manceau@clermont.in2p3.fr1

B hadron cross-section via single muonsin pp collisions at 14 TeV

with ALICE @ LHC

L. Manceau (LPC Clermont-Ferrand)

• Heavy ion collisions• Heavy flavours: QGP probes• ALICE detector overview• Method/Results• Summary/Outlooks

manceau@clermont.in2p3.fr2

Heavy ion collisions

machine SPS RHIC LHC

sNN (GeV) 17 200 5500

TQGP/Tc 1.1 1.9 3.0-4.2

ε (GeV/fm3)

3 5 15-60

τQGP (fm/c) ≤ 2 2-4 ≥ 10

Central Pb-Pb (Au-Au)

LHC: unprecedented conditions to study hot QCD matter

σc(LHC)= σc(RHIC) × 10

σb(LHC)= σb(RHIC) × 100

Super Proton Synchroton CERN (1986-2003):

• 1986-1994: early work on heavy ions

• 1994-2003: 7 experiments → NA44, NA45, NA49, NA50/60, NA52, WA97/NA57, WA98

Relativistic Heavy Ion Collider Brookhaven National Laboratory (2000):

• 4 experiments: STAR, BRAHMS, PHOBOS, PHENIX

manceau@clermont.in2p3.fr3

Open flavours:Quarkonia:

• Heavy mass → quarks are produced very early in the collision

• Interaction with deconfined medium

bdBucDge ,:.. 0

bbccJge b ,:..

Quarkonia suppression as a signature of deconfinement:

• Color screening of static potential between heavy quark pair → J/Ψ suppression

Matsui and Satz, Phys. Lett. B 178 (1986) 416

• Tsup. determined by lattice QCD

• Screening competes with recombination of uncorrelated pairs of heavy quarks?

vacuum

QGP

Heavy-flavours as probes of QGP (I)

capproach

hard processes

Sensitivity to

temperature

manceau@clermont.in2p3.fr4

Heavy quark Energy loss:

• collisions

• gluonstralhung:

• αs: strong interaction coupling const.

• CR: color couplling factor (q(g)→4/3(3))

• : medium transport coefficient

• L: path length

Heavy-flavours as probes of QGP (II)

2ˆ LqCE Rs

tpp

tAA

collAA dpdN

dpdN

NR

1 Key observable (J/Ψ, E loss…): nuclear modification factor →

QGPHadron gas

Sensitivity to energy densityq̂

+ Dead cone effect → gluon radiation suppressed at θ < mQ/EQ Q

Q Q

g

θ

Average number of NN collisions in a AA collision

• If no hot effects:

- RAA<1 low pt (shadowing)

- RAA=1 high pt

• hot effects → suppression:

- RAA<1 even at high pt

hard physics domain

soft physics domain

No hot effects

manceau@clermont.in2p3.fr5

SPS & RHIC results on heavy flavours

SPS: J/Ψ suppression in Pb-Pb• Debye screening not a unique scenario

(statistical hadronisation, comovers…)• Models cannot reproduce data in In-In

RHIC: J/Ψ suppression in Au-Au• Large uncertainties on cold nuclear effects• Larger suppression at forward angles?

RHIC: charm quenching ~ light hadron quenching• Non photonic vs. hadron RAA

• A challenge for models (recombination…)• Experiments disagree on charm cross-section (p-p)

Phys. Rev. C77 (2008) 024912

Phys. Rev. Lett. 98 (2007) 192301

Phys. Lett. B477 (2000) 28

manceau@clermont.in2p3.fr6

• Large theoretical uncertainties on cross-sectionshep-ph/0601164

Charm Beauty

• Unravel NLO processes

)(

d

D.L. Vititoe, PhD, Arizona Univ. (1996) (D0 exp.)

Testing NLO pQCD with heavy flavours

B[D] hadron cross-section in p-p @ LHC: motivations (I)

σ(B) [σ(D)] in p-p is the most natural normalisation for:• σ(Υ) [σ(J/Ψ)] in p-p, p-A & A-A: production, absorption, suppression, recombination (?)• σ(J/ψ) in p-p (→ p-A & A-A): N(B→J/Ψ)/N(direct J/Ψ) ~ 20% in 4π

→ Informations on the thermodynamical state of QCD medium : Ec, Tc

manceau@clermont.in2p3.fr7

B[D] hadron cross-section in p-p @ LHC: motivations (II)

New ratio to understand energy loss → mass, color charge

• R(D)/h color charge dependence • R(B)/h mass dependence • RB/D isolate mass dep.

