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

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Outline

• Motivation

• Long-range correlations and collectivity effects in pp and ppbar collisions (experiment and PYTHIA)

• ALICE

• Conclusions

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

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Can we see the initial state effects?

Motivation:

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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.

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].

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[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

Fig.1. Quark-gluon strings and schematics for studies of Long-Range Correlations[1]

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 !

.

[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

Fluctuations !

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Long-Range Correlations (LRC)CORRELATIONS BETWEEN OBSERVABLES MEASURED IN TWO

RAPIDITY INTERVALS

“BACWARD” (B) “FORWARD”(F) Y*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'', Eur.Phys.J.C.32.535-546(2004)

)( yn

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HOW TO MEASURE THE LONG RANGE CORRELATIONS:

Observables

Bn

i

i

BtB

Bt pn

p1

1

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:

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):

FB nn ,

Fn

i

i

FtF

Ft pn

p1

1

tFFF ptBnBnBt pornorp

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Usually: Correlation coefficients are defined – in the region where some linearity exists-- for the absolute values of observables as:

FnnnnnB nanF

Correlation coefficients(for the normalized observables):

F

FNnn

Nnn

B

nB

n

na

n

nF

Here the strength of the multiplicity correlation is measured by the coefficient

nn

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}

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NN PtN PtPt

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])

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[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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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

“Colour correlations” - probability that an additional interaction in the multiple interaction formalism gives two gluons, with colour connections to ‘nearest neighbours’ in momentum space

PARP(86)

D=66%

in v6.325“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

Collectivity Effects inPYTHIA v6.3

PYTHIAModel of multiple interactionsT. Sjöstrand, “Monte Carlo Generators”, European School of High-Energy Physics 2006, Aronsborg, Sweden, 27 June 2006

Final PYTHIA parameters were tuned using <pt>Nch-Nch correlation data: (report by A.Asryan at CERN, PWG2 31.03.08)

Energy, GeVPYTHIA

Parameters

17 31 200 540 900 1800

MSUB(91) 0 0 1 1 1 1

MSUB(92) 1 1 1 1 1 1

MSUB(93) 1 1 1 1 1 1

MSUB(94) 1 1 1 1 1 1

MSUB(95) 0 0 1 1 1 1

MSUB(96) 1 1 1 1 1 1

PARP(85) 90% 90% 90% 90% 90% 90%

PARP(86) 95% 95% 95% 95% 95% 95%

Values of parameters

Low pt production

Elastic scattering

Single diffraction

Single diffraction

Double diffraction

Semihard QCD

Gluon string fusion

Gluon string formation

Results are based on fitting of experimental data on Pt-N correlations in p-p and p-pbar 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

2008 Mar 31 Page 17

http://www.phys.ufl.edu/~rfield/cdf/

2,03,0

4,05,0

6,07,0

8,09,0

10,11,

12,

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

number of strings

PYTHIA PARP3 100%

PYTHIA PARP1 90%

PYTHIA PARP4 33%

PYTHIA PARP6 00%

EPEM Model

pp столкновения

900 ГэВ

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

Colour correlations and

Gluon-gluon string formation

in PYTHIA : influence on <p_t>Nch,

p+pbar collisions, 900 GeV

Distribution of # of particle emitting sources (strings) and “collectivity”

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“Collectivity” in PYTHIA

<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)

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Fig. 9. Correlation coefficient as a function of the 2 rapidity interval width. There is no gap between the “forward” and “backward” regions.

Predictions for ALICE: pp-collisions at 10 TeV

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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 long-range multiplicity correlation and selection of “the very central” events in pp-collisions at the LHC

Selection of “the very central events” using LRC dataPYTHIA-simulations: “high collectivity - left and

“ low collectivity” - rigth

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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) .Figures are for 2 values of rapidity gap: 0 (left column) and 3.34 (right column). Backward and forward rapidity intervals are of 0.2 units of rapidity.

Some predictions for ALICE: Collectivity and “Saturation”

effects in long-range multiplicity correlationCollectivity 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)

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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 correlationvs. “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

_

_

_

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!

29

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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) 1) to start with SCAN IN to start with SCAN IN η [-1.0, +1.0], ∈ δ = 0. 2 2)2) TO SCAN IN TO SCAN IN [0, 2π], 3) TO SCAN IN3) TO SCAN IN p_t, <1 Gev/c, 1-2GeV/c, p_t, <1 Gev/c, 1-2GeV/c, и и >2 GeV/c>2 GeV/c

Future : Future : “net-charge” LRC“net-charge” LRCFuture : Future : LRC for Strange and multistrange hyperonsLRC for Strange and multistrange hyperonsFuture : Future : TO SCAN INTO SCAN IN: η [-2.0, +2.0] ∈

-- 1.01.0 ƞƞ0 1.0

DetectorsDetectors: : ITS, TPC, FMDITS, TPC, FMD

Future : Future : TO SCAN INTO SCAN IN: η [-3.7,+4.7]∈

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0-0.8 -0.4 0.4 0.8

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

Fig/1. The complete set of 11 pseudoarpidity intervals proposed for LRC study within the TPC/ALICE domain

Pseudorapidity intervals for the 1st pp-collisions study (in the TPC domain)

LRC Library

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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.

Examples of the Long-Range correlations analysis AliROOT for ALICE at the LHC

10TeV

PDC’09 P-P data (run LHC9a4) PythiaPt -Nch correlation for [-0.8..0],[0..0.8] rapidity windows (September 2009)b ~ 0.009 GeV/c(PRELIMINARY)

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PDC’09 P-P data (run LHC9a4) PythiaPt -Nch correlation for [-0.2..0],[0..0.2] rapidity windows (September 2009)b ~ 0.016 GeV/c(PRELIMINARY)

Summary

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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.

AcknowledgemntsAuthors 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

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. 263-271

• 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 - Long-range correlations, p.1749)

Feasibility of the measurement of the long-range Feasibility of the measurement of the long-range correlations in terms of statistics and systematic errors correlations in terms of statistics and systematic errors during the first pp run at 0.9/10 TeV in 2008 in ALICE during the first pp run at 0.9/10 TeV in 2008 in ALICE

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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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Результаты PYTHIA v6.325

p-pbar при 200 ГэВ p-pbar при 540 ГэВ

p-antip столкновения

200 ГэВ

|η| ≤ 2.5

SppS (UA1)

p-antip столкновения540 ГэВ

|η| ≤ 2.5

ISR (ABCCDHW)

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Selection of “the very central events” using

LRC data

PYTHIA-simulations

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