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Baryon, Heavy Stable Particle and Strange Meson Production in ep-Collisions

XII International Conference on Hadron Spectroscopy Frascati , October 8 th -12 th , 2007. Baryon, Heavy Stable Particle and Strange Meson Production in ep-Collisions. Karin Daum – Wuppertal on behalf of the H1 and ZEUS collaborations. Outline: HERA & kinematics at HERA

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Baryon, Heavy Stable Particle and Strange Meson Production in ep-Collisions

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  1. XII International Conference on Hadron Spectroscopy Frascati, October 8th-12th, 2007 Baryon, Heavy Stable Particle and Strange Meson Production in ep-Collisions Karin Daum – Wuppertal on behalf of the H1 and ZEUS collaborations • Outline: • HERA & kinematics at HERA • Charged particle fragmentation function • Proton & Deuteron production • Strange particle production • Bose Einstein correlations • Conclusions Hadron07, Frascati, Oct., 11th 2007

  2. Protons 920 GeV • Electrons 27.6 GeV Results based on HERA-I data (~120 pb-1) - 3 times more to come The HERA accelerator DESY Hamburg-Germany Hadron07, Frascati, Oct., 11th 2007

  3. E = 27.6GeV E = 920 (820)GeV e p Dh(xp,)FF q Fragmentation process: xp (fraction of quark momentum carried by the hadron)  (energy scale of the quark) HERA kinematics ep-Kinematics: √s = 300-318 GeV (energy c.m.) Q2=-q2 (photon virtuality) x=xBJ (fraction of proton momentum carried by the struck quark) PDF 2 kinematic regimes : Q²  0 GeV² : Photoproduction (p) Q² > 1 GeV² : Electroproduction (DIS) h = PDF  M.E.  FF Hadron07, Frascati, Oct., 11th 2007

  4. ARIADNE for DIS Color dipol model (CDM) + String fragmentation Dh(xp,)FF q h = PDF  M.E.  FF Hadrons PYTHIA for p LEPTO for DIS LO ME + Parton showers + String fragmentation PDF Models for ep scattering How well do we understand particle production? Hadron07, Frascati, Oct., 11th 2007

  5. ± K± p d K0s  Dh(xp,)FF q h = PDF  M.E.  FF PDF Charged particle fragmentation function • H1 Inclusive fragmentation function: No distinction between ±, K±, p • Restricted to 100<Q²<10000 GeV² • Suppresses HO QCD effects not present in e+e- (e.g. boson-gluon-fusion, ISR) Use a reference frame closest to the situation in e+e-: (Breit-Frame) • Energy scales: ep-collisions: =Q/2 e+e--annihilation: =s/2=Ebeam Hadron07, Frascati, Oct., 11th 2007

  6. Steep rise with Q at small xp Population due to gluon splitting Steep fall with Q at large xp Depletion due to gluon radiation (ep)=Q/2, (e+e-)=s/2 Charged particle fragmentation function Overall agreement with e+e- except at large Q + small xp Hadron07, Frascati, Oct., 11th 2007

  7. Charged particle fragmentation function Comparison with NLO QCD predictions based on different fragmentation functions extracted from e+e- data Quite different QCD predictions Strong scaling violations in data - All calculations fail to describe them! (ep)=Q/2 Hadron07, Frascati, Oct., 11th 2007

  8. Charged particle fragmentation function ZEUS prel. HERA-I + HERA-II: 0.5 fb-1  very good agreement with H1 but 10 times more statistics Hadron07, Frascati, Oct., 11th 2007

  9. ± K± p d K0s  Dh(xp,)FF q h = PDF  M.E.  FF PDF Ed d3σd Ep d3σp σtot dpd3σtot dpp3 =B2( )2 Production of protons and deuterons ZEUS DIS: Q²>1 GeV² Coalescence Model: Baryons uncorrelated & inv. cross section same for p and n Relates proton to deuteron production: Coalescence parameter B2 (defines region of nucleon overlap): - Same for deuteron & anti-deuteron? - Process dependent? Hadron07, Frascati, Oct., 11th 2007

  10. σinv(d)  10-3·σinv(p) σinv(d) ≠ σinv(d) Production of protons and deuterons Not expected from coalescence model Hadron07, Frascati, Oct., 11th 2007

  11. B2(d)=(3.32±0.34 )10-2GeV2 B2(d)=(0.89±0.14 )10-2GeV2 +1.13 -1.15 +0.19 -0.20 Coalescence parameter B2 Coalescence parameter B2 depends on - primary process - centre-of-mass energy (less dependent in scattering off protons) Hadron07, Frascati, Oct., 11th 2007

