LHC与Tevatron数据揭示：大动量J/ψ对产生中的双parton散射与αs5效应

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本文主要探讨了在大型强子对撞机(LHC)的CMS实验和 Tevatron的D0实验中观测到的J/ψ对生产现象，特别关注了在高动量区域的物理现象。研究发现，这些最新的实验数据揭示了不同生产机制在不同动力学条件下的重要性，特别是双部分on散射(double parton scattering, DPS)和较高阶的αs5修正。在大动量条件下，单部分on散射(NLO)的贡献在J/ψ对的产生中占据主导地位，尤其是在具有较大横向动量时。这种发现有助于解决理论预测与实验结果之间存在的巨大差异，特别是在CMS实验中，大对不变质量区间的J/ψ对生成倾向于由双部分on散射主导，这表明在某些动力学条件下，双部分on散射对于理解这些高能粒子对的产生至关重要。文章首次对αs6处的主导阶次部分on散射类别进行了精确的量规不变和红外安全评估，重点关注PT-4（最短部分on动量之和）的情况。在双部分on散射占优势的情况下，J/ψ对的产生还涉及 charm态的激发，这与单部分on散射过程中的行为有显著区别。这种特性使得可以通过分析J/ψ对的生成特征来区分是双部分on散射主导（DPS）还是单部分on散射主导（SPS）的极端情况。总结来说，这篇研究不仅加深了我们对J/ψ对产生机制的理解，而且提供了重要的工具来测试量子色动力学(QCD)的更高阶修正，特别是双部分on散射效应在强相互作用中的角色。这对于完善理论模型和提高对高能物理现象预测的准确性具有重要意义。

Physics Letters B 751 (2015) 479–486

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

J/ψ-pair production at large momenta: Indications for double parton

scatterings and large α

contributions

Jean-Philippe Lansberg

, Hua-Sheng Shao

b,c

IPNO, Université Paris-Sud, CNRS/IN2P3, F-91406, Orsay, France

Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China

PH Department, TH Unit, CERN, CH-1211, Geneva 23, Switzerland

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

Article history:

Received

2 April 2015

Received

in revised form 26 October 2015

Accepted

28 October 2015

Available

online 3 November 2015

Editor:

J.-P. Blaizot

Keywords:

Quarkonium

production

Double

parton scattering

QCD

corrections

We demonstrate that the recent studies of J /ψ-pair production by CMS at the LHC and by D0 at the

Tevatron reveal the presence of different production mechanisms in different kinematical regions. We

ﬁnd out that next-to-leading-order single parton scattering contributions at α

dominate the yield at

large transverse momenta of the pair. Our analysis further emphasises the importance of double parton

scatterings – which are expected to dominate the yield at large J/ψ-rapidity differences – at large

invariant masses of the pair in the CMS acceptance, and thereby solve a large discrepancy between the

theory and the CMS data. In addition, we provide the ﬁrst exact – gauge-invariant and infrared-safe –

evaluation of a class of leading-P

−4

) next-to-next-to-leading-order contributions at α

, which can

be relevant in the region of large values of P

T min

= min(P

T 1

, P

T 2

). Finally, we derive simple relations

for the feed-down fractions from the production of an excited charmonium state with a J /ψ in the

case of the dominance of the double parton scatterings, which signiﬁcantly deviate from those for single

parton scatterings. Such relations can be used to discriminate these extreme scenarios, either DPS or SPS

dominance.

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

1. Introduction

Heavy-quarkonium production has attracted considerable inter-

est

in the high-energy physics community since the J /ψ discovery,

exactly forty years ago. It indeed probes the strong interaction at

the interplay of its perturbative and non-perturbative regimes [1].

It can also help to understand a new dynamics of hadron collision

where multiple (hard) parton scatterings (MPS) take place. MPS

are normally very rare since already a single (hard) parton scat-

tering

(SPS) is rare as compared to soft scatterings. Owing to the

high parton ﬂux at high energies, MPS should be likelier at the

LHC, starting with two short-distance interactions from a single

hadron–hadron collision, usually referred to as double parton scat-

tering

(DPS). These have been searched in 4-jets [2–4], γ + 3-jets

[5,6], W +2-jets [7,8], J/ψ + W [9], J/ψ + Z [10], 4-charm [11],

J/ψ +charm [11] and J/ψ + J /ψ [12] ﬁnal states.

E-mail address: lansberg@in2p3.fr (J.-P. Lansberg).

Along these lines, J /ψ-pair hadroproduction is of great interest.

First, it provides an original tool to study quarkonium produc-

tion

in conventional SPSs. Most of the earlier theoretical studies

are based on SPSs [13–22]; some using the colour-singlet model

(CSM) [23], others Nonrelativistic QCD (NRQCD) [24]. Moreover, it

is widely claimed that DPSs [25–28] could indeed be a signiﬁcant

source of J /ψ pairs at the LHC in proton–proton collisions and

in proton–nucleus/nucleus–nucleus collisions [29,30]. Generally, it

remains a poorly understood process. Its measurement with both

J/ψ decaying into a muon pair is a clean signal, accessible to most

experiments, which is complementary to the DPS studies based on

open charm mesons and hadronic jets. With respect to the lat-

ter,

it allows one to investigate the physics of DPS at lower scales

and lower x where different mechanisms may be at work (see e.g.

[31]).

The

ﬁrst observation of J/ψ-pair events dates back to that of

the CERN-NA3 Collaboration [32,33]. Recently, the LHCb [34], CMS

[35] and D0 [12] Collaborations reported their measurements at

the LHC and the Tevatron. In contrast to Kom et al. [25], we re-

cently

pointed out [21] that no deﬁnite conclusion on the presence

http://dx.doi.org/10.1016/j.physletb.2015.10.083

0370-2693/

SCOAP

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