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Combined search for four-top quarks production in proton-proton collisions at √s = 13 TeV with the ATLAS detector
No full textThe combination of two analyses searching for the production of four-top quarks (ttt¯ t ¯) using proton-proton collision data at a center-of-mass energy √s = 13 TeV with an integrated luminosity of 36 fb−1 recorded by the ATLAS experiment is presented. The considered final states are events with multiple jets, b-jets, and either: a) one lepton or two leptons with an opposite electric charge, or b) two leptons with the same electric charge or three leptons. Constraints are set on production ttt¯ t
¯ cross-section and on an effective field theory inducing four fermions contact interactions
Characterization of FBK SiPM arrays for the SCT medium size telescope prototype proposed for the CTA observatory
No full textThe Cherenkov Telescope Array (CTA) will represent the new generation of Imaging Atmospheric Cherenkov Telescopes (IACTs), aimed to detect very high-energy gamma-rays produced in atmospheric showers. The prototype
Schwarzschild-Couder Telescope (pSCT) has been inaugurated in January 2019 at the Fred Lawrence Whipple Observatory aiming to the extension of the CTA array baseline. Silicon Photomultipliers (SiPMs) are particularly suitable as optical units of IACTs to detect the low- and fast-intensity Cherenkov signal. The Near UltraViolet High-Density 6 × 6 mm2 SiPMs (NUV-HD3), produced by Fondazione
Bruno Kessler in collaboration with INFN, have been assembled in more than 100 arrays of 16 pixels. These optical modules have been characterized in the laboratories of INFN to be integrated on the camera of pSCT. In this contribution we report the characterization results of the SiPM arrays and on the uniformity of their
performances
Tests of lepton flavour universality in b → cν decays with τ − → μ−ντν¯μ at the LHCb experiment
No full textThe combination of lepton flavour universality measurements carried out in b → cν decays has shown possible hints of deviation with respect to the Standard Model. The LHCb experiment contributed to the combination with analyses of semi-tauonic decays with both leptonic and hadronic decays of the τ lepton. This document reports tests of lepton flavour universality in semileptonic b-meson decays performed by the LHCb experiment using the muonic τ decay channel
Measurements of the Higgs production cross section in the H → τ τ decay channel with the ATLAS experiment
No full textMeasurements of the Higgs production cross section in the H → ττ decay channel are presented. The analysis has been performed using 36.1 fb−1 of data collected by the ATLAS experiment at √s = 13 TeV proton-proton collisions at the Large Hadron Collider. The observed (expected) significance of the H → ττ signal excess over the expected background amounts to 4.4 (4.1) standard deviations. This result, combined with the data taken at √s = 7 and 8 TeV, leads to an observed (expected) significance of 6.4 (5.4) standard deviations and constitutes the first ATLAS observation of H → ττ . All the reported measurements are in agreement with the Standard Model predictions
Real-time selection using flavour-tagging algorithms in ATLAS
No full textThe physics program covered by the ATLAS Collaboration is broad and also includes final states characterized by the presence of b-hadrons in their final states. Specialized triggers that exploit flavour tagging techniques, the b-jet
triggers, have been developed for targeting these topologies. In this contribution the use of flavour tagging algorithms at online level and techniques to improve their performance will be presented
Lifetime measurement in the femtoseconds range in neutron-rich light nuclei with the AGATA tracking array
No full textAn extension of the Doppler-Shift Attenuation Method (DSAM) was implemented in order to perform nuclear state lifetime measurements down to tens-to-hundreds of femtoseconds in the case of complex reaction mechanisms,
such as heavy-ions transfer and deep-inelastic reactions. This novel technique will have an impact in future studies of exotic neutron-rich systems produced with highintensity radioactive ISOL-type beams. We describe here the method, in the context of an experiment realised with the aim of measuring the lifetime of excited states in neutron-rich light nuclei of C, N and O, with the combined use of the gamma detection AGATA and PARIS arrays, coupled to the VAMOS++ magnetic spectrometer in GANIL (France). The nuclei of interest were populated with low-energy transfer and deep-inelastic reactions induced by a 18O beam on a thick 181Ta target. As a test case for the technique validation, we show the lifetime measurement of the 1/2−
1 state at 3055.36(16) keV in 17O: a lifetime value of τ = 159+40−30 fs was obtained, in agreement with the literature. The impact of the excellent performance of the AGATA tracking array will be also highlighted. Finally, the new technique will be exploited to measure the lifetime of a newly discovered state in 18N, at 2404.6(13) keV
Characterization of the lutetium-yttrium orthosilicate scintillating crystals for the CMS experiment
No full textThe Compact Muon Solenoid (CMS) detector is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC starting in 2027. In particular, a new timing detector, the Mip Timing Detector (MTD) will measure minimum ionizing particles with a time resolution of 30–50 ps. The technology selected for the central part of the detector,
the Barrel Timing Layer, consists of scintillating crystals of lutetium yttrium orthosilicate doped with cerium (LYSO:Ce) read out with Silicon Photo-Multipliers.
