Beauty Production at HERA

1. HEP05 International Europhysics Conference on High Energy Physics EPS in Lisbon, Portugal. 21-27 July, 2005 Beauty Production at HERA Beate Naroska (Univ. Hamburg) Outline • Jets + Muons (H1, ZEUS) • D*muon (H1,ZEUS) • Di-muon (ZEUS)

2. Heavy Quark Production at HERA • At HERA heavy quarks mainly produced via photon-gluon fusion: γg→bb, cc in photoproduction c & bare produced rarely w.r.t. u, d, s ; also c ≈ 200 * b. Cross sections directly sensitive to gluon density in the proton Contributions from hadronic component of the photon expected: which and how much? TESTS OF QCD AND PROTON/ PHOTON STRUCTURE

3. Theoretical Description NLO calculations in massive schemes: FMNR photoproduction (hadronicresolved component small) (Frixione, Mangano, Nason, Ridolfi) HVQDIS DIS (no resolved component) (Harris, Smith) LO-ME+PS models used: PYTHIA photoproduction (DGLAP) (excitation+hadronic resolved) (Bengtsson, Sjostrand) CASCADE photoproduction (CCFM) (no resolved component) RAPGAP electroproduction (no resolved component) (H.Jung) Example: HVQDIS

4. Muon + Jet Events H1, ZEUS final: hep-ex/0502010; hep-ex/0405069;hep-ex/0312057 Select events with jets ET>6,7 GeV muon pT>2.5 GeV possibly scattered electron use PTrel and/or impact parameter δ to enrich and determine b fraction b fraction extracted by fit to PTrel (ZEUS) δ, PTrel (H1)

5. H1 and ZEUS Photoproduction Results (Muon + Jet Events) • Good agreement H1-ZEUS • Reasonable agreement with NLO calculations • ZEUS no excess at low pTmu

6. Results DIS Muon + Jet Events pT (µ) excess H1 and ZEUS η µ excess mainly in forward direction µ

7. Double Tag : Motivation and goals Two tag strategies: D*µ (H1 final, ZEUS prel.) µµ (ZEUS Prel. NEW) multi-tagged bb event no lifetime info used at present New No Jets: phase space of b production reaches to low pT(b)

8. H1: D*μ correlations Data sampleL = 89 pb -1 HERA I data, 97-00 Exploit el. charges of D*/µ to separate b events from charm and light quark background like-sign unlike-sign and separation in azimuth ΔΦ or ΔR (D*µ ) or use inv. mass Mµµ ++/- - and +-

9. D*μ correlations D* yield measured from the ΔM technique : ΔM = mKππs – MKπ Extract N(D*μ) from fit to Gaussian peak + background : N(D*μ) = 151 ± 22 ‘2D fit’ – simultaneous likelihood fit to ΔM in 4 correlation regions to extract c and b contributions D* peak and background shape from 1D fit 6 free parameters: Nc, Nb and four background regions (χ2 = 145.5 / 154 d.o.f)

10. FitResult V. good agreement between 2D fit and individual 1D fits Nc = 53 ± 12 Nb = 66 ± 17 Use these to calculate visible cross sections for : σcvis(ep → e D* μ X)=250±57±40 pb (NLO: 286+159-59) σbvis(ep → e D* μ X)=206±53±35 pb (NLO: 52+14-9) Charm: good agreement Beauty: data too high Visible kinematic region : pT (D*) > 1.5 GeV; |η(D*)| < 1.5; p(μ) > 2 GeV; |η(μ)| < 1.735; 0.05 < y < 0.75; Q2 < GeV2.

11. D*μ – (N)LO FMNR comparisons Normalized Cross Sections! • Expected deviations from LO due to higher order effects – flatter pT distribution and broader ΔΦ peak. • Good agreement with NLO calculation

12. D*μ – PYTHIA & CASCADE MC comparisons • Both MCs give a good description of the data • NB: Although different approaches to parton evolution are taken, the differences are smaller than the experimental errors

13. ZEUS di-m Events Data sampleL = 121 pb -1 HERA I data, 96-00 Aim: Total Cross Section Selection of muons with pT>1.5 (0.75) GeV Total calorimetric ET (θ>10o) >8 GeV (+implicit pT , η cuts; cleaning cuts) Remove J/ψ, ψ’, etc: Non isolation of muons less than 250 MeV around muons (2 GeV in charmonium regions) beauty BH + J/y+ y' charm LF background good MC description LOW MASS HIGH MASS

14. ZEUS:Signal Extraction • Signal extraction: • use non-isolated µ pairs, all inv. masses • Use data for background determination • fake muon background removed by taking difference between • like-sign and unlike sign samples (light flavour cancels) • charm contribution estimated with D*µ sample Example of breakdown into contributions and agreement with MC: non-isolated unlike-sign µ pairs

15. ZEUS µµ Events: Results More restrictive cuts on muons (pT>1.5 GeV, -2.2<η<2.5) For NLO comparison: two µ’s from different b’s Mµµ >3.25 GeV (PhP +DIS)

16. Comparison to NLO Calculations (Muon + Jet Events) Data in general above NLO pQCD up to 2 s.d. Good agreement between H1 and ZEUS

17. H1+ZEUS : Beauty from D*µ and Di-µ Events: NLO D*µ H1 (vis.) D*µ ZEUS PhP (rap.b<1, y range) D*µ ZEUS DIS (rap.b<1, y range) µµ ZEUS PhP +DIS tot.

18. Summary • Beauty results HERA I with jets and muon final • B Cross sections tend to be above NLO pQCD calculations • Shapes of differential distributions deviate from QCD only in few places (e.g. forward, low pTµ) • Double Tag Analyses started: D*µ, µµ - stat. limited reach to low pT(b)– total cross section possible • Measured cross sections higher than NLO QCD • Shape of Differential Distributions described: NLO effects visible

19. ZEUS : Beauty from Di-µ Events

20. ZEUS: Muon pT and h distributions non-isolated unlike-sign µ pairs Purity ~40-50% ΔΦ Signal extraction: charm contribution estimated by D*mu sample fake muon backgrnd removed by taking difference between like-sign and unlike sign samples (light flavour cancels)