N. Armesto et al., Phys. Rev. D 71 (2005) 054027 J. Phys. G 35 (2008) 054001

Measurement of σ(B) [σ(D)] in p-p is mandatory for understanding:• σ(B) [σ(D)] in p-A: shadowing & anti-shadowing → gluons pdf in nucleus• σ(B) [σ(D)] in A-A: energy loss → initial density of gluon, dissipative properties

(transport coefficient)

tDB

pp

tDB

AA

coll

DBAA dpdN

dpdN

NR

][

][][ 1

Dead cone effect

Stronger coupling of gluons with the medium

Light quarks (→ light hadrons) mainly created by gluons fusion

manceau@clermont.in2p3.fr8

Heavy ions @ LHC

ALICE

CMS

ATLAS

manceau@clermont.in2p3.fr9

ALICE @ LHC

• Central barrel (-0.9 ≤ η ≤ 0.9): (di-)electrons, photons, hadrons

• Muon spectrometer (-4 ≤ η ≤ -2.5): (di-)muons

• Backward, forward small acceptance detectors: multiplicity, centrality, luminosity

Muon Spectrometer (-4 ≤ η ≤ -2.5)

manceau@clermont.in2p3.fr10

ALICE muon spectrometer

Tracking: measurement of µ pt

• Position resolution < 100 μm (bending plane)

→ ΔM < 100 MeV/c² @ 10 GeV/c²

• 1.1 M read-out channels

Trigger: select high pt muons ( ~1GeV, ~2GeV)

• Time resolution < 2 ns• Rate < 1kHz• Decision in < 800 ns• 21000 read-out channels

- 4 ≤ η ≤ -2.5

dipole magnet

absorber

beam shield

muon filter

trigger chambers

tracking chambers

manceau@clermont.in2p3.fr11

B hadron cross-section

via single muons: method 1. Extract N( B) from “data”

– π/K subtraction– Combined Fit

2. Correct for integrated luminosity, detection efficiency, acceptance & decay kinematics

3. Get differential inclusive B hadron cross-section

MC

B

y

BB

B

y

BB

ppyd

d

L

Npp

yd

d

)(

)(1

dt

)()( 5.24

mintt

5.24

mintt

21,5.24: ttt pppy

manceau@clermont.in2p3.fr12

Method widely used and well documented

1. UA1: collisions @ , single muons & dimuons

C. Albajar et al., PLB 213 (1988) 405

2. CDF: collisions @ , single electrons

F. Abe et al., PRL 71 (1993) 4

3. D0: collisions @ , single muons & dimuons

B. Abbott et al., PLB 487 (2000) 264-272

TeVs 63.0

TeVs 8.1

TeVs 8.1

2.

1.

3.

ALICE :

4. collisions @ , single electrons

F. Antinori et al., ALICE-INT-2006-015

5. collisions @ , single electrons

F. Antinori et al., ALICE-INT-2005-33

6. collisions @ , single muons & dimuons

R. Guernane et al., ALICE-INT-2005-018

TeVs 14

TeVs 5.5

TeVs 5.5

4. 5.

6.

pp

pp

pp

pp

PbPb

PbPb

manceau@clermont.in2p3.fr13

• Physics Data Chalenge 2006

• Full simulation on grid

generation → reconstruction

• 1·106 single muon events

• Efficiency correction for muon detection in the acceptance

• Hypothesis: μ ← π,K perfectly subtracted

• Large yield over a broad pt range → Statistical error negligible

• PDC06:

– Extrapolated to 20 GeV

– Scaled → 3 scenarii:1. L=1030 cm-2 s-1 , T=1 month2. L=3.1030 cm-2 s-1, T=1 month3. L=3.1030 cm-2 s-1 , T=1 year(Nominal)

Simulation input & statistic estimates

manceau@clermont.in2p3.fr14

Extraction of N(µ←B)

• T: total number of muons • B: number of muons from

B → free parameter

• fc (fb) model dependent shape distribution of muons from D(B) decay

• R: number of muons from B over number of muons from D → free parameter fixed within 30%

Combined fit: (T-B) (fc+R·fb)

µ←B off by 0.5%

Chi2/ddl=0.07

manceau@clermont.in2p3.fr15

Systematic uncertainties

1. Theoretical predictions for D & B:

2. MC simulation: Get μ dN/dpt & Fit μ dN/dpt

→ biased shapes fc & fb

3. Investigate systematics

Charm

Beauty

Systematic uncertainties: 20%

µ←B off by 1%

µ←B off by 19%

µ←B off by 36%

1. Hadrons

BeautyCharm

2. Muons

3. Fits

hep-ph/0601164

manceau@clermont.in2p3.fr16

Decay kinematics corrections

• F(µ←B): Pythia simulation• 90% of B → μ in the

acceptance have a transverse momentum larger than pt

min

• ptmin: minimisation of the

correction dependence on shape distributions used in Pythia

MC

B

y

BB

B

y

BB

ppyd

d

L

Npp

yd

d

)(

)(1

dt

)()( 5.24

mintt

5.24

mintt

F(μ←B)

