Heavy Quarks in view of the LHC

Prague, 07.11.2007 Andrea Dainese 1

Heavy Quarks Heavy Quarks in view of the LHCin view of the LHC

Andrea DaineseAndrea DaineseINFNINFN

(ALICE Collaboration)(ALICE Collaboration)


LayoutHigh-pT (heavy-flavour) particle production in hadronic collisions –from pp to AA– in factorized QCD

pp baseline: pQCD calculationsnuclear effects, in initial and final state

What have we learnt at Tevatron and RHIC?

What will be new at the LHC?What do we expect?

What should we measure?

Experimental Perspectives at the LHC

PARTONPARTONENERGYENERGY

LOSSLOSS


Heavy-flavour production: ppproton-proton collisions: factorized pQCD approach

)pp(zDp

xPDFxPDF cDDccT

c

/d

ˆd)()( 21

)~Q~( 2221 ccMsxx

s /2

c

c D

D

x1

x2

Q2

s /2),(dd

RFDT

D

p

PDF:• Q2 evolution calculated in pQCD• initial condition from data (HERA)

FF: • non-perturbative • phenomenolgy + fit to data (e+e-)

calculable as perturbative series of strong coupling s(R)

22, Q~RF


pp QQ: pQCD calculations vs dataCalculation of partonic cross section

standard: Fixed Order (NLO) Massive (e.g. MNR code)

state-of-the-art: Fixed Order Next-to-Leading Log (FONLL)

Tp

more accurate at high pT

Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033

B production at Tevatron (1.96 TeV)is well described by FONLL

CDF, PRL91 (2003) 241804FONLL: Cacciari, Nason

Charm production slightly underpredictedat Tevatron (1.96 TeV)

Cacciari, Nason, Vogt, PRL95 (2005) 122001

& at RHIC (200 GeV)Q e+X

QM06 update later


Heavy-flavour production: AA

A

A

Binary scaling for hard yields: collDT

Dpp

DT

DAA NpNpN d/dd/d

Binary scaling is “broken” by:

c

c D

D

x

fgPb / fg

p

LHC RHIC SPSRAA <1 ~1 >1

Q2 = 5 GeV2

pT

RA

B

1

~2-4 GeV/c

kL kT

Cronin enhancement

• initial-state effects: PDF shadowing kT broadening (‘Cronin’)

medium formed in the collision

A

A c

cD

Du

• final-state effects energy loss? [next slide] in-medium hadronization

(recombination?)

recombination: pH = pq

fragmentation: pH = z pq

baryon/meson enhancement


Calculating Parton Energy Loss

cc

ccRsC

I

for )/( for /

dd

2

Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291.Zakharov, JTEPL 63 (1996) 952.Salgado, Wiedemann, PRD 68(2003) 014008.

BDMPS-Z formalismpath length L

kT

Radiated-gluon energy distrib.:

2

ˆ Tkq transport coefficient

2/ˆ 2Lqc LR c

sets the scale of the radiated energyrelated to constraint kT < , controls shape at << c

Casimir coupling factor: 4/3 for q, 3 for gRC

(BDMPS case)


Model vs RHIC “light” dataModel: pQCD + E loss probability + detailed collision geometryDensity ( ) “tuned” to match RAA in central Au-Au at 200 GeV

/fmGeV 144ˆ 2q

q

matches pT-indepence of suppression at high pT

Dainese, Loizides, Paic, EPJC 38 (2005) 461.

(Quark Matter 05)

Same theoretical calculation (SW quenching weights) and similar results in Eskola, Honkanen, Salgado, Wiedemann, NPA747 (2005) 511

Tpp

TAA

collTAA dpdN

dpdNN

pR//1)(


large RAA indep. of q q

Limited sensitivity of RAA

Strong suppression requires very large densitySurface emission scenarioRAA determined by geometry rather than by density itself

Limited sensitivity to

Need more differential observables:

massive partonsRAA vs reaction plane

study of jet shapes…

q

Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511.

?


Lower E loss for heavy quarks ?In vacuum, gluon radiation suppressed at < mQ/EQ

“dead cone” effect

Dead cone implies lower energy loss (Dokshitzer-Kharzeev, 2001):energy distribution d/d of radiated gluons suppressed by angle-dependent factorsuppress high- tail

Q

Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602.Dokshitzer and Kharzeev, PLB 519 (2001) 199.

