measurement of quenched energy flow for dijets in pbpb collisions with cms · pdf filefor the...
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Yen-Jie Lee (MIT)
Yen-Jie Lee (MIT)
For the CMS Collaboration
NPA Seminar
Yale, USA
15 October, 2015
Measurement of Quenched Energy Flow for
Dijets in PbPb collisions with CMS
Yen-Jie Lee (MIT) NPA Seminar @ Yale
Relativistic Heavy Ion Collisions
Trying to answer two important questions in the high density QCD:
Where is the critical point of the QCD phase diagram?
What is the property of Quark Gluon Plasma?
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Yen-Jie Lee (MIT)
Ideal World
NPA Seminar @ Yale
High Energy Quark
Medium
Quark Gluon Plasma Brick
3
Yen-Jie Lee (MIT)
Parton Cascade in Vacuum
NPA Seminar @ Yale
HadronizationParton shower
Hadrons
High Energy Jet
Large Virtuality Q
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Yen-Jie Lee (MIT)
Parton Cascade in Medium
NPA Seminar @ Yale
HadronizationParton shower
High Energy Jet
Large Virtuality Q
Hadrons
Medium
Medium Changes vs. Time
Space-time information is also important in heavy ion environment
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Yen-Jie Lee (MIT)
Parton Energy Loss Models
NPA Seminar @ Yale
Collisional
energy lossRadiative
energy lossAdS/CFT “drag force”
Perturbative QCD
Weak coupling limit
Holographic calculationStrong coupling limit
Two theoretical approaches:
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Yen-Jie Lee (MIT) NPA Seminar @ Yale 7
The High Energy Frontier
Large Hadron Collider
LHC
Pb+Pb collisions
2.76 TeV (2010-13)
14x jump with respect to RHIC!
2015: 5.1 TeV
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Lake Geneva
27 km circumference
CMS
ATLAS
LHCb
ALICE
France
Switzerland
RHIC
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Yen-Jie Lee (MIT) NPA Seminar @ Yale 8
CMS Detector
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Yen-Jie Lee (MIT) NPA Seminar @ Yale 9
CMS Detector
Inner tracker:
charged particles
vertex, isolation
solenoid
EM and Hadron calorimeters
photons, isolation, jet reconstruction
Muon
HCAL
ECAL
Tracker |η|< 2.5
|η|< 3.0
|η|< 5.2
|η|< 2.4
Pb
Pb
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Yen-Jie Lee (MIT)
Particle Reconstruction with CMS
NPA Seminar @ Yale
μ±
γ
Neutral Hadron
Charged Hadron
e±
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Yen-Jie Lee (MIT)
Heavy Ion Collision Recorded by the CMS Detector
NPA Seminar @ Yale 11
Yen-Jie Lee (MIT)
Underlying Event Background
NPA Seminar @ Yale
Jet
Goal: To study high pT jets event-by-event
How do we subtract the background from soft scatterings?
Take advantage of the large acceptance CMS detector:
Predict with the measured energy in the forward calorimeter
3<η<5-5<η<-3 |η|<2.5
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Yen-Jie Lee (MIT) NPA Seminar @ Yale
Underlying Event in Heavy Ion Collisions
Training done with minimum-bias events (optimized by SVD method)
CMS DP 2013/018
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Yen-Jie Lee (MIT)
Jet Reconstruction and Composition
NPA Seminar @ Yale
Anti-kT algorithm is used in the
most CMS publications
On average, charged hadrons
carry ~65% of the jet momentum
Measure the known part
Correct the rest by MC simulation
Optimize the use of calorimeter and tracker
Example: “Particle Flow” in CMS A typical high pT jet
Clustering
JetUE subtracted particles
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Yen-Jie Lee (MIT)
CMS Jet Reconstruction Strategy
NPA Seminar @ Yale
Remove underlying
events contribution
MC Simulation
PYTHIA
Validated with dijet,
photon(Z)-jet data
Raw jet energyBackground
subtraction
Jet energy
correctionJet energy
correction
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Yen-Jie Lee (MIT) NPA Seminar @ Yale
Jet Transverse Momentum SpectraN
ucle
ar
Modific
ation F
acto
r
Nuclear Modification Factor (RAA):
Ratio of the jet cross-section in PbPb
and pp scaled by the number of
nucleon-nucleon collisions
pPb Collisions
No significant modification
Head-on PbPb Collisions
Large suppression of high pT jet
Large final state effect observed in PbPb collisions
Is the jet structure modified in PbPb collisions?
