Simulation and first characterization of MAPS test structures with gain for timing applications

Thanks to their advantages in terms of easiness of manufacturing and reduced production costs, Monolithic Active Pixel Sensors (MAPS) represent an appealing solution for radiation imaging applications, which require to cover large areas with pixelated detectors. In the next upgrade of the ALICE detector, that will have to deal with the higher event rate resulting from the planned increase in the LHC luminosity, it is foreseen to include two additional sensor layers to perform Time of Flight (ToF) measurements. Trying to reach the challenging timing resolution required by the ALICE ToF layers, an internal gain layer has been included in the test structures of the third engineering run of the ARCADIA project to improve the timing performance of this MAPS technology. In the paper we will present an overview of the main results obtained from the electrical and the dynamic characterization of the fabricated devices, which have been compared with the behavior expected from the preliminary TCAD simulations carried out in the design phase. The experimental results confirmed the feasibility of embedding a gain layer in the ARCADIA 110 nm CMOS technology to develop monolithic LGADs

First results on monolithic CMOS detector with internal gain

: In this paper we report on a set of characterisations carried out on the first monolithic LGAD prototype integrated in a customised 110 nm CMOS process having a depleted active volume thickness of 48 μm. This prototype is formed by a pixel array where each pixel has a total size of 100 μm × 250 μm and includes a high-speed front-end amplifier. After describing the sensor and the electronics architecture, both laboratory and in-beam measurements are reported and described. Optical characterisations performed with an IR pulsed laser setup have shown a sensor internal gain of about 2.5. With the same experimental setup, the electronic jitter was found to be between 50 ps and 150 ps, depending on the signal amplitude. Moreover, the analysis of a test beam performed at the Proton Synchrotron (PS) T10 facility of CERN with 10 GeV/c protons and pions indicated that the overall detector time resolution is in the range of 234 ps to 244 ps. Further TCAD investigations, based on the doping profile extracted from C(V) measurements, confirmed the multiplication gain measured on the test devices. Finally, TCAD simulations were used to tune the future doping concentration of the gain layer implant, targeting sensors with a higher avalanche gain. This adjustment is expected to enhance the timing performance of the sensors of the future productions, in order to cope with the high event rate expected in most of the near future high-energy and high-luminosity physics experiments, where the time resolution will be essential to disentangle overlapping events and it will also be crucial for Particle IDentification (PID

First results on monolithic CMOS detector with internal gain

In this paper we report on a set of characterisations carried out on the first monolithic LGAD prototype integrated in a customised 110 nm CMOS process having a depleted active volume thickness of 48 $\mu$m. This prototype is formed by a pixel array where each pixel has a total size of 100 $\mu$m $\times$ 250 $\mu$m and includes a high-speed front-end amplifier. After describing the sensor and the electronics architecture, both laboratory and in-beam measurements are reported and described. Optical characterisations performed with an IR pulsed laser setup have shown a sensor internal gain of about 2.5. With the same experimental setup, the electronic jitter was found to be between 50 ps and 150 ps, depending on the signal amplitude. Moreover, the analysis of a test beam performed at the Proton Synchrotron (PS) T10 facility of CERN with 10 GeV/c protons and pions indicated that the overall detector time resolution is in the range of 234 ps to 244 ps. Further TCAD investigations, based on the doping profile extracted from $C(V)$ measurements, confirmed the multiplication gain measured on the test devices. Finally, TCAD simulations were used to tune the future doping concentration of the gain layer implant, targeting sensors with a higher avalanche gain. This adjustment is expected to enhance the timing performance of the sensors of the future productions, in order to cope with the high event rate expected in most of the near future high-energy and high-luminosity physics experiments, where the time resolution will be essential to disentangle overlapping events and it will also be crucial for Particle IDentification (PID)

Measurement of the production and elliptic flow of (anti)nuclei in Xe-Xe collisions at √sNN =5.44 TeV

Measurements of (anti)deuteron and (anti)He3 production in the rapidity range |y|<0.5 as a function of the transverse momentum and event multiplicity in Xe-Xe collisions at a center-of-mass energy per nucleon-nucleon pair of sNN=5.44 TeV are presented. The coalescence parameters B2 and B3 are measured as a function of the transverse momentum per nucleon. The ratios between (anti)deuteron and (anti)He3 yields and those of (anti)protons and pions are reported as a function of the mean charged-particle multiplicity density and compared with two implementations of the statistical hadronization model and with coalescence predictions. The elliptic flow of (anti)deuterons is measured for the first time in Xe-Xe collisions and shows features similar to those already observed in Pb-Pb collisions, i.e., the mass ordering at low transverse momentum and the meson-baryon grouping at intermediate transverse momentum. The production of nuclei is particularly sensitive to the chemical freeze-out temperature of the system created in the collision, which is extracted from a grand-canonical-ensemble-based thermal fit, performed for the first time including light nuclei along with light-flavor hadrons in Xe-Xe collisions. The extracted chemical freeze-out temperature Tchem=(154.2±1.1) MeV in Xe-Xe collisions is similar to that observed in Pb-Pb collisions and close to the crossover temperature predicted by lattice quantum chromodynamics calculations

Probing Strangeness Hadronization with Event-by-Event Production of Multistrange Hadrons

This Letter presents the first measurement of event-by-event fluctuations of the net number (difference between the particle and antiparticle multiplicities) of multistrange hadrons Ξ- and Ξ ̄+ and its correlation with the net-kaon number using the data collected by the ALICE Collaboration in pp, p-Pb, and Pb-Pb collisions at a center-of-mass energy per nucleon pair sNN=5.02 TeV. The statistical hadronization model with a correlation over three units of rapidity between hadrons having the same and opposite strangeness content successfully describes the results. On the other hand, string-fragmentation models that mainly correlate strange hadrons with opposite strange quark content over a small rapidity range fail to describe the data