11dd

dd

2

2

2

Q

Q

EmII

LIGHTHEAVY

Dokshitzer

22QQ

2 ])/([1

Em

Gluonsstrahlung probability

R = 105

Detailed massive calculation confirms this qualitative feature

(Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003)


Charm RAA at RHIC

effect of the mass

thermalized component

/fmGeV 144ˆ 2q

Small effect of mass for charm (~50% for D, ~30% for e) at low pT [large uncertainties!]Basically no effect in “safe” pT-region

Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027.

(extracted from light-flv hadron data)

larger uncertainties

other contributions become important


Charm + beauty + DY electrons at RHIC(pQCD baseline revised, and its uncertainties)

FONLL calculation: Cacciari, Nason, Vogt, PRL95 (2005) 122001Drell-Yan from: Gavin et al., hep-ph/9502372Comparison: Armesto, Cacciari, Dainese, Salgado, Wiedemann, PLB637 (06) 326

FONLL: electron spectrum may be ~50% c + ~50% b for 3 < pT < 8 GeV

We investigated the DY component: < 10% up to 10 GeV

Large uncertainty on b/c crossing point in pT: from scales/masses variation it changes from 3 to 9 GeV

PHENIX electron cross section in pp now quite OK also at high pT

PHENIX hep-ex/0508034

PHENIX, hep-ex/0609010

QM06 update

?

QM06 update


RAA of c and b electrons at RHIC

Armesto, Cacciari, Dainese, Salgado, Wiedemann, PLB637 (06) 326,

Due to larger mass of b quark electron RAA increased to ~0.4

Mass uncertainty (in E loss) and scales uncertainty (in pQCD b/c crossing) were studied

c

b

c+b

Theory predicts e RAA (~0.4)

larger than RAA (~0.2) e spectra in principle sensitive to mass hierarchy Perturbative uncertainty on the pp baseline comparable to model-intrinsic uncertainty in determination of

Preliminary STAR data not conclusive for comparison with theory

nucl-ex/0611018

QM06

Theory predicts e RAA (~0.4)

larger than RAA (~0.2) e spectra in principle sensitive to mass hierarchy Perturbative uncertainty on the pp baseline comparable to model-intrinsic uncertainty in determination of

Final data (QM06): electron RAA tends to be overestimated

Djordjevic, Gyulassy, Wicks, nucl-th/0512076


QM06RAA of c and b electrons at RHIC

nucl-ex/0611018nucl-ex/0611018

(Adil & Vitev)

Other approaches: include elastic E loss (Djordjevic, Gyulassy, Wicks) collisional dissociation of D/B mesons formed in the medium early after hard scattering (Adil & Vitev)









Novelties at LHC (1): Hard ProbesLHC: large hard cross sections!Our set of “tools” (probes) becomes richer

quantitatively: qualitatively:• heavy quarks

• + jet correlations• Z0 + jet correlations

bbRHIC

bbLHC

ccRHIC

ccLHC

100

10LO pQCD by I. Vitev,hep-ph/0212109


Heavy-quark production at the LHCpp: Important test of pQCD in a new energy domainRemember the “15-years saga of b production at Tevatron”*

Baseline predictions: NLO (MNR code) in pp + binary scaling (shadowing included for PDFs in the Pb)

ALICE baseline for charm / beauty: system :sNN :

Pb-Pb (0-5% centr.)5.5 TeV

p-Pb (min. bias) 8.8 TeV

pp14 TeV

4.3 / 0.2 7.2 / 0.3 11.2 / 0.5115 / 4.6 0.8 / 0.03 0.16 / 0.007

0.65 / 0.80 0.84 / 0.90 --

[mb] QQNN

QQtotN

Theoretical uncertainty of a factor 2—3 (next slide)* M.ManganoMNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.

98EKSshadowingC


Theoretical Uncertainties(HERA-LHC Workshop)

MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.

Evaluation of theoretical uncertaintiesbeautycharm

MRST2001 CTEQ6, CTEQ5, CTEQ4, :PDFs0.0040.0002 2/5.0 GeV 0.55.4

0.110.002 2/5.0 GeV 8.13.1 ,

bRFb

cTRFc

m

mm

CERN/LHCC 2005-014hep-ph/0601164


Model Comparisons(HERA-LHC Workshop)

Compare predictions by several different models

Good agreement between collinear factorization based calculations: FO NLO and FONLLkT factorization (CASCADE) higher at large pT

beautycharm

CERN/LHCC 2005-014hep-ph/0601164


Energy extrapolation via pQCD?Different systems (pp, p-Pb, Pb-Pb) will have different s valuesResults in pp at 14 TeV will have to extrapolated to 5.5 TeV (Pb-Pb energy) to compute, e.g., nuclear modification factors RAA

pQCD: “there ratio of results at 14 TeV/5.5 TeV has ‘small’ uncertainty”

charm beauty

12% 8%

MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.


