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Silicon vertex detector of the Belle II experiment
No full textThe silicon vertex detector (SVD) is installed at the heart of the Belle II experiment,taking data at the high-luminosity B-Factory SuperKEKB since 2019. The SVD is a four-layerdouble-sided strip detector with tracking and particle-identification capabilities. In this paper,we report on the performance of the reconstruction of SVD hits. The detector has shown a stableand above-99% hit efficiency, with a large signal-to-noise in all sensors since the beginning ofdata taking. Cluster position and time resolution have been measured with 2020 and 2022 data andshow excellent performance and stability. In particular, the cluster-position resolution isbetween 7 and 12 μm for the small-pitch sensors, in reasonable agreement with theexpectations, while the cluster time resolution is measured to be below 3 ns. The effect ofradiation damage is visible, but not affecting the performance. As the luminosity increases,higher machine backgrounds are expected and the excellent hit-time information in SVD can beexploited for background rejection. In particular, we have recently developed a novel procedure toselect hits by grouping them event-by-event based on their time. This new procedure allows asignificant reduction of the fake rate, while preserving the tracking efficiency, and it hastherefore replaced the previous cut-based procedure. We have developed a method that uses the SVDhits to estimate the track time (previously unavailable) and the collision time. It has a similarprecision to the estimate based on the drift chamber readout but its execution time is threeorders of magnitude smaller, allowing a faster online reconstruction that is crucial in a highluminosity regime. The track time is a powerful information that allows, together with theaforementioned grouping selection, to raise the occupancy limit above that expected at nominalluminosity, leaving room for a safety factor. Finally, in June 2022 the data taking of the BelleII experiment was stopped to install a new two-layer DEPFET detector (PXD) and upgrade componentsof the accelerator. The whole silicon tracker (PXD+SVD) has been extracted from Belle II, the newPXD installed, the detector closed and commissioned. We briefly describe the SVD results of thisupgrade
Ecological transition for the gas mixtures of the MRPC cosmic ray telescopes of the EEE Project
No full textThe Extreme Energy Events (EEE) Collaboration is fully involved in an ecological transition. The use of the standard gas mixture, CHF + SF, has stopped in favor of an alternative green mixture based on CHF with the addition of He or CO.The choise of these new mixtures is motivated by the significant lower Global Warming Potential (GWP) to reduce the emission of gases potentially contributing to the greenhouse effect.The EEE experiment consists of 61 muon telescopes based on Multigap Resistive Plate Chambers (MRPCs), each telescope composed of 3 chambers filled with gas.Several EEE detectors are today completely fluxed with the new ecological mixture. This contribution will report recent results about the telescope performance obtained from studies with the eco-friendly alternative mixture carried out in the last years
Charged-particle production as a function of the relative transverse activity classifier in pp, p–Pb, and Pb–Pb collisions at the LHC
No full textCorrelations in azimuthal angle extending over a long range in pseudorapidity between particles, usually called the "ridge" phenomenon, were discovered in heavy-ion collisions, and later found in pp and p–Pb collisions. In large systems, they are thought to arise from the expansion (collective flow) of the produced particles. Extending these measurements over a wider range in pseudorapidity and final-state particle multiplicity is important to understand better the origin of these long-range correlations in small collision systems. In this Letter, measurements of the long-range correlations in p–Pb collisions at = 5.02 TeV are extended to a pseudorapidity gap of ∆η ~ 8 between particles using the ALICE forward multiplicity detectors. After suppressing non-flow correlations, e.g., from jet and resonance decays, the ridge structure is observed to persist up to a very large gap of ∆η ~ 8 for the first time in p–Pb collisions. This shows that the collective flow-like correlations extend over an extensive pseudorapidity range also in small collision systems such as p–Pb collisions. The pseudorapidity dependence of the second-order anisotropic flow coefficient, v(η), is extracted from the long-range correlations. The v(η) results are presented for a wide pseudorapidity range of –3.1 < η < 4.8 in various centrality classes in p–Pb collisions. To gain a comprehensive understanding of the source of anisotropic flow in small collision systems, the v(η) measurements are compared with hydrodynamic and transport model calculations. The comparison suggests that the final-state interactions play a dominant role in developing the anisotropic flow in small collision systems.[graphic not available: see fulltext
Measurements of Chemical Potentials in Pb-Pb Collisions at <math display="inline"><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>5.02</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>
No full textThis Letter presents the most precise measurement to date of the matter-antimatter imbalance at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair sNN=5.02 TeV. Using the Statistical Hadronization framework, it is possible to obtain the value of the electric charge and baryon chemical potentials, μQ=-0.18±0.90 MeV and μB=0.71±0.45 MeV, with unprecedented precision. A centrality-differential study of the antiparticle-to-particle yield ratios of charged pions, protons, Ω baryons, and light (hyper)nuclei is performed. These results indicate that the system created in Pb-Pb collisions at the LHC is on average baryon-free and electrically neutral at midrapidity
