Evidence for a Narrow Exotic Anti- Charmed Baryon State *)

1. Evidence for a Narrow Exotic Anti-Charmed Baryon State *) Jan Hladký, Institute of Physics AS ČR Prague, H1 Collaboration Jan Hladký, Exotic Anti-Charm Baryon State *) published in Phys. Lett. B588 (2004) 17-28

2. Outlook: ~Introduction ~D* and D*p analysis ~ Conclusions Jan Hladký, Exotic Anti-Charm Baryon State

3. Motivation: Pentaquark problem HERA is also charm factory H1 detector has Si vertex detectors D* golden channel Charm baryons searches Jan Hladký, Exotic Anti-Charm Baryon State

4. Pentaquarks proposals Gell-Mann 1964 Several model concepts Lot of experiments - several successfull ? Jan Hladký, Exotic Anti-Charm Baryon State

5. C H A R G E Diakonov et al. Z.Phys. A359, 305 (1997) -2 -1 0 1 Quantum numbers of the states cannot be described by only 3 quark states, minimal configuration is 5 quarks !!! For all the rest it is enough 3 quark + Baryons built from meson-baryon, or qqqqq STRANGENESS S X−− +1 0 -1 -2 Pentaquarks from meson and baryon multiplets Mesons qq from SU(3)f Baryons qqq from SU(3)f Jan Hladký, Exotic Anti-Charm Baryon State

6. “Spaghetti” Calorimeter Liquid Ar Calorimeter e p Central Jet Chambers Drift chambers, acceptance: 15O < θ < 165O charge and timing information B = 1.15 T → measure transverse momentum of charged particles Tracking , Particle ID via dE/dx H1 experiment at HERA 27.6 GeV 820, 920 GeV Jan Hladký, Exotic Anti-Charm Baryon State

7. D* meson selection • 1996 – 2000 Data • Lint = 75 pb-1 • 1 GeV2 < Q2 < 100 GeV2 0.05 < y < 0.7 • pt (D*) > 1. 5 GeV • -1. 5<|η(D*)| < 1. • pt (K) + pt (p) > 2 GeV • Elasticity z(D*) > 0.2 { Good Signal/Background 3400 D*’s to start with D* signal region subsequently used Jan Hladký, Exotic Anti-Charm Baryon State

8. Proton selection • dE/dx calibrated for 1996-2000 data • parameterization accurate to 3-5% • 8% average resolution Most probable dE/dx Normalized likelihood based on: measured dE/dx & expectations for π, K, p and resolution: L(π)+L(K)+L(p) = 1 Final proton selection: (L(p)>0.1&&p(p)>2).or.L(p)>0.3 dE/dxused for background suppression Jan Hladký, Exotic Anti-Charm Baryon State

9. - p + K p - p s The D*- p analysis • Looking for a narrow state near threshold • Expected 4-particle mass resolution about 35 MeV not favourable for a narrow state use mass difference technique: m(D*p)-m(D*) • Cut on the normalized proton likelihood L(p) for pion suppression • Take a D* candidate add a track consistent with a proton and opposite charge of the D* using mp for its mass Jan Hladký, Exotic Anti-Charm Baryon State

10. Pentaquark in H1 setup e 27,6 GeV p 820/920 GeV K p Jan Hladký, Exotic Anti-Charm Baryon State

11. Significant peak in opposite sign D*p No enhancement in wrong charge D 1) No enhancement in D* MC (RAPGAP) 2) 1) Mass of same sign K±p± in m(D0) window 2) Also no peak from CASCADE or Beauty MC D*-p + cc in DIS for 1996 - 2000 M(D*p) = m(Kppp)-m(Kpp)+m(D*)PDG Background well described by D* MC and wrong charge D from data Jan Hladký, Exotic Anti-Charm Baryon State

12. Signal in both D*- p and in D*+ p M(D*p) = m(Kppp)-m(Kpp)+m(D*)PDG M(D*p)=3.096 ± 0.006 GeV M(D*p)=3.102 ± 0.003 GeV Signal of similar strength observed for both charge combinations at compatible M(D*p) Jan Hladký, Exotic Anti-Charm Baryon State

13. Signal region in D*- p richer in D*- D*pSide bands { { DM(D*) [GeV] M(D*p) [GeV] D*p signal region Normalization to the width of the windows in M(D*p) M(D*p) = m(Kp)-m(K)+m(D*)PDF Jan Hladký, Exotic Anti-Charm Baryon State

14. Is the D*-p signal due to protons? M(D*p)=3.104± 0.003 GeV Use this region with L(p)>0.5 M(D*p) = m(Kp)-m(K)+m(D*)PDF Jan Hladký, Exotic Anti-Charm Baryon State

15. D*side band =1.860.13 D*p side bands =1.740.06 Signal region =1.270.09 Is physics different in signal region? Fit slope with exp {-p(p)} DM(D*) [GeV] M(D*p) [GeV] The momentum spectrum of the particles in the signal region is harder than in the M(D*p) side bands Jan Hladký, Exotic Anti-Charm Baryon State

16. Lot of different tests have been made… …signal is not affected !!! Jan Hladký, Exotic Anti-Charm Baryon State

17. Significance estimation NS + Nb =95 D*p candidates (within 2s) Nb =45.02.8 from background + signal hypothesis (fit) 5.4 s •  Significance estimate based on the background only hypothesis Nb= 51.72.7 • Use of different background functions as well as the background model from data and MC • Significance determined in a binning free method • Background fluctuation probability 4 x 10-8 (Poisson)  5.4 σ (Gauss) Change in likelihood of fits: 6.2 σ Jan Hladký, Exotic Anti-Charm Baryon State

18. CONCLUSIONS * H1 has observed a narrow resonance in both D*- p and D*+ p M(D*p) =3099 3 (stat.)  5 (syst.) MeV , Gaussian width = 12  3(stat.) MeV. * Significance is 5.4 sigma. * Background fluctuation probability is smaller than 410-8. * The signal is also observed in an independent photoproduction sample. *It is interpreted as an anti-charmed baryon decaying into D*p and itscharge conjugate. * The minimal quark content is uudd . It is a candidate for a charmedpentaquark state. * Up to now is not confirmed by other experiments. Jan Hladký, Exotic Anti-Charm Baryon State

19. HAVE A GOOD TIME IN THE GOLDEN CITY PRAGUE ! OF Jan Hladký, Exotic Anti-Charm Baryon State

20. CONCLUSIONS Jan Hladký, Exotic Anti-Charm Baryon State