Limit on the production of a low-mass vector boson ine+e−→Uγ,<

Abstract

The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the U boson, with the KLOE detector at the DAΦNE e + e − collider. Using an integrated luminosity of 1.54 fb −1 , we studied the process e + e − → Uγ, with U → e + e − , using radiative return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90% CL upper limit on the mixing strength between the Standard Model photon and the dark photon, ε 2 , at 10 −6 -10 −4 in the 5-520 MeV/c 2 mass range.

Review on Dark Photon

“…A limit on the kinetic mixing parameter as a function of m U was set by using the same equation reported in Refs. [23] and [25]. The resulting exclusion plot is shown in Fig.…”

Search for dark forces with KLOE

“…No peak in the e + e − invariant mass spectrum was observed and an upper limit on the kinetic mixing parameter was thus extracted. The obtained upper limit covers m U between 2 MeV and 250 MeV and ranges from 10 −7 to 10 −5 [5] (see the KLOE (3) region in Fig. 1).…”

“…Moreover, search for the U boson in such energy range is of special interest as it could explain a number of recent puzzing astrophysical observations such as the excess of positrons in cosmic rays observed by AMS and PAMELA [1,2], 511 keV gamma rays from the galactic centre seen by INTEGRAL [3] or the annual modulation signal measured by DAMA/LIBRA [4]. The KLOE experiment has searched evidence of the U boson existence as a sharp resonance in the invariant mass spectrum of lepton or pion pairs produced in radiative processes e + e − → + − (γ) [5,6], e + e − → π + π − (γ) [7] and in decays of the φ meson [8,9], as well as in the dark Higgsstrahlunng process [10].…”

Radiative corrections ine+e−collisions with the BabaYaga event generator

“…Before concluding, it is worth mentioning that an extension of BabaYaga has been developed for dark photon searches at low energy via the radiative return method [10] and has been extensively used by the KLOE-2 collaboration to set limits on the dark photon couplings and mass [11].…”