Документ взят из кэша поисковой машины. Адрес оригинального документа : http://lav01.sinp.msu.ru/~igor/seminar/obraztsov_06_04_16.pdf Дата изменения: Tue Apr 5 08:59:04 2016 Дата индексирования: Sat Apr 9 23:21:25 2016 Кодировка:

Jet studies in Heavy Ions with CMS at Run I and plans for Run II (draft)
Stepan Obraztsov Skobeltsin Institute for Nuclear Physics Moscow, Russia SNP-RAS-16: Physics of Fundamental Interactions, 12-15 Apr 2016, JINR, Dubna (Russian Federation)


LHC Run I + Run II for heavy-ion physics
Run I I I I II II II II System Pb-Pb p-Pb p-p p-p Pb-Pb p-p p-Pb (preliminary) Pb-Pb (preliminary) s 2.76 5.02 2.76 2.76 5.02 5.02 8 5.02 Year 2011 2013 2011 2013 2015 2015 2016 2018 Luminosity (nb) 0.17 36. 1 4 20 0 5.6 0.56 27.87 ? ?

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The CMS Detector

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Di-jet energy imbalance : Pb-Pb
Pb Pb

A strong increase in the fraction of highly unbalanced di-jets in central Pb-Pb as compared with p-p and peripheral Pb-Pb direct observation of jet quenching
PPb b

The fraction of the energy that a jet loses increases monotonically with increasing collision centrality, and does not dramatically change with jet PT constant relative energy loss?
PRL 109 (2012) 152303
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Di-jet energy imbalance : p-Pb
No significant dijet transverse momentum imbalance in pPb. Confirms that the observed dijet transverse momentum imbalance in PbPb collisions is not originating from initial-state effects.

CMS-PAS-HIN-13-001

A strong modification of the dijet pseudorapidity distribution is observed. This indicates a strong correlation between the energy emitted at large pseudorapidity and the longitudinal motion of the dijet frame.


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Inclusive jet suppression in Pb-Pb

Pb

Pb

PPb b

CMS-PAS-HIN-12-004



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Jet suppression in p-Pb

arXiv:1601.02001





Small enhancement compared to pp reference run No significant assymetry was observed Jet spectra found to be softer away from midrapidity Baseline b and c jets studies!
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PLB 754 (2016) 59 CMS-HIN-15-012

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Inclusive jets fragmentation functions in Pb-Pb

Pb

Pb

PPb b

A modest but significant modification of fragmentation seen: An enhancement in fragment yield in central collisions for Enhancement is centrality-dependent

arxiv:1406.0932

Structure of reconstructed jets is modified towards an excess of particles at low pT.
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Jet shapes in Pb-Pb


Structure of reconstructed jets modified towards an excess of particles far from the jet axis
PLB 730 (2014) 243

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Jet-track correlations in Pb-Pb


JHEP 1602 (2016) 156

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Opportunities with Run II






Top quark: Top decays before thermalization of medium => Probes the early stages of the medium Z + j et : Measurement of Z-jet with large statistics (2k-4k can be collected which enables centrality dependent studies) Photon + jet: High precision photon jet analysis (and photon-tagged fragmentation function) Jet substructure measurements, quark gluon discrimination

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Summary


Many fundamental results on jets in dense medium from Run I Successful data-taking from 2011 to 2014 Direct observation on jet quenching Investigation on final state effects using jet shapes, fragmentation function. B and C tagged jets Detailed studies with new observables available in Run II Z/photon + jet Top quarks Jet substructure



Public results: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIN

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Backup slides

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Photon jet correlation in Pb-Pb

PLB 718 (2013) 773

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Elliptic flow of identified particles

ntified and & charged particles ow mass-ordering in Pb-Pb and p-Pb ronger in p-Pb)

CMS-HIN-14-002
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Centrality in Pb+Pb and p+Pb
JHEP 08 (2011) 141

PPb b

Pb

Pb

In Events are classified according to the p-Pb, only Pb-going side m percentile of the Pb-Pb inelastic cross easurement is used section based on total deposited energy in the forward calorimeters
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-dependence of in p-Pb

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Nuclear modifications factors in Pb-Pb (hadrons, jets, b-jets, secondary J/, electroweak probes) >1: enhancement R
~ "QCD Medium" "QCD Vacuum" RAA=1: no medium effect RAA<1: suppression
AA

No medium effects for electroweak hard probes (Z0, W, prompt ) Charged particles and jets are suppressed, suppression factors saturate at high transver momentum Observation of b-quark (via secondary J/'s) suppression B-jets (extracted using vertex info) seem suppressed on the similar level as inclusive jet


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