A study of the performances of LYSO samples from different producers has been performed last year in Rome; in this report the experimental setup is described and the optical measurements are presented
Study of the neutron-induced reaction 17O(n, α)14C at astrophysical energies via the Trojan Horse Method
No full textStellar nucleosynthesis processes are of vital importance for nuclear physics: all the heavy elements are created by neutron capture reactions that take place in stars. To correctly study such reactions the neutron abundance available in the environment must be known, which means that also the so-called “neutron poisons” must be considered. The present work will focus on the reaction 17O(n, α) 14C which removes neutrons from the stellar environment during the s-process. Even though the study of such reactions is of high interest, it still presents several technological problems regarding both the creation and characterization of the neutron beam and the radioprotection of the facility. Therefore, the Trojan Horse Method,an indirect method, has been chosen to study the 17O(n, α) 14C reaction in the energy region of astrophysical interest, from 300 keV in the center-of-mass frame down to zero. In the present work, after briefly recalling the main features of the method and reporting on the state of the art for the reaction cross-section measurements, the latest THM experiment will be presented
Can reference radiosounding measurements be used to improve historical time series?
No full textUpper-air radiosounding observations are undoubtedly a primary data source for the study of climate and for the atmospheric reanalysis. Nevertheless, historical radiosounding time series are affected by several systematic uncertainties due to change in the measurement sensors. As an alternative to the few existing approaches, in the frame of the Copernicus Climate Change Service (C3S), a novel approach, named RHARM (Radiosounding HARMonization), has been developed to provide a homogenized dataset of temperature, humidity and wind radiosounding profiles available from the Integrated Global Radiosonde Archive (IGRA) along with an estimation of the total uncertainty for each profile. Estimation of uncertainties has never been developed in previous homogenization algorithms. The homogenization is carried out for a substantial subset of IGRA radiosounding stations. Comparisons of trends calculated at 300 hPa over Europe in the period 2000–2018 using ERA5 ECWMF atmospheric reanalysis, IGRA and RHARM datasets show a good agreement for temperature with mutual differences within 0.05 K/da. For relative humidity, ERA5 shows a trend of −0.7%/da, while the trend for IGRA and RHARM is of 0.5%/da and 0.8%/da, respectively. The usefulness of comparing, for the first time, ERA5 and RHARM time series taking advantage of the RHARM uncertainty is also discussed
Evaluating normal tissue damage after hadrontherapy by chromosome aberration prediction
No full textIn cancer hadrontherapy, the Relative Biological Effectiveness (RBE) is calculated by considering cell survival as the endpoint of interest. Although this
is a good estimator of the beam effectiveness in eliminating the tumour cells, late damage in healthy tissues, including secondary tumours, is better correlated with chromosomal aberrations. In particular, dicentrics in blood lymphocytes are widely considered as a good biomarker of normal tissue damage, as the blood circulates
in all tissues and is inevitably exposed to radiation during the treatment. In this study, lymphocyte dicentrics were used as an ad hoc endpoint to evaluate the RBE for (late) normal tissue damage by means of BIANCA (BIophysical ANalysis of Cell death and chromosome Aberrations), a biophysical model that simulates radiationinduced chromosome aberrations and cell death. More specifically, BIANCA was applied to produce a radiobiological database that predicts lymphocyte dicentric induction as a function of dose, particle type and LET. Afterwards, an interface with the FLUKA code allowed predicting dicentric RBE along a C-ion SOBP, and
comparing it with cell survival RBE. This pilot study suggested that using the RBE for tumour cell survival along the entire beam might lead to an underestimation of
the risk of normal tissue damage