Zvi Citron for ATLAS 1 בסד 2 ATLAS ATLAS has world class jet reconstruction capability built from tracking and calorimetry PbPb runs at s276 TeV in 2010 8 μb 1 and 2011 15 nb ID: 781259
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Slide1
Jet Suppression Measured in ATLAS
Zvi Citron for ATLAS
1
בס"ד
Slide22
ATLAS
ATLAS has world class jet reconstruction capability built from tracking and
calorimetry
Pb+Pb runs at √s=2.76 TeV in 2010 (8 μb-1
) and 2011 (.15 nb-1); pp run in 2013 (4.0 pb−
1
);
p+Pb
in 2013 (29nb-1)
Slide33
‘Ancient History’
Full jet reconstruction with anti-
k
t
algorithm (R=0.4)
Azimuthal correlation consistent in all systems
p+p
, MC, and peripheral
Pb+Pb
consistent – asymmetry peaked at zero
Central
Pb+Pb
has peak away from zero
Momentum balance from hard scattering not kept within di-jets
Slide44
Jet Reconstruction and the Underlying Event
Anti-
k
t
(R=0.2 – 0.5) reconstruction
algorithm
Event-by-event background subtraction:
Anti-
k
t
reconstruction prior to a background subtraction
Underlying event estimated for each longitudinal layer and
ƞ
slice
Jets corrected for flow contribution to background
Underlying event fluctuations rejected by matching jets to track jets or electron/photon
Slide55
HI Jet Energy Scale Improvements
JES in
pp
collisions at ATLAS is studied
in situ from jet+boson events in combination with MC and is well understood
Much progress has been made for HI jet reconstruction understanding to ‘catch up’ with
pp
Compare HI jets with ‘standard’ jets
Direct comparison in
pp
data at 8
TeV
Take into account HI specifics: flavor admixture, quenching, algorithm differences
ATLAS-CONF-2015-
016
Slide6From R
CP
to R
AA
R
CP
is flat maybe even dropping out to 200
GeV
!
Use 2013
pp
data and calculate R
AA
Improve our observable
Improve our measurement
See something new – small but significantly positive slope
6
Slide77
From R
CP
to R
AA
High precision measurements over a large phase space
Slide88
Probing the Rapidity Dependence of Jet Suppression
arXiv:
1504.05169v1
PYTHIA8
Looking in different rapidity regions is looking at different jet flavor admixtures …
Not much shape seen in y
Full understanding needs to consider
p
T
and
y
Slide99
Inclusive Charged Particle R
AA
Precise measurements in
p
T ,
centrality, and rapidity
See
Petr’s
talk Wed @9:00
Slide1010
Jets in
p+A
Collisions
Similarly high precision measurements in
p+Pb
collisions
Slide1111
Jets in
p+A
Collisions
High precision jet reconstruction, robust
pp
data set
Large kinematic range to constrain (n)PDF
Slide1212
Jets in
p+A
Collisions
High precision jet reconstruction, robust
pp
data set
Large kinematic range to constrain (n)PDF
In central slices suppression (and enhancement!) observed
May be a consistent picture in
x
proton
…
Slide1313
Where Do We Stand?
ATLAS detector capabilities combined with jet reconstruction techniques have opened the door to well defined and well understood jets in HI
collisions
Leading the field in understanding jet reconstruction in HI
Run 1 in ATLAS has produced a wealth of jet analyses in
Pb+Pb
and
p+Pb
Yields and R
AA
Suppression ‘boundary conditions’, jet flavor effects
A
ngular
distribution
studies
path length in medium
[Helena: Tuesday@14:00
]
F
ragmentation studies, jet size studies
quenching mechanism
[Martin: 30
mins
ago
]
p+Pb
jets
nPDF
, some new questions …
Slide1414
Where Do We Go From Here?
New results from run 1 are still coming out with new perspectives on the problem of jet suppression
Increase in size of data set expected from run 2, understanding of systematic uncertainties is keeping pace
Jet suppression has been observed definitively – working towards quantitative precision to answer defined problems and new observables to spur deeper insight
Slide1515
Backup Information
Slide16Charged particle R
AA: arXiv:1504.04337
Jets in p+Pb: arXiv:1412.4092
Jet RAA: Phys. Rev. Lett. 114 (2015) 072302
Fragmentation in PbPb:Physics Letters B 739 (2014) 320–342
Jet angular distribution: Phys. Rev. Lett 111, 152301 (2013)
Jet
size
:
Phys. Lett. B 719 (2013) 220-241Di-jet
asym
:
Phys.Rev.Lett. 105 (2010)
252303
Jet Energy
Scale
ATLAS-CONF-2015-016
16
List of ATLAS Jet Results
Slide1717
Control of JES
Slide1818
Jet Quenching in JES
Start with MC based uncertainty using
Pyquen
;
Check with data driven approach
Slide1919
Control of JER