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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)
16-19.July.2007 ETD-HIC 2007, Montreal QC 3
Experimental LandscapeExperimental Landscape
Di-hadron suppression
Photon vs. Hadron suppression
Non-photonic electron suppression similar to light hadrons
STAR, Phys Rev Lett 91, 072304
16-19.July.2007 ETD-HIC 2007, Montreal QC 4
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 5
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 6
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 7
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 8
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 9
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 10
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 11
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 12
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.
16-19.July.2007 ETD-HIC 2007, Montreal QC 13
ALICEALICE
ALICE
HMPID
Muon Arm
TRD
PHOS
PMD
ITS
TOF
TPC
Size: 16 x 26 meters
Weight: 10,000 tons
16-19.July.2007 ETD-HIC 2007, Montreal QC 14
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 15
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 16
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 17
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 18
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)
16-19.July.2007 ETD-HIC 2007, Montreal QC 19
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 20
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 21
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 22
Electron Identification StudiesElectron Identification Studies
Electron p/E Electron/pion discrimination via cluster properties
Studies by Mark Heinz
16-19.July.2007 ETD-HIC 2007, Montreal QC 23
Electron/Pion IdElectron/Pion Id
1. p/E2. Cluster shape3. Cluster multiplicity
Combined cuts reduce pion background with small decrease in efficiency
16-19.July.2007 ETD-HIC 2007, Montreal QC 24
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)
16-19.July.2007 ETD-HIC 2007, Montreal QC 25
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 26
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
16-19.July.2007 ETD-HIC 2007, Montreal QC 28
ALICE ca. 11-July-2007ALICE ca. 11-July-2007
Installation proceeds apace…
16-19.July.2007 ETD-HIC 2007, Montreal QC 30
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)
16-19.July.2007 ETD-HIC 2007, Montreal QC 31
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