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

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

3. Production of Heavy Quarks
Predominantly via boson gluon fusion
Test of perturbative QCD:
multi-scale problem (Q2, mb2, pt2)
Directly sensitive to gluon density in the proton (PDFs)
F2bb measurements at high Q2 important for LHC e.g. bb->H
Heavy quark contribution to structure function

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(as2), massive FFNS (HVQDIS)
GM-VFNS PDFs
MSTW08 to NLO (as2) and NNLO
CTEQ 6.6 to NLO (as)
Monte-Carlo: LO (s)+Parton shower:
Collinear factorisation, DGLAP (RAPGAP)
KT factorisation, CCFM (CASCADE)

5. Contribution to Cross Section
HERA I result:
fraction of total DIS cross section from charm and beauty
large charm fraction (~30%)
small beauty fraction ~% (lower at low Q2)
mass thresholds visible
reasonable description by QCD

6. Tagging Heavy Quarks (c)
resonances D*, D+, D0,…
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(m,e)
mass
- transverse momentum ptrel relative to jet axis
lifetime (vertex detectors)
- reconstrucion of a secondary vertex
- impact parameter d

8. D* Cross Section H1 prelim-08-072 H1 prelim-08-074
good description by NLO calculation (HVQDIS) in wide Q2 range
Also at large Q2, where massive approach not expected to be appropriate

9. D* Cross Section D*
differential cross sections of several D mesons measured
reasonably described by NLO QCD (HVQDIS)
double differential in x and Q2 allows extraction of F2cc
H1 prelim D0 D+
ZEUS-prel
ZEUS-prel

10. D* Fragmentation

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

12. Charm and Beauty Cross Section
combine pTmiss||m, pTrel and impact parameter distributions
use 3D fit to decompose into beauty, charm and light flavour
Q2 > 20 GeV2, 0.01< y < 0.7, PTm > 1.5 GeV, -1.6 < hm < 2.3
c and b cross sections described by NLO (HVQDIS)
ZEUS-prel

13. Charm and Beauty Cross Section
beauty tends to be above NLO QCD at low Q2
may be measured double differentially in x, Q2 and extrapolated to full phase space to compare F2cc, F2bb

14. Inclusive Analysis (lifetime)
Inclusive analysis: use all tracks with hits in silicon detector (pt > 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)
Signed Impact parameter
Significance = d/s(d)
Charm and beauty asymmetric due to lifetime
Light flavours mostly symmetric
resolution
lifetime
H1 prelim

16. Neural Network
Improve separation power: use neural network for >= 3 tracks
Inputs: S1, S2, S3, SL, track pt, number of (SV) tracks
Sign given by S1. Subtract –’ve from +’ve to reduce syst. error

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

18. Measurements of F2bb Beauty structure function versus Q2
NNLO predictions available
Differences between NLO and NNLO small except for Q2<(mb)2

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

20. Measurements of F2cc Charm measurements span large range in Q2 and x
theory predictions have different inputs
-parton densities
-mass treatment
Differences for Q2<(2mc)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 F2cc and F2bb 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. CentralSiliconTracker
H1 Vertex Detector
CentralSiliconTracker
(30o <  < 150o)
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 

26. D* Fragmentation