Transcript Slide 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 + Before 2003 …. searches for flavor Issues with some of the data exotic baryons showed no evidence for such states. Summary & Conclusions Since 2003 …. Hadronic Physics has been very interesting. Argonne March 2, 2005 hep-ex/0412077 1 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. n ! K+K-n on a Carbon target. Phys. Rev. Lett. 91, 012002, (2003) The Dam Breaks …. Argonne March 2, 2005 2 Positive Sightings Experiment + 0c Decay 5 Reaction searched Claim publication LEPS + C12! K-K+n PRL 91 (2003) 012002 CLAS + d! K+K- np p! +K-K+n PRL 91 (2003) 252001, PRL 92 (2004) 032001 SAPHIR COSY K+Xe! K0SX’ Phys.Atom.Nucl.66(2003)1715 JINR + p+C3H8! K0SpX hep-ex/0401024 Argonne K0 + A! K0SpX BC at CERN & FNAL hep-ex/0309042 HERMES K+n pp! +K0Sp Phys.Lett.B595 (2004) 127 DIANA + K0Sp hep-ex/0401024 K+n p! K0SK+n Phys.Lett B572 (2003) 127 SVD K+n + pA! pK0SX + ep! e’pK0SX (quasi-real photoproduction) Phys.Lett.B585(2004) 213 ZEUS Phys.Lett.B592(2004)7 + pp! X Sp K0Sp PRL 92(2004)042003 0c ep! e’pD*-X H1 March 2, 2005 K0Sp 5 NA49 + K0Sp + ep! e’pK0SX Sp K0 K0Sp Phys.Lett.B588(2004)17 D*-p (Table by Alex Dzierba) 3 The Data Reported Significance 4.6 4.8 5.2 7.8 5 - - 50 4.2 4.4 6.7 ~5 0c ~5 Argonne 4.6 5.6 March 2, 2005 4.3 ~5.5 4 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 Argonne March 2, 2005 5 Statistics Experiment Signal Background Publ. Spring8 Spring8 SPAHIR CLAS (d)** CLAS (p) DIANA && HERMES COSY ZEUS SVD NOMAD Significance 1 2 3 4.8 5.2 7.8 4.4 6.7 4.3-6.2 4-6 4.6 5.6 4.3 4.6 4.4 7.3 5.9 6.9 4.4 6.0 4.2 5.9 7.0 4.4 4.3 3.2 3.8 5.2 4.4 4.7 3.4 3.5 3.6 4.7 6.4 3.6 3.4 2.6 2.9 4.3 3.5 3.9 2.7 3.0 2.7 3.7 4.7 2.8 2.7 43 75 4.2 5.8 5.8 8.0 4.2 5.8 3.4 4.7 51.7 5-6 7.0 5.0 4.1 19 56 55 43 41 29 18 51 57 230 41 33 17 162 56 54 35 44 9 150 95 1080 87 59 5 NA49 NA49 38 69 c H1 50.6 4.6 ** An improved analysis shows a less significant peak! && Shown to be charge exchange Argonne March 2, 2005 6 Zeus Result Phys. Lett. B591 (2004) 7. Fragmentation, Q2>20GeV2 Mass=1465 Width=15 368 Events Interesting Result ~6000 ~200 (1520) 230 + fragmentation is a good source of +! KS p is not manifestly Exotic. It could be a Argonne ? Observe: + mass=1.521 GeV width=6.1 MeV 230 Events on 1080 Background March 2, 2005 No Signal for: 5 , 0c 7 (U.Karshon, Pentaquark-04) LEPS C ! K+ K- X Assume that the reaction is n ! + KCalculate 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) , Argonne Highly unconstrained final states Unknown Backgrounds Many Cuts to pull out the signal March 2, 2005 8 CLAS + 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) Fit Evidence for higher mass , ‘ s and either the a2(1320) or f2(1270) is sharper. Disturbing Effect on the + ! Argonne March 2, 2005 NOT AN OFFICIAL CLAS RESULT9 COSY KS pp! ++ +! p + 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) Argonne No Particle Identification, No Momentum Measurement, No charge measurement. Pure Geometry and a zero constraint fit to the reaction March 2, 2005 10 Negative Reports ALEPH hep-ex/0408025,0410024 + c0 5 (+,K+,p)Cu ! PX + DELPHI CDF HyperCP hep-ex/0410027 SELEX (,p,)p! PX + E690 BES BaBar 5 Hadronic Z decays + WA89 DPF 2004 pp! PX + ZEUS QNP2004 - 5 e+e-! J/ ((2S) + + -N! PX hep-ex/0410029 HERA-B hep-ex/0407026 5 pA! PX + Accepted in PRL 5 pC(N)! K X + SPHINX hep-ex/0411005 e+e-! U (4S) + PHENIX hep-ex/0408064 5 nuc-ex/0404001 + K+p! K+ n + hep-ex/0412031 COMPASS Argonne 5 5 ep! PX + c0 KN! PX c0 hep-ex/0410080 PRD 70 (2004) 012004 BELLE Submitted to Phys. Lett. B L3 + c0 5 p! PX + hep-ex/0410080 Quark Confinement 2004 FOCUS Hadronic Z decays c0 hep-ex/0407026 LASS March 2, 2005 + AuAu! PX + (Table by Alex Dzierba) 11 The --(1861) Argonne March 2, 2005 12 NA49 5(1860) fixed target experiment at CERN - spectrometer 