Rare K decays: Present and perspectives with NA62

Rare kaon decays provide unique opportunity to test the Standard Model and probe its possible extensions. The final result on the lepton universality test by measuring the ratio RK = Γ(K+ → e+ν)/Γ(K+ → μ+ν) is presented as well as the status of the study of the rare decays K ± → π ± γγ and K+ → e+νγ. The primary goal of the NA62 experiment is the measurement of the Br(K+ → π+ν¯ν) decay with a precision of 10% in two years of data taking. The detector setup together with the analysis technique is described

Testing mu-e universality with Kl2 decays

The ratio R_K=Gamma(Ke2)/Gamma(Kmu2) provides a very powerful probe for the weak interactions structure. This ratio of decay rates is calculated with very high precision within the Standard Model but the corrections due to the presence of New Physics could be as high as 3%. The data obtained by the NA48 experiment at the CERN SPS accelerator during a 56 hours special run in 2004 has been analyzed.The precision of the preliminary result for R_K is two times better than the world average but is still insufficient to probe the existence of physics Beyond the Standard Model. Currently the experiment is taking data dedicated to the sub-percent precision measurement of R_K.Comment: for the NA48/2 collaboration; talk given at Kaon International Conference (KAON'07), Frascati, Italy, 21-25 May 200

Study of the performance of the NA62 Small-Angle Calorimeter at the DAΦ\PhiNE Linac

The measurement of $BR(K^+\to\pi^+\nu\bar{\nu})$ with 10% precision by the NA62 experiment requires extreme background suppression. The Small Angle Calorimeter aims to provide an efficient veto for photons flying at angles down to zero with respect to the kaon flight direction. The initial prototype was upgraded and tested at the Beam Test Facility of the DA$\Phi$NE Linac at Frascati. The energy resolution and the efficiency were measured and are presented.Comment: 5 pages, 7 figure

Time over threshold in the presence of noise

The time over threshold is a widely used quantity to describe signals from various detectors in particle physics. Its electronics implementation is straightforward and in this paper we present the studies of its behavior in the presence of noise. A unique comb-like structure was identified in the data for a first time and was explained and modeled successfully. The effects of that structure on the efficiency and resolution are also discussed.Comment: 6 pages, 8 figure

PADME: Searching for dark mediator at the Frascati BTF

Massive photon-like particles are predicted in many extensions of the Standard Model with a hidden sector accounting for dark matter candidates. They have interactions similar to the photon, are vector bosons, and can be produced together with photons. Most of the present experimental constraints on the dark photon (A) rely on the hypothesis of dominant decays to lepton pairs. The PADME experiment aims at searching for the e+e− → γA process in a positron-on-target experiment, assuming a decay of the A into invisible particles of the hidden sector.The positron beam of the DAΦNE Beam-Test Facility (BTF), produced by the LINAC at the Laboratori Nazionali di Frascati of INFN, will be used. The core of the experimental apparatus is a fine-grained, high-resolution calorimeter. It will measure with high precision the momentum of the photon in events with no other activity in the detector, thus allowing to measure the A mass as the missing mass in the final state. In about one year data taking, a sensitivity on the interaction strength (2 parameter) down to 10−6 is achievable, in the mass region from 1 MeV < MA < 23.7 MeV, running with 6000 positrons in 40 ns long bunches at 550 MeV beam energy. The experiment, now in the construction phase, is planned to run in 2018. The status of the PADME detector and the physics potential of PADME is reviewed

GEANT4-based full simulation of the PADME experiment at the DAΦNE BTF

A possible solution to the dark matter problem postulates that dark particles can interact with Standard Model particles only through a new force mediated by a “portal”. If the new force has a U(1) gauge structure, the “portal” is a massive photon-like vector particle, called dark photon or A′. The PADME experiment at the DAΦNE Beam-Test Facility (BTF) in Frascati is designed to detect dark photons produced in positron on fixed target annihilations decaying to dark matter (e+e-→γA′) by measuring the final state missing mass. The experiment will be composed of a thin active diamond target where a 550 MeV positron beam will impinge to produce e+e- annihilation events. The surviving beam will be deflected with a magnet while the photons produced in the annihilation will be measured by a calorimeter composed of BGO crystals. To reject the background from Bremsstrahlung gamma production, a set of segmented plastic scintillator vetoes will be used to detect positrons exiting the target with an energy lower than that of the beam, while a fast small angle calorimeter will be used to reject the e+e-→γγ(γ) background. To optimize the experimental layout in terms of signal acceptance and background rejection, the full layout of the experiment was modelled with the GEANT4 simulation package. In this paper we will describe the details of the simulation and report on the results obtained with the software

Relativistic calculations of the charge-transfer probabilities and cross sections for low-energy collisions of H-like ions with bare nuclei

A new method for solving the time-dependent two-center Dirac equation is developed. The time-dependent Dirac wave function is represented as a sum of atomic-like Dirac-Sturm orbitals, localized at the ions. The atomic orbitals are obtained by solving numerically the finite-difference one-center Dirac and Dirac-Sturm equations with the potential which is the sum of the exact reference-nucleus potential and a monopole-approximation potential from the other nucleus. An original procedure to calculate the two-center integrals with these orbitals is proposed. The approach is tested by calculations of the charge transfer and ionization cross sections for the H(1s)--proton collisions at proton energies from 1 keV to 100 keV. The obtained results are compared with related experimental and other theoretical data. To investigate the role of the relativistic effects, the charge transfer cross sections for the Ne^{9+}(1s)--Ne^{10+} (at energies from 0.1 to 10 MeV/u) and U^{91+}(1s)--U^{92+} (at energies from 6 to 10 MeV/u) collisions are calculated in both relativistic and nonrelativistic cases.Comment: 39 pages, 6 tables, 7 figure

Performance of the PADME calorimeter prototype at the DAΦ\PhiNE BTF

The PADME experiment at the DA$\Phi$NE Beam-Test Facility (BTF) aims at searching for invisible decays of the dark photon by measuring the final state missing mass in the process $e^+e^- \to \gamma+ A'$, with $A'$ undetected. The measurement requires the determination of the 4-momentum of the recoil photon, performed using a homogeneous, highly segmented BGO crystals calorimeter. We report the results of the test of a 5$\times$5 crystals prototype performed with an electron beam at the BTF in July 2016