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

Explore HERA kinematics, particle fragmentation, and strange meson production in ep-collisions. Understand color dipole model and string fragmentation using various PDF models. Dive into charged particle fragmentation functions and compare data with NLO QCD predictions. Analyze proton, deuteron, and strange particle production.

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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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