158 GeV/c proton beam width is below detector resolution Argonne March 2, 2005 13 Null Results 5(1860) HERA-B Argonne March 2, 2005 14 Null Result 5(1860) ALEPH and ZEUS also null result CDF FOCUS Argonne March 2, 2005 15 The 0c(3100) Argonne March 2, 2005 16 H1 at HERA Argonne March 2, 2005 17 Null Results ZEUS CDF FOCUS Argonne March 2, 2005 18 The +(1540) Argonne March 2, 2005 19 Bubble Chamber Argonne No signals in the Dalitz Plots March 2, 2005 (Taken from the PDG, 2004) 20 Scattering Data K+n P-wave Phase Shifts 1MeV wide resonance at 1540 Argonne March 2, 2005 21 Negative Results HERA-B +(1540) SPHINX pC! pK0SX BELLE (1520) pKS e+e-! (p K0)X ALEPH (1520) HyperCP Argonne BaBar K*(892) CDF March 2, 2005 +? 22 70 GeV p on Carbon Targets SPHINX 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+ KL N Detect No in either p Ks or n K+ Don’t See (1520) in p K-, n KS ~16000 (1520) nK+ pKL Argonne pKS Monte Carlo March 2, 2005 23 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- 16000 (1520)! pKS K- p Exclude: N ! (1520) K-p ! (1520) No signal in KS p Signal comes from KN! (1520)X Argonne It is very hard to produce the + In K+N interactions, but it falls apart into this just fine. March 2, 2005 24 SELEX 600Gev Beams (-,-,p,+ ) (67%,14%,18%, 1%) Very significant charmed baryon results. 0.1% of Data (1520) No + 2,800,000 Mass (K-p) Argonne Mass (KS p) March 2, 2005 Mass (KS p) 25 CDF Resonance Min. Bias (1520) 3276§ 327 K*+ 15695§ 775 + 18§ 56 90% CL + <89 pK- + cc Argonne +KS March 2, 2005 Jet>20GeV 4915§ 702 35769§ 1390 -56§ 100 <76 p KS + cc 26 The Numbers Positive Results 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 ________________________________________ * Estimate from cross section Argonne Some Negative Results 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 CDF 36000 1000 BaBar 258000 17000 HERA-B 18000 ZEUS 2600 160 WA89 676000 FOCUS March 2, 2005 25000 3000000 536000 84000 36000 27 Low Energy Experiments Kinematic Reflections 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 a2(1320)! K+K- +(1540) (1020) a2(1320)/f2(1270) CLAS f2(1270) Argonne Mass(+-) March 2, 2005 28 Kinematic Reflection? The CLAS d ! p n K+K- Data Mass (K+n) Mass (K+K) Kinematic Fit Argonne Mass (K-n) Solid lines are predicted using K+K- resonances March 2, 2005 (Dzierba, et al.) 29 Statistical Fluctuation You need to understand your background to claim a new discovery! CLAS Published Simple Physics Background Naïve Background Dzierba Background Argonne Chance of the Background Fluctuating into the observed signal March 2, 2005 30 Games Use Dzierba Background Generate 40 random spectra 3 are Fake 1 is CLAS Argonne March 2, 2005 31 Severe Cuts p! +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) j t!-j < 0.28 GeV2 cos *K+ < 0.6 Argonne After Cuts March 2, 2005 CLAS: Phys. Rev. Lett. 92, 032001,(2004) 32 Monte Carlo Study p ! a2/f2 a2 or f2 ! K+K- j YML( cos, ) j2 Y12 Raw j t!-j < 0.28 GeV2 and cos *K+ < 0.6 Argonne March 2, 2005 (Alex Dzierba) 33 Ghost Tracks + (p>2GeV/c)! pp Mass(+-) - Select KS It is easy to manufacture narrow peaks in the data near 1.5GeV that appear to decay to p KS . Argonne Mass(pKS“Create ) a +” March 2, 2005 (M. Longo QNP 2004) 34 5 Pentaquark One low statistics report by NA49 X 5(1860) Nine negative results. Null results in both similar and different production mechanisms. 1-2 orders of magnitude more data in known resonances. c Pentaquark X c(3100) 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 Argonne March 2, 2005 35 + 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? Argonne March 2, 2005 36 PDG 2004 Argonne March 2, 2005 37 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 Conclusions 2004 Jan. Jun. Dec. I hope that the issue can be settled soon – but I am not buying stock. Argonne March 2, 2005 38