Ricerc@Sapienza

We report a measurement of the mass difference between neutral charm-meson eigenstates using a novel approach that enhances sensitivity to this parameter. We use 2.3×106 D0→KS0π+π- decays reconstructed in proton-proton collisions collected by the LHCb experiment in 2011 and 2012. Allowing for CP violation in mixing and in the interference between mixing and decay, we measure the CP-averaged normalized mass difference xCP=[2.7±1.6(stat)±0.4(syst)]×10-3 and the CP-violating parameter Δx=[-0.53±0.70(stat)±0.22(syst)]×10-3. The results are consistent with CP symmetry.

The decay-time-dependent CP asymmetry in Bs0→J/ψK+K- decays is measured using proton–proton collision data, corresponding to an integrated luminosity of 1.9fb-1, collected with the LHCb detector at a centre-of-mass energy of 13TeV in 2015 and 2016. Using a sample of approximately 117 000 signal decays with an invariant K+K- mass in the vicinity of the ϕ(1020) resonance, the CP-violating phase ϕs is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the Bs0-B¯s0 system, Δ Γ s.

The three precision measurements of the cross section σ(e + e − → π + π − ) using initial state radiation by the KLOE collaboration provide an important input for the prediction of the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations.

Using 1.63 fb −1 of integrated luminosity collected by the KLOE experiment about 7 × 10 4 K S → π ± e ∓ ν decays have been reconstructed. The measured value of the charge asymmetry for this decay is A S = (−4.9 ± 5.7 stat ± 2.6 syst ) × 10 −3 , which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives A S = (−3.8 ± 5.0 stat ± 2.6 syst ) × 10 −3 and, together with the asymmetry of the K L semileptonic decay, provides significant tests of the CPT symmetry. The obtained results are in agreement with CPT invariance.

R&D activity on Cu photocathodes is under development at the SPARC_LAB test facility to fully characterize each stage of the photocathode ‘‘life’’ and to have a complete overview of the photoemission properties in high brightness photo-injectors. The nano(n)-machining process presented here consists in diamond milling, and blowing with dry nitrogen. This procedure reduces the roughness of the cathode surface and prevents surface contamination introduced by other techniques, such as polishing with diamond paste or the machining with oil.

Starting from the electric fields produced by a point charge and a dipole traveling inside a circular vacuum chamber, in this paper we derive a formalism for a complete set of equations that describe the electromagnetic fields and the longitudinal and transverse coupling impedances arising by the interaction of a beam with a perfectly conducting pipe in the case of elliptic geometry.

The Gamma Beam System (GBS) is a high brightness LINAC to be installed in Magurele (Bucharest) at the newELI-NP (Extreme Light Infrastructure — Nuclear Physics) laboratory. The accelerated electrons, with energiesranging from 280 to 720 MeV, will collide with a high power laser to produce tunable high energy photons(0.2–20 MeV ) with high intensity (1013photons/s), high brilliance and spectral purity (0.1%BW), through theCompton backscattering process. This light source will be open to users for nuclear photonics and nuclear physicsadvanced experiments.

Beam injection and extraction from a plasma module is still one of the crucial aspects to solve in order to producehigh quality electron beams with a plasma accelerator. Proper matching conditions require to focus the incominghigh brightness beam down to few microns size and to capture a high divergent beam at the exit without loss ofbeam quality. Plasma-based lenses have proven to provide focusing gradients of the order of kT/m with radiallysymmetric focusing thus promising compact and affordable alternative to permanent magnets in the design oftransport lines.

Plasma wake-field acceleration experiments are performed at the SPARC_LAB test facility by using a gas-filled capillary plasma source composed of a dielectric capillary. The electron can reach GeV energy in a fewcentimeters, with an accelerating gradient orders of magnitude larger than provided by conventional techniques.In this acceleration scheme, wake fields produced by passing electron beams through dielectric structures candetermine a strong beam instability that represents an important hurdle towards the capability to focus high-current electron beams in the transverse plane.

The current activity of the SPARC_LAB test-facility is focused on the realization of plasma-based accelerationexperiments with the aim to provide accelerating field of the order of several GV/m while maintaining theoverall quality (in terms of energy spread and emittance) of the accelerated electron bunch. In the following,the current status of such an activity is presented. We also show results related to the usability of plasmas asfocusing lenses in view of a complete plasma-based focusing and accelerating system