1. Volker D. Burkert Jefferson Lab N*2005 – Tallahassee, Florida, October 12-15, 2005 Have Pentaquark States been seen? Outline:  Brief introduction  Original evidence for & against pentaquarks  How can results be compared?  2 nd generation experiments and implications  Status of pentaquarks October 2005?  Conclusions

2. General idea of five-quark states has been around since late 60’s. Predicted masses range from 1500 to 1800 MeV, widths ~hundreds MeV. Bag models [R.L. Jaffe ‘76, J. De Swart ‘80], lightest pentaquark J p =1/2 - ; Soliton models [Diakonov, Petrov ‘84, Chemtob‘85, Praszalowicz ’87. Walliser‘92]. Pentaquark history A new wave of experimental searches was motivated by predictions in  SM model: Diakonov, Petrov, Polyakov. Z.Physics A359 (1997). A new wave of experimental searches was motivated by predictions in  SM model: Diakonov, Petrov, Polyakov. Z.Physics A359 (1997). Publications on pentaquarks Anti-decuplet q 4 q states J P = ½ +  + : M = 1530 MeV,  < 15 MeV

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

4. The  + width K + D, K + Xe X   = 0.9 +/-0.3 MeV W. Gibbs, Phys.Rev.C70, 054208 (2004)  Very narrow for a hadronically decaying particle with mass ~100 MeV above threshold:  + (1540)  nK +, pK 0 K + D  X  Measured width dominated by experimental resolution  Analysis of K + A data give limit of few MeV.  What can we say about event rates? K + n ->   =>  ~1 MeV, K - p ->   =>  ~16 MeV.      ~ 1.4% for formation. Sibirtsev et al.:   < 1 MeV From selected data sample

5. Non-evidence for Pentaquarks FOCUSBABAR BES CDF FOCUS SPHINX CDF DELPHI HyperCP HERA-B CDF 0c0c  -- + more

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

7. Upper limit on the  + cross section (95%c.l.) M(nK + )(GeV) Counts/4 MeV preliminary s g p  Q  K 0 < 1.25 nb @ 1.54 GeV/c 2 Fit with a sum of smooth function and a Gaussian with fixed width and centroid. CLAS:  p -> K 0 K + n K0K0 p  K*K* ++ K+K+ n Results put stringent limits on possible production mechanism, e.g. implies very small coupling to K*

8. Comparison with SAPHIR results cosq CM (K 0 ) > 0.5 L(1520) SAPHIR g11@CLAS Q + (1540) ? preliminary M(nK + ) (GeV) Counts M(nK + ) (GeV)M(nK 0 ) (GeV) Observed Yields SAPHIR N(  + )/N(  *) ~ 10% CLAS N(  + )/N(  *) < 0.2% (95%CL) Cross Sections SAPHIR  g p  Q  K 0 ~ 300 nb CLAS  g p  Q  K 0 < 2 nb

9. pKKγD    n  n        < 4-5 nb (95% CL) model dependent.  Set upper limit on cross section < 450pb  Upper limit on elementary cross section:  The new data show no signal no  signal Upper limit on  + production with CLAS. G10  In previous result the background is underestimated. New estimate of the original data gives a significance of ~3  possibly due to fluctuations. Talk by Nathan Baltzell in P2-B on  n  pK 0 K - channel.

10. Upper limit on   + from CLAS Results Publication Reaction JJ Experimental width 1/2 - 1/2 + 3/2 - 3/2 +   M. Guidal et al., 0.01nb0.22nb <5.7 MeV hep-ph/0507180 0.2nb1nb55nb 10nb < 4 MeV S. Nam et al., (2.7)nb 8nb(1)nb <(0.5) MeV hep-ph/0505134 2.7nb 200nb25nb < 1.7 MeV Y. Oh et al., NP A745 ~0.4nb ~1.6(100)nb < 0.8 MeV hep-ph/0412363 ~1.7nb~8.7(75)nb < 0.5 MeV C.M. Ko and W. Liu 15(30)nb < 0.08 MeV nucl-th/0410068 15(30)nb < 0.25 MeV W. Roberts 2nb5.2(~10)nb15.4nb1.8nb< 0.24 MeV nucl-th/0408034 3.5nb 11.2(~20)nb 48nb 4.nb< 0.4 MeV Theoretical cross sections are for   + =1 MeV ( ) – with K* exchange

