b hadron cross-section via single muons in pp collisions at 14 tev with alice @ lhc
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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
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