Transcript Jet quenching in heavy

Misura della produzione
di heavy flavour nel barrel di ALICE
Andrea Dainese
INFN – LNL
per la Collaborazione ALICE
MCWS, Frascati, 24.10.2006
Andrea Dainese
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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
MCWS, Frascati, 24.10.2006
Andrea Dainese
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c and b production at the LHC:
testing 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”*…
Cacciari, Frixione, Mangano, Nason
and Ridolfi, JHEP0407 (2004) 033
…and D production not yet fully reconciled 
CDF, PRL91 (2003) 241804
FONLL: Cacciari, Nason
* M.Mangano
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pQCD predictions for the LHC
Compare predictions by several different models (HERA-LHC Worksohp)
CERN/LHCC 2005-014
hep-ph/0601164
charm
beauty
Good agreement between collinear fact.-based calculations:
FO NLO (Mangano, Nason, Risolfi) and FONLL (Cacciari, Nason)
kt fact. CASCADE (Jung) higher at large pt
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Theoretical Uncertainties
Evaluation of theoretical uncertainties (HERA-LHC Workshop)
charm
beauty
CERN/LHCC 2005-014
hep-ph/0601164
1.3  mc  1.8 GeV
0.5   F , R / mT  2
0.002   c  0.11
4.5  mb  5.0 GeV
0.5   F /  R  2
0.0002   b  0.004
PDFs : CTEQ4, CTEQ5, CTEQ6, MRST2001
MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.
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ALICE baseline yields
Cross sections: NLO (MNR code)
mc=1.2 GeV, F=R=2mc; mb=4.75 GeV, F=R=mb
Yields: assuming sppinel = 70 mb at 14 TeV
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c and b production at the LHC:
a probe of small-x gluons
Probe unexplored small-x region with
HQs at low pt and/or forward y
down to x~10-4 with charm already at y=0
Window on the rich phenomenology of
high-density PDFs
gluon saturation / recombination effects
breakdown of factorization ?
Cartoon
increasing s
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
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The ALICE Detector
 M.Monteno
 D.Stocco
|h| < 0.9, B = 0.5 T
TPC + silicon tracker
g, e, p, K, p identification
MCWS, Frascati, 24.10.2006
Andrea Dainese
-4 < h < -2.5
muons
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ALICE heavy-flavour potential
HERA-LHC Workshop
CERN/LHCC 2005-014
hep-ph/0601164
MCWS, Frascati, 24.10.2006
1 year pp 14 TeV @ nominal lumin.
pT of Q-hadron [GeV]
ALICE combines
electronic (|h|<0.9),
muonic (-4<h<-2.5),
hadronic (|h|<0.9)
channels
ALICE covers low-pt
region
ALICE covers central and
forward regions
Precise vertexing in the
central region to identify
D (ct ~ 100-300 m) and
B (ct ~ 500 m) decays
100
ATLAS/CMS
(b)
LHCb
(b)
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ALICE
(b)
(c)
1
Andrea Dainese
-2
0
ALICE
(c/b)
2
4
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h of Q-hadron
A.Dainese (ALICE)
M.Smizanska (ATLAS)
C.Weiser (CMS)
U.Uwer (LHCb)
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Heavy-flavour analyses
Hadronic decays:
D0K-p+, D*+D0p+, D+K-p+p+, Ds+K+K0*/fp+…
Leptonic decays:
B e/ + X
Invariant mass analysis of lepton pairs: BB, DD,
BDsame, J/y, y’,  family, B J/Y + X
BB    (J/y )
e- correlations
In red, channels
studied in the
PPR Volume 2
CERN/LHCC 2005-030
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Vertexing: track d0 resolution
Resolution mainly provided by the 2 layers of silicon pixels
rec. track
Primary
Vertex
d0
Two layers:
r = 4 cm
r = 7 cm INFN
B
e
< 60 m (rf)
for pt > 1X GeV/c
Padova/Legnaro
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Effect of primary vertex uncertainty
s d 0( rf )  s track  s vertex
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 m
(ALICE LMAX ~ 1030 cm-2 s-1)
effect on d0 resolution
vertex resolution
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Hadron ID: Time-of-flight
TOF
Pb-Pb, dNch/dy=6000
Optimization for hadronic charm
decays was studied:
minimize probability to tag K as p
K id. required for D0 pt < 2 GeV/c
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Electron ID
Combined info from TRD (trans. rad.) and TPC (dE/dx)
TRD rejects 99% of the p and ALL heavier hadrons (pt > 1 GeV/c)
TPC further rejects residual pions (up to 99% at low p)
About 20% of electrons rejected
fraction of misidentified pions
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D0 K-p+ reconstruction
Main selection: displaced-vertex selection
pair of opposite-charge tracks with large impact parameters
increase S/B
good pointing of reconstructed3 D0 momentum to the primary vertex
by factor ~10 !
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Invariant mass analysis
Example (extrapolated to expectation for 109 pp events):
0.5-1 GeV/c
MCWS, Frascati, 24.10.2006
3-4 GeV/c
Andrea Dainese
12-14 GeV/c
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D0 K-p+: Results
inner bars: stat. errors
outer bars: stat.  pt-dep. syst.
not shown: 9% (Pb-Pb), 5% (pp, p-Pb)
normalization errors
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)
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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)
rec. track
Primary
Vertex
d0
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e
B
X
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Effect of electron identification
residual charm contribution
subtracted using D0 measurement
 3-5% syst. error
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B  e + X: Results
inner bars: stat. errors
outer bars: stat.  pt-dep. syst. errors
not shown: 5% normalization error
Using electrons in
2 < pt < 20 GeV/c
MC-based
procedure
à la UA1
obtain B meson
2 < ptmin < 30
GeV/c
1 year at nominal luminosity
(107 central Pb-Pb events, 109 pp events)
MCWS, Frascati, 24.10.2006
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Comparison to pQCD predictions
pp, s = 14 TeV
charm (D0  Kp)
beauty (B  e+X)
1 year at nominal luminosity
(109 pp events)
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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
1 year at nominal luminosity
~1 month
Detector configuration:
ITS + TPC + TOF
MCWS, Frascati, 24.10.2006
Detector configuration:
ITS + TPC + TRD
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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 < 20% up ~ 20-25 GeV/c
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EXTRA SLIDES
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LHC running conditions
pp nominal run
Pb-PB nominal run
Ldt = 5.1026 cm-2 s-1 x 106 s
Ldt dt = 3.1030 cm-2 s-1 x 107 s
5.1032 cm-2 PbPb run, 5.5 TeV
5.1037 cm-2 for pp run, 14 TeV
NPbPb collisions = 2 .109 collisions
Npp collisions = 2 .1012 collisions
Muon triggers:
~ 100% efficiency, ~ 1kHz
Electron triggers:
Bandwidth limitation
NPbPb central = 2 .108 collisions
Hadron triggers:
NPbPb central = 2 .107 collisions
Muon triggers:
~ 100% efficiency, < 1kHz
Electron triggers:
~ 50% efficiency of TRD L1
20 physics events per event
Hadron triggers:
Npp minb = 2 .109 collisions
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Beauty via single and di- muons
in central Pb-Pb collisions
Muons “identified” in the forward spectrometer (-4< h <-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 > 2-3 GeV/c
bb
bb dy ~ 1
 both muons
in the acceptance
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Di-muons invariant mass
Single muon cut: pt > 2 GeV/c
Di-muon combinatorial bkgd subtracted with evt-mixing
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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
s
B
min
t
vs p
systematic error
analysis in progress
down to ~1 GeV/c!
1 year at nominal luminosity
(107 central Pb-Pb events)
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