la fisica di alice - vietri sul mare, 31.05.2006 andrea dainese 1 andrea dainese infn legnaro...

La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 1

Andrea DaineseAndrea DaineseINFN LegnaroINFN Legnaro

Preparazione per laPreparazione per lamisura di produzione di Dmisura di produzione di D00

22°° Convegno Italiano sulla Fisica di ALICE Convegno Italiano sulla Fisica di ALICEVietri sul Mare (SA), 30/5-1/6, 2006Vietri sul Mare (SA), 30/5-1/6, 2006

+ misura del beauty + misura del beauty nel canale semi-elettroniconel canale semi-elettronico


Contents

Charm and beauty in ALICE: motivations

D0 K reconstruction

D0 cross section measurement in pp, pPb, Pb-Pb

A.D. & R.Grosso PhD theses, PPR v2

Beauty measurement via displaced electrons in pp and Pb-Pb

Antinori, A.D., Bombonati, Lunardon, Turrisi, Internal Notes to appear, PPR v2

Sensitivity in comparison to predictions, in pp (pQCD) and Pb-Pb (energy loss)


c and b production at the LHCImportant 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

LHC: NLO predictions (ALICE baseline for charm / beauty) system

:

s :

Pb-Pb (0-5% centr.)

5.5 TeV

p-Pb (min. bias)

8.8 TeV

pp

14 TeV

4.3 / 0.2 7.2 / 0.3 11.2 / 0.5

115 / 4.6 0.8 / 0.03 0.16 / 0.007

[mb] QQNNQQ

totN

LHC: Theoretical uncertainty of a factor 2--3

beauty charm HERA-LHC Workshop Proceedingsusing: Mangano, Nason, Ridolfi, NPB373 (1992) 295

2/5.0

2/5.0

GeV 0.55.4

GeV 8.13.1

,

RF

TRF

b

c

m

m

m

* M.Mangano

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

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


increasing s

HQs as a probe of small-x gluons 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

Cartoon

char

mbea

uty

Window on the rich phenomenology of high-density PDFsgluon saturation / recombination effects

non-linear terms in PDFs evolution

Possible effect: enhancement of charm production at low pt w.r.t. to standard DGLAP-based predictions

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


Pb-Pb collisions: Parton Energy Loss

Partons travel ~ 4 fm in the high colour-density medium

Energy loss (gluon radiation +

collisional?)

2 ˆ LqCE Rs

Casimir coupling factor:4/3 for quarks3 for gluons

Medium transport coefficient gluon density

Baier, Dokshitzer, Mueller, Peigne‘, Schiff, (BDMPS), NPB483 (1997) 291

(BDMPS)

Probe the medium

Carlos


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)

Detailed calculation confirms this qualitative feature, although effect is small and uncertainties significant (Armesto-Salgado-Wiedemann, 2003)

Exploit abundant massive probes at LHC & study the effect

by measuring the nuclear modification factor for D and B

Q

Dokshitzer, Kharzeev, PLB519 (2001) 199Armesto, Salgado, Wiedemann, PRD69 (2004) 114003

tBD

pp

tBD

AA

collt

BDAA dpdN

dpdN

NpR

/

/1)(

,

,,

222 ])/([

1

QQ Em

Gluonstrahlung probability


News from RHIC: heavy-flv decay electrons suppressed!

Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/0511257 Djordjevic, Gyulassy, Wicks, nucl-th/0512076

Radiative Radiative + Collisional

Energy loss calculations tend to underpredict suppression

Indirect measurement: non-photonic electrons (Dalitz and conversions subtracted); charm / beauty inclusive (uncertainty on pp baseline)


gq EE mass effect

Color-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

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

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


Beauty-to-Charm ratio: RB/D

Compare c and b same colour charge

Mass effect Enhancement of factor ~2, independent of (for )

)()()(/ tDAAt

BAAtDB pRpRpR

q̂/fmGeV 20ˆ 2q

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


D0 K-+ in ALICEExclusive reconstruction

direct measurement of the pt distribution

Weak decay with mean proper length c = 124 m

Large combinatorial background (dNch/dy)2

STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices

Measurement of Impact Parameters (ITS+TPC)

Measurement of Momenta (ITS+TPC)

Particle identification (TOF) to tag the two decay products


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

INFN Legnaro


Interaction vertex reconstruction in pp collisions

Vertex diamond stable for few hours; if beam focused, precise vertex position from average over many events

“Nominal” size of the beam: = 15 m in Pb-Pb

= 15 m in pp (L ~ 1032 cm-2 s-1)

150 m in pp (if L is reduced at ALICE IP to ~ 1030 cm-2 s-1)

In pp the E-by-E vertex position has to be reconstructed in 3D using tracks

Finding/fitting algorithm developed and optimized

vertextrackrd )(0

A.D. and M.Masera, ALICE-INT-2003-027.

as in Pb-Pbpp with charmpp min. bias


Selection of D0 candidates

increase S/Bby factor ~103!


