1. Charm and beauty with ALICE at LHC
Rosario Turrisi
University and INFN, Padova, Italy
for the ALICE Collaboration

2. Contents Why heavy ions at LHC The ALICE detector
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
Why heavy ions at LHC
The ALICE detector
The role of charm and beauty
Basic performances
Open flavors measurement sensitivity
Conclusions and Perspectives
Lead not only as shielding…

3. Why heavy ions at LHC PbPb @ = 5.5 TeV LHC high energy large volume
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
LHC
= 5.5 TeV
high energy
&
large volume
hadronic matter
strong interaction
plasma of quarks and gluons
QGP
At SPS (CERN) and RHIC (BNL) already
observed deconfinement signals.
At LHC:
more strictly μB=0
higher energy density
DEEP DECONFINEMENT!
Tc ~ 170 MeV
(μB=0)
c ~ 1 GeV/fm3
Lattice QCD with massless flavors
Baryon free environment (μB=0)
Exploration of the deconfined phase…

4. ALICE detectors Solenoid magnet B<0.5 T Central tracking system:
TPC (the largest ever…):
88 m3 , 510 cm length, 250 cm radius
Ar (90%) + CO2 (10%)
88 μs drift time
main tracking device, dE/dx
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
ALICE detectors
6 Layers, 3 technologies
Material budget < 1% of X0 per layer!
Silicon Pixels  vertices resolution in xy
(0.2 m2, 9.8 Mchannels)
Silicon Drift  resolution in z
(1.3 m2, 133 kchannels)
Double-sided Strip  connection w/TPC
(4.9 m2, 2.6 Mchannels)
PIXEL CELL
z: 425 mm
rf: 50 mm
Two layers:
r = 4 – 7 cm
9.8 Mch
Central tracking system:
Inner Tracking System
Time Projection Chamber
2 * 1.8 units of pseudo-rapidity

5. ALICE detectors Central tracking system: Transition Radiation Detector
2 * 1.8 units of pseudo-rapidity
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
ALICE detectors
6 layers for:
electron/pion separation at pt>1 GeV
factor 100 rejection at 2 GeV
tracking complement, mass resolution
100 
high pt trigger (onia studies)
Central tracking system:
Transition Radiation Detector
Time Of Flight
Multigap Resistive Plate Chambers
5 years R&D, and
 < 100 ps
pions, kaons, protons separation (see later)
electrons/pions at low pt

6. { ALICE detectors Cosmic rays trigger Forward detectors:
Photon Mult. Det.
Forward Mult. D., T0, V0, Zero Degrees Cal.
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
ALICE detectors
Specialized detectors:
High Momentum PID
PHOton Spectrometer {
MUON Spectrometer
2.4 <  < 4
+EMCal (under discussion)

7. Heavy flavors and heavy-ions
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
Why measure heavy flavors at LHC ?
quarkonium suppression: deconfinement signature
B J/ important background
open heavy flavors as natural normalization for QQ studies
interest in its own right (discovery potential!)
probes of the medium:
early formation (initial parton-parton), most energetic phase
energy loss (medium dependent?)
not covered here
=5.5 TeV
pp reactions, pQCD,
nuclear effects
(geometry, shadowing)
INPUT
OUTPUT
medium properties

8. Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
pQCD predictions
NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M PDF’s, EKS98 in Pb-Pb for shadowing
(shadowing = modification of PDF’s, causes reduction of cross section)
Taking into account F,R
a factor 4 arises between
min. and max. cross section…
in central
collisions
Mesons multiplicities
D0/ D0
B(s)+ b pp
0.19
0.0143
PbPb
140 9
In acceptance:
~5 D0  K
~0.85 B  eX

9. Performance studies
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
Detector description with the state-of-the-(ALICE)-art code AliRoot
Charm/beauty signal tuned to NLO pQCD pt spectrum
(custom tuning of PYTHIA)
Background from HIJING, 6000 charged particles per unit rapidity at midrapidity
Priorities:
the exclusive decay of the D0  K (golden channel):
test bench for secondary vertex detection, pid
very high background
inclusive b  eX decay
secondary vertices
electron identification
“easy” measurement of cross section

10. Total charged multiplicity
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
dNCH/dy
(y=0)
Current baseline:
Tested up to:
TPC + ITS
projection of the full  range
(front view)
60 <  < 62
if one does extrapolate from RHIC multiplicity, multiplicity is even less (<3000)