increasing s

Probe unexplored small-x region with HQs at low pT and/or forward y

down to x~10-4 with charm already at y=0

Eskola, Kolhinen, Vogt, PLB582 (2004) 157Gotsmann, Levin, Maor, Naftali, hep-ph/0504040

Window on the rich phenomenology of high-density PDFs: gluon saturation / recombination effects

Possible effect: enhancement of charm production at low pT w.r.t. to standard DGLAP-based predictions, even in pp!

c(DGLAP+non-linear)c(DGLAP)

Novelties at LHC (2): Small xccgg


Probing nuclear initial state PDFs with HQsShadowing in pA (AA)CGC in pA (AA)Double parton scattering in pA

)/( ppNpPbR collDpPb

c

c

Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61


Shadowing in pA (AA)CGC in pA (AA)Double parton scattering in pA

Saturation scale Qs2(x) ~ xg(x)A/RA

2 ~ xg(x)A1/3

At LHC for x~10-4, Qs~1.5-2 GeV > mc

For mT,c~Qs, charm prod. CGC-dominated:• scales with Npart in pA (not Ncoll)• harder pT spectra, since typical kT~Qs~1.5 GeV, while in standard factorization kT~QCD~0.2 GeV

Probing nuclear initial state PDFs with HQs

c

c

Kharzeev, Tuchin, NPA 735 (2004) 248 + LHC Predictions Workshop

CGC: very similar RpA for p, D, B, ~indep. of pt and rapidity


Shadowing in pA (AA)CGC in pA (AA)Double parton scattering in pA

probe “many-body” PDFs

normal and anomalous: different A dep.

signature: events with “tagged” DD (can use D0+e+ or e+e+) and ch. conj.NB: there is a “background” from normal bb events, but it can be estimated from measured single inclusive b cross section

predicted rate: cccc/cc ~ 10% (Treleani et al.)

Probing nuclear initial state PDFs with HQs

c

c

Cattaruzza, Del Fabbro, Treleani, PRD 70 (2004) 034022


Heavy Quark Energy Loss at LHC

~100 cc pairs and ~5 bb pairs per central Pb-Pb collisionExperiments will measure with good precision RAA for D and B, and for their decay leptons (as I’ll show in 5’)

What can we learn from a comparative quenching study of

massive and massless probes at the LHC?


Heavy Flavour RAA at LHCBaseline: PYTHIA, with EKS98 shadowing, tuned to reproduce c and b pT distributions from NLO pQCD (MNR)

(m/E)-dep. E loss with

MNR: Mangano, Nason, Ridolfi, NPB 373 (1992) 295.

/fmGeV 10025ˆ7ˆ 2* RHICLHC qq

Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. * EKRT Saturation model:Eskola, Kajantie, Ruuskanen, Tuominen, NPB 570 (2000) 379.


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

)()()( )(/)( t

hAAt

BDAAthBD pRpRpR

gq EE mass effect

For 10 < pT < 20 GeV, charm behaves like a m=0 quark,light-flv hadrons come mainly from gluonsRD/h enhancement probes colour-charge dep. of E lossRB/h enhancement probes mass dep. of E loss

Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027


LHC: Beauty-to-Charm ratio RB/D

Compare c and b: same colour chargeMass effect Enhancement of factor ~2, independent of (for )

)()()(/ tDAAt

BAAtDB pRpRpR

q/fmGeV 20ˆ 2q

Adapted from Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027


b Energy loss:Use W-decay muons as a reference

Conesa del Valle, Dainese, Ding, Martinez, Zhou, in preparation

early measurement for all experiments at the LHC!

single RCP(pt)


“American” predictions for RAA at LHC

Vitev, Adil, “Last Call for LHC Predictions” workshop Wicks, Gyulassy, “Last Call for LHC Predictions” workshop

Radiative+Collisional E lossà la GLV

D

B

D+B

D and B meson formation and dissociation inside the medium


Charm hadron ratios as probe of QGP properties

Yields of charm hadrons within statistical hadronization model

Rafelski, Kuznetsova, LHC Predictions Workshop

Ratio D/Ds as a probe of T at measured s/S

(PYTHIA: 6.92!)

