Charm production measurement

1
Charm production measurementStatus of PPR 6.5

• Andrea Dainese
• University of Padova

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Outline

• Exclusive D0 reconstruction
• ALICE sensitivity for charm
  production at the LHC
• physics motivation for charm at LHC
• reminder of results of detection study
• estimate of statistical errors
• estimate of (main) systematic errors
• errors combined and sensitivity to
• a nice surprise from the D0
• Status of PPR 6.5

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Charm present experimental picture
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Charm what do we expect at LHC ?

• Thermal charm production
• maximum predicted T 800-1000 MeV not much lower
  than charm mass
• some models predict additional production
  comparable to initial hard yield
  precise measure of cross sections in pp, (pA), AA
• Energy loss
• fast partons loose energy (mainly) by gluon
  radiation
• study energy loss of charm quarks
  (RAA AA/pp(pA) vs pt)
• dead cone effect suppresses energy loss in
  heavy quarks w.r.t. light quarks
  study D/p vs pt in AA (pA) and in pp

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Charm D0? Kp strategy

• Weak decay with mean proper length ct 124 mm
• Impact Parameter (distance of closest approach
• of a track to the primary vertex)
• of the decay products
• d0 100 mm
• STRATEGY invariant mass analysis of
  fully-reconstructed topologies originating from
  (displaced) secondary vertices
• Measurement of Impact Parameters
• Measurement of Momenta
• Particle identification to tag the two decay
  products

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Charm Results
S/B initial (M?3s) S/evt final (M?1s) S/B final (M?1s) Significance S/?SB (M?1s)
Pb-Pb 5 ? 10-6 1.3 ? 10-3 11 37 (for 107 evts)
pp 2 ? 10-3 1.9 ? 10-5 11 44 (for 109 evts)
Note in pp, large uncertainty on primary vertex
position beams de-focused to reduce luminosity
to 1030 cm-2s-1
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Binning Smoothing in dN/dpT pp

• Optimize binning in the range 0-14 GeV/c bin
  size increasing with pT
• good precision on measurement of pT slope
• small statistical error up to high pT
• Fit pT distributions to remove fluctuations due
  to reduced statistics of simulation at high pT
  (especially for Bkg)
• Use fitted function to obtain smooth dN/dpT for
  S and B

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Binning Smoothing in dN/dpT Pb-Pb
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Statistical Error

• Rel. Statisitical error on S expected to be
  1/Significance
• S (SB)observed Bestimated
• error on (SB)observed sqrt(SB)
• error on Bestimated negligible (uses info
  from wide range mass distr.)
• error on S error on (SB)observed
  sqrt(SB)
• relative error on S sqrt(SB)/S
  1/Significance
• This has been checked by generating and fitting a
  large number of invariant mass distributions,
  using as input parameters the results of the
  simulation, namely
• statistics for S and B VS pT
• width of D mass distribution VS pT
• slope of exponential bkg VS pT

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Statistical Error - pp

• Fit with expo gaus
• with 4 free parameters
• expo slope
• gaus integral (S)
• gaus mean
• gaus sigma
• (total integral fixed)
• Many (10,000) iterations
• study resolution on S
• (statistical error)
• study robustness of fit

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Statistical Error Pb-Pb
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Systematic Errors

• Main systematic errors considered
• correction for feed-down from beauty (B.R. B ? D0
  is 65!)
• error of 8 assuming present uncertainty
  (80) on _at_ LHC
• Monte Carlo corrections 10
• B.R. D0? Kp 2.4
• extrapolation from N(D0)/event to ds(D0)/dy
• pp error on (5, will be measured by
  TOTEM)
• Pb-Pb error on centrality selection (8)
  error on TAB (10)

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Charm d2s(D0)/dptdy and ds(D0)/dy
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Charm B? D a la CDF

• Impact parameter of D0 can be used to separate
  primary and secondary D0
• Background shape from
• side-bands in inv. mass
• Background subtracted

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Conclusions

• Pb-Pb and pp sensitivity studies being finalized
• Statistical errors on pt distribution estimated
• Main systematic errors considered
• Physics performance on charm X-section
  measurement
• Dominant systematic errors MC corrections and
• cross section normalization

Statistical Systematic
Pb-Pb 7 19
pp 3 14
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Outlook (1)

