OPMD

Abstract:

The MALTA2 sensor is the second prototype in the MALTA family of Depleted Monolithic Active Pixel Sensors, developed using a modified 180nm CMOS imaging process and optimized for operation in the high-radiation and high hit-rate conditions of future collider experiments. With a matrix of 224 × 512 pixels and a 36.4µm pitch, MALTA2 is designed for fast charge collection, low noise, and low power consumption. MALTA2 incorporates a low doped n − layer extending across the pixel matrix, which enhances the lateral depletion and charge collection by drift. This work evaluates a MALTA2 variant with very high n − layer doping for improved radiation hardness. The sensor has been neutron irradiated up to a fluence of 5 × 1 0 15 1 MeV n eq cm −2 and characterized in test beam campaigns at the CERN SPS using a 120 GeV/c mixed hadron beam. Hit detection efficiencies above 95% were achieved up to a fluence of 3 × 1 0 15 1 MeV n eq cm −2 . At 5 × 1 0 15 1 MeV n eq cm −2 , the hit detection efficiency measured was 64.9 ± 0.2 % at a substrate bias voltage of -60 V. To investigate this degradation, the effective active depth has been extracted as 20.3 ± 0.2 μ m from cluster size measurements as a function of the beam incident angle. The results from the very high doping will guide the development of prototypes featuring ultra-high n − layer doping, aiming to achieve greater radiation hardness in next-generation silicon tracking detectors.

Abstract:

This paper presents the first differential fiducial measurements of γγ → ττ using 1.93 nb−1 of Pb+Pb data at sNN=5.02$$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV recorded by the ATLAS detector. Events in which one of the τ -leptons decays into a muon and two neutrinos τ→ντν¯μμ$$ \tau \to {\nu}_{\tau }{\overline{\nu}}_{\mu}\mu $$ are selected and are categorized into three regions by the presence of an electron or either one or three charged-particle track(s) from the second τ-lepton decay. The measurement is performed in events where both Pb ions remain intact and no neutrons are emitted. Differential cross-sections are measured for seven variables in three fiducial regions at particle level. The measurements are compared to theory predictions with different photon flux models and spin correlation effects. For the fiducial region with one muon and one electron in the final state, comparisons to next-to-leading-order electroweak predictions are also made. The transverse momentum (pT) of the decay muon, the pT of the visible decay particles of the other τ-lepton, the total pT, invariant mass, and pseudorapidity of the visible particles from the di-τ system, and the rapidity and acoplanarity of the visible decay particles from either τ-lepton are measured. A maximum-likelihood fit to the muon transverse-momentum distributions in the three regions before unfolding is performed to extract the τ-lepton anomalous magnetic moment aτ and electric dipole moment dτ, the latter for the first time in heavy ion collisions. The observed 95% confidence level intervals are −0.057 < aτ< 0.035 and |dτ| < 2.7 × 10−16ecm.

Abstract:

This paper presents a measurement of the production cross-section of a W boson associated with one or two jets, where at least one jet originates from a b-quark. The data are collected with the ATLAS detector at the LHC in proton-proton collisions at s=13$$ \sqrt{s}=13 $$ TeV, corresponding to an integrated luminosity of 140 fb-1. Differential cross-sections are presented as a function of the transverse momentum of the b-jet for both the electron and muon decay modes of the W boson. The results corrected for all detector effects are presented in a fiducial region defined with basic lepton and jet kinematics, and compared with theoretical predictions. The combined fiducial cross-section of W + b-jets for the electron and muon channels is measured to be 16.6 ± 1.9 pb, which is consistent with the next-to-leading-order QCD prediction of 16.8 ± 2.3 pb. The relative precision of this measurement is improved by approximately a factor of two compared with the previous ATLAS measurement at s=7$$ \sqrt{s}=7 $$ TeV.