Heavy Quark Production in Electron Proton Collisions

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Heavy Quark Production in Electron Proton
Collisions

• Felix Sefkow
• DESY
• Heavy Quarks and Leptons 2004
• San Juan, Puerto Rico
• June 2, 2004

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Charm and beauty production at HERA
boson gluon fusion
parton disitributions
fragmentation function
vs 318 GeV

• Factorization
• proton structure, QCD dynamics with different
  hard scales, quark-hadron transition

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This talk

• probing fragmentation, proton structure and QCD
  dynamics with charm
• new measurements to further test QCD with beauty
• searching for the top
• Omitting many interesting results
• on heavy quarkonium and
• diffractive charm production.

on behalf of
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Charm signatures
D? D0p 30000 events

• D is the working horse
• all ground states measured

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Charm fragmentation

• HERA data compare well with ee- results
• support universality of charm fragmentation

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Proton structure

• Gluon distribution from scaling violation
  analysis of inclusive deep inelastic scattering
  data in NLO QCD

Leading order quark parton model picture
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Charm contribution

• DIS events with D mesons directly sensitive to
  gluon
• large gluon density charm
  contribution 25
• confirms boson gluon fusion picture
• quantitative test of NLO QCD

errors dominated by systematics (extrapolation to
full phase space)
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Photoproduction

• direct and resolved photon processes

in charmed dijet events, reconstruct momentum
fraction of parton from photon side
different angular dependences

• Different QCD schemes (CE LO in massless, NLO
  in massive)

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Dijet angular distributions

• Dijet events with D mesons
• steepness gluon propagator
• asymmetry charm excitation in the photon
• can identify regions in parton kinematics where
  higher orders important

reconstruct angle in rest frame of hard
subsystem (LO picture)
resolved
direct
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Charm Summary

• fragmentation universality checked
• becoming a tool for proton structure, constrains
  gluon distribution
• detailed studies of parton dynamics to guide
  perturbative QCD

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Beauty

• LEP2 and Tevatron data problems for NLO QCD
  (massive scheme)
• recently improvements in data and theory for
  p-bar p

(2?)
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Beauty signatures

• high mass, long lifetime muon ptrel and
  impact parameter
• enrich, cross-check, and use 2-dim fit

Example H1 DIS sample
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Photoproduction cross sections

• 1600 dijet events, ETjet gt 7(6) GeV

Theory NLO O(as2) in massive scheme

• agreement in general
• possible discrepancies at low pT, low x?

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DIS cross sections

• few 100 events
• one jet with ETjet gt 6 GeV in photon proton frame

• some deviations in ZEUS case,

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DIS cross sections

• agreement within errors in the H1 case

• NB comparisons made here for visible cross
  sections, i.e. after all experimental cuts (jet,
  mu, y, Q2)
• experimental data are consistent with the
  earlier, less precise results

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Inclusive tagging

• high Q2 gt 110 GeV2
• use all tracks with pT gt 0.5 GeV and Si tracker
  hits

Note the signal over background ratios!
Most events have a jet, with typically 1-2
good tracks
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Significance distributions
more than 1 track
1 track

• two samples
• cross check enrichment invariant mass of tracks

second highest significance
significance
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Extracting charm and beauty

• Method subtract negative signicance bins from
  positive
• 3 parameter fit (uds, c, b) to two distributions
  plus total events

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F2c and F2b

• compares well with D based F2c
• extends b production data to higher Q2

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Beauty summary

• HERA data somewhere above, but overall in
  reasonable agreement with QCD
• already with HERA 1 data first steps into
  inclusive tagging and higher Q2 region were
  possible
• more luminosity needed to match theoretical
  precision

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Unexpected ep events

• High pT leptons and large missing pT
• H1 observes excess in e and µ channel (ZEUS does
  not)
• ZEUS has 2 interesting t events (H1 has ts, but
  not at high pTX)

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Isolated leptons score card
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Top signatures ?

• Main Standard Model signal W production, peaks
  at low pTX
• Motivates search for anomalous single top
  production (via FCNC)

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Dedicated top search

• Reject wrong sign leptons, include hadron channel
  (no b tagging)
• Multivariate analysis, observables pTb, Mbl? /
  jets, cos ?Wl / q

• lepton and hadron channel consistent
• similar picture from cut based analysis (5/1.3,
  18/20.6 events)
• top cross section 0.2915-14 pb lt 0,55 pb _at_ 95
  CL

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Limits at HERA and elsewhere

• ZEUS limit (LO) includes Z
• H1 limit (NLO) is weaker because there are
  candidates

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Outlook on new data

• After luminosity upgrade HERA finally running
  well
• e, p currents 80-90, specific luminosity 2-3
  times higher, backgrounds tolerable
• New isolated lepton events rolling in

X
e
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Conclusion

• Heavy Quarks at HERA
• Charm powerful probe of proton structure and
  QCD dynamics
• Beauty currently enlarging and clarifying the
  picture with new data and new tools
• Top HERA alive and competitive at the energy
  frontier