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Yen-Jie Lee (MIT)
Inclusive Jet Shape and “Fragmentation Function”
NPA Seminar @ Yale
Jet shape PbPb / pp Charged particle in cone PbPb - pp
RJet
Energy
Jet Fragmentation function: how transverse momentum is distributed inside the jet cone
Jet shape: “the jet energy distribution” as a function of R
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Yen-Jie Lee (MIT)
Inclusive Jet Shape and “Fragmentation Function”
NPA Seminar @ Yale
Jet shape PbPb / pp Charged particle in cone PbPb - pp
Observation of energy redistribution inside the jet cone
(Some modification at large R; ~ one more low track pT)
The bulk of the Jet structure is actually pretty similar to that in pp
R
R
120 < Jet pT < 300 GeV/c
One more low pT particle
in the jet cone R=0.3
0-10% PbPb
Jet
Energy
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Yen-Jie Lee (MIT)
Probe the QGP with High Energy Quarks and Gluons
PP PbPb
medium
Increased rate of
asymmetric dijets
in central PbPb collisions
NPA Seminar @ Yale 19
Yen-Jie Lee (MIT)
Probe the QGP with High Energy Quarks and Gluons
PP PbPb PRC 84 (2011) 024906
PLB 712 (2012) 176
Small AJLarge AJ
(AJ~0.5)
Where does the
energy go?
medium
Increased rate of
asymmetric dijets
in central PbPb collisions
NPA Seminar @ Yale 20
Yen-Jie Lee (MIT)
Tracks in
the jet cone
ΔR<0.8
Tracks out of
the jet cone
ΔR>0.8
CMS
PRC 84 (2011) 024906
Significant Energy Flow Out of the Jet Cone
NPA Seminar @ Yale 21
Yen-Jie Lee (MIT)
Tracks in
the jet cone
ΔR<0.8
Tracks out of
the jet cone
ΔR>0.8
CMS
PRC 84 (2011) 024906
Significant Energy Flow Out of the Jet Cone
Jet collimation
Casalderrey-Solana, Milhano, WiedemannJ.Phys. G38 (2011) 035006
• Partons undergo Brownian motion
• Medium ”trims away” soft component to large angle
NPA Seminar @ Yale 22
Yen-Jie Lee (MIT)
Ex: Mehtar-Tani, SalgadoPLB 707 (2012) 156-159
Ex: Mehtar-Tani, SalgadoPLB 707 (2012) 156-159
Tracks in
the jet cone
ΔR<0.8
Tracks out of
the jet cone
ΔR>0.8
CMS
PRC 84 (2011) 024906
Significant Energy Flow Out of the Jet Cone
Decoherence
Jet collimation
Mehtar-Tani, SalgadoPLB 707 (2012) 156-159
• Color coherence (angular ordered radiation) is
destroyed in the strongly interacting medium
• Open up the phase space for wide angle radiation
NPA Seminar @ Yale 23
Yen-Jie Lee (MIT)
Tracks in
the jet cone
ΔR<0.8
Tracks out of
the jet cone
ΔR>0.8
CMS
PRC 84 (2011) 024906
Significant Energy Flow Out of the Jet Cone
Jet collimation
Turbulance cascade
Decoherence
• Effect of multiple branchings in medium:
“Quasidemocratic branching”
• Effective mechanism which brings soft
partons to large angle
Blaizot, Iancu, Mehtar-TaniPRL 111 052001 (2013)
NPA Seminar @ Yale 24
Yen-Jie Lee (MIT)
Tracks in
the jet cone
ΔR<0.8
Tracks out of
the jet cone
ΔR>0.8
CMS
PRC 84 (2011) 024906
Significant Energy Flow Out of the Jet Cone
Jet collimation
Turbulance cascade
Decoherence
Third jet quenching
• Vacuum-like parton shower also extend to
large angle as large as R~1.0
• The third jet may be quenched and produce
soft particles out of the small jet cone R=0.3
NPA Seminar @ Yale 25
Yen-Jie Lee (MIT)
Tracks in
the jet cone
ΔR<0.8
Tracks out of
the jet cone
ΔR>0.8
CMS
PRC 84 (2011) 024906
Significant Energy Flow Out of the Jet Cone
Jet collimation
Turbulence cascade
Decoherence
Third jet quenching
Strongly coupling
approach, hydro
• The medium takes energy away from the high
energy parton and turns that energy into heat /
collective motion of the medium.