11. Old and New Signal from LEPS/SPring8 MM C (γ,K ＋ ) GeV/c 2 Mix K ＋, K －,  from different events in LH 2 data.  (1520) contribution was removed from the sample. MM C (γ,K － ) GeV/c 2  (1520) ＋＋ preliminary  D -> K - K + X

12. K - p missing mass spectrum MMd(γ,K － p) GeV/c 2 Counts/5 MeV preliminary MMd(γ,K － p) GeV/c 2 Counts/5 MeV  * fitted in MM<1.52 GeV/c 2 ++ 1.6 GeV bump ** from sidebands preliminary ~5σ excess at 1.53 GeV/c 2 corresponding to  + 1.6 GeV bump was also seen. Signal emerges with selection of  *(1520) in M(K - p) LEPS

13. M(GeV) ZEUS  Signal seen at medium Q 2 and forward rapidity in both pK s and pK s Pentaquark Studies at HERA ep  eK 0 s pX High energy production mechanism?

14. ZEUS – Cross section on   M(GeV)    * ~ 5% (independent of Q 2 )

15. momentum, GeV/c 1 / 50MeV momentum spectra of K + and K - K+K+ n ++ Momentum range possibly contributing to  + formation. Belle – Low energy K + N scattering e + e -  K +/- X, K +/- A  pK 0, pK - Detector Tomography  Determine resonance width

16. Belle – Limit on  + Width 397 fb -1 K + A  pK 0 s Belle limit 90%CL    MeV (90% CL) @ M = 1.525–1.545 GeV No Not inconsistent with previous results.    from K + A  pK 0 s X & K + D  inclusive analysis no signal Belle:  < 0.64 MeV (90% CL) @ M = 1.539 GeV Γ Θ+ = Δm N Θ+ N ch σ ch 107mb B i B f Cahn,Trilling,PRD69,11501 (2004 ). DIANA

17.  + /  * cross section ratios ExperimentReactionEnergyσ(Θ + )/σ(Λ*) CDF pp  Θ + X 1960 GeV<3% HERA-B pA  Θ + X 42 GeV<2% SPHINX pA  Θ + X 12 GeV<2% Belle KA  Θ + X  2 GeV <2.5% LEPS AΘ+XAΘ+X  2 GeV  50% HERMES eD  Θ + X 7 GeV  200% CLAS-2(p) p Θ+Ksp Θ+Ks 4 GeV< 0.16% Consistent with <1 MeV width. Inconsistent with < 1 MeV width?

18. Hadron production in e + e - collisions Slope for Pentaquark ? Slope for baryons Slope for p.s. mesons Slope: Pseudoscalar mesons: ~ 10 -2 /GeV/c 2 (need to generate one qq pair) Baryons: ~ 10 -4 /GeV/c 2 (generate two pairs) Pentaquarks: ~ 10 -8 /GeV/c 2 (?) (generate four pairs)          = 1Mev  = 1MeV BR(  --   -  -)=0.5

19. BaBar Preliminary 233 fb –1 e + e – data SVT Beam pipe SVT support tube DCH inner wall e–e– e+e+ Veto beamspot R  2 cm Y [cm] X [cm] z profile Tomography with pK s 0 Vertices Y [cm] -0.2 < y < 0.7 cm -3.1< x < -2.2 cm Ta Be X [cm]  Quasi-real photoproduction experiments on nuclei

20. e - Be Electroproduction HERMES (e + d  K S 0 p + X) Hermes: ~5  M=1528  3 MeV HERMES: acceptance loss in low mass region? (PID requires p(p) >4.1 GeV/c; p(K S 0 )>3 GeV/c) Preliminary 233 fb –1 e + e – data HERMES ZEUS (e - p  e - K S 0 p + X) Zeus: ~5  M=1522  3 MeV  *  1480) ZEUS HERMES/BaBar comparison disturbing. ZEUS : High Q 2, no signal for Q 2 <1 BaBar: Quasi-real photons (quasi-real photoproduction)

21. pK + and pK - from 18.6 M d+Au at 200 GeV STAR d-Au results M (GeV/c 2 )   Is this a  ++ candidate ? Possible mechanism for production of multi-q/g states: Coalescence of out of QGP? Also a  + candidate ?? STAR Preliminary ?

