Open Heavy Flavour Measurement using Leptonic Final States

Open Heavy Flavour Measurement using Leptonic Final States at the ALICE Experiment

MinJung Kweon for the ALICE CollaborationPhysikalisches Institut, Universität Heidelberg

December 03rd 2010, December LHC Physics day for LPCC, CERN

MinJung Kweon, University of Heidelberg 03 December 2010, December LHC Physics day for LPCC, CERN 2

Open heavy flavour measurement via lepton channels

Proton-proton collisions- Measurement of heavy flavour production(charm and beauty) in p+p will provide important test of pQCD in a new energy domain and heavy ion reference

Heavy-ion collisions- Heavy quark energy loss in the medium

Complementary to heavy flavor hadronic decays(Andrea’s talk)

Measurement at lower energy

σ cc = 567 ± 57(stat) ±193(sys)µbσ bb = 3.2−1.1

+1.2 (stat)−1.3+1.4 (sys)µb

PHENIX @200 GeV, p+p

PRL 97,252002 (2006)

PRL 103,082002 (2009)

system:√sNN:

p+p14 TeV

charm/beauty

p+p7 TeV

charm/beauty

11.2/0.5 6.9/0.23

0.16/0.007 0.10/0.003

σ NNQQ[mb]

NtotalQQ

Cross sections cc(bb) at LHC x10(x100) larger than at RHIC

MNR code (NLO): Mangano, Nason, Ridolfi, NPB373 (1992) 295Theoretical uncertainty of a factor 2-3

Branching Ratios:c ⟶ l + X 9.6 %b ⟶ l + X 11 %b ⟶ c ⟶ l + X 10 %

High rate of lepton production from semi-leptonic decay

MinJung Kweon, University of Heidelberg 03 December 2010, December LHC Physics day for LPCC, CERN

Leptons in ALICE

MinJung Kweon QM09, Knoxville, 02 April 2009 5

A Large Ion Collider Experiment

ACORDE

EMCAL

TRD

TPC

ITS

TOF

PHOS

FMDV0

ZDC~116m from I.P.

DIPOLEMAGNET

ABSORBER

TRACKINGCHAMBERS

MUONFILTER

TRIGGERCHAMBER

ZDC~116m from I.P.

Collaboration: 31 countries, 109 institutes, > 1000 people

3

Muons at Forward Rapidity(-4<η<-2.5)

Inner Tracking SystemTime Projection ChamberTransition Radiation DetectorTime Of FlightElectroMagnetic Calorimeter

Electrons at Mid Rapidity (|η|<0.9)

Muon Spectrometer

capable from ~ 100 MeV to above 50 GeV


Trigger and Data Sample for p+p at 7 TeV

“Minimum bias”, based on interaction trigger:

• SPD(|η|<2) or V0-A(2.8<|η|<5.1) or V0-C(-3.7<|η|<-1.7)

• at least one charged particle in 8 η units

• ~95% of σinel

Single-muon trigger:•Muon trigger chamber and MinBias Trigger detectors

• forward muon in coincidence with Min Bias

Since March 31st 2010 until PbPb collision started, collected • ~8.5x108 minimum bias triggers

• ~1.3x108 muon triggers

Analysis shown here is based on• 1.6 nb-1 for electrons

• 3.49 nb-1 for muons

4

﹜﹜Activated in coincidence with the BPTX beam pickups

Trigger

Data


Analysis Approach via Electrons

(1) Measure inclusive electron transverse momentum spectrum

(2) Build background contributions spectrum described with an electron cocktail (photonic, Dalitz/dielectron decays of mesons, weak kaon decay, direct radiation, J/ψ and Υ)

(3) Measure heavy flavor semi-electronic decays by subtracting (2) from (1)

5

Heavier meson sources(η, η', ρ, ω, φ): implemented via mT scaling(verified for ƞ) Photon conversion sources: - Calculate photon conversion in the beam pipe and 1/3 of the first pixel layer (0.5 % X0)- Use the ratio of conversion to Dalitz electrons to estimate the e± contributions