• Produce extra soft particles in the final state
Casalderrey-Solana, Gulhan, Mihano, Pablos, Rajagopal, …
NPA Seminar @ Yale 26
Yen-Jie Lee (MIT)
Significant Energy Flow Out of the Jet Cone
Jet collimation
Turbulance cascade
Decoherence
Third jet quenching
Strongly coupling
approach, hydro
(1) How many particles are carrying
the missing energy?
(2) What is the angular distribution of the
quenched energy flow with respect to
the dijet axis?
NPA Seminar @ Yale 27
Yen-Jie Lee (MIT)
Measurement of the Quenched Energy Flow
NPA Seminar @ Yale
Difficulty: Large PbPb
underlying event (UE)
Leading jet
Subleading jet
Idea: Use all charged particles (pT>0.5 GeV/c)
Study the transverse momentum balance
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Yen-Jie Lee (MIT)
Datasets and Event Selection
pp
• 5.3 pb-1
• Jet trigger with pT > 80 GeV/c
• Track reconstruction:
• pT > 0.2 GeV/c
• Anti-kT Calorimeter jet
• With R=0.3
PbPb
• 150 μb-1
• Jet trigger with pT > 80 GeV/c
• Track reconstruction:
– pT > 0.4 GeV/c
• Anti-kT Calorimeter jet
– with R=0.3
– HF/Voronoi UE
subtraction
• Dijet selection:
– pT,1 > 120 GeV/c
– pT,2 > 50 GeV/c
– |η1|, |η2| < 1.6 (0.5)
– Δφ > 5π/6
• Charged particles:
– pT > 0.5 GeV/c
– |η| < 2.4
= 2.76 TeV
NPA Seminar @ Yale 29
Yen-Jie Lee (MIT)
Multiplicity Difference
What is the multiplicity of
the particles that balance the “extra”
lost pT?
φ1
φ2
NPA Seminar @ Yale 30
Yen-Jie Lee (MIT)
Multiplicity Difference
What is the multiplicity of
the particles that balance the “extra”
lost pT?
Compare the multiplicities in the leading and
subleading jet hemispheres
Direction of the dijet is defined as:
(In contrast to PRC 84 (2011) 024906, where
the leading jet direction was used)
Provide UE cancellation differential in ΔR
φ1
φ2
φdijet
φdijet =½(φ1 + (π-φ2))
NPA Seminar @ Yale 31
Yen-Jie Lee (MIT)
Multiplicity Difference (subleading – leading jet)
What is the multiplicity of
the particles that balance the “extra”
lost pT?
Compare the multiplicities in the leading and
subleading jet hemispheres
Direction of the dijet is defined as:
(In contrast to PRC 84 (2011) 024906, where
the leading jet direction was used)
Provide UE cancellation differential in ΔR
φ1
φ2
φdijet
φdijet =½(φ1 + (π-φ2))
Nch in subleading
jet hemisphere-Δmult =
NPA Seminar @ Yale
Nch in leading jet
hemisphere
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Yen-Jie Lee (MIT)
Multiplicity Difference (subleading – leading jet)
φ1
φ2
φdijet
Multiplicity difference between the subleading and leading hemisphere
is increasing vs. dijet asymmetry in pp and peripheral PbPb.
There are more charged particles in the subleading hemisphere
AJ = (pT,1-pT,2)/(pT,1+pT,2)
Three / multi-jet
events
Symmetric Dijet
Events
NPA Seminar @ Yale
arXiv 1509.09029
33
Yen-Jie Lee (MIT)
Multiplicity Difference (subleading – leading jet)
• This increase is larger in central PbPb
• The enhancement in PbPb compared to pp increases with centrality
• Large AJ, 0-10%: ~16 extra particles (pT>0.5 GeV) in the subleading jet hemisphere
φ1
φ2
φdijet
AJ = (pT,1-pT,2)/(pT,1+pT,2)
PbPb-PP
NPA Seminar @ Yale
arXiv 1509.09029
34
Yen-Jie Lee (MIT)
Missing pT||
? ?
