Andrea Dainese

1
Perspectives for heavy-flavour quenching studies
with ALICE

• Andrea Dainese
• INFN Legnaro
• ALICE Collaboration

2
Contents

• Motivation
• heavy quark energy loss
• from RHIC to LHC
• Possibilities with ALICE
• channels detector performance
• Nuclear modification factors
• pp, the importance of the baseline
• expected uncertainties and coverage in pt
• Understanding RAA
• the role of the initial state
• the role of hadronisation

3
Heavy Quark Energy Loss
? C.Salgado
(BDMPS)
Energy loss depends on
color coupling factor 4/3 for q, 3 for g
medium transport coefficient
Dead cone effect for heavy quarks in vacuum,
gluon radiation suppressed at q lt mQ/EQ
Baier, Dokshitzer, Mueller, Peigne, Schiff, NPB
483 (1997) 291. Salgado, Wiedemann, PRD 68(2003)
014008. Dokshitzer and Kharzeev, PLB 519 (2001)
199. Armesto, Salgado, Wiedemann, PRD 69 (2004)
114003.
4
News from RHIC heavy-flv decay electrons
suppressed!
Indirect measurement non-g electrons (Dalitz and
conversions subtracted) c / b inclusive (large
uncertainty on pp baseline!!)
Radiative
Radiative Collisional
Energy loss calculations tend to underpredict
suppression
Djordjevic, Gyulassy, Wicks, nucl-th/0512076
Armesto, Cacciari, Dainese, Salgado, Wiedemann,
PLB637 (06) 326.
5
Azimuthal asymmetry (v2)

• The azimuthal asymmetry --v2 or RAA(f)-- of D/B
  mesons in non-central collisions tests
• at low/moderate pt recombination scenario, v2 of
  c/b quarks, hence degree of thermalization of
  medium
• at higher pt path-length dependence of E loss in
  almond-shaped medium

PHENIX p0 v2
Cole _at_ Quark Matter 05
v2 from E loss Dainese, Loizides, Paic, EPJC 38
(2005) 461
6
LHC hard cross sectionslots of heavy
quarks!
large

• NLO predictions (ALICE PPR baseline for charm
  beauty)
• In pp, important test of pQCD in a new energy
  domain
• remember the 15-years saga of b production at
  the Tevatron
• and c production not yet fully reconciled

MNR code (NLO) Mangano, Nason, Ridolfi, NPB373
(1992) 295.
CDF, PRL91 (2003) 241804 FONLL Cacciari, Nason
Cacciari, Frixione, Mangano, Nason and Ridolfi,
JHEP0407 (2004) 033
? M.Cacciari
M.Mangano
7
Theoretical Uncertainties
CERN/LHCC 2005-014, hep-ph/0601164
NLO pQCD, pp, ?s 14 TeV
beauty
charm
MNR code Mangano, Nason, Ridolfi, NPB373 (1992)
295.
8
Heavy Flavour RAA at LHC

• Baseline PYTHIA, with EKS98 shadowing, tuned to
  reproduce c and b pT distributions from NLO pQCD
  (MNR)
• (m/E)-dep. E loss with

• EKRT Saturation model
• Eskola, Kajantie, Ruuskanen, Tuominen,
• NPB 570 (2000) 379.

Armesto, Dainese, Salgado, Wiedemann, PRD 71
(2005) 054027.
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Colour-charge and mass dep. of E loss with
Heavy-to-Light ratios at LHC
Heavy-to-light ratios Compare g ? h , c ? D
and b ? B
Armesto, Dainese, Salgado, Wiedemann, PRD71
(2005) 054027
10
Beauty-to-Charm ratio RB/D

• Compare c and b ? same colour charge
• Mass effect ? Enhancement of factor 2,
  independent of (for
  )

Adapted from Armesto, Dainese, Salgado,
Wiedemann, PRD71 (2005) 054027
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The ALICE Detector
h lt 0.9 TPC silicon tracker PID detectors
-4 lt h lt -2.5 muons
12
HVQ E loss How in ALICE
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Vertexing track d0 resolution

• D ct 100-300 mm, B ct 500 mm
• d0 ct
• d0 resolution mainly provided by the 2 layers of
  silicon pixels

