Investigating heavy quark energy loss with lepton-tagged jets Jennifer Klay California Polytechnic...

Investigating heavy quark energy loss with lepton-tagged jets

Investigating heavy quark energy loss with lepton-tagged jets

Jennifer KlayCalifornia Polytechnic State University

San Luis Obispo

Jennifer KlayCalifornia Polytechnic State University

San Luis Obispo

16-19.July.2007 ETD-HIC 2007, Montreal QC 2

hadrons

q

q

?

Theoretical MotivationTheoretical Motivation

Light quark(q): up, down, strange m ~ 300 MeV

Heavy quark(Q): charm, bottomm ~1-5 GeV

Gluon(g): self-interacting mediatorof strong force

Quarks (CR=4/3) vs. Gluons (CR=3) colour

charge dependence

€

ΔEBDMPS

∝α s CR ˆ q L2

Strong coupling

Casimir factor

Transport coefficient

Medium size

«Dead-cone» effect for θ0 < mQ/EQ

mass dependenceY.L.Dokshitzer and D.E. Kharzeev, Physics Letters B519, 199 (2001)


Experimental LandscapeExperimental Landscape

Di-hadron suppression

Photon vs. Hadron suppression

Non-photonic electron suppression similar to light hadrons

STAR, Phys Rev Lett 91, 072304


Heavy Quark Production in PYTHIAHeavy Quark Production in PYTHIA

E. N

orrb

in &

T. S

jost

rand

, Eur

. Phy

s. J

. C17

, 137

(20

00)

Pair Creation Leading Order: Back-to-back in azimuth (gluon in (c) causes kinematic shift but cross-sections determined by LO 2 2)

Flavour Excitation Scattering of Q(Q) out of initial state into final state by gluon or light quark (Virtuality of hard scatter must be > mQ

2)

Gluon Splitting No QQ in hard-scatter, but pair created within parton shower or during the fragmentation process of a gluon or a light quark

QCD Process classification: 2, 1, or 0 heavy flavours in hard-scattering final state


b-Jet Kinematics in PYTHIAb-Jet Kinematics in PYTHIA

Normalized to unit area for shape comparison

E. Norrbin & T. Sjostrand, Eur. Phys. J. C17, 137 (2000)

Similar results in HERWIG, ISAJET

See R.D. Field, Phys. Rev. D65 (2002) 094006 hep-ph/0201112

ΔΔpT

Leading order pairs come out back-to-back


How to find them?How to find them?

Semi-leptonic decay channel provides the signal sources to look for…

Find the jet with a B through the e,μ decay and you have your parton…

bB- (38%), B0 (38%), B0s

(11%), Λ0b(13%)

BlX, BDXlYBl- (9.30%), BDXl-Y(2.07%)Bl+(1.25%), BDXl+Y(7.36%)

bb->dilepton 0.020/eventBl1Xl1l2Y 0.018/event

Lin and Vogt, Nucl.Phys. B544 (1999) 339-354

Backgrounds:• Photonic electrons : 0, Dalitz, gama conversions Remove with Minv cut• Mis-identified particles• Leptons from underlying event


Lepton Jets at the TevatronLepton Jets at the Tevatron

CDF, Phys. Rev. D69 (2004) 072004 hep-ex/0311051

Herwig Simulation: bb di-jets within |η|<1.5

p+p, 1.8 TeV

Event selection: (69K e + 15K μ)

- di-jet with ETuncorr>15 GeV

(<ETparton> ~ 20 GeV)

- pT>8 GeV lepton within ΔR < 0.4

- Correction for fake tags

Good agreement between experiment/theory

In simulation these are due to Gluon-splitting


Heavy Quark Correlations at RHICHeavy Quark Correlations at RHIC

charm production

trigger side

probe side3.

83%

5

4%

~

10%

statistical errors only

A. Mischke, SQM2007

scaled by 2.86

essentially from B decays only

~70% from charm

~30% from beauty


Jet rate comparisonJet rate comparison

LHC is a jet factory

Full complement of hard observables accessible:

• Identified spectra, RAA

• Multi-hadron correlations

• Jets: Fragmentation function modifications, -jet coincidences, tagged heavy quark jets, …

• Quarkonia


Large Hadron Collider at CERNLarge Hadron Collider at CERNLatest Schedule:

Summer 2008: commission 14 TeV p+pWinter 2009: first 5.5 TeV Pb+Pb collisions?

Lac Leman

ALICE

CERN

SPS

LHC


Spectrum of jet observablesSpectrum of jet observables

Leading particle Spectra

Multi-hadron correlations

Jet reconstruction

Jet ET ~ 10-30 GeV

RAA

Fragmentation functions

Jet ET ~ 50-200 GeV

Tagged jets (-jet, b-jet)

106/mo.

10 GeV 20 GeV 50 GeV 100 GeV 200 GeV

1/event

Complementarity with RHIC

Exclusive to LHC, completely new regime

BUT! Need a trigger


Heavy quark jet productionHeavy quark jet production

AB

C

E. Norrbin & T. Sjostrand, Eur. Phys. J. C17, 137 (2000)

RHIC LHC

Charm 10 250

Bottom 0.05 5

Expected N(QQ) per central A+A Collision:

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.


