Large-size Resistive Micromegas have been chosen for the upgrade of the forward muon spectrometer of the ATLAS experiment, the New Small Wheel project. These chambers, together with small-strip Thin ...Gap Chambers (sTGC), allow reconstruction of high-momentum muon tracks in a high-radiation environment and provide a robust low-threshold single-muon trigger. A collaboration of seven INFN units built 32 SM1 type chambers, corresponding to one fourth of the total number needed for this upgrade. Each SM1 chamber has a surface of approximately 2 m2 and four sensitive layers. The production was shared among five INFN construction sites and it was completed in fall 2020. The construction methods, as well as the results of the quality tests done on components of the detector and on the assembled chambers, are reported in the present paper.
The production of prompt D0 mesons in proton-lead collisions in both the forward and backward rapidity regions at a center-of-mass energy per nucleon pair of √sNN = 8.16 TeV is measured by the LHCb ...experiment. The nuclear modification factor of prompt D0 mesons is determined as a function of the transverse momentum pT, and the rapidity in the nucleon-nucleon center-of-mass frame y*. In the forward rapidity region, significantly suppressed production with respect to pp collisions is measured, which provides significant constraints on models of nuclear parton distributions and hadron production down to the very low Bjorken-x region of similar to 10-5. In the backward rapidity region, a suppression with a significance of 2.0-3.8 standard deviations compared to parton distribution functions in a nuclear environment expectations is found in the kinematic region of pT 6 GeV/c and -3.25 < y* < -2.5, corresponding to x similar to 0.01.
The production rate of 𝐵 0 𝑠 mesons relative to 𝐵 0 mesons is measured by the LHCb experiment in 𝑝𝑝 collisions at a center-of-mass energy √𝑠=13 TeV over the forward rapidity interval ...2<𝑦<4.5 as a function of the charged particle multiplicity measured in the event. Evidence at the 3.4𝜎 level is found for an increase of the ratio of 𝐵 0 𝑠 to 𝐵 0 cross sections with multiplicity at transverse momenta below 6 GeV/𝑐, with no significant multiplicity dependence at higher transverse momentum. Comparison with data from 𝑒 + 𝑒 − collisions implies that the density of the hadronic medium may affect the production rates of 𝐵 mesons. This is qualitatively consistent with the emergence of quark coalescence as an additional hadronization mechanism in high-multiplicity collisions.
An amplitude analysis of A+c - pK- & pi;+ decays together with a measurement of the A+c polarization vector in semiOleptonic beauty hadron decays is presented. A sample of 400 000 candidates is ...selected from proton-proton collisions recorded by the LHCb detector at a center-of-mass energy of 13 TeV. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. The mass and width of the Ao2000 thorn state are also determined. A significant A+c polarization is found. A large sensitivity of the A+c - pK-& pi;+ decay to the polarization is seen, making the amplitude model suitable for A+c polarization measurements in other systems.
A search for CP and P violation in charmless four-body B-0 -> p (p) over barK(+)pi(-) decays is performed using triple-product asymmetry observables. It is based on proton-proton collision data ...collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 8.4 fb(-1). The CP- and P-violating asymmetries are measured both in the integrated phase space and in specific regions. No evidence is seen for CP violation. P-parity violation is observed at a significance of 5.8 standard deviations.
A search for the rare hadronic decay B-s(0) -> p (p) over bar is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to ...an integrated luminosity of 6 fb(-1). No evidence of the decay is found and an upper limit on its branching fraction is set at B(B-s(0) -> p (p) over bar) < 4.4(5.1)x 10(-9) at 90% (95%) confidence level; this is currently the world's best upper limit. The decay mode B-0 -> p<(p)over bar> is measured with very large significance, confirming the first observation by the LHCb experiment in 2017. The branching fraction is determined to be B(B-0 -> p (p) over bar) = (1.27 +/- 0.15 +/- 0.05 +/- 0.04) 10(-8), where the first uncertainty is statistical, the second is systematic and the third is due to the external branching fraction of the normalization channel B-0 -> K+pi(-). The combination of the two LHCb measurements of the B-0 -> p (p) over bar branching fraction yields B(B-0 -> p (p) over bar) (1.27 +/- 0.13 +/- 0.05 +/- 0.03) x 10(-8).
A search for the lepton-flavour violating decays B-0 -> K-*0 mu e(-/+) and B-s(0)-> mu(+/-)e(-/+) is presented, using proton-proton collision data collected by the LHCb detector at the LHC, ...corresponding to an integrated luminosity of 9 fb(-1). No significant signals are observed and upper limits of
B(B0→ K∗0µ+e−) < 5.7 × 10−9(6.9 × 10−9),
B(B0→ K∗0µ−e+) < 6.8 × 10−9(7.9 × 10−9),
B(B0→ K∗0µ±e∓) < 10.1 × 10−9(11.7 × 10−9),
B(B0s → φµ±e∓) < 16.0 × 10−9(19.8 × 10−9)
are set at 90% (95%) confidence level. These results constitute the world's most stringent limits to date, with the limit on the decay B-s(0) -> phi mu(+/-) e(-/+) the first being set. In addition, limits are reported for scalar and left-handed lepton-flavour violating New Physics scenarios.
Searches for CP violation in the decays D-(s)(+) -> eta pi(+) and D-(s)(+) -> eta'pi(+) are performed using pp collision data corresponding to 6 fb(-1) of integrated luminosity collected by the ...LHCb experiment. The calibration channels D-(s)(+) -> phi pi(+) are used to remove production and detection asymmetries. The resulting CP-violating asymmetries are A(CP) (D+ -> eta pi(+)) = (0.34 +/- 0.66 +/- 0.16 +/- 0.05)%, A(CP) (D-s(+) -> eta pi(+)) = (0.32 +/- 0.51 +/- 0.12)%, A(CP) (D+ -> eta'pi(+)) = (0.49 +/- 0.18 +/- 0.06 +/- 0.05)%, A(CP) (D-s(+) -> eta'pi(+)) = (0.01 +/- 0.12 +/- 0.08)%, where the first uncertainty is statistical, the second is systematic and the third, relevant for the D+ channels, is due to the uncertainty on A(CP) (D+ -> phi pi(+)). These measurements, currently the most precise for three of the four channels considered, are consistent with the absence of CP violation. A combination of these results with previous LHCb measurements is presented.
Using a proton-proton collision data sample collected by the LHCb detector and corresponding to an integrated luminosity of 5.7 fb -1 , the lifetime of the light B 0 s mass eigenstate, τ L , is ...measured using the B 0 s → J/ψη decay mode to be
τL = 1.445 ± 0.016(stat) ± 0.008(syst) ps.
A combination of this result with a previous LHCb analysis using an independent dataset corresponding to 3 fb -1 of integrated luminosity gives
τL = 1.452 ± 0.014 ± 0.007 ± 0.002 ps,
where the first uncertainty is statistical, the second due to the uncorrelated part of the systematic uncertainty and the third due to the correlated part of the systematic uncertainty.
