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Part 1: Have Pentaquark States been seen?

Part 1: Have Pentaquark States been seen?. New Hadrons: Facts and Fancy. Volker D Burkert Jefferson Lab. EINN 2005 – 19 - 20 September, Milos, Greece. LEPS. SAPHIR. This looks like a lot of evidence!. COSY-TOF. pp  S + Q + . The initial evidence for the Q +. CLAS-D. DIANA.

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Part 1: Have Pentaquark States been seen?

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  1. Part 1: Have Pentaquark States been seen? New Hadrons: Facts and Fancy Volker D Burkert Jefferson Lab EINN 2005 – 19 - 20 September, Milos, Greece

  2. LEPS SAPHIR This looks like a lot of evidence! COSY-TOF pp  S+Q+. The initial evidence for the Q+ CLAS-D DIANA 4.4 5.2 4.8 4.6 CLAS-p Neutrino SVD HERMES 7.8 6.7 5.6 ~5 K+N ->X ZEUS ~5 4.6 3

  3. FOCUS FOCUS HERA-B HyperCP SPHINX + more CDF CDF CDF Non-evidence for Pentaquarks BABAR BES X-- DELPHI X-- Q0c

  4. U. Meissner The Q+ width • Measured width dominated by • experimental resolution • Analysis of K+A data give limit of few MeV. K+D -> X U. Meissner K+D , K+Xe X Sibirtsev et al.: GQ < 1 MeV • Very narrow for a hadronically • decaying particle with mass ~100 MeV • above threshold: • Q+(1540) -> nK+, pK0 From selected data sample • What can we say about event rates? K+n -> Q+ =>G~1MeV, K-p -> L* => G~16 MeV. s(Q+)/s(L*) ~ 1.4% for formation. GQ = 0.9 +/-0.3 MeV W. Gibbs, Phys.Rev.C70, 054208 (2004)

  5. Are the results on Q+ consistent? Low energy – effective degrees of freedom, meson-baryon coupling High energy – quark degrees of freedom, fragmentation • Can the “positive” low statistics results be reproduced with high statistics, e.g. LEPS, CLAS_d, CLAS_p, SAPHIR, COSY, HERMES,..? • Is fragmentation at high energy an efficient way of generating pentaquarks? Why do some experiment (ZEUS, HERMES, SVD) see a signal while others don’t?

  6. Pentaquark talks at Workshop • C. Alexandrou - Pentaquarks on the Lattice • Paul Stoler - Searches for Pentaquarks on proton targets at JLab • R. Mizuk - Limit of the Q+ width from KN scattering at Belle • S. Niccolai - Searches for Pentaquark baryons on deuterium with CLAS • N. Muramatsu - Studies of Q+ with LEPS at SPring8 • A. Geiser - Study of Q+ and other Pentaquark searches at HERA • J. M. Izen - Search for Pentaquark baryons at BaBaR • S. Kabana - Search for exotic baryons at RHIC • U. Meissner - What do we know about the width of Q+ ? • Discussion - Where are we and what to do next in the Pentaquark search?

  7. C. Alexandrou Takahashi et al., Pentaquark04 and hep-lat/0503019 :JKN and J’KN on spatial lattice size ~1.4, 1.7, 2.0 and 2.7 with a larger number of configurations

  8. C. Alexandrou Summary of LQCD

  9. Counts/4 MeV preliminary M(nK+)(GeV) Paul Stoler: Upper limit on the Q+ cross section (95%c.l.) s g p Q+ K0< 1.25 nb @ 1.54 GeV/c2 CLAS: gp -> K-K0n Fit with a sum of smooth function and a Gaussian with fix width and centroid. g K0 Results put stringent limits on possible production mechanism, e.g. implies very small coupling to K* K* n p Q+ K+

  10. P Stoler: Comparison with SAPHIR results SAPHIR Observed Yields SAPHIR N(Q+)/N(L*) ~ 10% CLAS N(Q+)/N(L*) < 0.2% (95%CL) Cross Sections SAPHIR sg p Q+ K0 ~ 300 nb reanalysis 50 nb (unpublished) CLAS sg p Q+ K0 < 2 nb Counts Counts cosqCM(K0) > 0.5 cosqCM(K0) > 0.5 M(nK0) (GeV) M(nK+) (GeV) g11@CLAS Counts Counts L(1520) cosqCM(K0) > 0.5 preliminary cosqCM(K0) > 0.5 Q+(1540) ? M(nK0) (GeV) M(nK+) (GeV)

