charm and beauty with alice at lhc rosario turrisi university and infn, padova, italy for the alice...
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Charm and beauty with Charm and beauty with ALICE at LHCALICE at LHC
Rosario TurrisiRosario TurrisiUniversity and INFN, Padova, ItalyUniversity and INFN, Padova, Italy
for the ALICE Collaborationfor the ALICE Collaboration
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ContentsContents
• Heavy flavors and heavy ions• Key performances of ALICE
• Charm cross section and pt sensitivity
• Beauty cross section• Conclusions and Perspectives
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Heavy flavors and heavy-ionsHeavy flavors and heavy-ions
Why measure heavy flavors at LHC ?– Interest in its own right: discovery potential!
More specific to our issue (hot and dense matter):– quarkonium suppression: deconfinement signature– probes of the medium:
• early formation (initial parton-parton), most energetic phase• thermal (late) production ?• energy loss (medium dependent?)
– B J/ important background for direct J/ – open heavy flavors as natural normalization for QQ studies
pp reactions, pQCD, nuclear effects
(geometry, shadowing)medium propertiesINPUT OUTPUT
PbPb @ =5.5 TeVNNs
not covered here
K
e c D Kb B eX
openflavors
channels
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Quark energy loss: basicsQuark energy loss: basics
• Common explanation:
parton energy loss due to gluon radiation
– Average energy loss (BDMPS model):
CR Casimir factor = 3 for gluons 4/3 for quarksq = medium transport coefficient gluon density and momenta
2 ˆ LqCE Rs
path length L
c
g
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) 014008 [arXiv:hep-ph/0302184].
tpp
tAA
collAA dpdN
dpdN
NR
/
/1• Study to get the medium effect
RAA measured at RHIC with pions: clear high-pt suppression
RAA =1 if AA is superposition of independent pp collisions
Quark Matter Conference ’04
A.Dainese, C.Loizides and G.Paic, hep-ph/0406201
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Energy loss with heavy flavors ?Energy loss with heavy flavors ?
• Effect present in light mesons, what about other particles?– D,B meson originate from c,b quarks 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
q = 100 GeV2/fm at LHC1
tpp
tAA
collAA dpdN
dpdN
NR
/
/1
*Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202].
1. K.J.Eskola, K.Kajantie, P.V.Ruuskanen and K.Tuominen, Nucl. Phys. B570 (2000) 379 [hep-ph/9909456].
charm
beauty
• Comparison among -D-B in order!
extrapolation from q=15 GeV2/fm at RHIC… a worst case (q=100 GeV2/fm)!
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Cross sectionsCross sections
• NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M PDF’s, EKS98 in Pb-Pb for shadowing
(shadowing = modification of PDF’s, reduction of cross section)
Taking into account F,R
a factor 4 arises between min. and max. cross section…
In acceptance!D0/ D0 B(s)+ b
pp 0.19 0.0143
PbPb 140 9~0.5 D0 K
~0.2 B eX
Mesons multiplicities central collisions
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Tracking performanceTracking performance
impact parameter resolution:
σ= @ pt=1.3 GeV< 50 μm
< 150 μm z
EFFICIENCYpionskaons
pt resolution:
σ= 1(2)% @ 1(10) GeV 9% @ 100 GeV
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test beam: id. as e = 1 %
PID: e,PID: e,, K, p, K, pPbPb events, dN/dy=6000
TRDTRD
electrons
TPCTPC
hadrons
TOFTOF
Combined π/e ~ 10-4 @ pt~1-2 GeV
p (GeV/c)
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Selection cutsSelection cuts
• D0 K – decay topology– impact parameter of tracks (in bending plane, d0~100 μm)
– momenta– identification
~ 0.5 DD00 with |y|<1 with |y|<1but also 12000 but also 12000 charged charged /K/Kin PbPb collisionsin PbPb collisions
cos(pointing angle) vs. impact parameters product
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Performance: DPerformance: D00KK
• K, MINV integrated over pt
• 107 PbPb events (one-month run)• dN/dy(y=0) = 6000 (charged)
S/Binitial(M3)
S/evtfinal
(M1)
S/Bfinal
(M1)
SignificanceS/S+B(M1)
5 10-6 1.3 10-
3 11 %37
(for 107 evts)
measurement of pt distribution
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Charm energy loss in ALICECharm energy loss in ALICE
Current estimation of q = 100 GeV2/fm
mc=0mc=1.2 GeV/c2
N.Armesto, A.Dainese, C.A.Salgado and U.A.Wiedemann,
in preparation
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• 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
bb e+X: strategy e+X: strategy
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bb e+X: purity and statistics e+X: purity and statistics
background cure
charm electrons pt thr.
