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The pentaquark case: state-of-the-art

The pentaquark case: state-of-the-art. Sonia Kabana University of Nantes and Subatech, Nantes, France MESON2006 , 12 June 2006, Krakow. Contents I Introduction II Review of pentaquark candidates observed: +, ++, 0c, --, -, 0, N0, N0/0 I=1/2, Sigma

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The pentaquark case: state-of-the-art

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  1. The pentaquark case: state-of-the-art Sonia Kabana University of Nantes and Subatech, Nantes, France MESON2006, 12 June 2006, Krakow Contents I Introduction II Review of pentaquark candidates observed: +, ++, 0c, --, -, 0, N0, N0/0 I=1/2, Sigma vis a vis non-observations and theory III Conclusions and outlook

  2. I Introduction QCD allows for hadronic states other than qqq and qqbar, like: qqqq q-bar (pentaquarks), qq q-bar q-bar (tetraquarks) etc First ever mentioned: 1964, M. Gell-Mann, PLB 8 (1964) 214. H.J. Lipkin, PLB45 (1973) 267, R.L. Jaffe et al, PLB60 (1976) 201 Etc First prediction of the mass: 1987, M Preszalowicz, Chiral Soliton Model, hep-ph/0308114  Mass Z+ (uudds*) = 1530 MeV +- 100 MeV (error: M. Preszalowicz et al JHEP 0405:002, 2004 ) First prediction of the width: 1997, D. Diakonov, V. Petrov, M. Polyakov, Z. Phys. A 359(1997)305, Ch. Soliton Model  (uudds*, S=1/2, I=0 ) Width < 15MeV (30 MeV) M. Preszalowicz et al JHEP 0405:002, 2004

  3. Theory: Quark model, Correlated Quark models, Lattice etc Example of lattice results 2004 • Several recent studies ( F Csikor et al hep-lqt/0503012, K Liu, hep-lat/0510036 etc) • don’t find evidence for pentaquarks on the lattice, or masses higher than 1530 • MeV (N Ishi hep-lat/0601003) • Pentaquarks on the lattice unclear; • while ‘the absence of evidence is not evidence of absence’ (hep-lat/0504007) • Work in progres

  4. II Review of pentaquark candidates observed +, ++, 0c, --, -, 0, N0, N0/0 I=1/2, S

  5. uudd sbar +

  6. LEPS COSY-TOF pp  S+Q+. The initial evidence for Pentaquarks CLAS-D SAPHIR DIANA 4.8 4.4 5.2 4.6 CLAS-p Neutrino NA49 HERMES 6.7 7.8 4.2 6.7 ~5 1862MeV ZEUS SVD 5.6 5-6 ~5 4.6

  7. CLAS  d --> K+ K- p n CLAS, S. Stepanyan et al, PRL91 (2003) 252001, hep-ex/0307018 : exclusive reaction  d --> K+ K- p n trigger on p, K+, K- M(+) = 1542 +- 5 MeV, Width< 21 MeV, S/sqrt(B)= 5.2 +- 0.6 + --> K+ n --> K+K- *(1520) --> pK- Solid line: fit to S (gauss) +B --> S/sqrt(B)=5.8 Dotted line: MC simulated background --> S/sqrt(B)=4.8 Dashed-dotted: shape of events excluded by a *(1520) rejection cut (m ≠1485-1551 MeV) Results not confirmed by latest CLAS results

  8. CLAS  p -> pi+ K-K+ n CLAS, V. Kubarovsky et al., hep-ex/0311046,  p -> pi+ K-K+ n E( )= 3-5.47 GeV Pi+ + Cos *(pi)>0.8 Cos *(K)<0.6 • + production through N*(2400) --> + K- ? • Mass(theta+)=1555+-10 MeV, Width < 26 MeV, • S/sqrt(B)=7.8+-1  Confirmation of this result with higher statistics by CLAS is planned for 2007

  9. CLAS 2005  p  K0s K+ n LP2005 CLAS 342 , APS Tampa 2005 Counts/4 MeV SAPHIR N(Q+)/N(L*) ~ 9% CLAS N(Q+)/N(L*) < 0.5% (95% CL) SAPHIRsg p Q+ K0 ~ 200 (50) nb CLAS sg p Q+ K0 < 2 nb (95% CL) (1520- 1555 MeV) < 4 nb (1560 - 1600 MeV) M(nK+)(GeV) • This result disagrees with the SAPHIR observation. Significance of published Saphir result is very low : 4.8 sigma The cr. Sect. of this reaction was estimating first 200 nbar in PLB572 (2003)127 without error, updated in the DPG2005 to 50 nbar.