  11. + - ® γD K p K n • The new data show no signal • Set upper limit on cross section < 450pb • Upper limit on elementary cross section: nosignal g n -> Q+K- sQ+ < 4-5 nb (95% CL) model dependent. Silvia Niccolai Upper limit on Q+ production with CLAS. G10 G2 Background from G10 • In previous result the background is underestimated. New estimate of the original data gives a significance of ~3s, possibly due to fluctuations.

  12. Upper limit onGQ+from CLAS Results Theoretical cross section are forGQ+=1 MeV ( ) – with K* exchange

  13. Old and New Signal from LEPS/SPring8 N. Muramatsu gD -> K-X • Mix K＋, K－,  from different events in LH2 data. • (1520) contribution was removed from the sample. ＋ (1520) preliminary preliminary MMC(γ,K＋) GeV/c2 MMC(γ,K－) GeV/c2

  14. K-p missing mass spectrum N. Muramatsu * fitted in MM<1.52 GeV/c2 ~5σ excess at 1.53 GeV/c2 corresponding + 1.6 GeV bump was also seen. + preliminary 1.6 GeV bump Counts/5 MeV preliminary Counts/5 MeV * from sidebands MMd(γ,K－p) GeV/c2 MMd(γ,K－p) GeV/c2 Signal emerges with selection of L*(1520) in M(K-p)

  15. M(GeV) Pentaquark Studies at HERA A. Geiser ep -> eK0spX High energy production mechanism? ZEUS => Signal seen at medium Q2 and forward rapidity in both pKs and pKs

  16. ZEUS – Cross section onQ+ A. Geiser M(GeV) Q+/L* ~ 5% (independent of Q2)

  17. Baryon fragmentation s s u u Q+ d d d q Needs fewer quark pairs from the vacuum e Pentaquark less suppressed ? Pentaquark in fragmentation? Quark fragmentation u u d q Q+ e Pentaquark strongly suppressed ?

  18. K+ Q+ n BELLE – Low energy K+N scattering R. Mizuk e+e--> K+/- X, K+/-A -> pK0, pK- Detector Tomography momentum spectra of K+ and K- 1 / 50MeV momentum, GeV/c Momentum range possibly contributing to Q+ formation. =>Determine resonance width

  19. NΘ+ Nch σch 107mb Bi Bf ΓΘ+= Δm R. Mizuk Belle – Limit on Q+ Width GQ+ from K+A -> pK0sX & K+D -> inclusive analysis K+A -> pK0s Belle limit 90%CL 397 fb-1 DIANA No no signal Belle: G < 0.64 MeV (90% CL) @ M = 1.539 GeV G< 1 MeV (90% CL) @ M = 1.525–1.545 GeV Cahn,Trilling,PRD69,11501 (2004). Not inconsistent with previous results.

  20. Upper limit on cross section ratio σ(KNΘ(1540)+X) σ(KNΛ(1520)X) B(Λ(1520) pK-) B(Θ(1540)+  pK0) B(K0 KS π+π-) NΘ+ NΛ* εpK+ εpKs = <2.5% at the 90% C.L. εpKs/εpK+ from MC assuming that Θ+ and Λ(1520) kinematics is similar. Comparison with other experiments Consistent with <1 MeV width. ?

  21. Slope: Pseudoscalar mesons: ~ 10-2/GeV/c2 (need to generate one qq pair) Slope for p.s. mesons Slope for baryons Slope for Pentaquark ? Q+ + Q- X- - +X++ Hadron production in e+e- collisions J.M. Izen Baryons: ~ 10-4 /GeV/c2 (generate two pairs) Pentaquarks: ~ 10-8 /GeV/c2 (?) (generate four pairs) G= 1Mev G= 1MeV BR(X-- X-p-)=0.5

  22. BaBar Preliminary233 fb–1 e+e– data Tomography with pKs0 Vertices -0.2 < y < 0.7 cm -3.1< x < -2.2 cm Ta Be Ta Y [cm] Y [cm] Vetobeamspot R  2 cm e+ e– SVT X [cm] X [cm] SVT support tube DCH inner wall Beampipe z profile

