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Long-Range Multiplicity and
Transverse Momentum
Correlations in pp Collisions in
ALICE at the LHC
(for ALICE Collaboration)
A.ASRYAN, G.FEOFILOV, A.IVANOV, A.GREBENYUK,
P.NAUMENKO, V.VECHERNIN
V. Fock Institute for Physics of Saint-Petersburg State University
Reported by G.Feofilov , at the “V Workshop on Particle
Correlations and Femtoscopy” , 15 October 2009
Outline
• Motivation
• Long-range correlations and collectivity
effects in pp and ppbar collisions
(experiment and PYTHIA)
• ALICE
• Conclusions
07.07.2017
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Space-time evolution of relativistic nuclei
collisions.
I — initial state, II — QGP, III —mixed phase, IV — hadron gas, V — free
particles
I.L.Rosental, Yu.A.Tarasov, UFN, v 163, № 7б 1993
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Space-time evolution of relativistic nuclei
collisions.
I — initial state, II — QGP, III —mixed phase, IV — hadron gas, V — free
particles
I.L.Rosental, Yu.A.Tarasov, UFN, v 163, № 7б 1993
Can we see the initial state effects?
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Motivation:
Two stage scenario:
A.Capella, U.P.Sukhatme, C.--I.Tan and J.Tran Thanh Van, Phys. Lett.
B81 (1979) 68; Phys. Rep. 236 (1994) 225.
A.B.Kaidalov, Phys. Lett., 116B (1982) 459;
A.B.Kaidalov K.A.Ter-Martirosyan, Phys. Lett., 117B (1982) 247.
At the first stage a certain number of colour strings are formed stretched
in rapidity space between the incoming partons
At the second stage these strings decay into the observed secondary
hadrons.
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Motivation for studies of Long-Range Correlations:
“STRING FUSION”
Investigations of the charged particles long-range multiplicity correlations, measured for
well separated rapidity intervals, can give us information on the number of emitting
centers and hence on the fusion of colour strings[1].
Fig.1. Quark-gluon strings and schematics for studies of Long-Range Correlations[1]
[1] M.A.Braun, C.Pajares and V.V.Vechernin "Forward-backward multiplicity correlations, low p_t
distributions in the central region and the fusion of colour strings", Internal Note/FMD,
ALICE-INT-2001-16, CERN, Geneva, 2001, 13p
[2] Abramovskii V.A., Kancheli O.V. “On the multiplicity distribution of secondary hadrons” Letters
to JETP 31 (1980) 532
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Similar picture: formation of colour flux tubes
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Similar picture:
L.Mc Lerran et al.: Color Glass Condensate and Glasma
(see the report at the present Workshop)
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“Percolating color strings approach''.
With growing energy and/or atomic number of colliding particles, the number
of strings grows and they start to overlap, forming clusters [3-5].
E-by-E Fluctuations are due to the mixture of different type sources !
.
Fluctuations !
[3] M.A.Braun and C.Pajares, Eur. Phys. J. C16 (2000) 349.
M.A.Braun,R.S.Kolevatov,C.Pajares.V.V.Vechernin, ''Correlations between multiplicities and everage
transverse momentum in the percolating color strings approach'', Eur.Phys.J.C.32.535-546(2004)
[4] N.Armesto, C.Saldago, U.Wiedemann, PRL94 (2005) 022002.
[5] C. Pajares , arXiv:hep-ph/0501125v1 14 Jan 2005
Long-Range Correlations (LRC)
CORRELATIONS BETWEEN OBSERVABLES MEASURED IN TWO
RAPIDITY INTERVALS
 n ( y )
“BACWARD” (B)
“FORWARD”(F)
*THEORY:
•
A.Capella,A.Krzywicki, Phys.Rev. D18, no11,(1978),4120-4133
•
A.Capella and J.tran Thanh Van, Z.Phys, C18(1983).85:
•
A.Krzywicki, Phys.Rev. D29,No.5,(1984)1007-1009.
