Long range forward–backward rapidity correlations in proton–proton collisions at LHC

Brogueira, P.; Deus, J. Dias de; Pajares, C.

doi:10.1016/j.physletb.2009.04.025

Cited by 22 publications

(23 citation statements)

References 33 publications

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“…Long-range rapidity correlations uncover properties of the dynamical system at a very early stage. For that reason the FB multiplicity correlations have been studied experimentally [1,2] and theoretically [3][4][5][6][7][8]. In this paper we show that the wounded-nucleon approach [9] to the initial stage of the collisions leads to a new manifestation of the FB fluctuations: the torqued fireball.…”

Section: Introductionmentioning

confidence: 94%

Torqued fireballs in relativistic heavy-ion collisions

2011

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We show that the fluctuations in the wounded-nucleon model of the initial stage of relativistic heavy-ion collisions, together with the natural assumption that the forward (backward) moving wounded nucleons emit particles preferably in the forward (backward) direction, lead to an eventby-event torqued fireball. The principal axes associated with the transverse shape are rotated in the forward region in the opposite direction than in the backward region. On the average, the standard deviation of the relative torque angle between the forward and backward rapidity regions is about 20• for the central and 10• for the mid-peripheral collisions. The hydrodynamic expansion of a torqued fireball leads to a torqued collective flow, yielding, in turn, torqued principal axes of the transverse-momentum distributions at different rapidities. We propose experimental measures, based on cumulants involving particles in different rapidity regions, which should allow for a quantitative determination of the effect from the data. To estimate the non-flow contributions from resonance decays we run Monte Carlo simulations with THERMINATOR. If the event-by-event torque effect is found in the data, it will support the assumptions concerning the fluctuations in the early stage of the fireball formation, as well as the hypothesis of the asymmetric rapidity shape of the emission functions of the moving sources in the nucleus-nucleus collisions.PACS numbers: 25.75Gz, 25.75.Ld

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Section: Introductionmentioning

confidence: 94%

Torqued fireballs in relativistic heavy-ion collisions

2011

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“…Since the energy density achieved in high multiplicity events produced in pp collisions at LHC is comparable to the reached density in CuCu central collisions or AuAu peripheral collisions at √ s N N = 200 GeV, it is pertinent to wonder about the possibility to obtain a similar high density medium which would be reflected in experimental observables, similar to heavy-ion collisions. An illustration of this would be the predicted ridge structure [8,9] observed by CMS collaboration [10] in pp collisions. Also, the eventuality that other observables, as long range rapidity correlations [11,12,13], energy loss [14], or the elliptic flow [15,16], are measurable in pp collisions, has been reckoned with in different frameworks.…”

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confidence: 98%

High multiplicityppevents andJ/ψproduction at energies available at the CERN Large Hadron Collider

Ferreiro

Pajares

2012

Phys. Rev. C

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We discuss the dependence of J/ψ production on the charged particle multiplicity in proton-proton collisions at LHC energies. We show that, in the framework of parton saturation or string interaction models, the hard J/ψ production exhibits a significant growth with the multiplicity, which is stronger than linear in the high density domain. This departure from linearity, that should affect any hard observable, applies for high multiplicity proton-proton collisions in the central rapidity region and is a consequence of the parton saturation or the strong interaction among colour ropes that take place at LHC energies. Our assumption, the existence of coherence effects present in proton-proton collisions at high energy, can also be checked by studying the particular shape of the probability distribution associated to the J/ψ production.RHIC [1,2,3,4] and LHC [5,6,7] data on heavy-ion collisions have shown several important features which indicate the formation of a high density partonic medium with characteristic properties as the low shear viscosity and high opacity. Since the energy density achieved in high multiplicity events produced in pp collisions at LHC is comparable to the reached density in CuCu central collisions or AuAu peripheral collisions at √ s N N = 200 GeV, it is pertinent to wonder about the possibility to obtain a similar high density medium which would be reflected in experimental observables, similar to heavy-ion collisions. An illustration of this would be the predicted ridge structure [8,9] observed by CMS collaboration [10] in pp collisions. Also, the eventuality that other observables, as long range rapidity correlations [11,12,13], energy loss [14], or the elliptic flow [15,16], are measurable in pp collisions, has been reckoned with in different frameworks.We address here to the J/ψ production in high multiplicity pp collisions. We will show that the rise of J/ψ production in the highest multiplicity events observed by the ALICE collaboration [17] can be naturally explained as a consequence of string interaction or parton saturation. This feature is particularly important, since, due to the absence of nuclear effects in this case, it can be use as a baseline in order to disentangle different mechanism that are expected in heavy-ion collisions, as the J/ψ suppression due to sequential dissociation [18] or the J/ψ enhancement due to the recombination of uncorrelated c andc quarks [19].