Time-of-flight PID

TOF

Pb-Pb, dNch/dy=6000

Optimization for hadronic charmdecays was studied:minimize probability to tag K as

K id. required for D0 pt < 2 GeV/c


S/B

initial

(M3)

S/B

final

(M1)

Significance

S/S+B

(M1)

Pb-Pbcentral

5 10-6 10%~35

(for 107 evts,

~1 month)

pPbmin. bias

2 10-3 5%~30

(for 108 evts,

~1 month)

pp 2 10-3 10%~40

(for 109 evts,

~7 months)

Results

Note: with dNch/dy = 3000 in Pb-Pb, S/B larger by 4 and significance larger by 2

central Pb-Pb


Statistical Errors

(R.Grosso)


Feed-down from BeautyAt LHC energies

Fraction of D0 from chain b B0/B+ D0 not negligible

“Standard” NLO pQCD + Pythia fragmentation + BR:

Selections increase this ratio to ~10-15%

Results have to be eventually corrected for feed-down

systematic error from

uncertainty on b cross section

Possibility to have direct

estimate by D0 d0 (à la CDF)

%5~/ ccbb

%5.5)(/

)/()/(/

)(/

)(/0

000

0

0

DcdydN

XDBBBRBBbdydN

DcdydN

DbdydN


D0 cross section measurement

inner bars: stat. errorsouter bars: stat. pt-dep. syst. errorsnormalization error not shown: 9% Pb-Pb and p-Pb, 5% pp


B e + X: Detection strategy

1) Electron PID: reject most of the hadrons

2) d0 cut: reduce charm and bkg electrons (Dalitz, conv.)

3) Subtract (small) residual background (ALICE data + MC)

PrimaryVertex B

e

Xd0

rec. track


Electron identificationCombined info from TRD (trans. rad.) and TPC (dE/dx)

TRD rejects 99% of the and ALL heavier hadrons (pt > 1 GeV/c)

TPC further rejects residual pions (up to 99% at low p)

About 20% of electrons rejected

fraction of misidentified pions


Effect of electron identification (pp)


Errors Summaryd0 cut tuned vs pt to find best compromise between statistical and systematic errors from charm and bkg subtractions


Cross section of electrons from B

inner bars: stat. errorsouter bars: stat. pt-dep. syst. errorsnot shown: norm. error (5% pp, 9% Pb-Pb)

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


pp, s = 14 TeV

Comparison to pQCD predictions &perspectives for 1st month

1 year at nominal luminosity

1 month at ~ end 2007

Detector configuration:ITS + TPC + TOF

Expectations for first pp run:

Scaling of stat. errors according to Nevts

No dedicated cuts study

D0 K


pp, s = 14 TeV

Comparison to pQCD predictions &perspectives for 1st month

1 year at nominal luminosity

1 month at ~ end 2007

Detector configuration:ITS + TPC + TRD (~1/5 at end ’07)

Expectations for first pp run:

Scaling of stat. errors according to Nevts

No dedicated cuts study

B e + X


TDpp

TDAA

collT

DAA dpdN

dpdN

NpR

/

/1)(

Tepp

TeAA

collT

eAA dpdN

dpdN

NpR

/

/1)(

Charm and Beauty E Loss : RAA

mb = 4.8 GeV

Low pT (< 6–7 GeV)Also nuclear shadowing (here EKS98), in-medium hadr…

High pT (> 6–7 GeV)Only parton energy loss

D0 K B e + X



Interpretation of RAA: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 @ LHC:• kaons and hyperons• D meson RCP sensitivity under study

E lossonly

Statistical errors for107 min. bias Pb-Pb evts


Heavy-to-light ratios: RD/h


)()()(/ thAAt

DAAthD pRpRpR


Heavy-to-light ratios: RB/D


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


SummaryFeasibility studies for D0 and B measurements in pp, Pb-Pb (and pPb,only D0) carried out

many critical items identified and partially addressed: PID, d0 & primary vertex measurement, feed-down from beauty to charm

Results are very promisingpt coverage in the range 1--18 GeV/c for D0 and electrons from B

some physics “applications” identified and studied

First measurements in pp already after “first month” (107 evts)

D0: coverage up to pt ~ 7 GeV/c

B: total cross section; not much on pt dependence

Getting ready for first collisions:Long to-do list presented at May PWG3

Analyses to be performed / tuned on 2006 pp production (PDC06)

la fisica di alice - vietri sul mare, 31.05.2006 andrea dainese 1 andrea dainese infn legnaro...

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