22. WA89 Results   A  K s pX E  = 340 GeV SVD-2 – New Analysis  New analysis improves  + signal by factor 8. Total significance ~7.5    M = 1522 MeV = 12 MeV Nevnt = 205 Two independent data set: K S decays inside or outside the Vertex Detector E p = 70 GeV

23. Cascade Pentaquark   -- (1862) ? CDF pp  X HERA-B  State not produced in quark fragmentation or is severely suppressed. FOCUS AA AA < 0.0025/B range

24. Charmed Pentaquark  0 c (3100) ?  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 also claims incompatibility with H1. FOCUS FOCUS events H1 expected

25. Pentaquark Status @ N* 2005 GroupSignal Backgr. Significance publ.Comments ---------------------------------------------------------------------- SPring819174.6  3.2  SPring890260 4.8  SAPHIR55564.8  5.2  DIANA29444.4  CLAS(d)43545.2  4.4  CLAS(p)41357.8  4.7  18 9 6.7  3.5  HERMES 51150 4.3-6.2  3.6  ZEUS 230 1080 4.6  6.4  COSY 57 95 4-6  4.7  SVD 41 87 5.6  3.6  SVD-237020007.5  NA49 38 43 4.2  4.2  H1 50.6 51.7 5-6  5.0  SPring880 200 4.8     n  STAR2,250 150,000 3.5- 5    candidate G11 CLAS-p G10 CLAS-d s / b+s HERA-B, CDF, COMPASS ZEUS, FOCUS, BABAR ? B ELLE B A B AR 55 0c0c ++ WA89

26. The evidence for the  + in 10/2005 LEPS CLAS-p Neutrino pp   +  +. COSY-TOF DIANA ZEUS 4.6  4.4  CLAS-D 5.2  SAPHIR 4.8  7.8  HERMES ~5  6.7  SVD 5.6  ~5  4.6  33 K + N -  X

27. Concluding comments    0 c   Each one observed by single experiment.  Strong evidence against both states from several other experiments with comparable kinematics and claimed higher sensitivity  The collaborations observing the states should show that other measurements lack sensitivity, or re-examine their own results.

28. Concluding Comments  Two high statistics experiments on protons and deuterium (CLAS) contradict results that observed ~5  signals with same kinematics.  Within hadronic models the new CLAS results put limits on the widths. For most models   + < 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  D and  A experiments with lower statistics are consistent with CLAS cross section limit on neutrons.  Babar is challenging the HERMES results on  + with very high statistics.  New data/analysis from LEPS, SVD, and STAR, support  observations.  WA89 claims incompatibility with SVD results   

29. Outlook  The narrow   pentaquark is not in good health, but it is too early to pronounce it dead.  Ongoing efforts to further test previous results - new analyses underway from COSY, SPring8 - measurements planned at SPring8, JLab (CLAS, Hall A) - H1, ZEUS, HERMES high luminosity run until 2007 - higher statistics data from STAR, PHENIX - more statistics and analyses from B-factories (Belle, BaBar)  Even if the  pentaquark will not survive the next years of intense scrutiny, given the huge theoretical effort, we will still will have learned a lot about hadron structure and strong QCD.

31. SVD-2 – New Analysis   M = 1522 MeV = 12 MeV Nevnt = 205 M = 1523 MeV = 12 MeV Nevnt = 165 Two independent data set: K S decays inside or outside the Vertex Detector  New analysis improves  + signal  by factor 8. E p = 70 GeV A. Aleev et al., hep-ex/0509033

32. Summary of LQCD Group Method of analysis/criterion Conclusion Alexandrou and Tsapalis Correlation matrix, Scaling of weights Can not exclude a resonance state. Mass difference seen in positive channel of right order but mass too large Chiu et al. Correlation matrix Evidence for resonance in the positive parity channel Csikor et al. Correlation matrix, scaling of energies First paper supported a pentaquark, second paper with different interpolating fields produces a negative result Holland and Juge Correlation matrix Negative result Ishii et al. Hybrid boundary conditions Negative result in the negative parity channel Lasscosk et al. Binding energy Negative result Mathur et al. Scaling of weights Negative result Sasaki Double plateau Evidence for a resonance state in the negative parity channel. Takahashi et al. Correlation matrix, scaling of weights Evidence for a resonance state in the negative parity channel. J. Negele, Lattice 2005 Correlation matrix, scaling of weights Maybe evidence for a resonance state? C. Alexandrou