Perspectives for charm and beauty
quenching studies in ALICE
F. Antinori, C. Bombonati, A. Dainese, M. Lunardon and R. Turrisi
Padova – University and INFN
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Contents
Heavy quarks detection at mid-rapidity with ALICE
Main results of performance studies for charm and beauty
detection
Expected sensitivity with respect to the mass dependence
on quenching
Conclusions and perspectives
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Heavy quarks detection at mid-rapidity with ALICE
Different approaches for charm and beauty due to different
expected production cross sections (charm is more than 20 times
larger than beauty) and decay branching ratios. Taking advantage
of the expected good track impact parameter determination, the
most promising channels are:
Charm: exclusive reconstruction of D0 K-+
Beauty: inclusive measurement of electrons from
semi-electronic decays
We explored both possibilities with a detailed performance studies including:
• likely event generation (PYTHIA 6, HIJING) and cross section estimation (HVQMNR);
• tracking with complete detector simulation (geant 3.21) for ITS ( good impact
parameter reconstruction) and parameterized response of TPC;
• realistic PID parameterization in TPC, TOF and TRD;
• full analysis for Pb-Pb collisions @ 5.5 TeV and p-p @ 14 TeV.
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Heavy quarks detection at mid-rapidity with ALICE
key factor: good measurement of track impact parameter provided by the ITS (SPD)
Pb-Pb estimate
better than 60 mm (rf)
for pt > 1 GeV/c
9.8 Mch
Two layers:
r = 4 – 7 cm
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Charm: exclusive reconstruction of D0 K-+
Exclusive channel that allow direct measurement of pt distribution
Ideal tool to study RAA
Weak decay with mean proper length c = 124 mm
•
•
Large combinatorial background (dNch/dy = 6000 in central Pb-Pb!)
STRATEGY: invariant-mass analysis of fully-reconstructed topologies
originating from (displaced) secondary vertices
–Measurement of Impact Parameters (ITS+TPC)
–Measurement of Momenta (ITS+TPC)  pointing angle
–Particle identification (TOF) to tag the two decay products
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Charm: exclusive reconstruction of D0 K-+
inner bars: stat. errors
outer bars: stat.  pt-dep. syst.
not shown: 9% (Pb-Pb), 5% (pp, p-Pb)
normalization errors
Main systematic contributions:
• corr. for PID and selection eff.
(~10%)
• subtraction of feed-down from B
decays (~8% initially)
Down to pt ~ 0 in pp and p-Pb (1 GeV/c in Pb-Pb)
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Beauty: inclusive measurement of electrons from
semi-electronic decays

The semi-electronic decay channels has a good intrinsic B.R.:
h(b)  e +  + X
~ 10.2 %
and almost 100% of beauty hadrons decay through a charmed hadron, which
can again decay via single electron:
h(b)  h(c) +X  e +  + Y
giving a total B.R. for single electron of about
~ 10.9 %
21 %
Good detection and identification capabilities for electrons at mid rapidity
(TRD, TPC and Vertex detector) with ALICE down to low pt (~1 GeV/c)