light mesons electrons d0 thr.
charged pions identification
pT> 1 GeV
pT> 2 GeV
pT> 3 GeV
pT>2 GeV, 180 d0 600 m
90% purity
50,000 B's (including TRD efficiency)
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Conclusions & perspectivesConclusions & perspectives• ALICE has a good potential to measure heavy flavors in different channels• Charm:
– production cross section
– pt distribution
– study of energy loss
• Beauty:– Production cross section
• Coming up– reconstruction of b decay topologies
• b’s pt distribution, energy loss study
– additional D, D* channels– semi-electronic charm (beauty background!)– …
11% S/B, significance=37
pT> 1 GeVpT> 2 GeVpT> 3 GeV
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ALICE ALICE detectorsdetectors
Solenoid magnet B<0.5 T
TPC88 m3 , 510 cm length, 250 cm radius Ar (90%) + CO2 (10%)88 μs drift timemain tracking device, dE/dx
2 * 1.8 units of pseudo-rapidity
ITS- 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 m
r: 50 m
Two layers:r = 4 – 7 cm
9.8 Mch
TRD - 6 layers for:• electron/pion separation at pt>1 GeV
• factor 100 rejection at 2 GeV• tracking complement, mass resolution 100 MeV/c2 @ • high pt trigger (onia studies)
TOFTOF - Multigap Resistive Plate Chambers - Multigap Resistive Plate Chambers < 100 ps < 100 ps pions, kaons, protons separation (see later)electrons/pions at low pt
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60 < < 62
Total charged multiplicityTotal charged multiplicity
TPC + ITSprojection of the full range
(front view)
dNCH/dy (y=0)
Current baseline: 6000
Tested up to: 8000
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LHC run parametersLHC run parameters
System
pp
PbPb
√sNN
(TeV)
L0
(cm-2s-1)dN/dy
(y=0)
TRUN
(s/year)
geom
(b)
14.0 1034* 6 107 0.07
5.5 1027 2-8103 106 * * 7.7
Fall 2007
2008 *Lmax(ALICE) = 1031 ** Lint(ALICE) ~ 0.7 nb-1/year
Pile-up in TPC +and ion-density
limit
tuning orbeam offset
• and, later, more systems: pA, light ions (Sn, Kr, Ar,O) & other energies (pp @ 5.5 TeV).
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pQCD pQCD extrapolationsextrapolations
• NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M PDFs (EKS98 in Pb-Pb for shadowing)
Taking into account F,R
a factor 4 arises between min and max x-section…inclusive cross section alreadya valuable information!
