Karin DaumBEACH 2004, Chicago, June 29, Searches for Exotic Baryons at HERA Karin Daum – Wuppertal Outline: HERA & kinematics at HERA Strange Pentaquarks  + (Hermes, Zeus)  -- (Zeus) Exotic Anticharmed Baryon (H1, Zeus) Conclusions 6th International Workshop on Hyperons, Charm and Beauty Hadrons Chicago, June 27-July 3, 2004 on behalf of the H1, HERMES and ZEUS collaborations

Karin DaumBEACH 2004, Chicago, June 29, Protons 920 GeV Electrons 27.6 GeV The Hera accelerator DESY Hamburg Germany ep- collisions eN-fixed target

Karin DaumBEACH 2004, Chicago, June 29, Hera kinematics in ep collisions E = 27.6 GeV e E = 920 GeV p √s = GeV (energy c.m.) W=m(   p) (hadronic energy) Q 2 =-q 2 (photon virtuality) 2 kinematic regimes : Q  0 GeV : Photoproduction Q > 1 GeV : Electroproduction (DIS) D*p event in DIS  ss K p e

Karin DaumBEACH 2004, Chicago, June 29, Fixed target kinematics at Hera  ²H √s = 10 GeV (energy c.m.) W=m(   p) (hadronic energy) Q 2 =-q 2 (photon virtuality) E = 27.6 GeV e 2 kinematic regimes : Q  0 GeV : Photoproduction Q > 1 GeV : Electroproduction (DIS)

Karin DaumBEACH 2004, Chicago, June 29, The  search at HERMES + Kinematic Range: GeV 2 and W > 2 GeV Dual radiator RICH for PID Very good proton ID Aerogel

Karin DaumBEACH 2004, Chicago, June 29, The  search at HERMES + Hadron identification using RICH Suppress contamination from  p  Define appropriate event topology Unambiguous invariant mass reconstruction due to PID O(1000) K 0s0s Peak at 1528  2.6 MeV  =8  2 MeV; 3.7  Peak at 1527  2.3 MeV  =9.2  2 MeV; 4.3   bumps 78  18 events e + + ²H   + + X  K 0 s p + X

Karin DaumBEACH 2004, Chicago, June 29, The  search in ZEUS + DIS (Q 2 >1 GeV 2 ):96-00 data 121 pb -1 Identify K 0 s, Remove  p  and converted  ’s O(900,000) K 0s0s DIS (Q 2 >1 GeV 2 ):96-00 data 121 pb -1 Identify K 0 s Remove  p  and converted  ’s Limited particle identification via dE/dx select proton candidates p(p) 1.15 mips e + p   + + X  K 0 s p + X

Karin DaumBEACH 2004, Chicago, June 29, The  search in ZEUS + Clear signal visible only at Q²> 20 GeV² MC normalised to background, No  -bumps included Fit a 2nd Gaussian to account for some of the differences Peak at  1.5 MeV  =6.1  1.5 MeV; 4.6  221  48 events O(100,000) K 0s0s Signal seen for both charges: K 0 s p = 96  34  ! -

Karin DaumBEACH 2004, Chicago, June 29, Is there a  ++ at HERA HERMESZEUS Clear Signal for  (1520)  pK - No Signal for    pK +   + isoscalar

Karin DaumBEACH 2004, Chicago, June 29, The  search in eN collisions at HERA + ExperimentKinematics K 0 s p/ K 0 s HERMES √s, W, Q² small  7 % ZEUS √s, W, Q² large Signal at High Q² small W  0.2 % Effect of phase space/acceptance ? Factor: 35 !

Karin DaumBEACH 2004, Chicago, June 29, Search for  at ZEUS -- NA49 ZEUS analysis for DIS similar to NA49 p-p- 0-0-  --   -  - ΛΛ ΞΞ -+ All charge combinations Clean Ξ(1530) P 13 No signal at (1860) preliminary

Karin DaumBEACH 2004, Chicago, June 29, Evidence for anti-charmed baryon by H1 If a strange pentaquark Why not a charmed one also Experimentally best suited D* p Theoretically not favoured data 75 pb -1 DIS: Q²>1 GeV² Good Signal/Background 3400 D*’s in DIS to start with Golden channel D* +  D 0  s  (K  )  s D* signal region subsequently used {

Karin DaumBEACH 2004, Chicago, June 29, Particle identification Reasonable PID via dE/dx -all data calibrated - parameterisation accurate to 3-5% - MIP resolution 8% Most probable dE/dx Normalized likelihood based on: measured dE/dx & expectations for , K, p and resolution: L(  )+L(K)+L(p) = 1 Use dE/dx for background suppression

Karin DaumBEACH 2004, Chicago, June 29, Background well described by D* MC and “wrong charge D” from data Apply mass difference technique M(D*p)=m(K  p)-m(K  )+M PDG (D*) no enhancement in D* Monte Carlo no enhancement in wrong charge D equally significant signal visible in separate D *+ p and D *- p signal visible in different data taking periods _ narrow resonance at M=3099  3(stat.)  5 (syst.) MeV Opposite sign D*p mass distribution

Karin DaumBEACH 2004, Chicago, June 29, All events scanned: No anomalies observed e.g. split tracks, wrong reconstruction K -  s +  - p HERA-II Typical D*p candidates p   + + D 0 D* K - HERA-I s

Karin DaumBEACH 2004, Chicago, June 29, M(D*p) [GeV]  M(D*) [GeV] Look at the correlation of  M(D*) vs. M(D*p) Side band scaled to the width of the signal window in M(D*p) the (D*p) signal region is richer in D* D*p signal region (D*p) side bands D* window Does the resonance come from D*’s?