Ptmin = 6.4 GeV/c

F(μ←B) = 48.31

Muons pt 4-6 GeV/c

Ptmin

90%

manceau@clermont.in2p3.fr17

Inclusive differential B hadron cross-section

• Input distribution well reconstructed• 82% of the total cross-section is reconstructed • Statistical errors negligible (even in scenario 1 !)• Statistical errors from F(μ←B): from 0.1% to 6% at high pt

min

• Systematic errors from F(μ←B) negligible• Systematic errors from fit 20%• Error from normalisation ~5% (not included)• Results in agreement with σ(B) via dimuons (dimuons by X. Zhang)

manceau@clermont.in2p3.fr18

Heavy flavours and QGP @ LHC:• Probes: quarkonia + energy loss

• Key observable: RAA

B cross-section extraction:• Extraction of B cross-section for 3 ≤ ptmin ≤ 26GeV/c, statistical

errors are negligible, systematic errors are: 20%

Outlooks:• Realistic π/K subtraction → another source of error on muon yield (especially at low pt )

• Does this allows to extract σ(D) simultaneously ?

(work in progress)

Summary/Outlooks

Realistic distributions

including background

µ spectrometer

Interaction Point (IP)

Different distances between IP and muon

decay allow to discriminate signal (b/c) from background (π/K)

manceau@clermont.in2p3.fr19

Back up

manceau@clermont.in2p3.fr20

Inclusive differential B hadron cross-section via single electrons

C. Bombonati et al., PWG3, March 07C. Bombonati et al., PWG3, March 07 ALICE-INT-2006-015ALICE-INT-2006-015

Strategy:

1. Electron identification: dE/dx TPC, TRD

2. Impact parameter cut d0: ITS

cτ of B ~ 500µm → displaced vertex for electrons ~100 µm.

(π0 background reduction → loss of statistics)

• Different method → different stat. & different syst. → cross-check

Transverse Plane

TRD

TPC

ITS

manceau@clermont.in2p3.fr21

Electrons in central barrel

C. Bombonati et al., PWG3, March 07C. Bombonati et al., PWG3, March 07ALICE-INT-2006-015ALICE-INT-2006-015

manceau@clermont.in2p3.fr22

Efficiency correctionGlobal efficiency for μ detection in the acceptance (trigger & tracking):

framework developed by Z. Conesa del Valle (ALICE-Physics Week, Munster)

• Need some smoothing• New framework in progress: N. Le Bris

manceau@clermont.in2p3.fr23

Realistic input

PDC06

L=3.1030 cm-2 s-1 , T=107 s (Nominal)

L=1030 cm-2 s-1 , T=106 s

μ←πΚ perfectly subtracted

L=3.1030 cm-2 s-1, T=106 s

Realistic input:

• 3 statistical scenarii

• Fit PDC06: extrapolation 2 GeV/c ≤ pt ≤ 20 GeV/c• NLO calculation:

M.L. Mangano, P. Nason and G. Ridolfi,

Nucl. Phys. B 373 (1992) 295 →

mbcc 2.11

• Charm cross-section corrected

• Extrapolation to pt 20 GeV/c

• 3 statistical scenarii

PDC06:

• 106 single muon events

• 2 GeV/c ≤ pt ≤ 10 GeV/c

• Charm underestimated: → mb

cc677.5

manceau@clermont.in2p3.fr24

Statistics estimates

Scenarii:1. L=1030 cm-2 s-1 , T=106 s2. L=3.1030 cm-2 s-1, T=106 s3. L=3.1030 cm-2 s-1 , T=107 s (Nominal)

Large yield over a broad pt range (even in scenario 1 !)→ Statistical errors negligible

manceau@clermont.in2p3.fr25

Systematic uncertainties (I)

• Pythia is tuned to reproduce « Hera LHC » predictions on D and B hadron production cross-section: hep-ph/0601164

Hera LHC

D hadron B hadron D hadron B hadron

manceau@clermont.in2p3.fr26

Systematic uncertainties (II)

1. Get μ dN/dpt from D & B

2. Fit μ dN/dpt

3. Investigate systematics

1 Hadrons 2 Muons 3 Fit

manceau@clermont.in2p3.fr27

Hera LHC

Systematic uncertainties (IV)

Systematic errors:

• ~ Pt independent

• Charm ~ 15%• Beauty ~ 20%

Allow to constrain models

.