  10. g K0 K* n p Q+ K+ …..CLAS  p K0s K+ n vs theory • The reported non-observation in g p --> theta+ K0 do not disagree with the previous CLAS results on  p  pi+ K+ K- n assuming N0* -->theta+ K- What cross section do we expect ? • S. Nam et al, hep-ph/0403009 estimate 1 nbar for g p --> theta+ K0 for J^P 1/2+ and a 4 times higher one for n --> theta+ K-  CLAS may not be sensitive enough for the theta+ K0 However: large uncertainty on the theor. Predictions of cr sect. • Isospin asymetry leading to larger cross section for gamma n than gamma p channel : • Nam, Hosaka and Kim, hep-ph/0505134 , Lipkin and Karliner, hep-ph/0506084

  11. 1/2+ 1/2- 3/2+ 3/2- GQ = 1 MeV nb nb nosignal • CLAS limits of 2nb on the proton and of 5nb on the neutron do not exclude a theta+ with width=1 MeV for JP = 1/2-, 3/2+ (V.Burkert, LP2005) CLAS 2005 :  D  K- p K+ n (LP2005 paper 357) No signal seen. Set upper limits: sQ+ < 5 nb (95% CL) • This result disagrees with published previous CLAS result (PRL 91, 252001, 2003, hep-ex/0307018). • (LP2005) : In the above PRL result the background is underestimated. New estimate gives a significance of ~3s --> is possibly due to a fluctuation. W. Roberts (PRC70, 065201, 2004), effective lagrangian model

  12. CLAS vs models QNP06 Some model predictions lower than CLAS limits Model predictions of cr. Sections have large uncertainty

  13. LEPS preliminary results confirm the  + cand. peak Candidate peak with 90 counts as compared to 19 in PPRL91 (2003) 012002 T Nakano et al, Pentaquarks2004 LEPS new :gamma n  K+ K- n (p spectator undetected) PRL91 (2003) 012002 2004 • Latest results show peak at 1.53 GeV with higher stat. • Fermi motion correction done • Tight phi exclusion cut • Background from mixed events • No L(1520) cut T Nakano et al, Beijing 16-20 June 2005 • LEPS confirms theta+ observation with increasing statistics • Check reflexions, background estimate, corrections • Main contribution to the peak comes from the formation miss. Mom. region 0.42 GeV

  14. LEPS new: gamma D  L(1520) K+ n (Beijing2005) Nakano et al, 16-20 June 2005 Beijing Theta+ is indentified by K-p missing mass Major background process: can be estimated from H target S=85, B=200 S/sqrt(B)=6 Excesses are seen at 1.53 and 1.6 GeV 1.53 GeV peak independent of beam momentum (< or > 2.1 GeV)  unlikely to be due to kinematic Reflexions 1.6 GeV peak appears only for low beam momenta < 2.1 GeV. Different production mechanism than 1.53 GeV peak.

  15. Sideband subtraction to remove non-resonant background L(1520) LD2 L(1520) LH2 LD2 Counts/5 MeV M(K－p) GeV/c2 M(K－p) GeV/c2 MMd(γ,K－p) GeV/c2 1.50 < M(K－p) < 1.54 Fluctuations in the sideband spectra are removed by smearing Eg by 10 MeV (nearly equal to the resolution). 1.45 < M(K－p) < 1.50 or 1.54 < M(K－p) < 1.59 - 0.4 S =

  16. T Nakano QNP2006 γ Θ＋ L(1116) p p－ n forward angle detection p Search for g d  L(1116) Q+ • Large cross-section compared with L(1520). • Missing Mass resolution is worse. • No excess at 1.53 GeV nor at 1.6 GeV. Counts/5 MeV preliminary MMd(γ,p－p) GeV/c2

  17. Results of E522 • p-p K-Q+ T Nakano QNP2006 - Excess above background observed near 1530 MeV - Significance about 3

  18. M = 1523 MeV s = 12 MeV Nevnt = 165 V. Burkert, Lepton Photon 2005 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 Group Signal Backgr. Significance S/sqrt(S+B) publ. S/sqrt(B) SVD-2 41 87 5.6 3.6 SVD-2 370 2000 8.3 7.6Improved analysis

