Eur. Phys. J. C (2020) 80:128
https://doi.org/10.1140/epjc/s10052-020-7715-2
Regular Article - Experimental Physics
Prospects for Lorentz invariance violation searches with top pair
production at the LHC and future hadron colliders
Aurélien Carle
a
, Nicolas Chanon
b
, Stéphane Perriès
c
University of Lyon, Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822, 69622 Villeurbanne, France
Received: 27 November 2019 / Accepted: 4 February 2020
© The Author(s) 2020
Abstract This paper investigates the impact of hypotheti-
cal Lorentz invariance violation on the t
¯
t production at the
LHC and future hadron colliders. Possible deviations from
Lorentz symmetry remain poorly constrained in the top quark
sector. With a dedicated analysis of t
¯
t events produced at
the LHC, bounds in the top sector can be improved by up
to three orders of magnitude relative to the only measure-
ment existing so far, performed at Tevatron. The sensitivity
will be even further enhanced at the HL-LHC and future
colliders.
1 Introduction
Lorentz Invariance is a fundamental symmetry of the Stan-
dard Model (SM), however it is not expected to be conserved
necessarily at the high energy scale of quantum gravity (e.g.
in string theory [1] or quantum loop gravity [2]) where space-
time could undergo violent fluctuations. Quantum field the-
ories with non-commutative geometries introduce a funda-
mental length-scale, hence exhibiting Lorentz Invariance vio-
lation (LIV) [3]. Cosmologies with spacetime varying cou-
plings are natural in some grand unified theories and lead to
signatures of LIV [4]. Remnants from the symmetry breaking
would manifest themselves at a lower energy, and constitute
an appealing signature.
Such signatures are predicted within the “Standard Model
Extension” (SME) [5,6], an Effective Field Theory (EFT)
considering all possible Lorentz- and CPT-violating opera-
tors in the Lagrangian (CPT breaking implies Lorentz vio-
lation for local theories [7]) in a model-independent way,
preserving gauge invariance, renormalizability, locality and
observer causality. The SME was tested with atomic clocks,
a
e-mail: a.carle@ipnl.in2p3.fr
b
e-mail: n.chanon@ipnl.in2p3.fr (corresponding author)
c
e-mail: s.perries@ipnl.in2p3.fr
penning traps, matter and antimatter spectroscopy, colliders
and astroparticle experiments (for a review, see [8]), and an
impressive set of results was compiled [9].
At hadron colliders the quark sector can be probed. The
quark sector is constrained mostly with flavour measure-
ments from neutral meson mixing. The most recent search for
LIV and CPT breaking in the b-quark sector was performed at
LHCb, using changes in B
(s)
mixing with sidereal time [10].
However, within the SME, values of the EFT coefficients are
species-dependent and are different for each quark flavour.
In contrast to the b-quark sector, the top quark sector remains
a vastly unexplored area for LIV searches, and its SME coef-
ficients needs to be precisely measured. Furthermore, the top
quark is the only quark decaying before hadronizing, provid-
ing the unique possibility to perform a search for LIV free of
non-perturbative QCD effects.
Only one actual measurement was ever performed in the
top quark sector, at the DØ experiment (Tevatron). No evi-
dence for LIV was found, with a 10% absolute uncertainty on
the measured Lorentz violating (and CPT-conserving) SME
coefficients [11]. This sensitivity, well below the precision
obtained in the other quark sectors, calls for new measure-
ments at present and future colliders. The LHC is a top
factory, producing top quark pairs (t
¯
t) at a high rate, and
provides a unique opportunity for measuring precisely SME
coefficients in the top sector. In this paper, we will derive
the expected sensitivity to LIV using the top pair production
signature.
2 Theoretical setup
The SME describes the interaction of Lorentz-violating
“background fields” with the particles of the SM [6]. They
can arise in theories like the string scenario [1], where certain
fields acquire a non-zero vacuum expectation value thereby
spontaneously breaking the Lorentz symmetry.
0123456789().: V,-vol
123