Single Photon Searches Research Articles

Invisible and displaced dark matter signatures at Belle II

Many dark matter models generically predict invisible and displaced signatures at Belle II, but even striking events may be missed by the currently implemented search programme because of inefficient trigger algorithms. Of particular interest are final states with a single photon accompanied by missing energy and a displaced pair of electrons, muons, or hadrons. We argue that a displaced vertex trigger will be essential to achieve optimal sensitivity at Belle II. To illustrate this point, we study a simple but well-motivated model of thermal inelastic dark matter in which this signature naturally occurs and show that otherwise inaccessible regions of parameter space can be tested with such a search. We also evaluate the sensitivity of single-photon searches at BaBar and Belle II to this model and provide detailed calculations of the relic density target.

Bounds on dipole moments of tau-neutrino from single photon searches in SU(4)L × U(1)X model at CLIC and ILC energies

We investigate the dipole moments of the tau-neutrino at high-energy and high luminosity at linear electron–positron colliders, such as CLIC or ILC through the analysis of the reaction [Formula: see text] in the framework of the [Formula: see text] model. The limits on dipole moment were obtained for integrated luminosity of [Formula: see text] and mass ranging from 0.25 to 1.0 TeV. The estimated limits for the tau-neutrino magnetic and electric dipole moments at 95% of confidence level are [Formula: see text] and [Formula: see text] improved by 2–3 orders of magnitude compared to L3 and complement previous studies on the dipole moments.

Revised constraints and Belle II sensitivity for visible and invisible axion-like particles

Light pseudoscalars interacting pre-dominantly with Standard Model gauge bosons (so-called axion-like particles or ALPs) occur frequently in extensions of the Standard Model. In this work we review and update existing constraints on ALPs in the keV to GeV mass region from colliders, beam dump experiments and astrophysics. We furthermore provide a detailed calculation of the expected sensitivity of Belle II, which can search for visibly and invisibly decaying ALPs, as well as long-lived ALPs. The Belle II sensitivity is found to be substantially better than previously estimated, covering wide ranges of relevant parameter space. In particular, Belle II can explore an interesting class of dark matter models, in which ALPs mediate the interactions between the Standard Model and dark matter. In these models, the relic abundance can be set via resonant freeze-out, leading to a highly predictive scenario consistent with all existing constraints but testable with single-photon searches at Belle II in the near future.

Single-photon signals at CERN LEP in supersymmetric models with a light gravitino

We study the single-photon signals expected at CERN LEP in models with a very light gravitino ${(m}_{\mathrm{G\ifmmode \tilde{}\else \~{}\fi{}}}\ensuremath{\lesssim}{10}^{\ensuremath{-}3}\mathrm{eV})$. The dominant process is neutralino-gravitino production ${(e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\chi}\mathrm{G\ifmmode \tilde{}\else \~{}\fi{}})$ with subsequent neutralino decay via $\ensuremath{\chi}\ensuremath{\rightarrow}\ensuremath{\gamma}\mathrm{G\ifmmode \tilde{}\else \~{}\fi{}}$, giving a $\ensuremath{\gamma}+{\mathrm{E}}_{\mathrm{miss}}$ signal. We first calculate the cross section at arbitrary center-of-mass energies and provide new analytic expressions for the differential cross section valid for general neutralino compositions. We then consider the constraints on the gravitino mass from LEP 1 and LEP 161 single-photon searches, and possible such searches at the Fermilab Tevatron. We show that it is possible to evade the stringent LEP 1 limits and still obtain an observable rate at LEP 2, in particular, in the region of parameter space that may explain the CDF $\mathrm{ee}\ensuremath{\gamma}\ensuremath{\gamma}{+E}_{T,\mathrm{miss}}$ event. As diphoton events from neutralino pair production would not be kinematically accessible in this scenario, the observation of whichever photonic signal will discriminate among the various light-gravitino scenarios in the literature. We also perform a Monte Carlo simulation of the expected energy and angular distributions of the emitted photon, and of the missing invariant mass expected in the events. Finally we specialize the results to the case of a recently proposed one-parameter no-scale supergravity model.

Bounding the tau neutrino magnetic moment from single photon searches at LEP

We show that single photon searches at LEP constrain the tau neutrino magnetic moment to be less than O(10 −6) μ B . This bound is competitive with low energy ( √s ⋍ 30 GeV ) single photon searches.

Investigation of neutrino properties in the process e+e---> nu nu -bar gamma.

Assuming a nonvanishing neutrino magnetic moment $\ensuremath{\mu}$ we study $\ensuremath{\tau}$-neutrino properties in the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\nu}\overline{\ensuremath{\nu}}\ensuremath{\gamma}$ from the single photon searches at colliders. We find that for a sufficiently large value of neutrino mass, i.e., $m>2.1\ifmmode\times\else\texttimes\fi{}(\frac{{10}^{10}\ensuremath{\mu}}{{\ensuremath{\mu}}_{B}})$ MeV (where ${\ensuremath{\mu}}_{B}=\frac{e}{2{m}_{e}}$ is the Bohr magneton), the interference between the diagrams with ${Z}^{0}$ and $\ensuremath{\gamma}$ exchange becomes important and should be taken into account in future ${e}^{+}{e}^{\ensuremath{-}}$ experiments. Some cosmological and astrophysical implications of this new heavy-neutrino scenario are briefly discussed.

Limits on the ? neutrino electromagnetic properties from single photon searches ate + e ? colliders

We set limits on the magnetic moment and charge radius of the τ neutrino by examining the contributions to the processe+e−→v\(\bar \nu \)γ due to such interactions. We find thatK(ντ)<4×10−6 (i.e.μ(ντ)<4×10−6μB, μB=e/2me) and 〈r2〉<2×10−31 cm2 using the combined data of the MAC, ASP, CELLO, and Mark J collaborations for this process. We briefly discuss whether these bounds can be improved in any futuree+e− experiments.