Physics Letters B 783 (2018) 375–380
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Analysis of the anomalous electromagnetic moments of the tau lepton
in γ p collisions at the LHC
M. Köksal
a
, S.C.
˙
Inan
b
, A.A. Billur
b,∗
, Y. Özgüven
b
, M.K. Bahar
c
a
Department of Optical Engineering, Cumhuriyet University, 58140, Sivas, Turkey
b
Department of Physics, Cumhuriyet University, 58140, Sivas, Turkey
c
Department of Energy Systems Engineering, Karamanoglu Mehmetbey University, 70100, Karaman, Turkey
a r t i c l e i n f o a b s t r a c t
Article history:
Received
8 November 2017
Received
in revised form 9 July 2018
Accepted
10 July 2018
Available
online 11 July 2018
Editor:
A. Ringwald
In this study, we investigate the potential of the process pp → pγ
∗
p → pτ
¯
ν
τ
q
X at the LHC to examine
the anomalous electromagnetic moments of the tau lepton. We obtain 95% confidence level bounds on
the anomalous coupling parameters with various values of the integrated luminosity and center-of-mass
energy. The improved bounds have been obtained on the anomalous coupling parameters of electric
and magnetic moments of the tau lepton a
τ
and |d
τ
| compared to the current experimental sensitivity
bounds. The γ p mode of photon reactions at the LHC have shown that it has great potential for the
electromagnetic dipole moments studies of the tau lepton.
© 2018 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
The results obtained in the experimental studies of the anoma-
lous
magnetic moments of leptons contain both the estimated val-
ues
and the new physics contributions, which can not be predicted
by the Standard Model (SM). The tau lepton is more advantageous
than other leptons in determination of new physics effects since
the tau lepton has a larger mass. In many new physics theories,
new contributions arising from the anomalous magnetic moment
for a lepton with mass m are proportional to m
2
. For this reason,
since the mass of the tau lepton is much heavier than other lep-
tons,
providing anomalous magnetic moment of the tau lepton to
be more sensitive to electroweak and new physics loop contribu-
tions.
Additionally, the tau lepton has a much shorter lifetime than
other
leptons, so it is extremely difficult to measure the magnetic
moment of the tau lepton by using spin precession experiments.
Instead of spin precession experiments, high energy accelerator ex-
periments
have been done which include pair production of tau
leptons. However, in these experimental studies, a
τ
can not be
measured directly, since τ
¯
τγ contains off-shell photon or tau lep-
tons
(photon virtuality Q
2
= 10
5
–10
7
GeV
2
). The most sensitive
*
Corresponding author.
E-mail
addresses: mkoksal@cumhuriyet.edu.tr (M. Köksal),
sceminan@cumhuriyet.edu.tr (S.C.
˙
Inan), abillur@cumhuriyet.edu.tr (A.A. Billur),
phyozguvenyucel@gmail.com (Y. Özgüven), mussiv58@gmail.com (M.K. Bahar).
experimental bounds have been obtained for a
τ
through the pro-
cess
e
+
e
−
→e
+
e
−
τ
+
τ
−
at the 95% Confidence Level (C.L.) in LEP
is only of O(10
−2
) [1–3];
L3: −0.052 < a
τ
< 0.058,
OPAL: −0.068 < a
τ
< 0.065,
DELPHI: −0.052 < a
τ
< 0.013.
Given these conditions, it can be said that the use of accelerator
is more suitable to examine the anomalous magnetic moments of
the tau lepton.
The
SM theoretical prediction of the anomalous magnetic mo-
ment
of the tau lepton can be found by summing of all following
additives [4–7]:
a
QED
τ
=117324 × 10
−8
, (1)
a
EW
τ
=47 × 10
−8
, (2)
a
HAD
τ
=350.1 × 10
−8
. (3)
Hence, the SM value is obtained as a
SM
τ
= 0.00117721. Since this
value is far from the experimental sensitivity bounds, which is an
order of magnitude below leading QED calculations, more precise
experimental measurements should be made.
Another
interaction between the tau lepton and photon is CP vi-
olating
interaction which is induced by the electric dipole moment
|d
τ
|. The SM does not have sufficient information about origin of
https://doi.org/10.1016/j.physletb.2018.07.018
0370-2693/
© 2018 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
.