Research Article
Dark Photon Searches Using Displaced
Vertices at Low Energy 𝑒
+
𝑒
−
Colliders
Fabio Bossi
Laboratori Nazionali dell’INFN, Via E. Fermi 40, 00044 Frascati, Rome, Italy
Correspondence should be addressed to Fabio Bossi; fabio.bossi@lnf.infn.it
Received November ; Accepted January ; Published March
Academic Editor: Jean-Ren
´
e Cudell
Copyright © Fabio Bossi. is is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e
publication of this article was funded by SCOAP
.
e existence of a new, photon-like, massive particle, the
or dark photon, is postulated in several extensions of the Standard
Model. ese models are oen advocated to explain some recent puzzling astrophysical observations, as well as to solve the so far
unexplained deviation between the measured and calculated values of the muon anomaly. Dark photons can be produced at
+
−
colliders both in continuum events and in vector meson transitions and can eventually decay into an electron-positron pair. For
a proper choice of the parameters of the theory, a
can have a relatively long lifetime and can therefore be observed as an
+
−
vertex well separated by the primary interaction point. is case is discussed in reference to very high luminosity
+
−
colliders
either in construction or under study in several laboratories in the world. It is shown that a search strategy based on the detection
of displaced vertices can be in principle very eective in covering a rather wide and to date unexplored region of the theoretical
parameters space.
1. Introduction
In the Standard Model (SM), interactions among elementary
particles are mediated by the vector bosons of the strong,
weak, and electromagnetic forces. Experimental evidence
for the existence of those bosons is compelling and precise
measurements of their properties have been accumulated in
the past decades. New forces can have escaped detection so
far, either if their associated bosons are very heavy or if their
couplings to ordinary matter are weak enough. e latter
case has been advocated, among others, in models which
try to explain and reconcile among them several puzzling
astrophysical observations performed in recent years [–].
ey are sometimes also used to reconcile the measured value
of the muon anomaly to the SM prediction, which dier by
approximately by .(see, e.g., []).
If new, light, neutral bosons (which from now on will
be called
or dark photons) exist and if they are measur-
ably, albeit weakly, coupled with SM particles, they can be
produced and observed at colliding-beams and xed target
experiments [–]. In fact, there have been several attempts
to observe evidence for such particles, using data from
running facilities [–] or data mining old experiments
[, –]. Since no evidence for their existence was found,
limits have been set as a function of the
mass and of its
coupling to ordinary matter.
In the near future, new experiments under construction
are expected to extend those limits in a region of couplings
and/or masses so far unexplored. All of them are designed to
exploit the radiative production of the
by a very intense
electron or positron beam on a properly built high-target
[–]. e purpose of the present letter is to show that
comparable results can be obtained by high luminosity and
low energy electron-positron colliders, such as those under
construction or under study in several laboratories in the
world [–]. ese facilities will take advantage of two main
construction features which coherently conspire to enhance
their discovery potential: their very high goal luminosity
andtheusageofverycompactbeams(thesetwofeatures
are in fact strongly correlated). Actually, high luminosity
translates into the possibility of probing lower production
cross sections, that is, lower eective couplings between the
and ordinary matter. On the other hand, low couplings
translate into longer
decaypaths,especiallyforlow
Hindawi Publishing Corporation
Advances in High Energy Physics
Volume 2014, Article ID 891820, 8 pages
http://dx.doi.org/10.1155/2014/891820