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Heavy Flavour Production at HERA (H1/ZEUS)

Heavy Flavour Production at HERA (H1/ZEUS). Achim Geiser, DESY Hamburg Heavy Flavor Productions and Hot/Dense Quark matter, BNL, USA, 13. Dec. 05. introduction open heavy flavour production photoproduction

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Heavy Flavour Production at HERA (H1/ZEUS)

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  1. Heavy Flavour Production at HERA(H1/ZEUS) Achim Geiser, DESY Hamburg Heavy Flavor Productions and Hot/Dense Quark matter, BNL, USA, 13. Dec. 05 • introduction • open heavy flavour production • photoproduction • Deep Inelastic Scattering (F2) • inelastic quarkonium production (J/y) • HERA II and conclusions thanks to O. Behnke for some slides A. Geiser, Heavy Flavour Production at HERA

  2. The HERA ep collider and experiments HERA I: ~ 130 pb-1 (physics) HERA II so far: ~ 300 pb-1 (~ 200 pb-1 physics) goal: ~700 pb-1 till 2007 A. Geiser, Heavy Flavour Production at HERA

  3. Kinematics of Heavy Quark Production at HERA Q2 • Kinematic variables: s = 300 (318) GeV ep CM energy before (after) 1998 W= m(gp) gp CM energy Q2 = -q2photon virtuality, squared momentum transfer x= Bjorken scaling variable, for Q2 >> (2mQ)2 (!): momentum fraction of p constituent y = Bjorken scaling variable, inelasticity, for Q2 -> 0: g energy fraction (of e) =b,c g • Kinematic regimes: • Photoproduction:g quasi-real: Q2 < 1 GeV2, e escapes through beam pipe • Deep inelastic scattering (DIS):1 < Q2< (300 GeV)2, e visible in detector Q and Q can combine to bound state -> Quarkonium A. Geiser, Heavy Flavour Production at HERA

  4. Open Heavy Flavour production in ep scattering ,c , mc ~ 1.5 GeV ,c ,c multiscale problem -> terms [as ln (Q2/mQ2)]n,[as ln (pT2/mQ2)]n, etc. in perturbative expansion -> potentially large th. errors A. Geiser, Heavy Flavour Production at HERA

  5. pQCD approximations assume one dominant hard scale: (FO) NLO NLL FONLL which describes HERA data best? A. Geiser, Heavy Flavour Production at HERA

  6. Charm tags • suds : scharm : sbeauty ~ 2000 : 200 : 1 -> HERA ischarm factory • meson tag, e.g.D*-> K p p • lifetime tag, e.g. D+(or inclusive) always pTc > mc! A. Geiser, Heavy Flavour Production at HERA

  7. Charm in photoproduction QCD calculations using CTEQ5M1 + AFG structure functions mc = 1.5 +- 0.2 GeV, m02 = mc2 + pT2, mr = mf = m, m0/2 < m < 2m0 f(c->D*) = 0.235 ePeterson = 0.035 (FO NLO), 0.02 (FONLL) NLO (FMNR) reasonable agreement some deviations at forward h FONNL (Cacciari et al.) similar, not better at large pT NLL (Kniehl et al.) larger norm., shape not better A. Geiser, Heavy Flavour Production at HERA

  8. NLO vs. LO + parton shower "direct g" "resolved g" c -> jet c c -> jet c -> jet -> jet A. Geiser, Heavy Flavour Production at HERA

  9. NLO vs. LO + parton shower direct resolved enriched enriched data: charm + dijet NLO norm. OK shape X need NNLO or NLO+PS (MC@NLO) LO+PS shape OK norm. X Df(jj) A. Geiser, Heavy Flavour Production at HERA

  10. Charm fragmentation fractions consistent with universality of charm fragmentation HERA competitive with e+e- A. Geiser, Heavy Flavour Production at HERA

  11. Beauty tags with m+jets use m from semileptonic decay, separate b and c (can also use hadrons) A. Geiser, Heavy Flavour Production at HERA

  12. Beauty in photoproduction A. Geiser, Heavy Flavour Production at HERA

  13. Double tagging of bb pair • two direct flavour tags, e.g. D*+m or m+m -> large bg reduction, do not need jets -> access low pT and forward regions (proton direction) l.fl. bg. indirectly from like sign mm m+m-nonisol. -> measure total beauty production cross section at HERA: ~50% beauty s(ep -> bb + anything) = 16.1 +- 1.8stat+5.3-4.8,sys nb sNLO = 6.8 +3.0-1.7 nb (FMNR+HVQDIS) A. Geiser, Heavy Flavour Production at HERA

  14. Beauty cross sections vs. pTb pTb >> mb better described than pTb ~ mb ? photoproduction A. Geiser, Heavy Flavour Production at HERA

  15. The structure of the proton ~negligible to 0th order QCD (Q2 >> mq only!!): b,c pair production is "higher" order QCD correction in general: F2structure function is notPDF A. Geiser, Heavy Flavour Production at HERA

  16. Beauty contribution to F2 A. Geiser, Heavy Flavour Production at HERA

  17. Inclusive lifetime tags (H1) mirrored inclusive DIS most significant impact parameter S1 2nd most significant impact parameter S2 charm beauty A. Geiser, Heavy Flavour Production at HERA

  18. Beauty contribution to F2 A. Geiser, Heavy Flavour Production at HERA

  19. Beauty contribution to F2 HERA LHC, e.g. H Q2 >> mb2 A. Geiser, Heavy Flavour Production at HERA

  20. Comparison of b and c contributions A. Geiser, Heavy Flavour Production at HERA

  21. charm contribution to F2 -> test/constrain gluon density or (Q2 >> mc2) -> obtain virtual charm content (PDF) of proton A. Geiser, Heavy Flavour Production at HERA