• Study sensitivity to comparison with NLO pQCD
• Run MNR program with different choices of
  parameters (c-mass, PDF, shadowing) for pp and
  Pb-Pb
• check dependence of total cross section on
  parameters
• check dependence of pt shape on parameters
• study sensitivity of our errors bars to pQCD
  input and to shadowing (low-pt region)
• Study extrapolation to pt 0 in Pb-Pb
  (uncertainty on total X-section)
• Define strategy for comparison of different
  energies by means of pQCD

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Outlook (2)

• Observables to study shadowing, energy loss,
  thermal production
• total X-section and pt slope
• shadowing expected to suppress low pt
• energy loss expected not to change total
  X-section but increase pt slope how much?
  dependence on parton dE/dx
• thermal charm expected to increase total
  production and determine 2-component pt
  distribution (?)
• RAA RCP (central/peripheral)
• estimate errors on RAA from errors in Pb-Pb and
  in pp extrapolation of pp to 5.5 TeV using pQCD
• estimate errors on RCP
• study separately effect on RAA and RCP of
  shadowing, energy loss, thermal charm
• D/p ratio central/peripheral
• expected to increase with pt due to dead cone
  effect

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PPR chapter 6.5
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Contents of chapter 6.5
December 02

• 6.5.1 Charm and beauty production at LHC
• 6.5.2 Charm detection in hadronic channels
• 6.5.3 Charm and beauty detection in the
  semileptonic
• channels
• 6.5.4 Charm and beauty detection via e-m
  coincidences
• 6.5.5 Charm and beauty in pp collisions

Total 25 pages
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Contents of chapter 6.5
June 03 on the web

• 6.5.1 Physics motivations
• 6.5.2 Present experimental measurements of open
• charm production in heavy ion
  collisions
• 6.5.3 Charm and beauty production at LHC
• 6.5.4 Exclusive charm reconstruction in hadronic
• decay channels
• 6.5.5 Beauty detection in the semi-electronic
  decay
• channel
• 6.5.6 Charm and beauty detection in the
  semi-muonic
• decay channel
• 6.5.7 Charm and beauty via e-m coincidences

Total 43 pages
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6.5.3 Production at LHC

• Total cross sections in nucleon-nucleon
  collisions
• Extrapol. to Pb-Pb collisions
• Extrapol. to min. bias p-Pb _at_ 8.8 TeV (only for
  MRST PDF)
• Spectral shapes and tuning of event generators
• the comparison with NLO pQCD is shown for PYTHIA
  and for Pb-Pb collisions _at_ 5.5 TeV
• now also shown for pp collisions _at_ 14 TeV
• a small paragraph on HERWIG was included for
  completeness
• for p-Pb tuning of PYTHIA taken from R. Vogt and
  comparison not shown
• Hadronization and decays
• yields for hadrons in Pb-Pb, in pp and in p-Pb
• comparison for pT and y of quark and meson
  parametrized pT shape of D and B mesons, but only
  for Pb-Pb _at_ 5.5 TeV

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6.5.4 Hadronic channels

• D0 ? Kp analysis in Pb-Pb ?
• done for B 0.4 T and dNch/dy 6000 ?
• extrapolations to lower multiplicity (3000) ?
• extrapolations to other values of magnetic field
  should be included ?
• In pp
• analysis final but text still missing
• New nice results on B ? D0
• In p-Pb (Raffaele Grosso)
• strategy defined and tools ready
• results during summer
• Physics Performance
• Other channels D ? D0p (P. Hristov summer
  student),

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6.5.5 Semi-electronic B

• Detailed simulation of B ? e X done in Padova
• Pb-Pb 6000 B 0.4 Tesla
• Internal Note almost ready
• PPR text ready

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6.5.6 D and B with muons

• Study in progress by Rachid Guernane (same inputs
  as for other studies being used)
• For the moment only strategy in the PPR
• Philippe Crochet will work on the simulation
  starting from summer
• Hopefully results by autumn

6.5.7 D and B via e-m coincidences
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Summary

• Text in good shape
• introduction motivations, present data
• production / cross sections
• hadronic D0 in Pb-Pb
• semi-electronic B in Pb-Pb
• Work done, text missing
• hadronic D0 in pp (Andrea)
• Work in progress
• hadronic D0 in p-Pb (Raffaele)
• charm cross section from D0 more physics
  comparison with NLO pQCD and/or PYTHIA,
  comparison of pp, pA, AA (Andrea)
• D and B with muons (Rachid)
• e-m coincidences (Philippe)

chapter very healthy and growing !