•
N.S.Amelin, N.Armesto, M.A.Braun, E.G.Ferreiro and C.Pajares,
Phys. Rev. Lett. {\bf 73} (1994) 2813.
•
M.A.Braun and C.Pajares, Eur. Phys. J. {\bf C16} (2000) 349.
M.A.Braun,R.S.Kolevatov,C.Pajares.V.V.Vechernin, ''Correlations between
multiplicities and everage transverse momentum in the percolatin color strings
approach'',
07.07.2017 Eur.Phys.J.C.32.535-546(2004)
Y
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HOW TO MEASURE THE LONG RANGE CORRELATIONS:
Observables
For each event:
1) the event mean multiplicity in
BACKWARD or FORWARD rapidity
windows:
2) the event mean transverse
momentum for BACKWARD and
FORWARD rapidity windows:
nB , nF
1
pt B 
nB
Event-by-event:
We define the average value
of the observable in one rapidity
window
at the given value of another
observable in the second
window(regression):
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pt F
 pt B  nF
1

nF
or
nB

pt B
i
i 1
nF

pt F
i
i 1
 nB  nF
or
 ptB  ptF
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Usually:
Correlation coefficients are defined
– in the region where some linearity exists-for the absolute values of observables as:
 nB  nF  ann   nnnF
Here the strength of the multiplicity correlation
measured by the coefficient  nn
is
Correlation coefficients
(for the normalized observables):
 nB  n F
 nB 
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 ann   nn
N
N
nF
 nF 
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NA49 Collaboration and Feofilov G.A., Kolevatov R.S., Kondratiev V.P.,
Naumenko P.A. , Vechernin V.V., “Long-Range Correlations in PbPb
Collisions at 158 AGeV”. Reported in 2004 at XVII ISHEPP. In: Relativistic
Nuclear Physics and Quantum Chromodynamics, Proc. XVII Internat. Baldin
Seminar on High
Energy Physics Problems, vol.1, JINR, Dubna, 2005, 222-231
Min.bias data, 2 rapidity intervals: {-0.3,0.3} and {0.9,2.0}
NN
05 октября 2009
PtN
PtPt
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Long-range correlations and
collectivity effects in pp and
ppbar collisions:
experiment and PYTHIA
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Motivation: collectivity effects in pp
experiment, charged particle multiplicity
correlation
(ppbar collisions 0.3-1.8 TeV”, [2])
[2] E735 Collaboration, “Charged particle multiplicity correlations in ppbar collisions at
0.3-1.8 TeV”, Physics Letters B 353 (1995) 155-160
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Collectivity
Effects in
PYTHIA v6.3
PYTHIA
Model of multiple interactions
T. Sjöstrand, “Monte Carlo Generators”,
European School of High-Energy Physics
2006, Aronsborg, Sweden, 27 June 2006
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Parameters
Description
MSUB(91)
Elastic Scattering
MSUB(92)
Single Diffraction AB -> XB
MSUB(93)
Single Diffraction AB -> AX
MSUB(94)
Double Diffraction
MSUB(95)
Low Pt Production
MSUB(96)
Semihard QCD
PARP(85)
D=33%
in v6.325
PARP(86)
D=66%
in v6.325
“Colour correlations” - probability that an additional
interaction in the multiple interaction formalism gives
two gluons, with colour connections to ‘nearest
neighbours’ in momentum space
“Gluon-gluon string formation” - probability that an
additional interaction in the multiple interaction
formalism gives two gluons, either as described in
PARP(85) or as a closed gluon loop. Remaining
fraction is supposed to consist of quark–antiquark
pairs
Torbjörn Sjöstrand, Leif Lönnblad, Stephen
Mrenna, Peter Skands, “PYTHIA 6.3
Physics and Manual”, hep-ph/0308153, LU
TP 03–38, August 2003
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Final PYTHIA parameters were tuned using
<pt>Nch-Nch correlation data:
(report by A.Asryan at CERN, PWG2 31.03.08)
