Документ взят из кэша поисковой машины. Адрес оригинального документа : http://qfthep.sinp.msu.ru/talks/CMS_QFTHEP_Korotkikh_final_1.pdf Дата изменения: Tue Sep 7 08:50:52 2010 Дата индексирования: Mon Oct 1 19:55:14 2012 Кодировка:

(for CMS Collaboration)

Vladimir Korotkikh

Elliptic flow studies in heavyion collisions using the CMS detector at the LHC
QFTHEP2010, The XIXth International Workshop High Energy Physics and Quantum Field Theory
815 September 2010, Golitsyno (Russian Federation)


QGP in Heavy Ion collisions

P. Sorensen, International J.M.P.E. 2009. arXiv:0905.0174.

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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LHC experiments


ALICE

ATLAS

CMS

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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CMS experiment at the LHC

Silicon Tracker || < 2.4 Electromagnetic Calorimeter || < 3.0 Hadron Calorimeter
barrel and endcap with HFcalorimeter up to

|| < 3.0

|| < 5.2 Muon Chambers || < 2.4

Magnetic field: 3.8 Tesla

+ CASTOR detector 5.3 < || < 6.4 + TOTEM 5.3 < || <6.7 + Zerodegree calorimeter 8.3 < ||

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Tracker system: Silicon pixel layers ( 3 in barre | , i cap < | < 2.4) n s s layers (10 in barrel |l|| < 1.51 2 n n endap 1.1.5 ||| < 2.4) trip Silico < 1.5, 2 i endc 5 < Calorimeter system: ECAL ­ electromagnetic (crystals of lead tungstate PbWO4) || < 3.0 HCAL ­ hadronic (active plastic scintillator tiles interspersed between stainless steel and brass absorber plates) || < 3.0 HF ­ hadron forward (steel absorbers and embedded radiation hard quartz fibers) 3.0< || < 5.2

CMS experiment at the LHC

Muon Coil HCAL ECAL Tracker

Excellent coverage: Tracker ~ 5 units in rapidity and 2 in azimuthal angle Calorimeter > 10 units in rapidity and 2 in azimuthal angle Momentum resolution: ~ 2% of momentum resolution for tracks with pT < 100 GeV/c

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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CMS HI Tracking
· Based on standard pp tracking modules
Tracking algorithmic efficiency Efficiency ~ 70%, fake rate ~ 1%
85% of tracks in acceptance
Y(cm)

Single Strip Double Strip Pixel X(cm)

Transverse impact parameter resolution

Momentum resolution

Endcap 22.5%

Barrel ~1%

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Elliptic flow in noncentral heavyion events

transverse plane

p

y

)

px

Kolb P.F., Heinz U., nuclth/0305084

Initial spatial anisotropy results in elliptic flow of final particles. Azimuthal anisotropy of particles is a signature of thermalization.
Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Azimuthal distribution at the RHIC

R ­ azimuthal angle of the reaction plane

STAR Collaboration, Phys.Rev.Lett.90:032301,2003.

dN ( p ) = N 0 (1 + 2 v 1 c o s ( p - R ) + 2 v 2 c o s 2 ( p - R ) + ...) d Elliptic flow - R) > v2 = < cos 2(
= tan
-1

(py/px)

p

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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v2 ­ current data and prediction for LHC

Simple extrapolation for LHC: v2 = 0.07
v2(y=0) midcentrality

Simple extrapolation gives slight increasing of v2 for LHC energy The models predict for v2(if compare with RHIC): 1) decrease 2) increase 3) saturation
Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

Alessandro B et al., 2006 J. Phys. G: Nucl. Part. Phys. 32 1295

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v2 vs. pT ­ RHIC and LHC (two predictions)

N. Armesto et al., J. Phys. G 35 (2008) 054001.

A. K. Chaudhuri, Phys. Lett. B 672 (2009) 126

MPC parton cascade of Molnar for RHIC and LHC, b = 8 fm.

Viscous hydrodynamical calculations for RHIC and LHC, minimum bias collisions.

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Azimuthal correlations in pp and AuAu at 200 GeV
, P. Sorensen, International J.M.P.E. 2009. arXiv:0905.0174.

200 GeV, Au-Au minbias

2M events,

p-p - 11 M events

J. Adams et al (STAR), PRL 93, 252301

STAR (RHIC) resume: (AA pp) = flow

Relative degree of nonflow contribution A nature of nonflow effects in pp collisions is not clear
uQ *
evnt

=


i

cos[n( - pT )]

evnt

Mv2 ( pt ) < v2 >

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Predictions of the elliptic flow in p+p collisions
1. D. d'Enterria , G.Eyyubova, V.Korotkikh, I.Lokhtin, S.Petrushanko, L.Sarycheva, A.Snigirev. Estimates of hadron azimuthal anisotropy from multiparton interactions in protonproton collisions at sqrt(s) = 14 TeV Incomplete thermalization mod

Eur.Phys.J. C66:173(2010), ePrint: arXiv:0910.3029
ePrint: arXiv:0910.4844

el

2. S.K. Prasad et al., Elliptic flow ($v_2$) in pp collisions at LHC energy : A hydrodynamical approach. 3. P. Bozek, Observation of the collective flow in protonproton collisions.

