Argonne March 2, 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/
Argonne March 2, : 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, , (2003) + ! K + n The Dam Breaks ….
Argonne March 2, LEPS CLAS SAPHIR COSY DIANA JINR SVD ZEUS HERMES NA49 H1 PRL 91 (2003) C 12 ! K - K + n ++ ++ K+nK+n ++ K+nK+n PRL 91 (2003) , PRL 92 (2004) 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/ BC at CERN & FNAL hep-ex/ Phys.Lett.B585(2004) 213 Phys.Lett.B592(2004)7 PRL 92(2004) Phys.Lett.B588(2004)17 ++ ++ ++ ++ ++ 55 0c0c 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 ++ 55 0c0c Claim Decay (Table by Alex Dzierba) D *- p
Argonne March 2, 4.8 5.2 7.8 4.4 6.7 ~5 4.6 5.6 4.3 The Data Reported Significance 5 0 0c0c 4.2 ~5.5
Argonne March 2, A narrow structure whose width is less than experimental resolution Summary of Results ++ Old data constrain <1MeV 5 -- 5 0 c0c0 Na49: Mass: 1862 MeV Width < Resolution H1: Mass : 3100 MeV Width ~10 MeV Charge Exchange
Argonne March 2, Statistics Experiment Signal Background Significance Publ. 1 2 3 Spring Spring SPAHIR CLAS (d)** CLAS (p) DIANA && HERMES COSY ZEUS SVD NOMAD NA NA H ** An improved analysis shows a less significant peak! && Shown to be charge exchange 55 cc
Argonne March 2, 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= Events ?? ~6000 ~200 (1520) 230 + K S p is not manifestly Exotic. It could be a Interesting Result fragmentation is a good source of + !
Argonne March 2, 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
Argonne March 2, 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
Argonne March 2, 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 ++
Argonne March 2, Negative Reports CDFALEPH HyperCPDELPHI SELEXL3 FOCUSWA89 E690ZEUS BESHERA-B BELLESPHINX BaBarPHENIX COMPASS ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ 55 55 55 55 55 55 55 55 55 c0c0 c0c0 c0c0 c0c0 c0c0 hep-ex/ , ( +,K +,p)Cu ! PX hep-ex/ ( ,p, )p! PX Quark Confinement 2004 p! PX DPF 2004 pp! PX QNP PRD 70 (2004) e + e - ! J/ ( (2S) KN! PX hep-ex/ e + e - ! (4S) hep-ex/ Hadronic Z decays Submitted to Phys. Lett. B Hadronic Z decays hep-ex/ hep-ex/ - N! PX ep! PX hep-ex/ pA! PX Accepted in PRL pC(N)! K X hep-ex/ AuAu! PX nuc-ex/ (Table by Alex Dzierba) LASS hep-ex/ K + p! K + n + ++
Argonne March 2, The -- (1861)
Argonne March 2, 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)
Argonne March 2, HERA-B Null Results 5 (1860)
Argonne March 2, CDF FOCUS ALEPH and ZEUS also null result Null Result 5 (1860)
Argonne March 2, The 0 c (3100)
Argonne March 2, at HERA H1
Argonne March 2, CDF FOCUS ZEUS Null Results
Argonne March 2, The + (1540)
Argonne March 2, Bubble Chamber No signals in the Dalitz Plots (Taken from the PDG, 2004)
Argonne March 2, Scattering Data K + n P-wave Phase Shifts 1MeV wide resonance at 1540
Argonne March 2, 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
Argonne March 2, 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
Argonne March 2, 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 (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.
Argonne March 2, 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.
Argonne March 2, CDF Resonance Min. Bias Jet>20GeV 1520) 3276§ § 702 K * § § 1390 + 18§ § % CL + <89 <76 pK - + cc +KS+KS p K S + cc
Argonne March 2, Experiment s b (1520) Spring Spring SAPHIR CLAS(d) CLAS(p) DIANA 19 8 HERMES COSY ZEUS * 193 SVD NOMAD ________________________________________ s b D* ________________________________________ NA H ________________________________________ Experiment (1520) c ____________________________________ E ALEPH 2800 CDF BaBar HERA-B SPHINX HYPERCP COMPASS BELLE SELEX 2,800,000 ____________________________________ (1530) D D * ________________________________________________________ E ALEPH CDF BaBar HERA-B ZEUS WA FOCUS The Numbers Positive Results Some Negative Results * Estimate from cross section
Argonne March 2, 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 )
Argonne March 2, 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
Argonne March 2, 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!
Argonne March 2, Use Dzierba Background Generate 40 random spectra 3 are Fake 1 is CLAS Games
Argonne March 2, Severe Cuts p! + K + K - (n) missing CLAS: Phys. Rev. Lett. 92, ,(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
Argonne March 2, 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
Argonne March 2, 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)
Argonne March 2, 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
Argonne March 2, 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?
Argonne March 2, PDG 2004
Argonne March 2, Conclusions Pentaquark Stock Value Jan. Jun. Dec 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.