0.13PYTHIA: 0.19

Braun-Muntzinger, Stachel, LHC Predictions Workshop


Azimuth. asymmetry: v2 from flowv2 of D and B mesons in non-central collisions tests:

at low/moderate pt: recombination scenario, flow of c/b quarks (?), hence degree of thermalization of medium

Model: mult. scattering in expanding QGP ( elliptic flow)hadronization via coalescence + fragmentation

c: 15-20%

b: 5%

van Heese, Rapp, Greco, LHC Predictions Workshop


Azimuth. asymmetry: v2 from E lossv2 of D and B mesons in non-central collisions tests

at higher pt: path-length dependence of E loss in almond-shaped medium

Model: Radiative E loss (BDMPS)

RHIC LHC

c: 5-10%

Armesto, Cacciari, Dainese, Salgado, Wiedemann, PLB637 (06) 326 + LHC Predictions Workshop









Experimental study of heavy flavours in AA at the LHC

ATLASCMS


The ALICE DetectorThe ALICE Detector

||| < 0.9, B = 0.5 T| < 0.9, B = 0.5 TTPC + silicon trackerTPC + silicon tracker,,ee, , , K, p identification, K, p identification

-4 < -4 < < -2.5 < -2.5muonsmuons

ALICE Collaboration: >1000 people, 30 countries, ~ 90 Institutes

Size: 16 x 26 metersWeight: 10,000 tons


Getting Ready for Beam!Ready to move

TPC (largest ever) installed, ITS moving in

MUON arm: largest dipole ever


Open charm and beautyOpen charm and beauty

TPC (tracking)

TOF (K/ id)

ITS (vertexing)K

D0 K D+ K Ds KK D* D0 D0 K c Kp

understudy


understudy

B e+X B 5 pr. B J/ee

understudy

ITS (vertexing)TPC (tracking e/ id)TRD (e/ id)

e

TPC (tracking)ITS (vertexing)MUON (tracking,id)

B +X


understudy

B e+X B 5 pr. B J/ee

understudy


PrimaryVertex B

e

Xd0

rec. track

Vertexing: track d0 resolution

< 60 m (r)for pT > 1 GeV/c

Resolution mainly provided by the 2 layers of silicon pixels

PIXEL CELL

z: 425 m

r: 50 m

Two layers:r = 4 cmr = 7 cm

9.8 M


pair of opposite-charge tracks with large impact parameters good pointing of reconstructed D momentum to the primary vertexD0

Charm reconstruction: D0 K-+ & D+ K-++

Two vertexing algos with full error-matrix treatmentLarge combinatorial background (dNch/dy=6000 in Pb-Pb simul.)

Main selection: displaced-vertex selection

Invariant mass analysis

large distance (dPS) between primary and secondary vertexgood pointing of reconstructed D momentum to the primary vertex

D+

1 year at nominal luminosity(109 pp events, 107 central Pb-Pb events)

10

20

30

40

50

D+D0


Beauty in the barrel:displaced single electrons

PrimaryVertex B

e

Xd0

rec. track

ALICE has excellent electron identification capabilities (TRD + TPC)Displaced electrons from B decays can be tagged by an impact parameter cut

electron


Beauty in the barrel: multi-prong vertices, displaced J/ee

At the LHC, 20% of J/ from B decaysmeasurement of b cross section

Displaced di-electrons from J/ from B decays

J/ e+e-)/(

)/( /

JpM

JLT

Jxy

primarysecondary

J/ pseudoproper decay time (pt>5GeV)

Beauty decays in many (4-6) charged particles


Beauty via (forward) muons

inner bars: stat. errorsouter bars: syst. errors

Muons “identified” in the forward spectrometer (-4 << -2.5)

Pb-Pb 0-5%

single muons in the spectrometer:beauty dominates for pt > 2-3 GeV/c


Calibrating the probe (pp, s = 14 TeV)

D0 K B e + X

tpp

tAA

colltAA pN

pNN

pRd/dd/d1)( measured at 14 TeV, then

scaled by pQCD to 5.5 TeV

Expected sensitivity in comparison to pQCD:

1 year at nominal luminosity(109 pp events)


Charm and Beauty E Loss : RAA

mb = 4.8 GeV

D0 K

B e + X

1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)

D+ K

mC = 1.2 GeV

mC = 0

B eE loss calc.:Armesto, Dainese, Salgado, Wiedemann


Heavy-to-light ratios

1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)

)()()(/ thAAt

DAAthD pRpRpR probes colour-charge dep.

of QCD energy loss

)()()( D from eB from e/ tAAtAAtDB pRpRpR

probes mass dep.of QCD energy loss

E loss calc.:Armesto, Dainese, Salgado, Wiedemann


Charm v2: D+ exampleFirst estimate of statistical errors on D+ v2:

best sensitivity at intermediate pt: 3 – 7 GeV/c charm recombination

Under study: performance with D0 + D+

2107 min.bias evts 2107 6<b<9 fm evts

v2 calc. from Ko et al.


