Misura della produzione di heavy flavour nel barrel di ALICE

1
Misura della produzione di heavy flavour nel
barrel di ALICE

• Andrea Dainese
• INFN LNL
• per la Collaborazione ALICE

2
Layout

• Motivation for heavy-flavour measurements in pp
  at LHC theoretical predictions for c and b
  production
• Why ALICE is well-suited for these measurements
• Strategies and expected performance for
• D0 ? K-p
• B ? e? X
• Summary

3
c and b production at the LHCtesting pQCD at ?s
14 TeV

• Important test of pQCD in a new energy domain
  (7??sTEVATRON)
• remember the 15-years saga of b production at
  the Tevatron
• and D production not yet fully reconciled ?

Cacciari, Frixione, Mangano, Nason and Ridolfi,
JHEP0407 (2004) 033
CDF, PRL91 (2003) 241804 FONLL Cacciari, Nason
M.Mangano
4
pQCD predictions for the LHC
Compare predictions by several different models
(HERA-LHC Worksohp)
CERN/LHCC 2005-014 hep-ph/0601164
beauty
charm
Good agreement between collinear fact.-based
calculations FO NLO (Mangano, Nason, Risolfi)
and FONLL (Cacciari, Nason) kt fact. CASCADE
(Jung) higher at large pt
5
Theoretical Uncertainties
Evaluation of theoretical uncertainties (HERA-LHC
Workshop)
CERN/LHCC 2005-014 hep-ph/0601164
beauty
charm
MNR code Mangano, Nason, Ridolfi, NPB373 (1992)
295.
6
ALICE baseline yields

• Cross sections NLO (MNR code)
• mc1.2 GeV, mFmR2mc mb4.75 GeV, mFmRmb
• Yields assuming sppinel 70 mb at 14 TeV

7
c and b production at the LHCa probe of small-x
gluons

• Probe unexplored small-x region with HQs at low
  pt and/or forward y
• down to x10-4 with charm already at y0

• Window on the rich phenomenology of high-density
  PDFs
• gluon saturation / recombination effects
• breakdown of factorization ?

• Charm at low pt predicted to be sensitive
• DGLAP (coll. fact.) GLRMQ (nonlinear terms)
  enhancement
• BK approach (kt fact) suppression

Eskola, Kolhinen, Vogt, PLB582 (2004)
157 Gotsmann, Levin, Maor, Naftali, hep-ph/0504040
8
The ALICE Detector

• M.Monteno
• D.Stocco

h lt 0.9, B 0.5 T TPC silicon tracker g, e,
p, K, p identification
-4 lt h lt -2.5 muons
9
ALICE heavy-flavour potential
HERA-LHC Workshop CERN/LHCC 2005-014 hep-ph/060116
4

• ALICE combines electronic (hlt0.9), muonic
  (-4lthlt-2.5), hadronic (hlt0.9) channels
• ALICE covers low-pt region
• ALICE covers central and forward regions
• Precise vertexing in the central region to
  identify D (ct 100-300 mm) and B (ct 500 mm)
  decays

A.Dainese (ALICE) M.Smizanska (ATLAS) C.Weiser
(CMS) U.Uwer (LHCb)
10
Heavy-flavour analyses

• Hadronic decays
• D0?K-p, D?D0p, D?K-pp, Ds?KK0/fp
• Leptonic decays
• B? e/m X
• Invariant mass analysis of lepton pairs BB, DD,
  BDsame, J/y, y, ? family, B ?J/Y X
• BB ?m m m (J/y m)
• e-m correlations

In red, channels studied in the PPR Volume
2 CERN/LHCC 2005-030
11
Vertexing track d0 resolution
Resolution mainly provided by the 2 layers of
silicon pixels
? 9.8 M
12
Effect of primary vertex uncertainty

