Search for lepton-flavour-violating decays of Higgs-like bosons.

A search is presented for a Higgs-like boson with mass in the range 45 to 195 GeV/c2 decaying into a muon and a tau lepton. The dataset consists of proton-proton interactions at a centre-of-mass energy of 8 TeV , collected by the LHCb experiment, corresponding to an integrated luminosity of 2 fb-1 . The tau leptons are reconstructed in both leptonic and hadronic decay channels. An upper limit on the production cross-section multiplied by the branching fraction at 95% confidence level is set and ranges from 22 pb for a boson mass of 45 GeV/c2 to 4 pb for a mass of 195 GeV/c2

The PADME electromagnetic calorimeter

The PADME experiment, hosted at Laboratori Nazionali di Frascati in Italy, is going to start its data taking in September 2018. It is designed to search for the Dark Photon (indicated by the symbol A′), an hypothetical particle that can explain the Dark Matter elusiveness, possibly produced in the reaction e + e - → A′ γ. Together with the target, the segmented electromagnetic calorimeter is the most important component of the experiment, since it is needed to detect the recoil photon energy and position, in such a way to measure the A′ mass. It will consist of 616 2.1 × 2.1 × 23.0 cm3 BGO crystals arranged in a cylindrical shape and read by HZC photomultipliers with a diameter of 1.9 cm. Here we present the results obtained during the measurements performed on the scintillating units with a radioactive source and test beams, together with an overall description of the entire experiment

Measurement of J/ψ production in association with a W ± boson with pp data at 8 TeV

A measurement of the production of a prompt J/ψ meson in association with a W± boson with W± → μν and J/ψ → μ+μ− is presented for J/ψ transverse momenta in the range 8.5–150 GeV and rapidity |yJ/ψ| < 2.1 using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton-proton centre-of-mass energy of s = 8 TeV and correspond to an integrated luminosity of 20.3 fb−1. The ratio of the prompt J/ψ plus W± cross-section to the inclusive W± cross-section is presented as a differential measurement as a function of J/ψ transverse momenta and compared with theoretical predictions using different double-parton-scattering cross-sections. [Figure not available: see fulltext.]

Observation of an Excited Bc+ State

Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date

Characterisation and performance of the PADME electromagnetic calorimeter

The PADME experiment at the LNF Beam Test Facility searches for dark photons produced in the annihilation of positrons with the electrons of a fixed target. The strategy is to look for the reaction e+ + e− → γ + A0, where A0 is the dark photon, which cannot be observed directly or via its decay products. The electromagnetic calorimeter plays a key role in the experiment by measuring the energy and position of the final-state γ. The missing four-momentum carried away by the A0 can be evaluated from this information and the particle mass inferred. This paper presents the design, construction, and calibration of the PADME’s electromagnetic calorimeter. The results achieved in terms of equalisation, detection efficiency and energy resolution during the first phase of the experiment demonstrate the effectiveness of the various tools used to improve the calorimeter performance with respect to earlier prototypes

Commissioning of the PADME experiment with a positron beam

The PADME experiment is designed to search for a hypothetical dark photon A' produced in positron-electron annihilation using a bunched positron beam at the Beam Test Facility of the INFN Laboratori Nazionali di Frascati. The expected sensitivity to the A'-photon mixing parameter ϵ is 10-3, for A' mass ≤ 23.5 MeV/c 2 after collecting ∼1013 positrons-on-target. This paper presents the PADME detector status after commissioning in July 2019. In addition, the software algorithms employed to reconstruct physics objects, such as photons and charged particles, and the calibration procedures adopted are illustrated in detail. The results show that the experimental apparatus reaches the design performance, and is able to identify and measure standard electromagnetic processes, such as positron bremsstrahlung and electron-positron annihilation into two photons

Search for the B s 0 → μ + μ − γ decay

A search for the fully reconstructed Bs0→ μ+μ−γ decay is performed at the LHCb experiment using proton-proton collisions at s = 13 TeV corresponding to an integrated luminosity of 5.4 fb−1. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are setBBs0→μ+μ−γ<4.2×10−8, mμ+μ−∈2mμ1.70GeV/c2, BBs0→μ+μ−γ<7.7×10−8, mμ+μ−∈1.70, 2.88GeV/c2, BBs0→μ+μ−γ<4.2×10−8, mμ+μ−∈3.92mBs0GeV/c2, at 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2mμ, 1.70] GeV/c2 dimuon mass region excluding the contribution from the intermediate ϕ(1020) meson, and in the region combining all dimuon-mass intervals

A model-independent measurement of the CKM angle γ in partially reconstructed B ± → D * h ± decays with D → K S 0 h + h − ( h = π, K )

A measurement of CP-violating observables in B± → D*K± and B± → D*π± decays is made where the photon or neutral pion from the D*→ Dγ or D*→ Dπ0 decay is not reconstructed. The D meson is reconstructed in the self-conjugate decay modes, D → KS0π+π− or D → KS0K+K−. The distribution of signal yields in the D decay phase space is analysed in a model-independent way. The measurement uses a data sample collected in proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of approximately 9 fb−1. The B± → D*K± and B± → D*π±CP-violating observables are interpreted in terms of hadronic parameters and the CKM angle γ, resulting in a measurement of γ = (92−17+21)°. The total uncertainty includes the statistical and systematic uncertainties, and the uncertainty due to external strong-phase inputs

Measurement of the Z boson production cross-section in pp collisions at s = 5. 02 TeV

The first measurement of the Z boson production cross-section at centre-of-mass energy s = 5.02 TeV in the forward region is reported, using pp collision data collected by the LHCb experiment in year 2017, corresponding to an integrated luminosity of 100 ± 2 pb−1. The production cross-section is measured for final-state muons in the pseudorapidity range 2.0 20 GeV/c. The integrated cross-section is determined to beσZ→μ+μ−=39.6±0.7stat±0.6syst±0.8lumipb for the di-muon invariant mass in the range 60 < Mμμ< 120 GeV/c2. This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling constant. Based on a previous LHCb measurement of the Z boson production cross-section in pPb collisions at sNN = 5.02 TeV, the nuclear modification factor RpPb is measured for the first time at this energy. The measured values are 1.2−0.3+0.5 (stat) ± 0.1(syst) in the forward region (1.5