  19. Diana 2006 hep-ex/0603017 K+ beam with 850 MeV momentum incident on a liquid Xenon in a bubble chamber : K+ n  K0s p K+ + Xe -> Q++Xe’ -> (K0++p) +Xe’ Larger statistics confirms candidate signal of 1st publication with S=60, B=68 S/sqrt(B)=7.3 M=1537+-2 MeV, < 9 MeV A new estimate of intrinsic width =0.36+-0.11 MeV, (previous value 0.9+-0.3 MeV) do not contradict Belle upper limit

  20. 445<pbeam< 525 MeV/c pbeam<445 MeV/c pbeam>525 MeV/c K+ Q+ n Kaon Scattering DIANA/ITEP hep-ex/0603017 K+ + XeQ++Xe’(K0++p) +Xe’ Total cross-section is proportional to the decay width More pictures were analyzed. Peak appears in mom. range of p(beam)=445-525 MeV consistent with Fermi spearing of a narrow resonance

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

  22. 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 Baryons: ~ 10-4 /GeV/c2 (generate two pairs) Pentaquarks: ~ 10-8 /GeV/c2 (?) (generate four pairs)

  23. ZEUS M(GeV) At HERA ep coll. theta+ candidate is produced in baryon fragmentation ep -> eK0spX Q+produced mostly at forward rapidity hLab > 0, and Q2 > 20 GeV2.

  24. DIANA N / 2 MeV/c2 mpKs (GeV/c2) Belle – Limit on Q+ Width GQ+ from K+A -> pK0sX & K+D -> inclusive analysis K+A -> pK0s Belle limit 90%CL 397 fb-1 Belle: G < 0.64 MeV (90% CL) @ M = 1.539 GeV T Nakano QNP2006 G< 1 MeV (90% CL) @ M = 1.525–1.545 GeV Cahn,Trilling,PRD69,11501 (2004). Not inconsistent with previous results.

  25. PDG 2006 : Two stars for theta+

  26. Theta++ uudusbar

  27. 18.6 M d+Au events STAR preliminary H Huang et al D+Au Collisions at 200 GeV • Conversion Coulomb Interaction L(1520) Coulomb Interaction After background subtraction pK+ : A 3.5-5.0 sigma signal is seen Mass is ~1.53 GeV/c2. Full width ~15 MeV. Do we understand the residual background?

  28. AuAu 62.4 GeV Results -- ++ • An excess above background is also seen in AuAu 62.4 GeV data from 20-80% centrality bin, 5.1 M events. • --/++ = 0.47 +- 0.2 ++ plus --

  29. Au+Au results STAR preliminary Au+Au 62 GeV Kaon p&pt (0.2, 0.6) Proton p&pt (0.3, 1.5) • AuAu 62 GeV data • 20-80% centrality bin • 5.6 M events • Weak Signal (3sigma) if any Au+Au 62 GeV Au+Au 200 GeV Kaon p&pt (0.2, 0.6) Proton p&pt (0.3, 1.5) • Year 4 AuAu 200 GeV data • 20-80% centrality bin • 10.7 M events • No Significant Signal (2s) Au+Au 200 GeV

  30. Cu+Cu 62.4 GeV Run 5 Data STAR preliminary • Year 5 CuCu 62 GeV data • 0-70% centrality bin • 16.5 M events • No signal at all !! Kaon p&pt (0.2, 0.6) Proton p&pt (0.3, 1.5) Is There an Obvious Contradiction ?

  31. CLAS theta++

  32. Comparison to Upper Limits from CLAS There qre null results on theta++pK+ from several experiments e.g. Saphir, Zeus etc Estimate in STAR for d+Au at sqrt(s) 200 GeV q++/L ~ 0.35% q++/L(1520) ~ 5% New CLAS limit for  p K- q++ with q++ pK+ and E(g)=1.8-3.8 GeV q++/L(1520) < 0.023% (95% CL) hep-ex/0605001 • - CLAS UL q++/L* (0.023%) below STAR raw estimate of q+/L* (3.5%) by ~ 170. • Does this definitely prove the STAR result false ?? CLAS and STAR study different collision systems, different energy and use different event selection. The investigated production mechanism of q++ may be different in STAR and CLAS as -CLAS studies one exclusive reaction. STAR studies inclusiveq++ production For example the mentioned CLAS Upper Limit does not access q++ production with an associated pion (CLAS statement in hep-ex/0605001), while STAR does. Note that the only still alive and of good significance theta+ signal of CLAS is in this channel (PRL92 032201 2004) to be confirmed with higher stat. In 2007.