• Vertex position reconstructed event-by-event
  using tracks
• More precise vertex pos. in (x,y) from mean over
  many events
• Beam spread at ALICE I.P. may be as large as
  50-100 mm
• (ALICE LMAX 1030 cm-2 s-1)

effect on d0 resolution
vertex resolution
13
Hadron ID Time-of-flight
TOF
Pb-Pb, dNch/dy6000
Optimization for hadronic charm decays was
studied minimize probability to tag K as p
K id. required for D0 pt lt 2 GeV/c
14
Electron ID

• Combined info from TRD (trans. rad.) and TPC
  (dE/dx)
• TRD rejects 99 of the p? and ALL heavier hadrons
  (pt gt 1 GeV/c)
• TPC further rejects residual pions (up to 99 at
  low p)
• About 20 of electrons rejected

15
D0? K-p reconstruction

• Main selection displaced-vertex selection
• pair of opposite-charge tracks with large impact
  parameters
• good pointing of reconstructed D0 momentum to
  the primary vertex

16
Invariant mass analysis

• Example (extrapolated to expectation for 109 pp
  events)

0.5-1 GeV/c 3-4
GeV/c 12-14 GeV/c
17
D0? K-p Results
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events) 1 year with 1month of
p-Pb running (108 p-Pb events)
Down to pt 0 in pp and p-Pb (1 GeV/c in Pb-Pb)
18
B ? e X Detection strategy

1. Electron PID reject most of the hadrons
2. d0 cut reduce charm and bkg electrons (Dalitz, g
   conv.)
3. Subtract (small) residual background (ALICE data
   MC)

19
Effect of electron identification
residual charm contribution subtracted using D0
measurement ? 3-5 syst. error
20
B ? e X Results
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
21
Comparison to pQCD predictions
pp, ?s 14 TeV
charm (D0 ? Kp)
beauty (B ? eX)
1 year at nominal luminosity (109 pp events)
22
Perspectives for the 1st month at 14 TeV

• Expected statistical errors for a low-stats
  sample
• Scaling of statistical errors according to ?Nevts
• No dedicated cuts study yet

D0 ? Kp
B ? e X
Detector configuration ITS TPC TOF
Detector configuration ITS TPC TRD
23
Summary

• Charm and beauty production study at the LHC
• test of QCD in a new energy domain
• at low pt access to low-x gluon dynamics
  saturation?
• ALICE is well-equiped for heavy-flavour studies
• using several different channels / strategies
• acceptance down low pt at central and forward
  rapidity
• small extrapolation for total cross section
• With 109 events (nominal year)
• 5 statistical error on total cross sections (c
  and b)
• statistical error lt 20 up 20-25 GeV/c

24
EXTRA SLIDES
25
LHC running conditions
Pb-PB nominal run
pp nominal run
?Ldt dt 3.1030 cm-2 s-1 x 107 s 5.1037 cm-2
for pp run, 14 TeV Npp collisions 2 .1012
collisions
?Ldt 5.1026 cm-2 s-1 x 106 s 5.1032 cm-2
PbPb run, 5.5 TeV NPbPb collisions 2 .109
collisions
????
????
Muon triggers 100 efficiency, lt 1kHz
Muon triggers 100 efficiency, 1kHz
Electron triggers 50 efficiency of TRD
L1 20 physics events per event
Electron triggers Bandwidth limitation
NPbPb central 2 .108 collisions
Hadron triggers Npp minb 2 .109 collisions

Hadron triggers NPbPb central 2 .107
collisions
????
????
26
Beauty via single and di- muons in central
Pb-Pb collisions

• Muons identified in the forward spectrometer
  (-4lt ? lt-2.5)
• 15 interaction lengths, but..
• muon pt threshold as low as 1-1.5 GeV/c

? single muons in the spectrometer beauty
dominates for pt gt 2-3 GeV/c
27
Di-muons invariant mass

• Single muon cut pt gt 2 GeV/c
• Di-muon combinatorial bkgd subtracted with
  evt-mixing

28
Open Beauty with Muons Results

• Combined fit of low-mass, high-mass dimuons and
  single muons with shapes from MC to extract muons
  from B
• Use MC to exctract
• down to 1 GeV/c!

systematic error analysis in progress
1 year at nominal luminosity (107 central Pb-Pb
events)