φ1
φ2
φdijet
½(φ1 + (π-φ2))
φi, pTi
What is the multiplicity and
pT spectra of the particles that
balance the lost pT?
NPA Seminar @ Yale
Dijet axis
Charged particle
azimuthal angle
Projection to dijet axis
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Yen-Jie Lee (MIT)
Missing pT|| vs. AJ
NPA Seminar @ Yale
PP 0-10% PbPb
More energy flow
in the leading jet direction
More energy flow
in the subleading jet direction
arXiv 1509.09029
The momentum imbalance inside the jet cone is restored
if we consider all particles in the event
(in both pp and PbPb collisions)
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Yen-Jie Lee (MIT)
Missing pT|| vs. AJ
• Missing pT from high pT particles increases as a function of AJ
• In pp Balanced by 2-8 GeV/c particles
• In 0-10% PbPb Balanced by particles with pT < 4 GeV/c
NPA Seminar @ Yale
PP 0-10% PbPb
More energy flow
in the leading jet direction
More energy flow
in the subleading jet direction
arXiv 1509.09029
37
Yen-Jie Lee (MIT)
φ1
φ2
φdijet
Missing pT|| vs. Δ
? ?Calculate the missing pT for charged
particles that fall in slices of Δ
φ2
What is the angular distribution of
these particles with respect to the
dijet system?
NPA Seminar @ Yale 38
Yen-Jie Lee (MIT)
φ1
φ2
φdijet
Missing pT|| vs. Δ
φ2
NPA Seminar @ Yale
? ?Calculate the missing pT for charged
particles that fall in slices of Δ
What is the angular distribution of
these particles with respect to the
dijet system?
39
Yen-Jie Lee (MIT)
φ1
φ2
φdijet
Missing pT|| vs. Δ
φ2
NPA Seminar @ Yale
? ?Calculate the missing pT for charged
particles that fall in slices of Δ
What is the angular distribution of
these particles with respect to the
dijet system?
40
Yen-Jie Lee (MIT)
Missing pT|| vs. Δ in pp
NPA Seminar @ Yale
Integrated curve
from 0-ΔR
Contribution from third jet
Asymmetry inside the jet conearXiv 1509.09029
Subleading jet direction
Leading jet direction
0.5-300 GeV/c
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Yen-Jie Lee (MIT)
Missing pT|| vs. Δ in pp
NPA Seminar @ Yale
Integrated curve
from 0 to Δ
Contribution from third jet
Asymmetry inside the jet conearXiv 1509.09029
Subleading jet direction
Leading jet direction
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Yen-Jie Lee (MIT)
Missing pT|| vs. Δ
NPA Seminar @ Yale
Inclusive AJ
Subleading jet direction
Leading jet direction
arXiv 1509.09029
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Yen-Jie Lee (MIT)
Missing pT|| vs. Δ
NPA Seminar @ Yale
Inclusive AJ
Subleading jet direction
Leading jet direction
arXiv 1509.09029
Open circles:
Integrated over
particle pT
Slight modification of the
cumulative energy flow
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Yen-Jie Lee (MIT)
Missing pT|| vs. Δ
High pT imbalance
at small Δ
NPA Seminar @ Yale
arXiv 1509.09029
Inclusive AJ
Subleading jet direction
Leading jet direction
Slight modification of the
cumulative energy flow
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Yen-Jie Lee (MIT)
Missing pT|| vs. Δ
High pT imbalance
at small Δ
Balanced by low pT particles
in subleading jet direction
Extends upto large Δ
NPA Seminar @ Yale
arXiv 1509.09029
Inclusive AJ
Subleading jet direction
Leading jet direction
Slight modification of the
cumulative energy flow
46
Yen-Jie Lee (MIT)
Anti-kT Jets with Different R Parameters
Jets reconstructed with
R=0.5 gives ”wider” jet
Jets reconstructed with
R=0.2 gives ”narrower” jet
Jet shape from PYTHIA
• Jets are only meaningful if the algorithm is defined
• Different parameter R select different sets of dijet events!!
