Preliminary results and status of the MUNU experiment

We built a low background detector to measure the _ee⁻ elastic cross section at low energy. The detector has been installed close to a nuclear reactor in Bugey and it is running since almost one year. After having reduced the electron background by more than 2 orders of magnitude we are now taking data to be sensitive to a neutrino magnetic moment in the region below 10⁻¹⁰ Bohr magnetons.     

Antiproton identification below threshold with the AMS-02 RICH detector

The Alpha Magnetic Spectrometer(AMS-02),which is installed on the International Space Station(ISS),has been collecting data successfully since May 2011.The main goals of AMS-02 are the search for cosmic anti-matter,dark matter and the precise measurement of the relative abundance of elements and isotopes in galactic cosmic rays.In order to identify particle properties,AMS-02 includes several specialized sub-detectors.Among these,the AMS-02 Ring Imaging Cherenkov detector(RICH) is designed to provide a very precise measurement of the velocity and electric charge of particles.We describe a method to reject the dominant electron background in antiproton identification with the use of the AMS-02 RICH detector as a veto for rigidities below 3 GV.A ray tracing integration method is used to maximize the statistics of  with the lowest possible e background,providing 4 times rejection power gain for e background with respect to only 3% of  signal efficiency loss.By using the collected cosmic-ray data,e contamination can be well suppressed within 3% with β≈ 1,while keeping 76% efficiency for  below the threshold.     

A lithium experiment in the program of solar neutrino research

Experiments sensitive to pp neutrinos from the Sun are very promising for precise measurement of the mixing angle ϑ ₁₂. A νe ⁻ scattering experiment (XMASS) and/or a charged-current experiment (indium detector) can measure the flux of electron pp neutrinos. One can find the total flux of pp neutrinos from a luminosity constraint after the contributions of ⁷Be and CNO neutrinos to the total luminosity of the Sun are measured. A radiochemical experiment utilizing a lithium target has high sensitivity to the CNO neutrinos; thus, it has a good promise for precise measurement of the mixing angle and for a test of the current theory of evolution of the stars. The text was submitted by the authors in English.     

Astroparticle physics with AMS-02

The main physics goals of the AMS-02 experiment in the astroparticle domain are searches for antimatter and dark matter. The discovery potential of primordial antimatter by AMS-02 is presented, emphasizing the completeness of the AMS-02 detector for these searches. Meanwhile, antiproton detection suffers from a large secondary interaction background; the anti-⁴He or anti-³He signal would allow one to probe the Universe for existence of antimatter. The expected signal in AMS-02 is presented and compared to results from present experiments. The e⁺ and antiproton channels will contribute to the dark matter detection studies. A SUSY neutralino candidate is considered. The expected flux sensitivities in a three-year exposure for the e⁺/e^? ratio and antiproton yields as a function of energy are presented and compared to other direct and indirect searches.     

A large scale double beta and dark matter experiment: On the physics potential of GENIUS

The physics potential of GENIUS, a recently proposed double beta decay and dark matter experiment is discussed. The experiment will allow to probe neutrino masses down to 10^?(2–3) eV. GENIUS will test the structure of the neutrino mass matrix, and therefore implicitly neutrino oscillation parameters comparable or superior in sensitivity to the best proposed dedicated terrestrial neutrino oscillation experiments. If the 10^-3 eV level is reached, GENIUS will even allow to test the large angle MSW solution of the solar neutrino problem. Even in its first stage GENIUS will confirm or rule out degenerate or inverted neutrino mass scenarios, which have been widely discussed in the literature as a possible solution to current hints on finite neutrino masses and also test the ν_e ? ν_μ hypothesis of the atmospheric neutrino problem. GENIUS would contribute to the search for R-parity violating SUSY and right-handed W-bosons on a scale similar or superior to LHC. In addition, GENIUS would largely improve the current 0νββ decay searches for R-parity conserving SUSY and leptoquarks. Concerning cold dark matter (CDM) search, the low background anticipated for GENIUS would, for the first time ever, allow to cover the complete MSSM neutralino parameter space, making GENIUS competitive to LHC in SUSY discovery. If GENIUS could find SUSY CDM as a by-product it would confirm that R-parity must be conserved exactly. GENIUS will thus be a major tool for future non-accelerator particle physics.     