 misidentification probability ~ 10-4
heavier particles ~ 0
loss of detected electrons ~ 40%
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Beauty: inclusive measurement of electrons from
semi-electronic decays
Detection strategy:
- electron ID in TPC+TRD
- impact parameter cut (B c ~ 500 mm)
moreover: large b mass  hard electron
spectrum  better selection at high pt
for |d0| > ~ 100 mm beauty gets dominant
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Beauty: inclusive measurement of electrons from
semi-electronic decays
Additional topics for p-p study:
- study of the primary vertex reconstruction tuned on electron
track impact parameter distributions;
- optimized impact parameter cut for each pt bin.
no vertex reconstruction
chosen method
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Beauty: inclusive measurement of electrons from
semi-electronic decays
inner bars: stat. errors
outer bars: stat.  pt-dep. syst. errors
not shown: normalization error 9 (5) %
for Pb-Pb (pp)
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Main systematic contributions:
• corr. for PID and selection eff. (~10%)
• subtraction of electrons from charm
decays (<5% using direct D0 meas.)
Beauty: inclusive measurement of electrons from
semi-electronic decays
Extraction of a ptmin-differential cross section for B mesons
Using electrons in
2 < pt < 20 GeV/c
MC-based
procedure
à la UA1
obtain B meson
2 < ptmin < 30
GeV/c
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Heavy quarks detection at mid-rapidity with ALICE
Sensitivity to mass dependence on quenching
Low pt (< 8–10 GeV/c)
Nuclear shadowing,
recombination?
‘High’ pt (10–20 GeV/c)
here energy loss can be studied
(it’s the only expected effect)
1 year at nominal luminosity
(107 central Pb-Pb events, 109 pp events)
Pb-Pb
pp
Dainese, EPJC33 (2004) 495
12 Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005 E loss calc: Armesto, Dainese, Salgado Wiedemann,
PRD71 (2005) 054027
Heavy quarks detection at mid-rapidity with ALICE
Sensitivity to mass dependence on quenching
Low pt (< 8–10 GeV/c)
Nuclear shadowing,
recombination?
‘High’ pt (10–30 GeV/c)
here energy loss can be studied
1 year at nominal luminosity
(107 central Pb-Pb events, 109 pp events)
Pb-Pb
pp
Possible sensitivity to mass effects
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005 E loss calc: Armesto, Dainese, Salgado Wiedemann,
PRD71 (2005) 054027
Conclusion and perspectives
We explored the capabilites of ALICE in detecting charm and
beauty at mid-rapidity via the exclusive D0 K-+ reconstruction and
inclusive single-electron detection;
the results for charm show the possibility of having a precise
measurement of pt–differential cross section of charmed mesons from
1 up to 20 GeV/c;
in the case of beauty, it is possible to extract a ptmin-differential
cross section for B mesons from 2 up to 30 GeV/c;
the analysis of the RAA for heavy mesons seems to offer a good tool
for jet quenching studies at LHC;
in particular, the preliminary analysis of the RAA for B mesons
seems to be very promising and need further and better investigation.
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
HAVE A NICE DINNER!
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Open Beauty detection in Pb-Pb at
LHC with ALICE:
perspectives for the semi-electronic decay channel
Assumption on beauty production at LHC:
N qq
115
X-section from NLO calculations :
in Pb-Pb @ 5.5 TeV (5% tot)
in pp @ 14 TeV
flavor
charm
beauty
4.6
charm
beauty
0.16
0.007
high
uncertainty:
1.8 - 7.3
Semi-electronic channel ~ 20 % , ALICE accept. for these electrons ~ 24 %
 in Pb-Pb ~ 0.4 beauty electrons / event
Statistics for 107 central events (~ 1 month Pb-Pb run): ~ 4 M beauty electrons
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Extraction of a minimum-pT-differential
cross section for B mesons
Using UA1 MC method (*), also adopted by ALICE m
(thanks to R.Guernane for useful discussions)
The B meson cross section per unit of rapidity at midrapidity with pTB > pTmin
is obtained from a scaling of the electron-level cross section measured within
a given electron phase space e
d B B
min
(
p

p
)
T
T
B
d
dy
( pTB  pTmin )   e,beauty ( e )

meas
dy
 B ( e )
The semi-electronic
B.R. is included here
MC
  e,beauty (e )
The phase space used is
meas
FeB
 e  {pT ,  , d 0 } where pT are the previously used bins,
 = [-0.9, 0.9] and d0 = [200,600] mm
(*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405
C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Extraction of a minimum-pT-differential
cross section for B mesons
Using UA1 MC method, also adopted by ALICE m
Evaluation of
F
e B
and determination of the optimal pTmin
1) we used the B  e + X decays
from PYTHIA.
F
e B
is the ratio of the red area to
the blue one.
here pTe = [3,4] GeV/c
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005
Systematic errors (Pb-Pb)
• Error on MC corrections for tracking, selection, ID efficiencies
• Error on subtraction of charm electrons (curr.tly from D0 measure)
• Error on normalization to cross section per NN collision
Error on e from charm
(propagated from D0 meas.)
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Marcello Lunardon - Jet Quenching Day – Padova, 29.09.2005