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AcceptanceAcceptance
-6
-4
-3
-2
-1
0
1
2
3
4
90o 180o 270o 360o
Rap
idit
y
Azimuth
FMD -5.4 < < -1.6
PMD -2.3 < < -3.5
FMD 1.6 < < 3
Muon arm 2.4 < < 4
ITS+TPC+TRD+TOF: -0.9 < < 0.9
ITS multiplicity -2 < < 2
HMPID -.45 < < 0.45
PHOS -.12 < < 0.12
SPD multiplicity -2<<2
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b->e+X: contaminationb->e+X: contamination
pt bin [GeV/c]
d0 threshold [m] % S ( bc/b ) % Bcharm % Bother elec. Ns [x104]
1.0 – 1.6 200 – 300 40 – 60 (30%) 30 – 20 30 – 20 9 – 5
1.6 – 2.2 150 – 300 80 – 90 (15%) 20 – 10 – 6 – 2
2.2 – 3.0 150 – 300 > 90 (10%) < 10 – 4 – 2
3.0 – 5.0 100 – 300 > 95 (10%) < 5 – 4 – 1
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Particle identificationParticle identification
Various techniques…
… in a wide momentum range
2 ||<0.9
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Charm detection performanceCharm detection performance
S/Binitial(M3)
S/evtfinal
(M1)
S/Bfinal
(M1)
SignificanceS/S+B(M1)
Pb-Pb 5 10-6 1.3 10-3 11 % 37
(for 107 evts,~1 month)
pp 2 10-3 1.9 10-5 11 % 44
(for 109 evts,~1 year)
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Expected multiplicity/running Expected multiplicity/running conditionsconditions
• ALICE optimized for dN/dy(y=0) =4000-6000, tested extensively up to 8000• Extrapolating from RHIC…
hep-ph0104010
5
√s (GeV)10 102 103 102 103 104
1.0
5.0
10.0
15.0
Nch
/(0
.5N
part)
dN
ch/d|
<1
2
5
103
dNch/d ~ 1300dNch/d ~ 2500
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DD00 K K--++:: dd22(D(D00)/dp)/dpttdy and ddy and d(D(D00)/dy)/dy
d(D0)/dy for|y| < 1 and pt > 1 GeV/c (65% of (pt > 0)) statistical error = 7 % systematic error = 19 % from b = 9 % MC correction = 10% B.R. = 2.4 % from AA to NN = 13 %
d(D0)/dy for|y| < 1 and pt > 0
statistical error = 3 % systematic error = 14 % from b = 8 % MC correction = 10% B.R. = 2.4 % inel = 5 %
inner bars: statisticalouter bars: systematic
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Signal history, errors for Signal history, errors for PbPbPbPb
Selection effectiveness…SignalTotal D0 / event 141decaying in K 5.4with K and in acc. 0.5after track rec. 0.14after (,) rejection 0.13after selection cuts 0.0013
Background
reduced by a factor ~10-7
10-2
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Energy loss vs. dead coneEnergy loss vs. dead cone
D/h ratio: R
D/h = R
AAD / R
AAh
q = 4 GeV2/fm at LHC requiringsame hadron suppression as at RHIC
Quantitative difference heavy/light mesons measurement?
RD/h
~ 2
in hot QGP
sensitive tomedium density
E gluons/quarks energy loss ~ 2
E gluons/quarksfragmentation ~ 1/2
dead cone makes the difference!
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General motivationGeneral motivation
• A Large Ion Collider Experiment is the LHC experiment dedicated to the study of the Quark Gluon Plasma…
QGP a (locally) thermally equilibrated state of matter in which color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes.“Partons are deconfined”
strong interaction
LHC
PbPb @ = 5.5 TeVNNs
hadronic matter
QGP
high energy &
large volume
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Performance studiesPerformance studies
• 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
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QGP evidences and probesQGP evidences and probes
At LHC (Pb-Pb @ 5.5 ATeV):• more strictly μB=0• higher energy density
• SPS experiments got some evidence that matter may behave in odd ways (not just as “typical” hadrons)
• RHIC exps show confirmation of the new behaviour,mostly with light mesons and hadrons
• Possible improvements: – experimental smoking gun of QGP? (see f.e. T. Hallman talk at ICHEP
2004, Beijing, China)– study of QGP properties?
DEEP DECONFINEMENT?
larger volume
longer lifetime
• Hard cross section dominant• Could heavy flavors represent a good tool at LHC?