Electron Cocktail

Conv.Dalitz

=BRγγ × 2 × 1− e

−7 9×XX0⎛

⎝⎞⎠ × 2

BRDalitz × 2

π0 Dalitz decay sources: the π0 measured spectrum(Fit with Hagedorn function and use PYTHIA

electron decay kinematics)


Electron Identification

6

[J. Phys. G: Nucl. Part. Phys. 34 (2007) S769–S773]

[Phys.Lett.B666:533 (2008)]

I Vitev, A Adil and H van Hees,

Currently up to 4 GeV/c based on the Time Projection Chamberand the Time of Flight detector (TOF resolves TPC crossings)

momentum p (GeV/c)1 10

dE/d

x in

TPC

(a.u

.)

0

50

100

150

200

250

dp

K

e

pp @ 900 GeV

ALICE performancework in progress

momentum p (GeV/c)0 0.5 1 1.5 2 2.5 3 3.5 4

0.4

0.6

0.8

1

1

10

210

K

pALICE Performance

= 900 GeV (2009 data)sp+p at

TPC

TOF

Soon extend to higher momentum with the Transition Radiation Detector and the ElectroMagnetic Calorimeter


Electron Identification in Steps

7

Kaon & Proton Rejection with TOF(3 from the electron line in TOF)

Current ToF resolution: 130 ps ⟶ clean rejection of

K (for p < 1.5 GeV/c)p (for p < 3 GeV/c)

Further hadron rejection with TPCMomentum dependent cut on number of sigmas from the electron line in TPC

Subtract remaining hadron background

!"#$%&'(#$)*&+",-)./0&12%/34/&')*560&7)$"68"*&9:0&;:9:<=>#/43)4423?@/3=A"&&&&&&&&&& 9B

!#A*).&C).-#63.#-3).&&&&&D,&E&F&G"HI4J

K/"!"#$#&DL1C&AMIANJ&-)&"/-36#-"&-2"&*"/3A5#(&2#A*).&4).-#63.#-3).

! 1#*#6"-*3O"&-2"&4).-#63.#-3).&$/&6)6".-56&&P&

! K/"&-2"&,#*#6"-*3O#-3).&-)&4)**"4-&-2"&3.4(5/3$"&/,"4-*560&-)&/58-*#4-&-2"&*"/3A5#(&2#A*).&4).-#63.#-3).

%

!

Gaussian fits of TPC dE/dx distributions in momentum slices ⟶ hadron contamination as function of momentum p (< 4 GeV/c)

e

π


Uncorrected Inclusive Electron Spectrum

8

Corrections to the raw electron spectrum for- geometrical acceptance- reconstruction efficiency- detector resolutionwith PYTHIA+PHOJET


Excess from open heavy flavors (including J/ψ, direct radiation)

Systematic errors on input π0 spectrum (+20% 40%) is propagated to the cocktail (Will be reduced in near future!)

No systematic errors are shown yet on the corrected inclusive electron spectrum

Cocktail and Corrected Inclusive Electron SpectrumRatio Data/CocktailData & Cocktail


Perspectives

10

] [electron

TPC dE/dx - <dE/dx>|-10 -8 -6 -4 -2 0 2 4 6 8 10

Cou

nts

1

10

210

310

410without TRD

with TRD

p = 2GeV/c

Pion Rejection Factor: 90Electron Efficiency: 0.51

ALICE Performance24/09/2010

!"#$%&#'()*%+,-,.%/0123%!)"45%67"4'#%37)89#':*;<="*8>'88?>@A*><$)%%%%%%%%%% ++

37)89#'="A:)9>8%2"7'#>B)9)#

6'#%)7)89#':%8":$>$"9)*%CD&2%$3E$FG.%3=2/0%87H*9)#*%"**>A:)$I !"#$%&'()&*+(&,-'

Provide good e/π separation from 1 to ~15 GeV/c Provide possibility to trigger (L1) on high pT

identified particles

Transition Radiation DetectorTPC dE/dx slice w/o and with TRD

ElectroMagnetic CalorimeterE/p distributions

Extend good electron identification at higher momentum with TRD and EMCal


Separation of beauty contributions

11

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CD#%;E)8>"79>)*

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! 3I8)77):9%(&-/&?%8"E"(>7>9>)*.>GE"89%E"#"G)9)#%#)*'7D9>':%R%%