? 9.8 M
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Hadron ID with the TOF
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
15
Electron ID with TPC and TRD

• 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

? C.Blume
? C.Bombonati
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Charm reconstruction D0? K-p

• Ideal tool to study RAA and low pt effects
• Large combinatorial background (dNch/dy6000 in
  central Pb-Pb!)
• Main selection displaced-vertex selection
• pair of opposite-charge tracks with large impact
  parameters
• good pointing of reconstructed D0 momentum to
  the primary vertex

17
Beauty via displaced electrons

• ALICE has excellent electron identification
  capabilities
• Displaced electrons from B decays can be tagged
  by an impact parameter cut

? C.Bombonati
? R.Turrisi
18
Expected pt coverage
Relative statistical errors
D0 ? Kp
B ? e X
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
19
Role of pp reference for RAA (experience from
RHIC)

• Exclusive measurements at same energy in AA and
  pp (e.g. p0 at 200 GeV)
• experimental reference sufficient for solid
  observation of high-pt quenching
• not sufficient for interpretation in terms of
  parton energy loss
• ? theoretically-understood reference needed
• Inclusive measurement at same energy in AA and pp
  (e.g. cb electrons at 200 GeV)
• ? theoretically-understood reference needed
• also for observation (see Carlos talk)

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Role of pp reference for RAA (at LHC)

• Exclusive measurements at different energy in AA
  and in pp
• ? Need to calibrate the probe translate the
  pp reference from 14 to 5.5 TeV

21
Calibrating the probe (pp, ?s 14 TeV)
Expected sensitivity in comparison to pQCD
D0 ? Kp
B ? e X
22
Expected Sensitivity to RAA
D0 ? Kp
B ? e X
23
Understanding RAA
D0 ? Kp
B ? e X
Warning ? 5 suppression ? ? 2.2 larger
statistical errors!
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
24
The role of the initial state

• Effect of nuclear modification of the initial
  state PDFs may be tackled by charm measurement in
  pPb

25
Understanding RAA
D0 ? Kp
B ? e X
RHIC beware of in-medium hadronisation
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The role of hadronisation

• Lowish pt D and B mesons may hadronise inside the
  medium via coalescence ? no clean study of parton
  E loss
• Up to which pt is this relevant?
• ? Study particle type-dependence of RCP

RHIC

• ALICE _at_ LHC
• kaons and hyperons
• D meson RCP sensitivity under study

E loss only
? breakdown of n-quark scaling of v2 can also
help to identify safe pt region
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Heavy-to-light ratios in ALICE
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
28
Beauty via forward muons

• Muons identified in the forward spectrometer
  (-4 lt?lt -2.5)

? single muons in the spectrometer beauty
dominates for pt gt 2-3 GeV/c
inner bars stat. errors outer bars syst. errors
? N.Bastid
Pb-Pb 0-5
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Conclusions

• Observation of (large) heavy-quarks quenching at
  RHIC has boosted the interest for these studies
  at LHC
• ALICE at LHC in excellent position
• large production cross sections
• dedicated detectors (ITS, TRD, MUON)
• Promising performance for RAA of D mesons and
  electrons from B mesons
• Other observables are under study
• muons from B at forward rapidity
• use of Ws as a reference
• heavy-quark jet studies (azimuthal correlations,
  beauty multi-prong vertices
  , b-tagged jets)

? J.Faivre
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EXTRA SLIDES
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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
????
????
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3-body decays D and Ds

• D complementary to D0 measurement, important
  systematic check
• D (ct 310 mm) ? Kpp with BR 9.2 compared
  to
• D0 (ct 124 mm) ? Kp with BR 3.8
• better separation and higher BR, but
  worse comb. background
• preliminary studies similar performance as for
  D0 expected
• Ds probe of hadronization?
• from fragmentation (PYTHIA) Ds(cs) / D(cd)
  0.6
• from stat. hadronization Ds/D gs / gq 1 in
  QGP?
• Ds (ct 150 mm) ? KKp with BR 4.4
• worse conditions than D, but large resonant
  fraction in decay (through fp or K0K) will help
  in comb. background rejection