F2cc and F2bb Production at H1

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-gtH
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(?s2), massive FFNS
(HVQDIS) GM-VFNS PDFs MSTW08 to NLO (?s2) and
NNLO CTEQ 6.6 to NLO (?s)? 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(?,e)?
• mass
• - transverse momentum ptrel relative to jet
  axis
• lifetime (vertex detectors)?
• - reconstrucion of a secondary vertex
• - impact parameter ?

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

• differential cross sections of several D mesons
  measured
• reasonably described by NLO QCD (HVQDIS)?
• double differential in x and Q2 allows
  extraction of F2cc

D
H1 prelim-08-072
D0
D
ZEUS-prel-07-034
ZEUS-prel-07-009
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D Fragmentation
11
D Fragmentation

• RAPGAP MC pT,jetgt 3 GeV, parameters consistent
  with ee-
• no jet sample (low photon gluon COM) needs
  harder frag.
• Similar story for HVQDIS

DESY-08-080
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Charm and Beauty Cross Section

• combine pTmiss???, pTrel and impact parameter
  distributions
• use 3D fit to decompose into beauty, charm and
  light flavour

• Q2 gt 20 GeV2, 0.01lt y lt 0.7, PT? gt 1.5 GeV, -1.6
  lt ?? lt 2.3
• c and b cross sections described by NLO (HVQDIS)?

ZEUS-prel-08-007
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

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Inclusive Analysis (lifetime)?

• Inclusive analysis use all tracks with hits in
  silicon detector (pt gt 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 ??????
Charm and beauty asymmetric due to lifetime Light
flavours mostly symmetric
resolution
lifetime
H1 prelim-08-173
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Neural Network

• Improve separation power use neural network for
  gt 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

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Inclusive b Cross Section

• comparison of different methods acceptance
• ? Inclusive (H1VTX) gt90
• ????? ptrel (ZEUS 03/04 ??) 20-35
• ??? ptrel ??(ZEUS 05 ?) 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 Q2lt(mb)2

19
Inclusive Charm Cross Section

• comparison of different methods acceptance
• Inclusive (H1 HERA I II VTX) gt70
• 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 F2cc

• Charm measurements span large range in Q2 and x
• theory predictions have different inputs
• -parton densities
• -mass treatment
• Differences for Q2lt(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!

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Back Up
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Scale Uncertainty (c)?
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Scale Uncertainty (b)?
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H1 Vertex Detector
CentralSiliconTracker (30o lt ? lt 150o)?

• Rebuilt to take into account HERA II beamline
• Double layer double sided strips
• Precise determination of impact parameter in
  transverse plane
• Resolution of d for hits in both layers

Signed impact parameter ?
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D Fragmentation