  33. 0c uudd cbar

  34. 0c 0c candidate and its antiparticle seen by H1 • First evidence for e p --> theta_c^0 (uuddc*) -> D*- p -> (anti-D0 pi-) p -> (K+pi-pi-) p • Mass= 3099 +- 3 +- 5 (syst) MeV Width < 12+-3 MeV Non observations: Zeus using similar cuts and larger statistics EurPhys J C38 2004 29 hep-ex/0409033, FOCUS (photon+p at Fermilab) hep-ex/0412021

  35. Xi--, Xi-, Xi^0 Xi-- ssdd ubar Xi0 duss dbar Xi- ddss dbar

  36. NA49 pp collisions at sqrt(s)=17 GeV Xi--, Xi^0, Xi^- NA49 coll., C. Alt et al, PRL92(2004)042003, hep-ex/0310014 K. Kadija NA49, JLAB2003 Walliser,Kopeliovich predicted the Xi(27-plet) mass near 1850 MeV JETP97 433 (2002) Chir. Sol. Model postdicted the Xi(anti-10) near 1850 MeV (J Ellis et al, hep-ph/0401127) • Xi^- (1850) --> Xi* pi- (preliminary) while Xi^+ (1860) --> Xi* pi+ Not seen • Xi--(1862+-2) --> Xi- pi- • Xi^0 (1864+-5)--> Xi- pi+ Width<18 MeV • --> Xi^- (and Xi^0) pentaquarks could be from anti-10 or from 8

  37. PDG : 1 star for theta0_c and Xi(1860) Observed by only one experiment each

  38. N0/Xi0 N0 udsd sbar Xi0 udss dbar

  39. STAR Coll., S. Kabana et al, hep-ex/0406032 • N0/Xi0 I=1/2 Au+Au(min.bias, √s=200 GeV)-->  K0s Observation of a possible narrow peak at 1733.6 +-0.5 +- 5 MeV Cut out upper ~10% of (tot) to suppress background --> S/(B)=30.6/ ( 35.4)= 5.15,  <4.6 +-2.4 MeV STAR Au+Au coll. 200 GeV preliminary Blue line: mixed event background Best Significance obtained in semiperipheral ev.: S/(B)=19.36/ (10.64)=5.93

  40. No cut on centrality STAR Coll., S. Kabana et al, hep-ex/0406032 : STAR Au+Au coll. 200 GeV preliminary S/(B)=40.55/ (83.45)= 4.44

  41. (1232) p() pi-(K0s) + K0s(pi+ pi-) = 1232+497.67 = 1729.7 MeV • Could fake possibly a peak near 1734 MeV ? • - Difficult to result to a narrow peak ( width ~120 MeV) • -Test 1: Cut more on DCA(p,pi) to primary vertex  does not destroy the peak STAR Au+Au coll. 200 GeV preliminary Test 2: Cut Inv.Mass( p() pi-(K0s) ) out of  mass +- 30 MeV does not destroy the peak

  42. Investigations of systematic errors: • Split track investigation: Cut on nr of hits(tracks) > 25 (maximal possible 45) STAR Au+Au coll. 200 GeV preliminary

  43. Split track investigation II : | MomentumZ(pos. track(Lambda) – MomentumZ(pos. track(K0s) | < 30 MeV | MomentumZ(neg. track(Lambda) – MomentumZ(neg. track(K0s) | < 30 MeV | MomentumZ(pos. track(K0s) | < 100 MeV | MomentumZ(neg. track(Lambda) – MomentumZ(neg. track(K0s) | < 100 MeV

  44. N0/Xi0(1730) --> Lambda K0s candidate STAR Au+Au coll. 200 GeV preliminary S Kouznetsov et al, Graal, Trento, Feb 2004 S. Kabana et al, hep-ex/0406032 S/(B)=5.15 1734+-0.5 MeV hep-ex/0504026, P Aslanyan et al 1727 MeV • Seen in 2 decay channels. The Sigma-K+channel tags the strangeness content as ssbar --> N0 candidate (Graal) • Consistent with a partial wave analysis of old data suggesting two narrow N states at 1680 and/or1730 MeV width < 30 MeV(nucl-th/0312126, R Arndt et al) 1750+-18MeV 10 GeV beam

  45. N0(1670) --> eta n candidate Near the lower mass peak of 1680 width < 30 MeV suggested by nucl-th/0312126, R Arndt et al Could be an N member of the anti-10 S. Kouznetsov, NSTAR2004 and Trento2005 1670 MeV

  46. A Sigma pentaquark candidate 1980: Sigma(3170) state published and included in PDG FWHF < 20 MeV (Phys Lett B 89B 1 (1979) 125) K- p  pi- R+ K-p bubble chamber exp. Seen by two experiments Not ‘searched and not found’

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