• Jet width dependent studies
NPA Seminar @ Yale 47
Yen-Jie Lee (MIT)
“Shooting Jets with Different Width” through the Medium
NPA Seminar @ Yale
pp
PbPb
PbPb - pp
R= 0.2 R= 0.3 R= 0.4 R= 0.5
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Yen-Jie Lee (MIT)
“Shooting Jets with Different Width” through the Medium
NPA Seminar @ Yale
Narrower jets Wider jets
• Quenched energy distribution depends on the R parameter
used in the Anti-kT algorithm
49
Yen-Jie Lee (MIT)
“Shooting Jets with Different Width” through the Medium
NPA Seminar @ Yale
Narrower jets Wider jets
• Quenched energy distribution depends on the R parameter
used in the Anti-kT algorithm
• Hint of narrower leading jet (or wider subleading jet) in
PbPb collisions?
50
Yen-Jie Lee (MIT)
“Shooting Jets with Different Width” through the Medium
NPA Seminar @ Yale
Narrower jets Wider jets
• Quenched energy distribution depends on the
R parameter used in the Anti-kT algorithm
• Hint of narrower leading jet (or wider
subleading jet) in PbPb collisions?
51
Yen-Jie Lee (MIT)
•Outlook
NPA Seminar @ Yale
LHC Run II (2015)
Comparison to Theory and Outlook
52
Yen-Jie Lee (MIT)
Significant Energy Flow Out of the Jet ConeJet collimation
NPA Seminar @ Yale
Turbulence cascadeDecoherence
Third jet quenching Strongly coupling
approach, hydro
0-10% PbPb collision
~16 extra particles (pT>0.5 GeV) in the
subleading jet hemisphere
53
Yen-Jie Lee (MIT)
Significant Energy Flow Out of the Jet ConeJet collimation
NPA Seminar @ Yale
Turbulence cascadeDecoherence
Third jet quenching Strongly coupling
approach, hydro
54
Yen-Jie Lee (MIT)
Jet Data vs. JEWEL event generator
NPA Seminar @ Yale
JHEP03(2013)080
A Jet Quenching Monte Carlo based
on weak coupling approach:
Reasonable description of jet FF, jet
RAA and charged hadron RAA
Hadron RAA Jet RAA
Jet Fragmentation Function
55
Yen-Jie Lee (MIT)
Hybrid Model with Strong Coupling Approach
NPA Seminar @ Yale
JHEP 1410 (2014) 19
Jet RAA
Dijet Asymmetry
Jet FF
Quark/Gluon Ratio
Motivate high pT flavor tagged jet analysis: (heavy) quark vs. gluon jets
PYTHIA+”Ads Drag”
56
Yen-Jie Lee (MIT)
Heavy Flavor Meson
NPA Seminar @ Yale
Very high pT heavy flavor meson (from quark jets):
complementary to the high pT heavy flavor jets
PRL 108, 022301 (2012)
PLB 666, 320 (2008)
57
Yen-Jie Lee (MIT)
Particle Identification with CMS
NPA Seminar @ Yale
Υ(1S)
Υ(2S)
D0
Excellent capability of (decay) particle identification with CMS
58
Yen-Jie Lee (MIT)
Flavor Dependence of Jet QuenchingCMS-PAS-HIN-15-005
b→J/ψ
D0
Fully reconstructed D0 → K-π+ over a wide kinematic range
Charged Hadrons
NPA Seminar @ Yale 59
Yen-Jie Lee (MIT)
Outlook:Identified Heavy Flavor Jet and Mesons
NPA Seminar @ Yale
B meson
b-jet
2013 5.02 TeV pPb data (35/nb)
2015-17 5.1 TeV PbPb data (~1.5/nb)
B meson
b-jet
2011 2.76 TeV PbPb data (0.15/nb)
b-jet
HL-LHC (10/nb): (b)-jet quenching at O(TeV)
D(*) meson
(Artist’s impression)
c-jet
c-jet
D(*) meson
60
Yen-Jie Lee (MIT)
• An iterative feedback cycle between theory and experiment has started!
• Quenched jet event generator
• A systematical comparison between models and data
• LHC Run II:
• High statistics Photon-Jet and the first Z-Jet measurements
• High statistics (di-)jet measurement up to pT ~ 1 TeV
• Multi-jet correlation
• Flavor dependence of the parton energy loss from low to high pT with jets and mesons
Outlook
NPA Seminar @ Yale
… Stay tuned!!!
Generator Experiment
Used to derive correction or to compare with data
Feedback and improve the generator / model
61
Yen-Jie Lee (MIT)
BACK-UPBackup slides
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