Multimuons in cosmic-ray events as seen in ALICE at the LHC

ALICE is a large experiment at the CERN Large Hadron Collider. Located 52 meters underground, its detectors are suitable to measure muons produced by cosmic-ray interactions in the atmosphere. In this paper, the studies of the cosmic muons registered by ALICE during Run 2 (2015–2018) are described. The analysis is limited to multimuon events defined as events with more than four detected muons (Nμ > 4) and in the zenith angle range 0◦ 100) obtained with QGSJET-II-04 and SIBYLL 2.3d is compatible with the data, while EPOS-LHC produces a significantly lower rate (55% of the measured rate). For both QGSJET-II-04 and SIBYLL 2.3d, the rate is close to the data when the composition is assumed to be dominated by heavy elements, an outcome compatible with the average energy Eprim ∼ 1017 eV of these events. This result places significant constraints on more exotic production mechanisms

First Measurement of Hypernuclei and Antihypernuclei at the LHC

In this Letter, the first evidence of the (Formula presented) antihypernucleus is presented, along with the first measurement at the LHC of the production of (anti)hypernuclei with mass number (Formula presented), specifically (Formula presented) and (Formula presented). In addition, the antiparticle-to-particle ratios for both hypernuclei ((Formula presented) and (Formula presented)) are shown, which are sensitive to the baryochemical potential of the strongly interacting matter created in heavy-ion collisions. The results are obtained from a data sample of central Pb-Pb collisions, collected during the 2018 LHC data taking at a center-of-mass energy per nucleon pair of (Formula presented). The yields measured for the average of the charge-conjugated states are found to be (Formula presented) for the (Formula presented) and (Formula presented) for the (Formula presented), and the measured antiparticle-to-particle ratios are in agreement with unity. The presence of (Formula presented) and (Formula presented) excited states is expected to strongly enhance the production yield of these hypernuclei. The yield values exhibit a combined deviation of (Formula presented) from the theoretical ground-state-only expectation, while the inclusion of the excited states in the calculations leads to an agreement within (Formula presented) with the present measurements. Additionally, the measured (Formula presented) and (Formula presented) masses are compatible with the world-average values within the uncertainties

Studying the interaction between charm and light-flavor mesons

The two-particle momentum correlation functions between charm mesons (D and D ) and charged light-flavor mesons (π and K ) in all charge combinations are measured for the first time by the ALICE Collaboration in high-multiplicity proton–proton collisions at a center-of-mass energy of √s = 13 TeV. For DK and D K pairs, the experimental results are in agreement with theoretical predictions of the residual strong interaction based on quantum chromodynamics calculations on the lattice and chiral effective field theory. In the case of Dπ and D π pairs, tension between the calculations including strong interactions and the measurement is observed. For all particle pairs, the data can be adequately described by Coulomb interaction only, indicating a shallow interaction between charm and light-flavor mesons. Finally, the scattering lengths governing the residual strong interaction of the Dπ and D π systems are determined by fitting the experimental correlation functions with a model that employs a Gaussian potential. The extracted values are small and compatible with zero

Proton emission in ultraperipheral Pb-Pb collisions at TeV

The first measurements of proton emission accompanied by neutron emission in the electromagnetic dissociation (EMD) of Pb208 nuclei in the ALICE experiment at the Large Hadron Collider are presented. The EMD protons and neutrons emitted at very forward rapidities are detected by the proton and neutron zero degree calorimeters of the ALICE experiment. The emission cross sections of zero, one, two, and three protons accompanied by at least one neutron were measured in ultraperipheral Pb208-Pb208 collisions at a center-of-mass energy per nucleon pair sNN=5.02TeV. The 0p and 3p cross sections are described by the RELDIS model within their measurement uncertainties, while the 1p and 2p cross sections are underestimated by the model by 17-25%. According to this model, these 0p, 1p, 2p, and 3p cross sections are associated, respectively, with the production of various isotopes of Pb, Tl, Hg, and Au in the EMD of Pb208. The cross sections of the emission of a single proton accompanied by the emission of one, two, or three neutrons in EMD were also measured. The data are significantly overestimated by the RELDIS model, which predicts that the (1p,1n), (1p,2n), and (1p,3n) cross sections are very similar to the cross sections for the production of the thallium isotopes Tl206,205,204

Medium-induced modification of groomed and ungroomed jet mass and angularities in Pb–Pb collisions at sNN=5.02

The ALICE Collaboration presents a new suite of jet substructure measurements in Pb–Pb and pp collisions at a center-of-mass energy per nucleon pair sNN=5.02 [Figure presented]. These measurements provide access to the internal structure of jets via the momentum and angle of their constituents, probing how the quark–gluon plasma modifies jets, an effect known as jet quenching. Jet grooming additionally removes soft wide-angle radiation to enhance perturbative accuracy and reduce experimental uncertainties. We report the groomed and ungroomed jet mass mjet and jet angularities λακ using κ=1 and α>0. Charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm with resolution parameter R=0.2. A narrowing of the jet mass and angularity distributions in Pb–Pb collisions with respect to pp is observed and is enhanced for groomed results, confirming modification of the jet core. By using consistent jet definitions and kinematic cuts between the mass and angularities for the first time, previous inconsistencies in the interpretation of quenching measurements are resolved, rectifying a hurdle for understanding how jet quenching arises from first principles and highlighting the importance of a well-controlled baseline. These results are compared with a variety of theoretical models of jet quenching, providing constraints on jet energy-loss mechanisms in the quark–gluon plasma