HYDRO model HYDRO model

Acta Phys. Pol. B41 (2010) 837,,ePrint: arXiv:0911.2392



4. J.CasalderreySolana, U.A. Wiedemann. Eccentricity fluctuations make flow measurable in high multiplicity pp collisions. Hot spots MC PRL 104,102301(2010) , ePrint: arXiv:0911.4400 [hepph] 5. G. Ortona, et al., Elliptic flow in high multiplicity protonproton collisions at $\sqrt s$ = 14 TeV as a signature of deconfinement and quantum energy density fluctuations

model

ePrint: arXiv:0911.5158v1 [hepph]

3+1D HYDRO model

6. A.K. Chaudhuri, Phys.Lett. B692, 15, 2010

ePrint: arXiv:0912.2578v1 [hepph], ePrint: arXiv:0912.2578v1 [hepph]

HYDRO model with hot spots HYDRO model

7. M.Luzum, P.Romatschke, Phys.Rev.Lett.103: 262302, 2009

1 12 Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

V2 from 0.03 till 0.15 in various models

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From A+A to p+p at LHC
A+A RA 6 fm p+p Rp 0.56 fm

1.Transition to small spatial scale 2.Change multiplicity dN/dy1000 to dN/dy 10 3.Transverse overlap area

AT 85 fm 2 at b = 0

AT 0.85 fm 2 at b = 0

Y X
Particle density on unit overlap area is the same order in A+A and in p+p collisions

Y X
dN / dy AA AT dN / dy pp AT

(

)

=(

)

1 mb

-1

13 Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Flow prediction in pp collisions

A +A
P. Sorensen, International J.M.P.E. 2009. arXiv:0905.0174.

p +p
ratio

Eccentricity scaling and incomplete thermalisation model

1. D. d'Enterria , G.Eyyubova, V.Korotkikh, I.Lokhtin, S.Petrushanko, L.Sarycheva, A.Snigirev, Eur.Phys.J. C66:173(2010)

AT = 4S

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

Rrms(ep)=0.89fm

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From RHIC to LHC: time and statistics for first heavyion run
Physics protonproton run at the LHC has started in November 2009 at s = 0.9, 2.36, 7 TeV. The heavyion run is expected in the NovemberDecember 2010 Pb+Pb collisions at s = 2.76 TeV per nucleon pair CMS expected integrated luminosity L=10 b 1 ~ 4080M events
Statistical reach at CMS will be better or comparable with the RHIC results

Elliptic flow ­ one of the priorities of the CMS heavyion group for the first heavyion run at the LHC

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Central Pb+Pb Events on LHC
Extrapolation from RHIC data:
ch

Mean of predictions : about dNch/d 1500

(Bjorken)~ 1560 GeV/fm
T/Tc ~ 2 4

3

· Simple extrapolation of RHIC results suggests dN/dych <1500 · Use HYDJET tuned to dN/dy (charged) ~ 3000
· Wide multiplicity distribution · Contains a significant amount of "mini" Jets.

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Reconstruction of the reaction plane in CMS
CMS Tracker Reconstructed Tracks (||<2.4)
The reaction plane at the CMS can be determined independently by different detector subsystems and in different pseudorapidity windows.

CMS Calorimeters ECAL (||<3) and HCAL (||<5.2)

HYDJET generator was used to simulate PbPb events at the LHC.
I.P. Lokhtin and A.M. Snigirev, Eur. Phys. J. C 46 (2006) 211, http://lokhtin.web.cern.ch/lokhtin/hydro/hydjet.html

GEANTbased software was used to simulate CMS responses.
Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Elliptic Flow V

2

Reaction plane z

Find the r

Methods: · Event plane, RP · Two and more particle correlation eaction plane with calorimeters and tracker

y

x

HYDJET, PbPb, b=9 fm Event plane resolution with ECAL: 0.37 radian

Azimuthal ET distribution

Perspective experimental HI CMS studies: 1.V2 with particle identification (ligth and heavy quarks) 2. RP dependence of Nuclear modification factor 3. RP dependence of backward peak in two particle correlations Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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v2 vs. pt and ­ CMS tracker, PbPb b=9 fm
Tracks with pT >0.9 GeV/c
(by Event Plane method) The uncertainties of the CMS Tracker detector is not higher than 3%
v2{EP} in generated events reconstructed
G.Kh.Eyyubova, V.L. Korotkikh, I.P. Lokhtin, S.V. Petrushanko, L.I. Sarycheva, A.M. Snigirev ,David Krofcheck , CMS AN2007/004

CMS preliminary

Further study with LYZ method in
G.Kh.Eyyubova, V.L. Korotkikh, I.P. Lokhtin, S.V. Petrushanko, L.I. Sarycheva, A.M. Snigirev , , Phys.Atom.Nucl.71:2142, 2008

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Energy independence of correlator in pp
<


i

cos[2(i - pT )] >

RHIC




i

cos[2( i - pT )] M -1

For particles relatively to direction of leading particle

PYTHIA pp 200 7000 GeV


i

cos[2(i - M -1

lead pT

)]
evnt

= v2jet ( pT ) < v

jet 2

>

The correlator in pp collisions describes an angular form of particle azimuthal distribution relatively to leading particle direction. v2jet (pT) is anisotropy parameter for string fragmentation particles, which may be independent on energy.

Quasiscaling on energy? It may be interesting effect in pp collisions.
Paper in preparation

Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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Summary
CMS is an excellent detector for studying minimum bias QCD and heavyion physics. Azimuthal correlations in pp is important reference for HI and can give unique information on jet fragmentation. v2 study in HI collisions at LHC energy can give new information on collective phenomena of QGM. PbPb collisions are expected at the LHC in November in Run1 at 2.76 TeV with the most early publication in 2011 year. CMS detector at the LHC is ready to study elliptic flow by different detector subsystems, in different pseudorapidity windows and by different methods.
Vladimir Korotkikh (CMS Collaboration, SINP MSU), QFTHEP2010

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