1 Heavy Flavour Content of the Proton Motivation Experimental Techniques charm and beauty cross sections in DIS for the H1 & ZEUS Collaborations Paul Thompson University of Birmingham

2 Available Data Many preliminary analyses on full HERA II data Working on final publication and combination of results In total ~500pb -1 of high energy data collected per experiment luminosity upgrade in 2001 detectors adjusted ZEUS: new micro vertex detector

3 Production of Heavy Quarks Predominantly via boson gluon fusion Test of perturbative QCD: multi-scale problem (Q 2, m b 2, p t 2 ) ‏ Directly sensitive to gluon density in the proton (PDFs) ‏ Heavy quark contribution to structure function F 2 bb measurements at high Q 2 important for LHC e.g. bb->H

4 Predictions for Heavy Quark Production Number of theoretical approaches: Massless (Zero Mass), massive (Fixed Flavour) and general mass (GM) flavour number schemes. QCD Calculations: Fixed order NLO(  s 2 ), massive FFNS (HVQDIS) GM-VFNS PDFs MSTW08 to NLO (  s 2 ) and NNLO CTEQ 6.6 to NLO (  s ) ‏ Monte-Carlo: LO (  s )+Parton shower: Collinear factorisation, DGLAP (RAPGAP) ‏ K T factorisation, CCFM (CASCADE) ‏

5 HERA I result: Contribution to Cross Section fraction of total DIS cross section from charm and beauty large charm fraction (~30%) ‏ small beauty fraction ~% (lower at low Q 2 ) ‏ mass thresholds visible reasonable description by QCD

6 Tagging Heavy Quarks (c) ‏ resonances D*, D +, D 0,… Full HERA II statistics (~350pb -1 ) ‏ resonances and decay length tagging using vertex detectors

7 Tagging Heavy Quarks (b) ‏ Beauty quarks rarely produced, use properties of beauty hadrons: semileptonic decays( ,e) ‏ mass - transverse momentum p t rel relative to jet axis lifetime (vertex detectors) ‏ - reconstrucion of a secondary vertex - impact parameter 

8 D* Cross Section good description by NLO calculation (HVQDIS) in wide Q 2 range Also at large Q 2, where massive approach not expected to be appropriate H1 prelim H1 prelim

9 D* Cross Section differential cross sections of several D mesons measured reasonably described by NLO QCD (HVQDIS) ‏ double differential in x and Q 2 allows extraction of F 2 cc H1 prelim ZEUS-prel ZEUS-prel D0D0 D+D+ D*D*

10 D* Fragmentation

11 D* Fragmentation RAPGAP MC: p T,jet > 3 GeV, parameters consistent with e + e - no jet sample (low photon gluon COM) needs harder frag. Similar story for HVQDIS DESY

12 combine p T miss , p T rel and impact parameter distributions use 3D fit to decompose into beauty, charm and light flavour Q 2 > 20 GeV 2, GeV, -1.6 <   < 2.3 c and b cross sections described by NLO (HVQDIS) ‏ Charm and Beauty Cross Section ZEUS-prel

13 Charm and Beauty Cross Section beauty tends to be above NLO QCD at low Q 2 may be measured double differentially in x, Q 2 and extrapolated to full phase space to compare F 2 cc, F 2 bb

14 Inclusive Analysis (lifetime) ‏ Inclusive analysis: use all tracks with hits in silicon detector (p t > 0.3 GeV) H1 CST rebuilt to account for HERA II beamline Precise determination of impact parameter in transverse plane Signed impact parameter 

15 Inclusive Analysis (lifetime) ‏ Charm and beauty asymmetric due to lifetime Light flavours mostly symmetric Signed Impact parameter  Significance =  resolutionlifetime H1 prelim

16 Neural Network Improve separation power: use neural network for >= 3 tracks Inputs: S 1, S 2, S 3, S L, track p t, number of (SV) tracks Sign given by S 1. Subtract –’ve from +’ve to reduce syst. error

17 Inclusive b Cross Section comparison of different methods [acceptance]  Inclusive (H1VTX) [>90%]  p t rel (ZEUS 03/04  ) [20-35%]  p t rel +  (ZEUS 05  ) [25-50%] ZEUS tend to be higher than H1 generally described by NLO QCD (FFNS, GM-VFNS) ‏

18 Measurements of F 2 bb Beauty structure function versus Q 2 NNLO predictions available Differences between NLO and NNLO small except for Q 2 <(m b ) 2

19 Inclusive Charm Cross Section comparison of different methods [acceptance] -Inclusive (H1 HERA I II VTX) [>70%] -Mu ptrel+  (ZEUS HERA II  ) [25-50%] -D* cross sections [20-70%] different methods agree well wealth of precise measurements combine to improve precision

20 Measurements of F 2 cc Charm measurements span large range in Q 2 and x theory predictions have different inputs -parton densities -mass treatment Differences for Q 2 <(2m c ) 2

21 Conclusions Wealth of new measurements of the heavy flavour content of the proton from HERA I and HERA II data. Extraction of structure functions F 2 cc and F 2 bb allow comparison of many different measurement techniques. Data are described by (N)NLO pQCD calculations. Data help to constrain theory mass treatments and PDFs (in time for LHC!). Final results with full HERA statistics expected soon!

22 Back Up

23 Scale Uncertainty (c) ‏

24 Scale Uncertainty (b) ‏

25 H1 Vertex Detector Rebuilt to take into account HERA II beamline Double layer double sided strips Precise determination of impact parameter in transverse plane Resolution of |δ| for hits in both layers: Signed impact parameter  C entral S ilicon T racker (30 o <  < 150 o )‏

26 D* Fragmentation