charm and beauty with alice at lhc

Charm and beauty with ALICE at Charm and beauty with ALICE at LHCLHC

Rosario TurrisiRosario TurrisiUniversity and INFN, Padova, ItalyUniversity and INFN, Padova, Italy

for the ALICE Collaborationfor the ALICE Collaboration

Rosario TurrisiRosario TurrisiBeach 2004 Beach 2004

Saturday, July 03, 2004Saturday, July 03, 2004

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ContentsContents

Why heavy ions at LHCWhy heavy ions at LHC The ALICE detectorThe ALICE detector The role of charm and beautyThe role of charm and beauty Basic performances Basic performances Open flavors measurement sensitivityOpen flavors measurement sensitivity Conclusions and PerspectivesConclusions and Perspectives



33

Why heavy ions at LHCWhy heavy ions at LHC

strong interaction

NNsLHC

PbPb @ = 5.5 TeV

hadronic matter

plasma of quarks and gluonsQGP

high energy &

large volume

Exploration of the deconfined phase…Exploration of the deconfined phase…

Tc ~ 170 MeV(μB=0)

c ~ 1 GeV/fm3

Lattice QCD with massless flavorsBaryon free environment (μB=0)

At SPS (CERN) and RHIC (BNL) alreadyobserved deconfinement signals.

At LHC:• more strictly μB=0• higher energy density

DEEP DECONFINEMENT!



44

ALICE ALICE detectorsdetectors

Solenoid magnet B<0.5 T 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

22 * 1.8 units of pseudo-rapidity * 1.8 units of pseudo-rapidity

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 Central tracking system:• Inner Tracking System • Time Projection Chamber



55


Central tracking system:•Transition Radiation Detector• Time Of Flight

22 * 1.8 units of pseudo-rapidity * 1.8 units of pseudo-rapidity

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)

Multigap Resistive Plate Multigap Resistive Plate ChambersChambers5 years R&D, and5 years R&D, and < 100 ps < 100 ps pions, kaons, protons separation (see later)electrons/pions at low pt



66


+EMCal (under discussion)

MUON Spectrometer

Specialized detectors:• High Momentum PID• PHOton Spectrometer

Forward detectors:• Photon Mult. Det.• Forward Mult. D., T0, V0, Zero Degrees Cal.

Cosmic rays trigger

2.4 < 2.4 < < 4 < 4



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Heavy flavors and heavy-Heavy flavors and heavy-ionsions

Why measure heavy flavors at LHC ?Why measure heavy flavors at LHC ? quarkonium suppression: deconfinement signaturequarkonium suppression: deconfinement signature BB J/ J/ important background important background open heavy flavors as natural normalization for QQ studiesopen heavy flavors as natural normalization for QQ studies interest in its own right (discovery potential!)interest in its own right (discovery potential!) probes of the medium:probes of the medium:

– early formation (initial parton-parton), most energetic phaseearly formation (initial parton-parton), most energetic phase– energy loss (medium dependent?)energy loss (medium dependent?)

pp reactions, pQCD, nuclear effects

(geometry, shadowing)medium propertiesINPUT OUTPUT

not covered here

PbPb @ =5.5 TeVNNs



88

pQCD predictionspQCD predictions

NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M NLO pQCD (Mangano-Nason-Ridolfi), average of MRST e CTEQ5M PDF’s, EKS98 in Pb-Pb for shadowingPDF’s, EKS98 in Pb-Pb for shadowing

(shadowing = modification of PDF’s, causes reduction of cross section)(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 acceptance:DD00/ D/ D00 BB(s)(s)+ + bb

pppp 0.190.19 0.01430.0143

PbPbPbPb 140140 99~5 D0 K

~0.85 B eX

Mesons multiplicities

in central collisions



99

Performance studiesPerformance studies

Detector description with the state-of-the-(ALICE)-art code Detector description with the state-of-the-(ALICE)-art code AliRootAliRoot

Charm/beauty signal tuned to NLO pQCD pCharm/beauty signal tuned to NLO pQCD ptt spectrum spectrum (custom tuning of PYTHIA)(custom tuning of PYTHIA) Background from HIJING, 6000 charged particles per unit Background from HIJING, 6000 charged particles per unit

rapidity at midrapidity rapidity at midrapidity Priorities:Priorities: the exclusive decay of the Dthe exclusive decay of the D0 0 K K (golden channel): (golden channel):

– test bench for secondary vertex detection, pidtest bench for secondary vertex detection, pid– very high backgroundvery high background

inclusive b inclusive b eX decay eX decay– secondary vertices secondary vertices – electron identificationelectron identification– ““easy” measurement of cross sectioneasy” measurement of cross section



1010

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



1111

Tracking performanceTracking performance

impact parameter resolution:impact parameter resolution:

σσ= @ p= @ ptt=1.3 GeV=1.3 GeV< 50 μm < 150 μm z

pptt resolution: resolution:

σσ= 1(2)% @ 1(10) GeV= 1(2)% @ 1(10) GeV

9% @ 100 GeV9% @ 100 GeV

EFFICIENCYpionskaons



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test beam: id. as e = 1 %

PID: e,PID: e,, K, p, K, p PbPb eventsdN/dy=6000

TRDTRD

electrons

TPCTPC

hadrons

TOFTOF

Combined π/e ~ 10-4 @ pt~1-2 GeV

p (Gev/c)



1313

Selection cutsSelection cuts

DD0 0 K K – decay topologydecay topology– impact parameter of tracks impact parameter of tracks

(in bending plane, (in bending plane, dd00~100 ~100 μμmm))

– momentamomenta– identification identification

~ 0.5 DD00 with |y|<1 with |y|<1but also 12000 but also 12000 charged charged /K/Kin PbPb collisionsin PbPb collisions

impact parameters product



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Performance: DPerformance: D00KK

K,K, M MINVINV integrated over p integrated over ptt 101077 PbPb events (one-month PbPb events (one-month

run)run) dN/dy(y=0) = 6000 (charged)dN/dy(y=0) = 6000 (charged)

S/BS/B

initialinitial

(M(M33))

S/evtS/evt

finalfinal

(M(M11))

S/BS/B

finalfinal

(M(M11))

SignificanceSignificance

S/S/S+BS+B

(M(M11))

5 5 10 10-6-6 1.3 1.3 10 10-3-3 11 %11 % 3737

(for 10(for 1077 evts, evts,

~1 month)~1 month)

measurement of pt distribution

Significance



1515

Quark energy loss: basicsQuark energy loss: basics

Origin: parton energy loss due to gluon radiationOrigin: parton energy loss due to gluon radiation

– Average Average energy lossenergy loss (BDMPS model): (BDMPS model):

CCRR Casimir factor = Casimir factor = 33 for gluons for gluons 4/34/3 for quarks for quarksq = medium transport coefficient q = 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 quenching effect

h

RAA =1 means AA is superposition of independent pp collisions

Quark Matter Conference ’04



1616

Energy loss with charm?Energy loss with charm?

Effect present in light mesons, what about other particles?Effect present in light mesons, what about other particles?– D meson originate from c quark D meson originate from c quark Cr = 4/3, whereas light flavors= 4/3, whereas light flavors originate mainly from gluons (C=3)originate mainly from gluons (C=3)– Dead cone effectDead cone effect**: due to destructive interference, : due to destructive interference, gluons radiation is

suppressed at angles < mQ/EQ

nuclear shadowing effect

bars= statistical errorshadow= syst. err. (MC+centrality+theory extr.)

q = 4 GeV2/fm at LHC requiringsame hadron suppression as at RHIC

tpp

tAA

collAA dpdN

dpdN

NR

/

/1

(shadowing = modification of PDF’s, (shadowing = modification of PDF’s,

causes reduction of cross section)causes reduction of cross section)

*Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202].



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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?Quantitative difference heavy/light mesons measurement?

RD/h

~ 2

in hot QGP

sensitive tomedium density

E gluons/quarks E gluons/quarks

energy loss ~ 2 energy loss ~ 2 E gluons/quarksE gluons/quarks

fragmentation ~ 1/2fragmentation ~ 1/2

dead cone makes the difference!



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Task: Task:

tag ~ 0.8 etag ~ 0.8 e /event from b decays among ~ 10 /event from b decays among ~ 1033 electrons electrons

from other sourcesfrom other sources Main backgrounds:Main backgrounds:

– pions misidentified as electrons– Dalitz decays– charm semi-electronic decays– photon conversions in the detector materials– strange decays

Strategy:Strategy:– high impact parameter: high impact parameter: cc ~ 500 ~ 500 μμm m for beauty for beauty – high momenta: beauty harder than lighter flavors high momenta: beauty harder than lighter flavors – electron/pion separation critical electron/pion separation critical

bb e+X: strategy e+X: strategy



1919

PPtt and d and d00 comparison comparison

beauty electronscharm electronscharged pions



2020

bb e+X: purity and e+X: purity and statisticsstatistics

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 400mm

90% purity

50,000 B's (including TRD efficiency)



2121

Conclusions & Conclusions & perspectivesperspectives

ALICE has a good potential to measure ALICE has a good potential to measure

heavy flavors in different channelsheavy flavors in different channels Charm:Charm:

– production cross sectionproduction cross section

– pptt distribution distribution

– study of charm energy lossstudy of charm energy loss Beauty:Beauty:

– Production cross sectionProduction cross section

Coming upComing up– b’s pb’s ptt distribution distribution

– additional D, Dadditional D, D** channels channels– semi-electronic b/c deconvolutionsemi-electronic b/c deconvolution– exclusive b decaysexclusive b decays

11% S/B, significance=37

pT> 1 GeVpT> 2 GeVpT> 3 GeV

charm and beauty with alice at lhc

Documents

parton energy loss

monthquark energy loss

perspectiveswhy heavy

gev tracking complement

pt1 gev factor

b exmesons multiplicities

gevp gevcselection cuts

shadowing shadowing