  12. ± K± p d K0s  ZEUS Different regimes is ep-kinematic: 1. DIS: Q²>25 GeV² 2. DIS: 5<Q²<25 GeV² 3. p: Q²≈0, 2 jets, ET > 5 GeV  acts as a quasi-real target  may get internal structure (resolves into partons) Distinction of direct  from resolved  via observable x calculated from the two jets: x≈1  direct  x«1  resolved  Dh(xp,)FF q jet h = PDF  M.E.  FF PDF Strange particle production • Due to the s-quark mass ms • fragmentation into K0s,  is • suppressed w.r.t. , p • Strangeness suppression factor s Hadron07, Frascati, Oct., 11th 2007

  13. Strange particle production (DIS) 5<Q²<25 GeV² Q²>25 GeV²5<Q²<25 GeV² Q²>25 GeV² pT pT pT pT     ARIADNE s=0.3(CDM) overall reasonable – but shapes not so good ARIADNE s=0.22 systematically too small (from previous result) LEPTO s=0.3 (PS) fails Hadron07, Frascati, Oct., 11th 2007

  14. Strange particle productionp   pT pT x x Resolved  Intact  (direct) PYTHIA reasonable in pt and  PYTHIA off in shape of x (small x) Hadron07, Frascati, Oct., 11th 2007

  15. Resolved  Intact  (direct) - especially @ small x Strange baryon-to-meson ratio DIS5<Q²<25 GeV² Q²>25 GeV²  pT pT pT   x p Model in DIS (ARIADNE) s=0.3 quite good (10%) Model in p (PYTHIA) off in all distributions for x=1 same baryon-to-meson ratio as in DIS and e+e- Hadron07, Frascati, Oct., 11th 2007

  16. Distance in phase space characterized by: r = source size of particle emission Q12 = distance in 4-momentum space = -(p1-p2)2 Correlation function (static Gaussian source): R(Q12) = 1 + exp(-r2Q212) experimentally: R(Q12) = Double ratio (reduced sensitivity to models) R(Q12) = P(Q12)data Pmix(Q12)data P(Q12)MCnoBEC Pmix(Q12)MCnoBEC P(Q12) Pref(Q12) 0 0 Bose-Einstein correlations for K±K±, Ks Ks Identical bosons prefer to be produced close in phase space Hadron07, Frascati, Oct., 11th 2007

  17. +0.09 -0.08 +0.47 -0.53 +0.15 -0.08 +0.11 -0.08 =0.70±0.19 =0.37±0.07 r=0.57±0.09 r=0.63±0.09 0 0 Bose-Einstein correlations for K±K±, Ks Ks R(Q12) Q12 Q12 Bose-Einstein correlations clearly established for K±K± pairs Marginal for Ks Ks pairs due background from f0(980) Ks Ks Consistent results on source radius 00 00 Hadron07, Frascati, Oct., 11th 2007

  18. Consistent results on r: - ep (DIS) vs. e+e- - K±K± vs. Ks Ks - Kaons vs. charged particles 00 Bose-Einstein correlations Hadron07, Frascati, Oct., 11th 2007

  19. Conclusions • Charged particle fragmentation function in ep collisions • shows significant scaling violations • agrees reasonably with e+e- annihilation data • NLO QCD calculations fail to describe scaling violations • Deuteron/Anti-deuteron production • invariant d(d) cross section 1/1000 of p(p) • coalescence parameter B2 (nucleon overlap) not universal • Strange particle production in ep collisions • reasonably described in DIS with s=0.3 (LEP tuning) • model fails to describe (Λ+Λ)/K0s in resolved p • consistent (Λ+Λ)/K0s ratios in DIS, direct p and e+e-  a single parameter s not sufficient • Bose-Einstein correlations • established for K±K± and K0s K0s in DIS • consistent source radii for all processes & boson pairs Hadron07, Frascati, Oct., 11th 2007

  20. p/p  1 d/d « 1 Production of protons and deuterons d/p in DIS (ZEUS) same as in p (H1) Hadron07, Frascati, Oct., 11th 2007

  21. N(Ks0) Nch T= p DIS pT  pT  Strange-to-light meson ratio Data prefer strangeness suppression factor 0.3 in DIS and p Range of T consistent with values obtained in e+e- Hadron07, Frascati, Oct., 11th 2007

  22. 0 0 Possible f0(980) contribution inKs Ks Simultaneous fit of MC with BEC and Flatté for f0(980) Hadron07, Frascati, Oct., 11th 2007

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