Radon-induced background and methods of its elimination in the EDELWEISS-II experiment

The EDELWEISS-II experiment is aimed at direct search for nonbarion cold dark matter. The important problem of the experiment is a decrease in the ²²²Rn background and its daughter products without which it is impossible to achieve a record sensitivity to the scattering cross section of dark matter particles. A highly sensitive radon detector has been developed by means of which the facility shield is optimized and the total gamma-background is halved. The detector is used in the EDELWEISS-II facility for continuous monitoring of the radon content in the process of data sampling that plays the key role for correct data interpretation.     

Constraining dark matter properties with gamma-rays from the Galactic Center with Fermi-LAT

We study the capabilities of the Fermi-LAT instrument on board of the Fermi mission to constrain particle dark matter properties, as annihilation cross section, mass and branching ratio into dominant annihilation channels, with gamma-ray observations from the Galactic Center. Besides the prompt gamma-ray flux, we also take into account the contribution from the electrons/positrons produced in dark matter annihilations to the gamma-ray signal via inverse Compton scattering off the interstellar photon background, which turns out to be crucial in the case of dark matter annihilations into μ⁺μ⁻ and e⁺e⁻ pairs. We study the signal dependence on different parameters like the region of observation, the density profile, the assumptions for the dark matter model and the uncertainties in the propagation model. We also show the effect of the inclusion of a 20% systematic uncertainty in the gamma-ray background. If Fermi-LAT is able to distinguish a possible dark matter signal from the large gamma-ray background, we show that for dark matter masses below ∼200 GeV, Fermi-LAT will likely be able to determine dark matter properties with good accuracy.     

Gamma-rays from nearby clusters: Constraints on selected decaying dark matter models

Recently, the Fermi-LAT Collaboration reported upper limits on the GeV gamma-ray flux from nearby clusters of galaxies. Motivated by these limits, we study corresponding constraints on gamma-ray emissions from two specific decaying dark matter models, one via grand unification scale suppressed operators and the other via R-parity violating operators. Both can account for the PAMELA and Fermi-LAT excesses of e^±$e^{\pm }$. For GUT decaying dark matter, the gamma-rays from the M49 and Fornax clusters, with energy in the range of 1 to 10 GeV, lead to the most stringent constraints to date. As a result, this dark matter is disfavored with conventional model of e^±$e^{\pm }$ background. In addition, it is likely that some tension exists between the Fermi-LAT e^±$e^{\pm }$ excess and the gamma-ray constraints for any decaying dark matter model, provided conventional model of e^±$e^{\pm }$ background is adopted. Nevertheless, the GUT decaying dark matter can still solely account for the PAMELA positron fraction excess without violating the gamma-ray constraints. For the gravitino dark matter model with R-parity violation, cluster observations do not give tight constraints. This is because a different e^±$e^{\pm }$ background has been adopted which leads to relatively light dark matter mass around 200 GeV.     

Direct and indirect detection of dark matter in D6 flavor symmetric model

We study fermionic dark matter in a non-supersymmetric extension of the standard model with a family symmetry based on D₆ ×[^(Z)]₂×Z₂D_{6} \times\hat{Z}_{2}\times Z_{2}. In our model, the final state of the dark matter annihilation is determined to be e ⁺ e ⁻ by the flavor symmetry, which is consistent with the PAMELA result. At first, we show that our dark matter mass should be within the range of 230 GeV–750 GeV in the WMAP analysis combined with μ→eγ constraint. Moreover, we simultaneously explain the experiments of direct and indirect detection, by simply adding a gauge and D ₆ singlet real scalar field. In the direct detection experiments, we show that the lighter dark matter mass ≃230 GeV and the lighter standard model Higgs boson ≃115 GeV are in favor of the observed bounds reported by CDMS II and XENON100. In the indirect detection experiments, we explain the positron excess reported by PAMELA through the Breit–Wigner enhancement mechanism. We also show that our model is consistent with there being no antiproton excess, as suggested by PAMELA.     

