1860)  c (3100) X X

36. Argonne March 2, 2005 36 11 low-statistics reports near 1500 MeV  + Pentaquark 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  +. K S p is not strangeness exotic Not really consistent with ALEPH, BaBar, BELLE, CDF, … What does H1 have to say on this?

37. Argonne March 2, 2005 37 PDG 2004

38. Argonne March 2, 2005 38 Conclusions Pentaquark Stock Value Jan. Jun. Dec. 2004 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.