Values of parameters
Results are based on fitting
of experimental data on Pt-N
correlations in p-p and ppbar collisions from 17 to
1800 GeV.
In PYTHIA version 6.4 and
higher these values of
parameters are set as
default. See also R. Fields’
studies in
http://www.phys.ufl.edu/~rfield/cdf/
2008 Mar 31
Energy,
GeV
31
200
540
900
1800
MSUB(91)
0
Elastic scattering
0
1
1
1
1
MSUB(92)
1
Single diffraction
1
1
1
1
1
MSUB(93)
1
Single diffraction
1
1
1
1
1
MSUB(94)
1
Double diffraction
1
1
1
1
1
MSUB(95)
0
Low pt production
0
1
1
1
1
MSUB(96)
1
Semihard QCD
1
1
1
1
1
90%
90%
90%
90%
90%
PARP(86)
95%
Gluon string95%
formation
95%
95%
95%
95%
PYTHIA
Parameters
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PARP(85)
Gluon string90%
fusion
Page 17
“Collectivity” in PYTHIA
Distribution of # of particle emitting
sources (strings) and “collectivity”
0,9
Colour correlations and
Gluon-gluon string formation
in PYTHIA : influence on <p_t>Nch,
p+pbar collisions, 900 GeV
0,8
PYTHIA PARP3 100%
0,7
PYTHIA PARP1 90%
0,6
PYTHIA PARP4 33%
0,5
PYTHIA PARP6 00%
EPEM Model
0,4
pp столкновения
900 ГэВ
0,3
0,2
0,1
0
2,0
3,0
4,0
5,0
6,0
7,0
number of strings
8,0
9,0
10,
11,
12,
Effective Multi Pomeron Exchange Model
(EPEM):
N. Armesto, A. Asryan, D. Derkach, G. Feofilov,
“Analysis of pt-Nch Correlations in pp and
ppbar Collisions”, ALICE physics week, Erice,
Italy, 09 December 2005
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<pt>Nch-Nch correlation and collectivity effects in pp and ppbar collisions
at 17-1800 GeV [5]
Fig.4. Experimental data and model [5]
[5] N. Armesto, D. Derkach, G. A. Feofilov, “pt–Multiplicity Correlations in a Multi-pomeron Exchange
Model With String Collectivity Effects”; Physics of Atomic Nuclei, 71,No.12, 2087-2095(2008).
Long-range multiplicity correlation in ppbar collisions from 0.3-1.8
TeV: experiment E735 ( Physics Letters B 353 (1995) 155-160)
and our PYTHIA 6.4 results
(no fits!)
Fig.8. Correlation coefficient as a function of the rapidity gap between
two rapidity intervals (“backward” and “forward” intervals of 0.2 units ).
Long-range multiplicity correlation in ppbar collisions from
0.3-1.8 TeV: experiment (E735 Physics Letters B 353
(1995) 155-160, LEFT FIGURE) and our PYTHIA 6.4
results(RIGHT)
Fig. 9. Correlation coefficient as a function of the 2 rapidity interval width. There is no
gap between the “forward” and “backward” regions.
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Predictions for ALICE:
pp-collisions at 10 TeV
Fig.10. The n-n correlation strength for pp data, as a function of rapidity gap
for pp collisions at √sNN = 10 TeV at ALICE for 2 sets of collectivity parameters :
0.33,0.63} (pink circles), 0.9, 0.95(black circles)
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“Saturation” effect in longrange multiplicity correlation
and selection of “the very
central” events in
pp-collisions at the LHC
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Selection of “the very central events” using LRC data
PYTHIA-simulations: “high collectivity - left and
“
low collectivity” - rigth
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Some predictions for ALICE: Collectivity and “Saturation”
effects in long-range multiplicity correlation
Collectivity effects in
PYTHIA
In case of large
collectivity parameter
set, the “plateau”
observed in multiplicity
correlation is expected
to start earlier and to
have lower value: at the
level of <nB>~120 in vs.
<nB>~170 (see left
column for 0 gap).
