1. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 1 Evidence for a Narrow Exotic Anti-Charmed Baryon State *) Jan Hladký, Institute of Physics AS ČR Prague, H1 Collaboration *) published in Phys. Lett. B588 (2004) 17-28

2. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 2 ~ Introduction ~ D* and D*p analysis ~ Conclusions Outlook:

3. Low-x Wshop, 18.9.04, Prague 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

4. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 4 Pentaquarks proposals Gell-Mann 1964 Several model concepts Lot of experiments - several successfull ?

5. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 5 Pentaquarks from meson and baryon multiplets Baryons qqq from SU(3) f Baryons built from meson-baryon, or qqqqq Mesons qq from SU(3) f 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 Diakonov et al. Z.Phys. A359, 305 (1997) ++  −− C H A R G E -2 0 1 STRANGENESS S -2 0 +1

6. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 6 ee p Liquid Ar Calorimeter “Spaghetti” Calorimeter Central Jet Chambers Drift chambers, acceptance: 15 O < θ < 165 O 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

7. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 7 1996 – 2000 Data L int = 75 pb -1 1 GeV 2 < Q 2 < 100 GeV 2 0.05 < y < 0.7 p t (D*) > 1. 5 GeV -1. 5< |η(D*)| < 1. p t (K) + p t (p) > 2 GeV Elasticity z(D*) > 0.2 D* signal region subsequently used { D* meson selection Good Signal/Background 3400 D*’s to start with

8. Low-x Wshop, 18.9.04, Prague 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 dE/dx used for background suppression 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

9. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 9 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 m p for its mass K -  s +  - p

10. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 10 Pentaquark in H1 setup K p e 27,6 GeV p 820/920 GeV

11. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 11 M( D*p ) = m( K  p )-m( K  )+m( D* ) PDG Significant peak in opposite sign D*p No enhancement in D* MC ( RAPGAP ) 2) 2) Also no peak from CASCADE or Beauty MC Background well described by D* MC and wrong charge D from data No enhancement in wrong charge D 1) 1) Mass of same sign K ±  ± in m( D 0 ) window D* - p + cc in DIS for 1996 - 2000

12. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 12 Signal in both D *- p and in D *+ p M( D*p ) = m( K  p )-m( K  )+m( D* ) PDG Signal of similar strength observed for both charge combinations at compatible M ( D*p ) M( D*p )=3.096 ± 0.006 GeV M( D*p )=3.102 ± 0.003 GeV

13. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 13 M(D*p) = m(K  p)-m(K  )+m(D*) PDF M( D*p ) [GeV]  M( D* ) [GeV] D*p signal region { { D*p Side bands Normalization to the width of the windows in M(D*p) Signal region in D* - p richer in D* -

14. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 14 M(D*p) = m(K  p)-m(K  )+m(D*) PDF Use this region with L(p)>0.5 Is the D* - p signal due to protons? M( D*p )=3.104 ± 0.003 GeV

15. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 15 Fit slope with  exp {-  p(p)} The momentum spectrum of the particles in the signal region is harder than in the M( D*p ) side bands Signal region  =1.27  0.09 D* side band  =1.86  0.13 D*p side bands  =1.74  0.06 M( D*p ) [GeV]  M( D* ) [GeV] Is physics different in signal region?

16. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 16 Lot of different tests have been made… …signal is not affected !!!

17. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 17 Significance estimation  Significance estimate based on the background only hypothesis N b = 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 N S + N b = 95 D*p candidates (within 2  N b = 45.0  2.8 from background + signal hypothesis (fit) 5.4 

18. Low-x Wshop, 18.9.04, Prague 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 its charge conjugate. * The minimal quark content is uudd. It is a candidate for a charmed pentaquark state. * Up to now is not confirmed by other experiments.

19. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 19 HAVE A GOOD TIME IN THE GOLDEN CITY PRAGUE ! OF

20. Low-x Wshop, 18.9.04, Prague Jan Hladký, Exotic Anti-Charm Baryon State 20 CONCLUSIONS