Physics Letters B 795 (2019) 339–345
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Extending the constraint for axion-like particles as resonances
at the LHC and laser beam experiments
C. Baldenegro
a
, S. Hassani
b
, C. Royon
a
, L. Schoeffel
b,∗
a
University of Kansas, Lawrence, KS, United States of America
b
CEA Saclay, Irfu/DPhP, Gif-sur-Yvette, France
a r t i c l e i n f o a b s t r a c t
Article history:
Received
12 March 2019
Received
in revised form 16 May 2019
Accepted
14 June 2019
Available
online 17 June 2019
Editor:
A. Ringwald
We study the discovery potential of axion-like particles (ALP), pseudo-scalars weakly coupled to Standard
Model fields, at the Large Hadron Collider (LHC). Our focus is on ALPs coupled to the electromagnetic
field, which would induce anomalous scattering of light-by-light. This can be directly probed in central
exclusive production of photon pairs in ultra-peripheral collisions at the LHC in proton and heavy-
ion
collisions. We consider non-standard collision modes of the LHC, such as argon-argon collisions at
√
s
NN
= 7TeV and proton-lead collisions at
√
s
NN
= 8.16 TeV, to access regions in the parameter space
complementary to the ones previously considered for lead-lead and proton-proton collisions. In addition,
we show that, using laser beam interactions, we can constrain ALPs as resonant deviations in the
refractive index induced by anomalous light-by-light scattering effects. If we combine the aforementioned
approaches, ALPs can be probed in a wide range of masses from the eV scale up to the TeV scale.
© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
Charge-parity (CP) violation is an important consequence of
the Standard Model (SM) of particle physics. Though CP violation
is inherent in the construction of the SM, there is a longstand-
ing
question of why quantum chromodynamics (QCD) seems to
preserve CP symmetry, since in principle there could be CP vi-
olating
terms in the QCD Lagrangian density. Indeed, the strong
CP problem is supported by the absence of a neutron electric
dipole moment [1]. To solve it, scalar or pseudo-scalar complex
fields, called axions, have been postulated [2–4]. It has been spec-
ulated
that cold axions could have been produced in abundance
during the QCD phase transition in the early universe and that
they may constitute one element of the cold dark matter [5]. Ax-
ions
considered in these models have small masses (below the
meV scale), and have been heavily constrained by dedicated axion
helioscopes. More generally, pseudo-scalars coupled to SM parti-
cles,
known as axion-like particles (ALP), appear in theories with
spontaneously broken global, approximate, symmetries as pseudo
*
Corresponding author.
E-mail
addresses: c.baldenegro@cern.ch (C. Baldenegro), samira.hassani@cern.ch
(S. Hassani),
christophe.royon@cern.ch (C. Royon), laurent.olivier.schoeffel@cern.ch
(L. Schoeffel).
Nambu-Goldstone bosons. For instance, ALPs appear in supersym-
metric
extensions of the SM or string theories [6–9]. The focus of
this letter is on ALPs with a coupling to photons. ALPs with these
couplings have been heavily constrained for sub-eV masses, but for
masses above the eV scale and up to the TeV scale, collider-based
searches in electron-positron or hadron-hadron collisions are nec-
essary.
The problem of searching for these particles relying only on
their coupling to photons aggravates in hadronic colliders, where
the dominant interactions are nuclear in nature.
In
this letter, we discuss the sensitivity to ALPs weakly coupled
to the electromagnetic field in the context of light-by-light scatter-
ing
in a wide domain in mass, benefitting from the fact that the
LHC can accelerate protons and heavy-ions [10–13]. First, we ex-
pose
how the LHC data can be used to extend the search for ALPs
beyond what is currently accessible or expected for masses above
a few GeV and up to a few TeV [13–15], with an emphasis on
non-standard collision modes of the LHC. It has been shown that
searches based on ultra-peripheral collisions in lead-lead collisions
constrain ALPs between masses of 1 GeV to about 100 GeV [14],
whereas searches based on proton-proton collisions using the pro-
ton
tagging technique can constrain ALPs masses between ∼ 500
GeV and 2 TeV [15]. These searches can be seen as the extreme
ends of the high intensity frontier (lead-lead) and the high energy
frontier (proton-proton) of photon-photon collisions at the LHC.
https://doi.org/10.1016/j.physletb.2019.06.029
0370-2693/
© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.