  23. Preliminary233 fb–1 e+e– data e-Be Electroproduction ZEUS (e-pe-KS0p + X) ZEUS *(1480) Zeus: ~5 M=15223 MeV Hermes: ~5 M=15283 MeV (quasi-real photoproduction) HERMES (e+dKS0p + X) HERMES HERMES/BaBaR comparison disturbing. ZEUS : High Q2, no signal for Q2<1 BaBaR: Quasi-real photons HERMES: acceptance loss in low mass region? (PID requires p(p) >4.1 GeV/c; p(KS0)>3 GeV/c)

  24. STAR d-Au results Q D pK+ and pK- from 18.6 M d+Au at 200 GeV S. Kabana Possible mechanism for production of multi-q/g states: Coalescence of out of QGP? STAR Preliminary ? M (GeV/c2) A Q++ candidate ? Also a Q+ candidate ??

  25. M = 1523 MeV s = 12 MeV Nevnt = 165 Private info from SVD group SVD-2 – New Analysis Two independent data set: KS decays inside or outside the Vertex Detector Ep = 70 GeV M = 1522 MeV s = 12 MeV Nevnt = 205 • New analysis improves Q+ signal by factor 8. The results maybe in conflict with new WA89 results (to be published shortly).

  26. pp-> pXX gA FOCUS < 0.0025/B range Cascade Pentaquark X5--(1862) ? HERA-B CDF • State not produced in quark fragmentation or is severely suppressed. gA FOCUS

  27. Charmed PentaquarkQ0c(3100) ? FOCUS H1 expected FOCUS events H1 expected FOCUS events • Upper limit factor 4 lower than H1 results. Claim is that results are incompatible with H1. • Signal also in photo- production • Claim kinematical uniqueness. • Possible production mechanism - PGF. • FOCUS experiment claims incompatibility with H1.

  28. s/ b+s G11 CLAS-p G10 CLAS-d HERA-B, CDF, COMPASS ZEUS, FOCUS, BABAR Pentaquark Status @ EINN 2005 Group Signal Backgr. Significance publ.Comments ---------------------------------------------------------------------- SPring8 19 17 4.6s 3.2s SPring8 90 260 4.8s SAPHIR 55 56 4.8s 5.2s DIANA 29 44 4.4s 3.4s CLAS(d) 43 54 5.2s 4.4s CLAS(p) 41 35 7.8s 4.7s 18 9 6.7 3.5s HERMES 51 150 4.3-6.2 3.6s ZEUS 230 1080 4.6 6.4s COSY 57 95 4-6 4.7s SVD 41 87 5.6 3.6s SVD-2 370 2000 7.5s Improved analysis NA49 38 43 4.2 4.2s H1 50.6 51.7 5-6 5.0s SPring8 80 200 4.8s L*(K+n) STAR 2,250 150,000 3.5-5sQ++candidate ? BELLE Q+ ? BABAR X5 Q0c

  29. Concluding comments Q+(1540) • Two high statistics experiments on protons and deuterium (CLAS) contradict results that observed ~5s signals with same kinematics. • Within hadronic models the new CLAS results put limits on the widths. For most models GQ+ < 0.5 MeV. New limit from Belle not (yet?) in contradiction with 1 MeV limit. Increase in statistics could change that. • Need to examine if gD and gA experiments with lower statistics are consistent with CLAS cross section limit on neutrons . • Sensitivity to Q+ at high energy appears in baryon fragmentation not in quark fragmentation. This could explain some of the null results at high energies. • Babar is challenging the HERMES results on Q+. • New data/analysis from LEPS, SVD-2, and STAR, support Q observations.

  30. Outlook • TheQ pentaquarkis not in good health, but itis • still alive. • - new analyses underway from COSY, SVD-2, SPring8 • - measurements planned at SPring8, JLab • - H1, ZEUS, HERMES high luminosity run until 2007 • - higher statistics data from STAR, PHENIX • - more statistics and analyses from B-factories • Should the Q pentaquark not survive the next few years of intense scrutiny we will have to examine why so many experiments observed the signal in the first place.

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