Karin DaumBEACH 2004, Chicago, June 29, Physics changes on-resonance ? Look at momentum distribution of proton candidates w/o dE/dx No dE/dx cuts ! The momentum spectrum of the particles in the signal region is harder than in the M(D*p) side bands At large p(p) (>2 GeV) Signal more pronounced

Karin DaumBEACH 2004, Chicago, June 29, Photo-production more difficult due to large non-charm background but independent confirmation of the signal D*p in photo-production total: 4900 D* to start D*p peak at the same mass in  p no enhancement in non-charm bg 95 % bg due to non-charm Background well described by wrong charge D from data

Karin DaumBEACH 2004, Chicago, June 29, Background only hypothesis: N b =51.7±2.7 Background fluctuation probability: 4x10 -8 (Poisson)=5.4  (Gauss) 5.4  Significance estimate

Karin DaumBEACH 2004, Chicago, June 29, Search for charmed PQ,  c  D*p, in ZEUS D.I.S. Selection differs from H1 analysis

Karin DaumBEACH 2004, Chicago, June 29, Search for charmed PQ,  c  D*p, in ZEUS Photoproduction + DIS

Karin DaumBEACH 2004, Chicago, June 29, Conclusions  Positive evidence for the production of  + at HERA  No doubly charged partner   + is an isoscalar  large differences in the  + / K 0 s yields from HERMES and ZEUS  Negative results on the search for  -- by ZEUS  Evidence for a neutral anti-charmed baryon state decaying to D*p from H1 - not confirmed by ZEUS prelim.

Karin DaumBEACH 2004, Chicago, June 29, Backup Slides

Karin DaumBEACH 2004, Chicago, June 29, Like-sign D*p mass distribution no significant peak in like-sign D*p no enhancement in D* Monte Carlo no enhancement in wrong charge D Background well described by D* MC and “wrong charge D” from data

Karin DaumBEACH 2004, Chicago, June 29, M(D*p)=3.104  GeV Use this region with L(p)>0.5 Does the resonance come from protons ? P(p)<1.2 GeV dE/dx >1.15 Signal is there for well identified protons = 0.92

Karin DaumBEACH 2004, Chicago, June 29, Is the physics different in the signal region?  Single particle momentum spectra are steeply falling  This feature is preserved in the combinatorial background of invariant mass analyses  In decays particles are also emitted in the direction of flight  Particles from a decay should have a harder spectrum than the combinatorial background Check the proton momentum ! H1

Karin DaumBEACH 2004, Chicago, June 29, 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 the physics different in the signal region?

Karin DaumBEACH 2004, Chicago, June 29, D*p rest frame wrong mass assignment correct mass assignment M(D*  ) [GeV] M(D*p) [GeV] M(D*  ) [GeV] 2-Body Decay independent of decay angle cos  * only for correct mass assignment CPQ MC Basics of kinematic tests

Karin DaumBEACH 2004, Chicago, June 29, wrong mass assignment correct mass assignment M(D*  ) [GeV] M(D*p) [GeV] M(D*  ) [GeV] 2-Body Decay Do we see a band like structure in the M(D*p)-M(D*x) plane in data?  Let’s have a look D*p rest frame CPQ MC Integrated in cos  * Basics of kinematic tests

Karin DaumBEACH 2004, Chicago, June 29, Sign for X D*p: available phase space in D*  completely used Go to the D*p signal region Signal due to D*  ? NO!

Karin DaumBEACH 2004, Chicago, June 29, Lots of further kinematic test Reflections from a possible signal in D*K mass distribution: ruled out Possible contributions from D*  D  with  -conversion: ruled out Possible contributions from D /D  D K: ruled out Possible peak structures in all possible mass correlations with all possible mass hypotheses of the particles making the D* and the D*p system to search for real or fake resonances, e.g , , , K, , f no enhancements found Possible peak structures in all possible mass correlations among the proton candidate the remaining charged particles of the event with all possible mass assignments to search for real or fake peaks, no enhancements found S1 S S0S

Karin DaumBEACH 2004, Chicago, June 29, Remarks on D*p searches at LEP D* signals for different x E LEP are produced predominantly by beauty R b  22%, R c  17% D* acceptance vs. x E ?

Karin DaumBEACH 2004, Chicago, June 29, Remarks on D*p searches at LEP LEP are produced predominantly by beauty R b  22%, R c  17% cc  0.488

Karin DaumBEACH 2004, Chicago, June 29, Remarks on D*p searches at LEP beauty charm

Karin DaumBEACH 2004, Chicago, June 29, D* from D*p and direct D* at HERA MC cc  0.56 D*’s from D*p significantly softer than normal D*’s Should also hold for LEP ! cc  0.43