  22. inelastic J/y production • Colour Singlet (CS) contribution directly calculable (see e.g. talk G. Bodwin) available at LO and NLO • Colour Octet (CO) contribution introduced in NRQCD to describe Tevatron data, not directly calculable, parametrized from Tevatron -> prediction for HERA, LO only A. Geiser, Heavy Flavour Production at HERA

  23. inelastic J/y photoproduction • CS LO->NLO ~factor 3-10! z = fraction of g energy carried by J/y (in p rest frame) A. Geiser, Heavy Flavour Production at HERA

  24. inelastic J/y electroproduction CS + kt-factorization pT*(J/y) > 1 GeV LO CS+CO NLO CS Color Octet contribution not really needed to describe HERA data A. Geiser, Heavy Flavour Production at HERA

  25. Detector upgrades for HERA II upgrades most relevant for heavy flavour production: H1 Fast Track Trigger ZEUS Micro-Vertex Detector (MVD) A. Geiser, Heavy Flavour Production at HERA

  26. Charm in HERA II data first 30 pb-1 of HERA II data • HERA I "excess" in charm e-p/e+p cross section at high Q2 was statistical fluctuation(as expected) A. Geiser, Heavy Flavour Production at HERA

  27. Beauty in HERA II data • First preliminary results using new ZEUS MVD: • first 30 pb-1 of HERA II data • combine muon pTrel with impact parameter (muon+dijet events) • Outlook: improve by ~ order of magnitude + new double differential measurements A. Geiser, Heavy Flavour Production at HERA

  28. Summary and Conclusions • Heavy Flavour production in e-p collisions is good testing ground for perturbative QCD • charm production: reasonably described, no clear preference between "massive" NLO and "massless" NLL calculations. NNLO or NLO+PS needed for some regions of phase space. charm fragmentation measurements competitive with e+e-. • beauty production: reasonable description at high pTb getting worse (but still acceptable) at low pTb? problem with threshold region? • DIS (F2): both charm and beauty well described first measurement of F2bb • inelastic J/y production: data acceptably described by both LO CS+CO, and NLO CS only. CO not really needed. • HERA II performing well. Expect improved results soon! A. Geiser, Heavy Flavour Production at HERA

  29. Tagging semileptonic beauty decays pTrel 1) pTrel : pT of m with respect to jet axis 2) impact parameter of m (or h) with respect to primary vertex (H1: all, ZEUS: HERA II only) 3)D*m and mm correlations A. Geiser, Heavy Flavour Production at HERA

  30. Beauty cross sections vs. Q2 different pTb scales ! (massless) no clear trend A. Geiser, Heavy Flavour Production at HERA

  31. Perturbative QCD calculations for open heavy flavour (opt) • Monte Carlo Programs main purpose: efficiency calculations and qualitative QCD predictions • LO matrix elements + parton shower (leading log), DGLAP (collinear) parton evolution: PYTHIA, HERWIG, RAPGAP (direct + resolved), AROMA (direct only) • BGF matrix element + gluon cascade, CCFM (angular ordered) gluon evolution: CASCADE • NLO QCD calculations main purpose: quantitative QCD predictions • Fixed Order (aas2, as3), massive (FO): heavy quarks produced at perturbative level, reliable for pT ~ mQ (FMNR, HVQDIS: Frixione et al., Harris + Smith) • ReSummed, massless approach (RS): „massless“ heavy quarks are active constituents of p and g,masses only used for final state kinematics, resums next-to-leading log (NLL) contributions of large logs in Q/mQ, pT/mQtoall orders, reliable for pT >> mQ (Kniehl, Kramer, Cacciari, ...) • matched calculations of both schemes (FONLL): FO at low pT, RS at large pT (Frixione, Nason, Cacciari) A. Geiser, Heavy Flavour Production at HERA

  32. caveats for data - theory comparison structure functions + QCD matrix elements theoretical error bb correlations MC orself-consistency of QCD simplefragmentation & decay MC + model assumptions? models jet algorithm related errors? MC acceptance correction data experimental error parton level cross-section parton level cross-section visible cross-section visible cross-section A. Geiser, Heavy Flavour Production at HERA

  33. Processes for Open Heavy Quark Production (Q = c,b) • dominant Leading Order (LO) QCD diagram: a) directBoson(g)-Gluon-Fusion (BGF) => heavy quark propagator • „resolved“ photon (or p) contributions (in LO + parton shower (PS) picture) => gluon (dominant) + quark propagators b) c) d) + + ... „Q-excitation“ in photon hadron-like photon alternativeinterpretations of b): • LO excitation of „heavy quark in photon“ (+ parton shower evolution) LO+PS Monte Carlos (DGLAP), „massless“ QCD calculations • NLO pointlike photon diagram (massive fixed order QCD calculations) • LO BGF diagram + gluon cascade (CCFM, CASCADE Monte Carlo) A. Geiser, Heavy Flavour Production at HERA

  34. Why study heavy flavour production at HERA? • HERA, Queen of the greek gods, sister and wife of ZEUS, is known for her beauty and charm, but also for her guile ... • Heavy quarks are heavy (mb,mc) useful scale for perturbative QCD => reliable predictions (in principle ...) often multi-scale problem (mQ,pT,Q2,...) => large uncertainties (in practice ...) • unique to HERA: photon - gluon initial state A. Geiser, Heavy Flavour Production at HERA

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