Conclusions

LHC: heavy quarks factory!Heavy quarks as probes of QCD in extreme conditions

low pt: probe small-x structure of p and nucleus intermediate pt: probe medium thermalisation (reco/flow) high pt: probe medium density via energy loss

ALICE in excellent position:dedicated detectors (ITS, TRD, MUON)promising performance for all key measurements


Appendix:QUARKONIA at LHC


H.Satz

Quarkonia at LHC: (cc)

J/ suppression & regeneration?

c, ’ suppression (J/ TD ~ 1.5-2 Tc)?Satz, CERN Heavy Ion Forum, 09/06/05

SPSRHICLHC

30

enhanced suppression

enhanced regeneration

TLHC >> J/ TD Wong, PRC 72 (2005) 034906Alberico, hep-ph/0507084

Becattini, PRL95 (05) 022301

Statistical hadronization: huge enhancements for cc, cc, Bc, ccc

e.g. 1000 for ccc/D from pp to Pb-Pb


productionproduction

RHICRHIC LHCLHC

Vogt, hep-ph/0205330

Quarkonia at LHC: (bb) d/dy @ LHC ~20 x RHIC melts only at LHC

’ TD ~ J/ TDWong, PRC 72 (2005) 034906Alberico, hep-ph/0507084

Small regenerationGrandchamp et al., hep-ph/0507314

’ can unravel J/ suppression vs. regeneration

Gunion and Vogt,

NPB 492 (1997) 301

’/ vs pt sensitive to system temp. & size


Quarkonia at LHC:experimental challenges

Important contribution to production from B J/(’) + X ~20% of J/~40% of ’

Normalization: Drell-Yan not available for normalization (from qq, while quarkonia

from gg at LHC; and small cross section at LHC) W, Z?

Different Q2, x

Open heavy flavour, but …Energy loss?Thermal charm production?

Possible alternative: RAA (à la PHENIX)

Need to measure this!


ITS (vertexing)TPC (tracking)TRD (e/ id)

MUON (tracking,id)

e e

QuarkoniaMeasured both in the di-electron (midrapidity, TRD) and di-muon (forward rapidity, MUON) channel


+- +- +-e+e-

Quarkonia acceptances

-4<<-2.5

J/

-4<<-2.5

acce

ptan

ce (%

)

J/


Particle Charmonia +- Charmonia e+e- Bottonia +- Bottonia e+e-

Bkg-subtracted

mass plot

acc. -4 < < -2.5 || < 0.9 -4 < < -2.5 || < 0.9M res. 65 MeV 35 MeV 90 MeV 90 MeV

J/ 150, ’ 7 J/ 245 30, ’ 12,

’’ 8 21, ’ 8

perf. , ?’ , ??’ , ’, ?’’ , ?’, no ’’

pt J/ 0-20 GeV J/ 0-10 GeV 0-8 GeV --

Quarkonia PerformanceBkg input: dNch/dy=4000 in central Pb-Pb. for 1 month

BSS

BSS /


Medium effect on Quarkonia:Quarkonia/BB , Quarkonia RAA

Normalization of quarkonia yields: BB yield (from intermediate-mass di-leptons), but b E loss?

Possible alternative: RAA (à la PHENIX),

but different c.m.s. energy, need p-Pb for initial-state effects

Plots for channel


EXTRA SLIDES


LHC running conditions

Ldt = 5.1026 cm-2 s-1 x 106 s 5.1032 cm-2 PbPb run, 5.5 TeVNPbPb collisions = 2 .109 collisions

Ldt dt = 3.1030 cm-2 s-1 x 107 s 5.1037 cm-2 for pp run, 14 TeVNpp collisions = 2 .1012 collisions

Muon triggers: ~ 100% efficiency, ~ 1kHz Electron triggers: Bandwidth limitation NPbPb central = 2 .108 collisions

Muon triggers: ~ 100% efficiency, < 1kHz

Pb-PB nominal run pp nominal run

Electron triggers: ~ 50% efficiency of TRD L1 20 physics events per event

Hadron triggers: NPbPb central = 2 .107 collisions

Hadron triggers: Npp minb = 2 .109 collisions


D0 K-+: Selection of D0 candidates

increase S/Bby factor ~103!

central Pb-Pb events


Expected Sensitivity to RAA

D0 K B e + X

15% systematic from efficiency corrections 15%12% theory uncertainty in energy extrapolation 8%

-- charm electron subtraction ~5%8% normalization error (<Ncoll>) 8%

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Heavy Quarks in view of the LHC