LHC pPb碰撞中BFKL动力学在矢量介子光产生中的探索

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本文主要探讨了在CERN LHC的pPb碰撞中，利用BFKL动力学研究矢量介子（如ρ介子、J/ψ）的光子产生现象。BFKL动力学，源自巴库林-弗里德曼-李维奇-凯特勒（Balitsky-Fadin-Kuraev-Lipatov）理论，是一种在高能量子色动力学中描述强相互作用的非线性修正，特别适用于处理在大动量转移（large-t）条件下的过程。作者们假设在pPb碰撞中，单重态的彩色交换在传递大动量时起主导作用，这使得他们能够应用BFKL的非正向解来计算Pb-p碰撞转化为Pb+矢量介子+jet+X的反应过程中，尤其是rapidity gap（即在粒子产生的狭缝中的空缺）的分布以及总横截面积。rapidity在高能物理中是一个关键概念，它表示粒子产生的方向相对于碰撞中心的快慢程度，这对于理解碰撞能量的分配至关重要。研究的焦点在于估计这些过程在LHC的能量条件下发生的概率，考虑到BFKL方程在高能和大动量转移下的行为。通过对BFKL方程的解析，研究人员能够预测出这些过程的动态特性，并将其与现有的实验数据进行比较，以验证BFKL动力学的有效性。值得注意的是，LHCb实验组的探测能力在这类事件中得到了充分考虑，研究预测了在LHCb的实验范围内，与BFKL动力学相关的横截面会有显著的增强。这不仅证明了在大型强子对撞机上观察此类过程的可能性，而且也为实验上探测BFKL动力学提供了一种新的途径。这篇论文为理解在高能环境下矢量介子光子生产的过程提供了重要的理论基础，展示了BFKL动力学在解释这种复杂碰撞中的重要作用，并为未来的实验设计和数据解读提供了指导。同时，它也强调了实验验证BFKL理论预言对于深化我们对强相互作用理解的重要性。

Physics Letters B 776 (2018) 424–429

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Probing the BFKL dynamics in the vector meson photoproduction

at large-t in pPb collisions at the CERN LHC

V.P. Gonçalves

∗

, W.K. Sauter

High and Medium Energy Group, Instituto de Física e Matemática, Universidade Federal de Pelotas, Caixa Postal 354, CEP 96010-900, Pelotas, RS, Brazil

a r t i c l e i n f o a b s t r a c t

Article history:

Received

18 October 2017

Received

in revised form 26 November 2017

Accepted

28 November 2017

Available

online 2 December 2017

Editor: A.

Ringwald

Keywords:

Vector

meson production

BFKL

formalism

Photon-induced

interactions

The photoproduction of vector mesons in pPb collisions at LHC energies is investigated assuming that

the color singlet t-channel exchange carries a large momentum transfer t. The rapidity distributions and

total cross sections for the process Pb p → Pb ⊗ V ⊗ jet + X, with V = ρ, J/ and ⊗ representing a

rapidity gap in the ﬁnal state, are estimated considering the non-forward solution of the BFKL equation

at high energy and large-t. A comparison with the predictions obtained at the Born level also is

presented. We predict a large enhancement of the cross sections associated to the BFKL dynamics in the

kinematical range probed by the LHCb Collaboration. Moreover, our results indicate that the experimental

identiﬁcation can be feasible at the LHC and that this process can be used to probe the BFKL dynamics.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

The study of hadronic collisions at the Large Hadron Collider

(LHC) offers a unique possibility to probe the theory of the strong

interactions – the Quantum Chromodynamics (QCD) – in a new

and hitherto unexplored energy regime [1]. In the last decades,

several approaches were proposed to describe the QCD evolution

at high energies [2]. One them is the BFKL approach, proposed

by Lipatov and collaborators [3] in the late 1970s to describe the

Regge limit of hadronic reactions, which predicts that the cross

sections will have a steep increasing with the center-of-mass en-

ergy.

As this behavior implies the violation of unitarity at very

high energies, the BFKL approach is expected to be valid only in

a limited kinematical window between the standard DGLAP de-

scription

of the QCD evolution and more sophisticated non-linear

approaches [2]. Such aspect implies that the probe of the BFKL dy-

namics

is a theoretical and experimental challenge. During the last

years, promising results have been obtained in treatment of the

Mueller–Navelet jets [4,5] and dihadron production separated by a

large rapidity gap [6] as well related experimental measurements

were performed at the LHC [7]. However, such results indicate e.g.

that in order to discriminate between the next-to-leading ﬁxed or-

der

calculation and the BFKL prediction for the Mueller–Navelet

jets a very precise measurement would be needed, which become

the probe of the BFKL dynamics in these processes a hard task.

Corresponding author.

E-mail

addresses: barros@ufpel.edu.br (V.P. Gonçalves),

werner.sauter@ufpel.edu.br (W.K. Sauter).

An alternative to probe the BFKL dynamics is the study of

photon-induced interactions at the LHC [8], where the maxi-

mum

photon–photon and photon–hadron center-of-mass energies

present in these reactions are at least one order of magnitude

larger than those reached in previous e

−

and ep (A) colliders. In

recent years, several authors have investigated the impact of the

BFKL evolution on observables that can be measured in photon-

induced

interactions at the LHC [9–14]. Such studies indicated that

a future experimental analysis of these observables at the LHC

could provide valuable information on the QCD dynamics. In par-

ticular,

the results presented in Refs. [11,12] for the vector meson

photoproduction at larg e momentum transfer in hadronic collisions

demonstrated that the magnitude of the cross sections for the pho-

toproduction

of ρ, J/ and ϒ in pp and AA collisions is large and

that an experimental analysis is, in principle, feasible at the LHC.

Our goal in this paper is to complement these previous studies by

the analysis of diffractive vector meson photoproduction at large-t

pPb collisions. Differently from symmetric hadronic collisions

(pp and AA), where the rapidity distributions of the vector mesons

in the ﬁnal state receive contributions from photon–hadron inter-

actions

with small and large center-of-mass energies, in the case of

pPb collisions, the process is dominated by γ p interactions, with

the photons generated by the nucleus. Consequently, the relation

between the rapidity distributions and the energy dependence of

the γ p cross section is determined unambiguously. In other words,

the analysis of this observable can be used to probe the energy

evolution predicted by the BFKL dynamics.

https://doi.org/10.1016/j.physletb.2017.11.069

0370-2693/

SCOAP

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