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“…Here we would like to emphasize the similarities between both approaches string percolation [1][2] and color glass condensate (CGC) or glasma [3] [4] and to show some predictions on rapidity long range correlations ridge structures [5][6] [7][8], width of the normalized multiplicity distributions and elliptic flow [9].…”

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confidence: 99%

“…In fact the area occupied by the strings divided by the area of the effective string gives the number of effective strings [5] [6],…”

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Rapidity long range correlations, parton percolation and color glass condensate

Bautista¹,

Deus²,

Pajares³

2011

AIP Conference Proceedings

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Abstract. The similarities between string percolation and Glasma results are emphasized, special attention being paid to rapidity long range correlations, ridge structure and elliptic flow. As the string density of high multiplicity pp collisions at LHC energies has similar value as the corresponding to Au−Au semi-central collisions at RHIC we also expect in pp collisions long rapidity correlations and ridge structure, extended more than 8 units in rapidity. In string percolation the relevant parameter is the transverse string density η, η ≡ N s πr 2 0 /πR 2 where N s is the number of strings, πr 2 0 the radial size of a single string and πR 2 the transverse size of the collision. η behaves like N 2/3 part and s ∆ . String percolation leads to reduction of particle density at mid-rapidity, and because of energy-momentum conservation, to an increase of the rapidity length of the effective strings. The basic formulae are, for particle density and forwhere F(η) is the color reduction factor, F(η) ≡ (1 − e −η )/η, and µ and < p 2 T > 1 are the particle density and the averaged transverse momentum squared of the single string (< p 2 T > 1 r 2 0 ≃ 1 4 ), 1 F(η) or more specifically in the large η limit, √ η, plays the role of the saturation scale of CGC. Indeed, from (1), the transverse size 1 Presented at the conference Quark Confinement and hadron spectrum IX. correlation is r 2 0 F(η) and 1/Q 2 s the corresponding one in CGC.As far as color electric field is concerned the effective strings can be identified with the flux tubes of the Glasma picture. In fact the area occupied by the strings divided by the area of the effective string gives the number of effective strings [5][6],which in the high density limit is equivalent to Q 2 s R 2 the number of flux tubes of the Glasma.In the process of fusion of strings one has to take care of the energy momentum conservation, which implies an increase in the length in rapidity of the string, thus the length of a cluster of N s strings is given byOne further notes that overall conservation of energy/ momentum regimes for the number of strings to behave aswhere Y is the beam rapidity, Y = ln( √ s/m) and λ = 2/7. Therefore ∆y Ns ≃ 2λ ∆YAs in the CGC the length in rapidity of the classical fields is 1/α s (Q 2 s ) and as the saturation scale is power behaved in Y , we end up in a formula of the kind of (5). Therefore longitudinal extension of the cluster of strings in string percolation as in the CGC, increases with energy as log(s), giving rise to long range rapidity correlations, even for pp at LHC. Notice that the transverse

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Long range forward–backward rapidity correlations in proton–proton collisions at LHC

Cited by 22 publications

References 33 publications

Torqued fireballs in relativistic heavy-ion collisions

Torqued fireballs in relativistic heavy-ion collisions

High multiplicityppevents andJ/ψproduction at energies available at the CERN Large Hadron Collider

Rapidity long range correlations, parton percolation and color glass condensate

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