PS%T,%UG%"9%-%M)NO8Q

Excellent vertex capabilities, impact parameter resolution → (~ 75 μm at 1 GeV/c)

Select electrons from heavy flavour decays via minimum distance of closest approach cuts ⟶ increase S/B

B jet tagging by selecting jets containing secondary vertex

!"#$%&'(#$)*&+",-)./0&12%/34/&')*560&7)$"68"*&9:0&;:9:<=>#/43)4423?@/3=A"&&&&&&&&&& B

C("4-*)./D&EF)&#.#(%/3/&#,,*)#42"/

!"#$%&'#$($")&)('%*%+&$!,

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! E2"&*"6#3.3.@&/,"4-*560&K*)6&2"#$%&K(#$)*&/"63Q"("4-*).34&A"4#%/0&3/&5/"A&-)&6"#/5*"&-2"&-./01234'-567/'624'03689:'-7.;;';3-91.2

<",#*#-"&8"#5-%

primary vertex

secondary vertex

p

r

ℓIP

quasi secondary

particle

Jet Axis

Analysis is ongoing in both directions


Strategy of µ± ←HF Extraction in pp data @ 7 TeV

Road Map

1 Event and track selection;

2 background subtraction;

3 correction for the acceptance and reconstruction efficiency;

4 obtain muon pt spectrum from HF, dNµ←HF /dpt |−4<η<−2.5;

5 convert muon pt spectrum to muon differential cross section, dσµ←HF /dpt |−4<η<−2.5;

6 disentangle open charm & bottom components, dσµ←D/B/dpt |−4<η<−2.5;

7 from muon cross sections to open charm & bottom cross sections, dσD/B/dpt |−4<η<−2.5.

X. M. Zhang (LPC, IOPP & QLPL) measure µ ←HF @ LHC/ALICE RQW 2010, 25-28 October 2010 7 / 18

Analysis Approach via Muons

The ALICE muon Spectrometer

1 Front Absorber: reduces hadron yield & decreases decay µ yield by limiting the free path ofprimary K/π.

2 Magnet Dipole: 3 Tm integrated field perpendicular to the beam axis.3 Tracking System:

multi-wire CPC with 1.1 M readout channels,position resolution � 100 µm ⇒ σp/p ∼ 1% ⇒ σM ∼ 100 MeV/c2 @ 10 GeV/c2(separation of Υstates).

4 Trigger System:

RPC with 21000 readout channels;time resolution < 2 ns, rate < 1 kHz & decision in < 800 ns;two programmable trigger pt cuts among,pt ∼ 0.5 GeV/c (min) pt ∼ 1 GeV/c (J/Ψ) pt ∼ 2 GeV/c (Υ).

5 MUON Filter: stop hadrons and low pt muon tracks.


(1) Remove hadrons and low pt secondary muons by requiring a muon trigger signal(2) Remove decay muons by subtracting MC dN/dpt normalized to data at low pt• alternative method: use muon distance of closest approach to primary vertex

(3) What is left are muons from charm and beauty (4) Apply efficiency corrections

Magnet

Absorber

TriggerChambers

TrackingChambers

Filter

B

Muon sources(MC)

Analysis approach


Background subtraction and Efficiency Estimation

13

Forward muons: Analysis!

Hard Probes 2010, Eilat, Israel, 15.10.10 Andrea Dainese! 18!

! Most delicate analysis step: subtraction of residual secondary and decay muons from !, K " pt > 2 GeV/c: secondary contribution small (<10%)

o from MC, and varied by 100% " subtract decay muons using two different PYTHIA

tunes (Perugia-0 and ATLAS-CSC)

! Resulting systematic error on HF muons: " 30% # 20% from low to high pt

! Efficiency >87% for pt>2.5 GeV/c

Forward muons: Analysis!

Hard Probes 2010, Eilat, Israel, 15.10.10 Andrea Dainese! 18!