Similar is the result for
the gap=3.4 units(right
column)
Fig.11. Collectivity and “Saturation” effect in long-range multiplicity
correlation: PYTHIA predictions for ALICE, pp collisions at √sNN = 10 TeV for 2
sets
of collectivity parameters : 0.33,0.63} (lower raw), 0.9, 0.95(upper raw) .
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Figures are for 2 values of rapidity gap: 0 (left column) and 3.34 (right column).
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“Saturation” effects in long-range multiplicity correlation
vs. “collectivity in PYTHIA” (PARP(85) and PARP(86)):
Multiplicity “plateau”
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“Saturation” effects in long-range <p_t>-multiplicity correlation
vs. “collectivity in PYTHIA” (PARP(85) and PARP(86):
:
<p_t>-”plateau”
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“Saturation” _effects in long-range <p_t>-multiplicity correlation for strange
particles Λ, 
<multipllclty> -“plateau” vs. “collectivity in PYTHIA” (PARP(85) and
PARP(86)):
_

For “plateau” events:
“High” collectivity:
<nB_lamdas>/<Nch_plateau>=
1.8/60.3=0.03 (!)
“Low” collectivity:
<nB_lambdas>/<Nch_plateau>=
2.3/98=0,023
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Features of “the plateau” (PYTHIA) events:
increase of collectivity effects in PYTHIA
(of Colour correlations and Gluon-gluon string formation)
leads to:
1) Increased formation of the number of paticle
emitting sources
2) Damping of the mean multipliicty of “plateau”
events
3) Increased <p_t> values for “plateau” events
3) 1.5 increase of yields Λ/<Nch> for “plateau”
events
 The very central рр-collisions!
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The 1st measurements of <n>n, <p_t>n and <p_t>p_t
correlations in рр collisions in ALICE at the LHC:
- 1.0
0
1.0
1) to start with SCAN IN η∈ [-1.0, +1.0], δ = 0. 2
2) TO SCAN IN [0, 2π],
3) TO SCAN IN p_t, <1 Gev/c, 1-2GeV/c, и >2 GeV/c
Future : “net-charge” LRC
Future : LRC for Strange and multistrange hyperons
Future : TO SCAN IN: η∈ [-2.0, +2.0]
Detectors: ITS, TPC, FMD
Future : TO SCAN IN:
η∈ [-3.7,+4.7]
ƞ
Pseudorapidity intervals for
the 1st pp-collisions study
(in the TPC domain)
The following set of pseudoarpidity intervals
(“windows”) were selected within the
TPC/ALICE domain (see Fig.1):
1. Correlation in full rapidity interval [-0.8 ..
0.8]
2. Backward-forward correlation using data
from symmetrical –variable width- windows
of 0.2,0.4,0.6,0.8 pseudorapidity units
3. Correlation for symmetrical windows of
0.2,0.4,0.6, units, - scanning of the gap
width
-0.8
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-0.4
0
0.4
0.8
Fig/1. The complete set of 11 pseudoarpidity intervals proposed f
or LRC study within the TPC/ALICE domain
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LRC Library
LRC Library includes 5 classes: TFit, TLRC, TNN, TPtN, TPtPt,
Long Range Correlation library algorythms provide:
Vizualization of regression curves, calculation of correlation
coffecients, statistical errors estimates of N-N, Pt-N and Pt-Pt
correlation coefficients.
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Examples of the Long-Range correlations
analysis AliROOT for ALICE at the LHC
10TeV
PDC’09 P-P data (run LHC9a4) Pythia
Pt -Nch correlation for [-0.8..0],[0..0.8] rapidity windows (September 2009)
b ~ 0.009 GeV/c
(PRELIMINARY)
PDC’09 P-P data (run LHC9a4) Pythia
Pt -Nch correlation for [-0.2..0],[0..0.2] rapidity windows (September 2009)
b ~ 0.016 GeV/c
(PRELIMINARY)
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Summary
1) It is proposed to start study of the <n>n, <p_t>n and
<p_t> p_t Long-Range Correlations (LRC) in рр collisions
in ALICE at the LHC.