Results from PAMELA,ATIC and FERMI: Pulsars or dark matter?

It is well known that dark matter dominates the dynamics of galaxies and clusters of galaxies. Its constituents remain a mystery despite an assiduous search for them over the past three decades. Recent results from the satellite-based PAMELA experiment show an excess in the positron fraction at energies between 10 and 100 GeV in the secondary cosmic ray spectrum. Other experiments, namely ATIC, HESS and FERMI, show an excess in the total electron (e ⁺ + e ⁻) spectrum for energies greater than 100 GeV. These excesses in the positron fraction as well as the electron spectrum can arise in local astrophysical processes like pulsars, or can be attributed to the annihilation of the dark matter particles. The latter possibility gives clues to the possible candidates for the dark matter in galaxies and other astrophysical systems. In this article, we give a report of these exciting developments.     

Searching for universal behaviour in superheated droplet detector with effective recoil nuclei

Energy calibration of superheated droplet detector is discussed in terms of the effective recoil nucleus threshold energy and the reduced superheat. This provides a universal energy calibration curve valid for different liquids used in this type of detector. Two widely used liquids, R114 and C₄F₁₀, one for neutron detection and the other for weakly interacting massive particles (WIMPs) dark matter search experiment, have been compared. Liquid having recoil nuclei with larger values of linear energy transfer (LET) provides better neutron-γ discrimination. Gamma (γ) response of C₄F₁₀ has also been studied and the results are discussed. Behaviour of nucleation parameter with the effective recoil nucleus threshold energy and the reduced superheat have been explored.     

Radiative events as a probe of dark forces at GeV-scale <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> colliders

High-luminosity e ⁺ e ⁻ colliders at the GeV scale (flavor factories) have been recently recognized to be an ideal environment to search for a light weakly coupled vector boson U (dark photon) emerging in several new physics models. At flavor factories a particularly clean channel is the production of the U boson in association with a photon, followed by the decay of the U boson into lepton pairs. Beyond the approximations addressed in previous works, we perform an exact lowest order calculation of the signal and background processes of this channel. We also include the effect of initial- and final-state QED corrections neglected so far, to show how they affect the distributions of experimental interest. We present new results for the expected statistical significance to a dark photon signal at KLOE/KLOE-2 and future super-B factories. The calculation is implemented in a new release of the event generator BabaYaga@NLO, which is available for full event simulations and data analysis.     

Capabilities of the Gamma-400 Gamma-ray Telescope for Observation of Electrons and Positrons in the TeV Energy Range

The space-based GAMMA-400 gamma-ray telescope will measure the fluxes of gamma rays in the energy range from ∼20 MeV to several TeV and cosmic-ray electrons and positrons in the energy range from several GeV to several TeV to investigate the origin of gamma-ray sources, sources and propagation of the Galactic cosmic rays and signatures of dark matter. The instrument consists of an anticoincidence system, a converter-tracker (thickness one radiation length, 1 X₀), a time-of-flight system, an imaging calorimeter (2 X₀) with tracker, a top shower scintillator detector, an electromagnetic calorimeter from CsI(Tl) crystals (16 X₀) with four lateral scintillation detectors and a bottom shower scintillator detector. In this paper, the capability of the GAMMA-400 gamma-ray telescope for electron and positron measurements is analyzed. The bulk of cosmic rays are protons, whereas the contribution of the leptonic component to the total flux is ∼10⁻³ at high energy. The special methods for Monte Carlo simulations are proposed to distinguish electrons and positrons from proton background in the GAMMA-400 gamma-ray telescope. The contribution to the proton rejection from each detector system of the instrument is studied separately. The use of the combined information from all detectors allows us to reach a proton rejection of up to ∼1 × 10⁴.