11. Tracking performance < 50 μm   < 150 μm z pt resolution:
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
impact parameter resolution:
 σ= @ pt=1.3 GeV
pt resolution:
σ= 1(10) GeV
100 GeV
< 50 μm  
< 150 μm z
EFFICIENCY
pions
kaons

12. PID: e,, K, p PbPb events dN/dy=6000 test beam: p id. as e = 1 %
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
PbPb events
dN/dy=6000
test beam:
p id. as e = 1 %
Combined π/e ~ pt~1-2 GeV
electrons
TPC
TRD
p (Gev/c)
TOF
hadrons

13. Selection cuts impact parameters product D0  K
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
D0  K
decay topology
impact parameter of tracks (in bending plane, d0~100 μm)
momenta
identification
~ 0.5 D0 with |y|<1
but also 12000
charged /K
in PbPb collisions
sottolineare correlazione d*d/costh
impact parameters product

14. Performance: D0K K, MINV integrated over pt
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
S/B
initial
(M3s)
S/evt
final
(M1s)
Significance
S/S+B
5  10-6
1.3  10-3
11 % 37
(for 107 evts,
~1 month)
K, MINV integrated over pt
107 PbPb events (one-month run)
dN/dy(y=0) = 6000 (charged)
measurement of pt distribution
Significance

15. Quark energy loss: basics
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
path length L c g
Origin: parton energy loss due to gluon radiation
Average energy loss (BDMPS model):
CR Casimir factor = 3 for gluons 4/3 for quarks
q = medium transport coefficient  gluon density and momenta
Study to get the medium effect h
spiegare meglio figura
RAA =1 means AA is superposition
of independent pp collisions
RAA measured at RHIC with pions:
clear quenching effect
Quark Matter Conference ’04
R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, Nucl. Phys. B483 (1997) 291.
C.A.Salgado and U.A.Wiedemann, Phys. Rev. D68 (2003) [arXiv:hep-ph/ ].

16. Energy loss with charm?
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
Effect present in light mesons, what about other particles?
D meson originate from c quark Cr = 4/3, whereas light flavors
originate mainly from gluons (C=3)
Dead cone effect*: due to destructive interference, gluons radiation is suppressed at angles  < mQ/EQ
*Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/ ].
bars= statistical error
shadow= syst. err. (MC+centrality+theory extr.)
q = 4 GeV2/fm at LHC requiring
same hadron suppression as at RHIC
nuclear shadowing effect
(shadowing = modification of PDF’s,
causes reduction of cross section)

17. Energy loss vs. dead cone
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
Quantitative difference heavy/light mesons measurement?
E gluons/quarks
energy loss ~ 2
E gluons/quarks
fragmentation ~ 1/2
D/h ratio:
RD/h = RAAD / RAAh
q = 4 GeV2/fm at LHC requiring
same hadron suppression as at RHIC
eliminare????
dead cone makes the difference!
RD/h ~ 2
in hot QGP
sensitive to
medium density

18. b e+X: strategy
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
Task:
tag ~ 0.8 e /event from b decays among ~ 103 electrons
from other sources
Main backgrounds:
pions misidentified as electrons
Dalitz decays
charm semi-electronic decays
photon conversions in the detector materials
strange decays
Strategy:
high impact parameter: c ~ 500 μm for beauty
high momenta: beauty harder than lighter flavors
electron/pion separation critical

19. Pt and d0 comparison beauty electrons charm electrons charged pions
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
beauty electrons
charm electrons
charged pions

20. b e+X: purity and statistics
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
pT> 1 GeV
pT> 2 GeV
pT> 3 GeV
background cure
charm electrons pt thr.
light mesons electrons d0 thr.
charged pions identification
pT>2 GeV, 180  d0  400mm
90% purity
50,000 B's (including TRD efficiency)

21. Conclusions & perspectives
Rosario Turrisi
Beach 2004
Saturday, July 03, 2004
ALICE has a good potential to measure
heavy flavors in different channels
Charm:
production cross section
pt distribution
study of charm energy loss
Beauty:
Production cross section
Coming up
b’s pt distribution
additional D, D* channels
semi-electronic b/c deconvolution
exclusive b decays
11% S/B, significance=37
pT> 1 GeV
pT> 2 GeV
pT> 3 GeV