2) This will provide a new information on the number of
particle emitting sources, formed in the collisions and to
select a class of unique
events that might be
characterized as “the very central collisions” , possessing
the maximal energy density
3) “Saturation effects” in <n>n or <p_t>n correlations in pp
collisions, - in case if they are confirmed experimentally, are important for the future analysis of possible formation
and hadronisation processes of the QGP.
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Acknowledgemnts
Authors are grateful to T. Sjöstrand
for permanent interest to these studies and
fruitful discussions.
THANK YOU FOR YOUR ATTENTION!
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BACK-UP SLIDES
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Since 2002: Long-Range Correlations as a
method to study string fusion
pheneomenon in ALICE
•
P.A.Bolokhov, M.A.Braun, G.A.Feofilov, V.P.Kondratiev, V.V.Vechernin,
Internal Note/PHY.ALICE-INT-2002-20(2002)16p;
•
P.A.Bolokhov, M.A.Braun, G.A.Feofilov,V.P.Kondratiev and
V.V.Vechernin,\\``Forward-Backward Correlations in Relativistic Heavy Ion
Collisions''.In: Relativistic Nuclear Physics and Quantum
Chromodynamics.\\Proceedings of the XVI International Baldin Seminar on
High Energy PhysicsProblems (2002),vol.1, JINR, Dubna, 2004, pp. 263271
•
P.A.Bolokhov, M.A.Braun, G.A.Feofilov,V.P.Kondratiev and
V.V.Vechernin,\\ ``Experimental Studies of Colour String Fusion at ALICE'‘ ,
In: Relativistic Nuclear Physics and Quantum Chromodynamics.\\
Proceedings of the XVI International Baldin Seminar on High Energy
Physics Problems (2002), vol.1.,JINR, Dubna, 2004, pp. 272-278
ALICE collaboration “ALICE: Physics Performance Report, Volume II”, J.
Phys. G: Nucl. Part. Phys. 32 (2006) 1295-2040 (Section: 6.5.15 - Longrange correlations, p.1749)
•
Feasibility of the measurement of the long-range
correlations in terms of statistics and systematic errors
during the first pp run at 0.9/10 TeV in 2008 in ALICE
1). Short 900 GeV min bias pp run is interesting for this analysis to start and to
compare to the existing data on multiplicity correlation
N-N long-range correlation : Statistics about 1 - 2 x 10^5 events
should be sufficient for the comparison to the existing data at 900 GeV(
E735 Collaboration, “Charged particle multiplicity correlations in ppbar collisions at
0.3-1.8 TeV”, Physics Letters B 353 (1995) 155-160 ) ,where about 150000 events
data were accumulated
2). 10 TeV min bias run has to provide 2-3 x 10^5 of events
for p_t-n correlation coefficient determination (This corresponds to [-1..0], [0..1]
rapidity windows).
In a case of smaller windows of 0.2 units of rapidity the minimal required
statistics will be 1 - 2 x 10^6 .
N-N long-range correlation saturation: study will
require statistics of about 10^7 events.
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# of particle emitting sources (strings)
for pp- collisions at 10 TeV (PYTHIA)
Distribution of
and Nch cuts
0.35
0.3
Nchb Max Cut = 20
0.25
Nchb Max Cut = 40
0.2
Nchb Max Cut = 60
Nchb Max Cut = 80
0.15
Nchb Max Cut = 100
0.1
Nchb Max Cut = 120
0.05
0
1
-0.05
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2
3
4
5
6
7
8
9
10
11
12
13
# of strings (PYTHIA)
14
15
16
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Результаты PYTHIA v6.325
p-pbar при 200 ГэВ
p-antip столкновения
200 ГэВ
|η| ≤ 2.5
SppS (UA1)
05 октября 2009
p-pbar при 540 ГэВ
p-antip столкновения
540 ГэВ
|η| ≤ 2.5
ISR (ABCCDHW)
42
Selection of
“the very central
events” using
LRC data
PYTHIAsimulations
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