..

perf

perfsyst

N

NN

N

N

manceau@clermont.in2p3.fr28

Systematic error on decay kinematics & acceptance correction

Systematic error is negligible

90%

60%

20%

90%

60%

20%

manceau@clermont.in2p3.fr29

Sources of systematic uncertainties

Sources Beauty Charm

Fit 20% 15%

Decay kinematics negligible negligible

Normalisation 5% 5%

Total (quadratic summation)

~ 21% ~ 16%

manceau@clermont.in2p3.fr30

π/K subtraction: simulation input• Physics Data Chalenge 2008 • Full simulation on grid

generation → reconstruction• 2·105 single muon events• Efficiency correction for muon

detection in the acceptance• Realistic π/K background

Primary π/K fly longer

than heavy flavours

Sources cτ

B mesons 491.1 µm

D mesons 311.8 µm

π 7.8045 m

K 3.713 m

absorber

Interaction Point (IP)

µ spectrometer

manceau@clermont.in2p3.fr31

b/c

π/K subtraction: simulation input• Physics Data Chalenge 2008 • Full simulation on grid

generation → reconstruction• 2·105 single muon events• Efficiency correction for muon

detection in the acceptance• Realistic π/K background

Primary pi/K fly longer

than heavy flavours

Sources cτ

B mesons 491.1 µm

D mesons 311.8 µm

π 7.8045 m

K 3.713 m

Heavy Flavours

Primary π/K

Secondary π/K

IP

IP

IP

absorber

absorber

absorber

µ

π/Kµ

π/Kπ/K

µ

manceau@clermont.in2p3.fr32

IP absorberOrigin

z = 0 zabsorption

Point where π/K is

absorbed

zvertex

d = 90 cm a ~ 40 cmz

Primary π/K subtraction method

IP displacement:

• Gaussian smearing of the µ vertex distribution

• π/K prim. fly different distances event by event:

- IP closer to absorber → less proba. to decay before absorption → less µ produced

- IP further to absorber → more proba. to decay before absorption → more µ produced

µ counts decrease ~ linearly with IP to absorber distance

dN/dz slice (pt = 1GeV)

Fit dN/dz slice for each pt

pt = 1GeV

α = 39+-13

β = 6672+-172

Fit fonction :

N : normalisation →

σ = 5.3 cm

α, β: free parameters:

• π/K prim. → dN/dpt = (a+d)α(pt)

• b+c+ π/K sec. → = dN/dpt = β(pt)

1²2

²

z

eN

)]()([²2

²

tt

z

pzadpeN

d²N/dptdz

dN/dz

manceau@clermont.in2p3.fr33

Secondary π/K subtraction (I)

Cut µ tracks wich don’t match with a trigger signal:

• Low energy µ (mainly µ ← π/K) → don’t pass through the iron filter

• High energy µ (mainly µ ← b,c) → deliver a trigger signal

No cutMatching

with trigger Rejection rate:

• b →15%

• c → 23%

• π/K prim. → 69%

• π/K sec. → 74%

Subtraction method doesn’t allows to substract secondary π/K

manceau@clermont.in2p3.fr34

Matching with trigger

Secondary π/K subtraction (I)

Subtraction method doesn’t allows to substract secondary π/K

Cut µ tracks wich don’t match with a trigger signal:

• Low energy µ (mainly µ ← π/K) → don’t pass through the iron filter

• High energy µ (mainly µ ← b,c) → deliver a trigger signal

No cut Rejection rate:

• b →15%

• c → 23%

• π/K prim. → 69%

• π/K sec. → 74%

manceau@clermont.in2p3.fr35

Secondary π/K subtraction (II)

Distance of Closest Approach : distance between the extrapolated track and the interaction vertex, measured in the plane orhogonal to the beam pipe and containing the vertex itself

Cut on DCA: → b/c DCA< < π/K prim. DCA < π/K sec. DCA

Cut rejecting a

maximum of π/K

π/K sec.

π/K prim.

beautycharm

Rejection rate

Matching trigger cut is already applied

DCA π/K prim.

DCA π/K sec.

DCA

b/c

π/K sec.π/K prim.

µ←b/c

µ←π/K prim.

µ←π/K sec.

Cut rejecting a

maximum of π/K

manceau@clermont.in2p3.fr36

Subtraction results

No Cut Trigger Matching

Trigger Matching +

DCA cut

DCA cut chosen to reject:

~ 5% b & c (saving statisic)

~ 10% primary π/K

~ 40% secondary π/K

Fit method → Primary π/K subtracted until 0.5 GeV(below no effeciency correction)

Matching Trigger + Cut DCA→ Secondary π/K subtracted until 1 GeV

manceau@clermont.in2p3.fr37

D hadron cross-section