ALICEALICE

ALICE

HMPID

Muon Arm

TRD

PHOS

PMD

ITS

TOF

TPC

Size: 16 x 26 meters

Weight: 10,000 tons


Tracking/PIDTracking/PID

B field = 0.5 T good pattern recognitionLong lever arm good momentum resolutionMaterial budget: vertex outer TPC < 0.1 X0

TPC dE/dx~5.5-6.5%

ALICE PPR CERN/LHCC 2003-049

Central Pb+Pbp+p

ΔpT/pT

ITS (Silicon): 4<r<44 cm, 6 layersTPC: 85<r<245 cm, 159 pad rowsTRD: 290<r<370 cm, 6 layers

Robust, redundant tracking: 100 MeV/c to 100 GeV/c

107 Central Pb+Pb events

Kp


ALICE Electromagnetic CalorimeterALICE Electromagnetic Calorimeter

Lead-scintillator sampling calorimeterShashlik fiber geometry Avalanche photodiode readout

Coverage: ||<0.7, Δ=110°~13K towers (ΔxΔ~0.014x0.014)Depth ~21 X0

Design resolution: E/E~1% + 8%/√E

• Upgrade to ALICE• ~17 US and European institutions

Current expectations:• 2009 run: partial installation• 2010 run: fully installed and commissioned


Acceptance/triggering/ratesAcceptance/triggering/rates

L = 5 x 1026 cm-2 s-1; Δt = 106 s; 50 GeV jet Rate ~ 1 Hz

ALICE Acceptance ||< 0.7, Δ~2/3 (calorimetry)

||< 0.9, Δ=2 (tracking)

Interaction Rate ~4 kHz

L1 Out/HLT In 800 Hz

Data-to-tape 50 Hz (25 MB events)

Nbe(pT>40 GeV/c) ~3x104


Jet triggering with EMCALJet triggering with EMCAL

A.

Mis

chke

an

d P

. Ja

cob

s, A

LIC

E I

NT

-20

05

-50

• Background rejection ~ factor of 10• Centrality dependent threshold• Good efficiency above ~60 GeV


Jet-finding in Heavy Ion CollisionsJet-finding in Heavy Ion Collisions

kT algorithms

Cone jet finders

p+p

Sum energy within cone of R = √(2+2)

Conceptually simple

Small cones may have own trigger bias

Pb+Pb

Allow for arbitrary shaped jets follow the energy flow

Less bias on intra-jet shape

N3 combinatorics

Many methods under investigation in ALICE

In all cases, a background subtraction method is necessary

FastJet, M. Cacciari, G. Salaam hep-ph/0512210

Geometric nearest neighbor search

N3 Nlog(N)


Cone finder resultsCone finder results

Pb+Pb: ΔE/E~30% for Ejet = 100 GeV

Comparable to p+p

R = 0.3, pT > 2 GeV/c

Background is subtracted event-by-event using information from outside cone within event and

statistical average of background from all events


What contributes to resolution?What contributes to resolution?p+p, pure simulation

Intrinsic limit to resolution if “hidden” neutrals (n,K0

L,) are excluded

Jet resolution is affected by the cuts (R,pT) which are necessary to reduce the background/fluctuations in Pb+Pb

hadron calorimetry vs. tracking

Trade-off: resolution vs. background rejection

pT cut has modest effect, R more dramatic


Contributions to electron yieldsContributions to electron yields

-PYTHIA 6.22 for shapes

-Cross-sections from NLO (Dainese, y<0.9)

• Charm: 2.14 mb

• Bottom: 0.082 mb

• W: 6.5 nb (NLO,Vogt)

ALICE EMCAL acceptance

Calculation by Mark Heinz

W electrons can be distinguished with

isolation cuts


Electron Identification StudiesElectron Identification Studies

Electron p/E Electron/pion discrimination via cluster properties

Studies by Mark Heinz


Electron/Pion IdElectron/Pion Id

1. p/E2. Cluster shape3. Cluster multiplicity

Combined cuts reduce pion background with small decrease in efficiency


Visualizing events in ALICEVisualizing events in ALICE

(TRD and TOF not shown)

K+

B0 (pT=41.8GeV) e+ (pT=16.8GeV) + e

(pT=3.3GeV) +

e+

b+b scatter, Q2~50 GeV

D- (pT=21.9GeV) light hadrons

(pT=8.8GeV)

(pT=16.8GeV)


Putting it togetherPutting it together

Pb+Pb only Pb+Pb/p+p

Investigate the differences in fragmentation distributions for tagged and un-tagged jets

How similar/different

are they?

Simulation studies in progress for EMCAL review


Summary/OutlookSummary/Outlook

High production rate for heavy quarks and jets at LHC

LHC Jet Identification in heavy ions opens up new observable for investigating flavor-dependent medium coupling

Experimental requirements

Jet triggering

Good jet-finding for pTjet > 30 GeV in heavy ions

PID/Momentum resolution for eID/jet fragmentation studies

Secondary vertex reconstruction

Are you ready? Collisions are just around the corner!

b-tagging via leptons in jet/di-jet events


Empty ALICE (last year)Empty ALICE (last year)


ALICE ca. 11-July-2007ALICE ca. 11-July-2007

Installation proceeds apace…


BackupBackup


Jet-finding ChallengesJet-finding ChallengesMore than one pT > 7 GeV/c particle per event ~1-2 TeV of energy within jet cone of R ~1

Charged particles within jets*

Charged particles from Pb+Pb Background*

Cone radius, REne

rgy

with

in c

one,

E(R

)

pT cuts/small cone radii can suppress background, but also influence jet energy resolution

Trade-off with hadron calorimetry vs. tracking

for jet reconstruction

*(Similar for charged + neutral)


BackgroundsBackgroundsFluctuations in background energy within jets caused by:

• Event-by-event impact parameter variations

• Poissonian fluctuations of uncorrelated particles

• Correlated particles from other sources (e.g. overlapping low ET jets)

• In- and Out-of-Cone fluctuations

Fluctuations get worse with larger cones

Investigating heavy quark energy loss with lepton-tagged jets Jennifer Klay California Polytechnic...

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