未来强子对撞机对leptoquark对生产敏感度：di-muon di-jets通道

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本文主要探讨了未来大型强子对撞机（LHC）的高光度（HL-LHC）和高能量（HE-LHC）模式，以及潜在的100 TeV未来圆形对撞机（FCC-hh）在探测leptoquark（LQ）对生产方面的敏感性。LQ是一种假设的粒子，它具有介于夸克和轻子之间的特性，对于解释中性点电荷B异常现象具有重要意义。研究者针对LQ的μ加射线衰变模式进行了深入分析。作者们着重关注的是di-muon di-jets（一对μ子和一对喷射物）这个特定通道，这是LQ信号的一个可能迹象。他们利用标准模型（SM）的背景模拟以及考虑了实际的检测器效果，以评估这些未来对撞机在不同能量下对LQ的质量范围内的探测能力。他们的分析基于ATLAS Run II实验的搜索结果，这提供了基准来验证和优化他们的计算。在研究中，发现HL-LHC对于最高1.8 TeV的LQ质量具有相当高的敏感度，这意味着它有可能在这范围内观察到LQ的存在。HE-LHC的敏感性则更为显著，可以达到4.8 TeV，显示出更高的能量对寻找这类粒子有着显著的优势。而FCC-hh作为下一代的大型对撞机，其对LQ的敏感性更是惊人，能够探测到质量高达13.5 TeV的LQ，这是现有技术的一大突破。这项工作不仅提供了对未来粒子物理实验的预测性结果，也强调了高能物理实验在探索新物理现象中的关键作用。通过比较不同对撞机的性能，研究人员能够确定优先级和资源分配，以最大程度地提高发现新物理的可能性。此外，文章的开放获取性质意味着这一成果可以被全球的物理学家自由查阅和进一步研究，推动了科学知识的共享和进步。

Eur. Phys. J. A (2020) 80 :170 Page 3 of 14 170

−

Fig. 3 Example Feynman diagrams of LQ pair production at a hadron

collider followed by subsequent decay of each LQ into μj

Table 1 Design centre of mass energies and integrated luminosities of

the LHC Run II and future hadron colliders

√

s (TeV) L (ab

−1

)

LHC 13 0.14

HL-LHC 14 3

HE-LHC 27 15

FCC-hh 100 20

must carry colour to preserve SU(3) and therefore, by SU(3)

gauge symmetry, must couple to gluons via the QCD cou-

pling constant.

Run II of 13 TeV running at the LHC has produced

some 139 fb

−1

of integrated luminosity each for ATLAS

and CMS. A search for NCBA-solving LQs using all of this

data is eagerly awaited, having not appeared yet. The next

phase of LHC running will be in the 14 TeV high-luminosity

phase (HL-LHC), with a design integrated luminosity of 3

−1

. This phase will provide much new information on the

NCBAs [34] concurrently with Belle II [35,36]. At the same

time, direct searches for new particles [37] may include S

One potential future LHC upgrade would be to insert 16

Tesla magnets into the current LHC ring, resulting in the

high energy LHC (HE-LHC), running at a nominal energy of

27 TeV with a design integrated luminosity of 15 ab

−1

[38].

Ultimately, such magnets could be placed within a much

larger tunnel, resulting in the Future Circular Collider, which

could collide protons (FCC-hh) at a centre of mass energy

√

s = 100 TeV with a design luminosity of 20 ab

−1

[39,40].

We arrive at the question central to this paper, which is:

For LQs which ﬁt the NCBAs, what is the LQ mass

sensitivity of future hadron colliders?

We wish to estimate the sensitivity for the Run II, HL-LHC,

HE-LHC and FCC-hh options. Table 1 summarises the centre

of mass energies and integrated luminosities that will be used

for each collider in our estimates. We hope that this will help

inform the European Strategy for particle physics, which is

currently deliberating on various scientiﬁc priorities.

A previous estimate of future collider sensitivity to S

LQs

consistent with the NCBAs was made in Ref. [19], which

projected current sensitivity to higher centre of mass ener-

gies and luminosities. However, the sensitivity estimate had

two highly dubious approximations. The ﬁrst was that experi-

mental efﬁciency and acceptance did not change with centre

of mass energy. In fact, at large m

and at high energies

(particularly at FCC-hh), the decay products from LQs will

be highly boosted. This has two effects: the muons will be

pushed closer to the jets, meaning that more of them will fail

isolation criteria. Also, at higher energies, the muon momen-

tum resolution is likely to be very poor, since such hard

muons can only be bent to a limited extent by the magnets.

This will also affect the signal efﬁciency from peak broad-

ening. The second dubious approximation was that the LQs

are produced exactly at threshold. This is likely to introduce

large uncertainties. We shall rectify these approximations in

our paper by performing a fast simulation of the signal and

backgrounds, as well as including detector response. The

ﬁrst of these approximations has already been found to have

non-trivial effects upon the predicted future hadron collider

sensitivity of Z



explanations of the NCBAs [22,41]. The

estimate in this paper should be much more accurate than the

previous pioneering determination in Ref. [19].

Searches for LQ pair production with subsequent decays

of each into a muon and a jet have already been performed at

the 13 TeV LHC. The ATLAS Collaboration set a 95% con-

ﬁdence level lower limit on m

of 1.05 TeV from 3.2 fb

−1

of pp collisions [42]. This is a simple cut-based analysis,

which we adopt for estimating future hadron collider sensi-

tivity. More recent experimental analyses were made more

sophisticated in order to squeeze more sensitivity out of them.

The CMS Collaboration maximise their sensitivity using a

multi-dimensional optimisation of the ﬁnal selection for each

in 36 fb

−1

of delivered beam at the LHC [43], ﬁnding

a 95% CL lower bound of m

> 1.28 TeV. The ATLAS

collaboration has also performed a search in 36 fb

−1

of 13

TeV pp collisions for LQs decaying to muons and jets. They

utilise differential cross-section measurements and boosted

decision trees to obtain a lower bound of m

> 1.23 TeV.

However, such a level of sophistication is unnecessary for

our purposes, where the uncertainties involved in estimating

future collider sensitivities (for example because we do not

yet know the experimental design) are much larger than the

gain in sensitivity. Thus, following the much simpler method-

ology in Ref. [42] is sufﬁcient for our purposes. The NCBAs

predict that there should be couplings between S

and

b, μ

from the ﬁrst term in Eq. 5. Thus we expect a decay channel

→

bμ to be open. In the experimental analysis we choose,

the bottom quark remains untagged and is counted merely as a

light jet. We note that the second term in Eq. 5 may simultane-

ously predict S

decays to top quarks and muons. This mode

is more complicated than the one we choose for analysis,

and we leave it for future work. For a discussion of potential

analysis strategies for this decay mode, see Ref. [44].

Collider sensitivity to LQ pair production is limited by SM

background rates. Therefore the estimation of such back-

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