     

Limits on the neutrino magnetic moment from solar neutrino experiments

If neutrinos have non-vanishing mass and non-vanishing magnetic moments, then electron neutrinos emitted in nuclear reactions in the solar interior may undergo flavour oscillations, spin precession or resonant spin-flavour precession. Assuming equal values for the magnetic moments of all neutrino flavours and using the data from Homestake and SuperKamiokande we obtain an upper limit on the neutrino magnetic moment and find μ_νe ≤ (2.2 − 2.3) × 10⁻¹⁰μ_B, within four standard solar models. We also point out that this limit may be further reduced if the detector threshold energy for the ν_e,χe⁻ scattering is decreased.     

Measurement of photoelectron yield of the CDEX-10 liquid argon detector prototype

The China Dark Matter Experiment (CDEX) is a low background experiment at China Jinping Underground Laboratory (CJPL) designed to directly detect dark matter with a high-purity germanium (HPGe) detector. In the second phase, CDEX-10, which has a 10 kg germanium array detector system, a liquid argon (LAr) anti-Compton active shielding and cooling system is proposed. To study the properties of the LAr detector, a prototype with an active volume of 7 liters of liquid argon was built and operated. The photoelectron yields, as a critically important parameter for the prototype detector, have been measured to be 0.051-0.079 p.e./keV for 662 keV γ rays at different positions. The good agreement between the experimental and simulation results has provided a reasonable understanding and determination of the important parameters such as the surviving fraction of the Ar₂^* excimers, the absorption length for 128 nm photons in liquid argon, the reflectivity of Teflon and so on.     

Search for the electron-positron decay of axions and axionlike particles at a nuclear power reactor at Bugey

A search for the decay of isoscalar penetrating particles into ane ⁺ e-pair has been performed at the nuclear power reactor Bugey 5, situated close to Lyon (France). The detector set-up, consisting of an arrangement of large-area multiwire proportional chambers, and the data analysis are described. No excess of decay events over background has been observed. For standard axions, therefrom, stringent upper limits for the branching ratio 〈Γ _a /Γ _M ^γ , averaged over the entire reactor gamma spectrum of magnetic multipolarity, have been obtained. Analysis in terms of the decay χ→e ⁺+e ^? of a more general axionlike boson χ yields new constraints for the decay constantf _χ which enhance existing laboratory limits considerably.     

Oscillations of three generations of neutrinos and the solar neutrino problem

The resonant neutrino oscillations in matter are assumed to be responsible for the observed reduction in the capture rate for the ³⁷Cl detector. The expression of the probability that a solar v_e reaches the Earth as a v_e is given in the case of three generations. In the small mixing angle approximation, we describe all the regions of neutrino parameters which give rise to a capture rate of 2.1 SNU for ³⁷Cl and we give the corresponding prediction for the ⁷¹Ga detector.     

Status of the MUNU experiment

We built a low background detector based on a 1 m³ time projection chamber surrounded by an active anti-Compton shielding. The detector has been installed near a nuclear reactor in Bugey for the experimental study of the scattering. A low threshold, around 500 keV, can be set on the electron recoil energy, giving the experiment a sensitivity to the magnetic moment down to 3·10⁻¹¹ Bohr magnetons.     

Supersymmetry parameter analysis: SPA convention and project

High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e ⁺ e^- linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.     

Search for Stueckelberg <Emphasis Type="Italic">Z</Emphasis>′ at LHC

We present the discovery potential for heavy Z′ gauge bosons in the Z′→e ⁺ e ⁻ decay channel at the Large Hadron Collider. The analysis focuses on the direct search for the massive Z′ bosons predicted by the Stueckelberg extension of the Standard Model. Using signal and background simulated events, and taking into account the basic parameters of the Compact Muon Solenoid detector, the discovery reach for the Stueckelberg Z′ is found to be in the range between 800 and 900 GeV/c² for an integrated luminosity of 30 fb⁻¹.