! Most delicate analysis step: subtraction of residual secondary and decay muons from !, K " pt > 2 GeV/c: secondary contribution small (<10%)

o from MC, and varied by 100% " subtract decay muons using two different PYTHIA

tunes (Perugia-0 and ATLAS-CSC)

! Resulting systematic error on HF muons: " 30% # 20% from low to high pt

! Efficiency >87% for pt>2.5 GeV/c

Most delicate analysis step: subtraction of residual secondary and decay muons from π, K• pt > 2 GeV/c: secondary contribution small(~ 3 %)• use different PYTHIA tunes (Perugia-0 and ATLAS-CSC), vary secondary yields to evaluate systematics

Resulting systematic error on HF muons:• 30 % ⟶ 20 % from low to high pt

Efficiency > 87 % for pt > 2.5 GeV/c


Combined Charm and Beauty Cross Section

14

Preliminary Results

The pQCD (FONLL) calculation reproduces well the shape and is in agreement with data withinerrors.


The pQCD (FONLL) calculation reproduces the shape and is in agreement with data within errors.

Next steps: muon DCA method will allow to

reduce systematics due to background subtraction

improved spectrometer alignment already deployed

extend pt reach(up to 20 GeV/c) by increasing the statistics

Extract beauty cross section (dominates muon spectrum above few GeV/c)

prepare reference for Pb-Pb RAA

Int. Lumi:3.49 nb-1


Summary

15

An inclusive electron spectrum is compared to cocktails describing electrons from meson decays and photon conversions

An excess is observed at high pt coming from heavy flavor, J/ψ decays and direct radiation

Analysis based on impact parameter is ongoing to separate the beauty contribution

The differential production cross section as a function of pt of muons from HF have been measured in 2 GeV/c < pt < 6.5 GeV/c, −4 < η < −2.5

The results are in agreement with the FONLL predictions within errors

Analysis on the Pb+Pb data is ongoing!

Figure 3 shows the measured RAA and vHF2 of heavy-

flavor electrons in 0%–10% central and minimum biascollisions, and our corresponding !0 data [6,29]. Thedata indicate strong coupling of heavy quarks to the me-dium. While at low pT the suppression is smaller than thatof !0, RAA of heavy-flavor decay electrons approaches the!0 value for pT > 4 GeV=c although a significant contri-bution from bottom decays is expected at high pT . Thelarge vHF

2 indicates that the charm relaxation time is com-parable to the short time scale of flow development in theproduced medium. It should be noted that much reduceduncertainties and the extended pT range of the present datapermit the comparisons of RAA and v2 of the heavy andlight flavors.

More quantitative statements require theoretical guid-ance. Figure 3 compares the RAA and v2 of heavy-flavorelectrons with models calculating both quantities simulta-neously. A pQCD calculation with radiative energy loss(curves I) [30] describes the measured RAA reasonably wellusing a large transport coefficient q̂ ! 14 GeV2=fm,which also provides a consistent description of light hadron

suppression. This value of q̂ would imply a stronglycoupled medium. In this model the azimuthal anisotropyis only due to the path length dependence of energy loss,and the data clearly favor larger vHF

2 than predicted fromthis effect alone.

Npart0 50 100 150 200 250 300 350

AA

R

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1.4 = 200 GeVNNsAu+Au @

> 0.3 GeV/cT

: p±e > 3.0 GeV/c

T : p±e

> 4.0 GeV/cT

: p0π

FIG. 2 (color online). RAA of heavy-flavor electrons with pTabove 0.3 and 3 GeV=c and of !0 with pT > 4 GeV=c asfunction of centrality given by Npart. Error bars (boxes) depictstatistical (point-by-point systematic) uncertainties. The right(left) box at RAA ! 1 shows the relative uncertainty from thep" p reference common to all points for pT > 0:3#3$ GeV=c.

AA

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= 200 GeVNNsAu+Au @

0-10% central(a)

Moore &Teaney (III) T)π3/(2

T)π12/(2

van Hees et al. (II)

Armesto et al. (I)

[GeV/c]pT

0 1 2 3 4 5 6 7 8 9

HF

2v

0

0.05

0.1

0.15

0.2

(b)minimum bias

AA R0π > 2 GeV/c

T, p2 v0π

HF2 v±, eAA R±e

FIG. 3 (color online). (a) RAA of heavy-flavor electrons in0%–10% central collisions compared with !0 data [6] andmodel calculations (curves I [30], II [31], and III [32]). Thebox at RAA ! 1 shows the uncertainty in TAA. (b) vHF

2 of heavy-flavor electrons in minimum bias collisions compared with !0

data [29] and the same models. Errors are shown as in Fig. 2.

[GeV/c]pT

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)]-2

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eV/c

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1 10×10-20% 0 10×20-40% -1 10×40-60% -2 10×60-92%

/42mb-2 10×p+p = 200 GeVNNsAu+Au @

FIG. 1 (color online). Invariant yields of electrons from heavy-flavor decays for different Au" Au centrality classes and forp" p collisions, scaled by powers of 10 for clarity. The solidlines are the result of a FONLL calculation normalized to thep" p data [18] and scaled with hTAAi for each Au" Aucentrality class. The inset shows the ratio of heavy-flavor tobackground electrons for minimum bias Au" Au collisions.Error bars (boxes) depict statistical (systematic) uncertainties.

PRL 98, 172301 (2007) P H Y S I C A L R E V I E W L E T T E R S week ending27 APRIL 2007

172301-5







Npart0 50 100 150 200 250 300 350

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172301-5

Exciting to see the result of heavy quark energy loss at LHC!

We got surprise by the result of heavy quark energy loss at RHIC!


BACKUP SLIDES

16

MinJung Kweon, University of Heidelberg 03 December 2010, December LHC Physics day for LPCC, CERN 17!"#$%&#'()*%+,-,.%/0123%!)"45%67"4'#%37)89#':*;<="*8>'88?>@A*><$)%%%%%%%%%% -B

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Cocktail Ingredient(Other mesons and Conversion electrons)

19

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2'8C9">7%1:A#)$>):9*=)*':*%":$%&?'9':%2':4)#*>':*

!"#$%"&'(")*+),

! 1:87D$)$E%-.'-/.'0.'1.'2

! 1FG7)F):9)$%4>"%(3')4#5%+6


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!"#$%"&'(")*+),

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µ ←Primary K/π Subtraction: Vertex Unfolding Fitting

d2Nµ

dptdvz=

d2Nc/bµ

dptdvz+

d2Nprimary K/πµ

dptdvz+

d2Nsecondary K/πµ

dptdvz(neglected)

1

ρ(vz )

d2Nµ

dptdvz∼

d2Nc/bµ

dptdvz+ (L+ vz )× (

1

L+ < vz >

d2Nprimary K/πµ

dptdvz)

Method has been already successfully tested on simulations;

expected linear increase of muon yield w/ the vertex position evidenced with data;

high statistics is needed.



Systematic Error

background subtraction: from 20% to 7% with pt ;

alignment: 2%× pt ;

detector response: 5%;

model bias: 20%;

min-bias cross section: 10% (not included);

total: from 29% to 24.4% with pt ;



Charm and Beauty Separation

22

Outlook: σB/D in pp @ 14 TeV via (di)muons

Simulated Results

input distributions are well reconstructed;

nice agreement between single muon and dimuon channels;

systematic errors are 20% for B and D in the single muon channel and, 15% for B and 20% for D in thedimuon channel;

92% (33%) of σB (σD ) is reconstructed via single muons and, 84% (34%) of σB (σD ) is reconstructedvia dimuons;

this analysis procedure is currently applied to pp data at 7 TeV.


Input distributions are well reconstructed; nice agreement between single muon and dimuon channels

Systematic errors are 20% for B and D in the single muon channel and, 15% for B and 20% for D in the dimuon channel

This analysis procedure is currently applied to p+p data at 7 TeV

D and B separation by fitting with pQCD shapes

Simulated results in p+p @ 14 TeV via (di)muons

PYTHIAPYTHIA

Documents

Open Heavy Flavour Measurement using Leptonic Final States