Large black hole entropy from the giant brane expansion
No full textWe show that the Bekenstein-Hawking entropy of large supersymmetric black holes in AdS × S emerges from remarkable cancellations in the giant graviton expansions recently proposed by Imamura, and Gaiotto and Lee, independently. A similar cancellation mechanism is shown to happen in the exact expansion in terms of free fermions recently put-forward by Murthy. These two representations can be understood as sums over independent systems of giant D3-branes and free fermions, respectively. At large charges, the free energy of each independent system localizes to its asymptotic expansion near the leading singularity. The sum over the independent systems maps their localized free energy to the localized free energy of the superconformal index of U(N) = 4 SYM. This result constitutes a non-perturbative test of the giant graviton expansion valid at any value of N. Moreover, in the holographic scaling limit N → ∞ at fixed ratio , it recovers the 1/16 BPS black hole entropy by a saddle-point approximation of the giant graviton expansion
A plastic scintillation muon veto for sub-Kelvin temperatures
No full textRare-event search experiments located on-surface, such as short-baseline reactor neutrino experiments, are often limited by muon-induced background events. Highly efficient muon vetos are essential to reduce the detector background and to reach the sensitivity goals. We demonstrate the feasibility of deploying organic plastic scintillators at sub-Kelvin temperatures. For the NUCLEUS experiment, we developed a cryogenic muon veto equipped with wavelength shifting fibers and a silicon photo multiplier operating inside a dilution refrigerator. The achievable compactness of cryostat-internal integration is a key factor in keeping the muon rate to a minimum while maximizing coverage. The thermal and light output properties of a plastic scintillation detector were examined. We report first data on the thermal conductivity and heat capacity of the polystyrene-based scintillator UPS-923A over a wide range of temperatures extending below one Kelvin. The light output was measured down to 0.8 K and observed to increase by a factor of 1.61 ± 0.05 compared to 300 K. The development of an organic plastic scintillation muon veto operating in sub-Kelvin temperature environments opens new perspectives for rare-event searches with cryogenic detectors at sites lacking substantial overburden
The DUNE Far Detector Vertical Drift Technology. Technical Design Report
No full textDUNE is an international experiment dedicated to addressing some of the questions at the forefront of particle physics and astrophysics, including themystifying preponderance of matter over antimatter in the early universe. The dual-site experiment will employ an intense neutrino beam focused on a near and a far detector as it aims to determine the neutrino mass hierarchy and to make high-precision measurements of the PMNS matrix parameters, including the CP-violating phase. It will also stand ready to observe supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model.The DUNE far detector implements liquid argon time-projection chamber (LArTPC) technology, and combines the many tens-of-kiloton fiducial mass necessary for rare event searches with the sub-centimeter spatial resolutionrequired to image those events with high precision. The addition of a photon detection system enhances physics capabilities for all DUNE physics drivers and opens prospects for further physics explorations. Given its size, the far detector will be implemented as a set of modules, with LArTPC designs that differ from one another as newer technologies arise.In the vertical drift LArTPC design, a horizontal cathode bisects the detector, creating two stacked drift volumes in which ionization charges drift towards anodes at either the top or bottom. The anodes are composed of perforated PCB layers with conductive strips, enabling reconstruction in 3D.Light-trap-style photon detection modules are placed both on the cryostat's side walls and on the central cathode where they are optically powered.This Technical Design Report describes in detail the technical implementations of each subsystem of this LArTPC that, together with the other far detector modules and the near detector, will enable DUNE to achieve its physics goals
Improving topological cluster reconstruction using calorimeter cell timing in ATLAS
No full textClusters of topologically connected calorimeter cells around cells with large absolute signal-to-noise ratio (topo-clusters) are the basis for calorimeter signal reconstruction in the ATLAS experiment. Topological cell clustering has proven performant in LHC Runs 1 and 2. It is, however, susceptible to out-of-time pile-up of signals from soft collisions outside the 25 ns proton-bunch-crossing window associated with the event's hard collision. To reduce this effect, a calorimeter-cell timing criterion was added to the signal-to-noise ratio requirement in the clustering algorithm. Multiple versions of this criterion were tested by reconstructing hadronic signals in simulated events and Run 2 ATLAS data. The preferred version is found to reduce the out-of-time pile-up jet multiplicity by for jet GeV and by for jet GeV, while not disrupting the reconstruction of hadronic signals of interest, and improving the jet energy resolution by up to 5% for 20< p_{\textrm{T}} < 30 GeV. Pile-up is also suppressed for other physics objects based on topo-clusters (electrons, photons, -leptons), reducing the overall event size on disk by about in early Run 3 pile-up conditions. Offline reconstruction for Run 3 includes the timing requirement
Light-flavor particle production in high-multiplicity pp collisions at = 13 TeV as a function of transverse spherocity
No full textResults on the transverse spherocity dependence of light-flavor particle production (π, K, p, ϕ, K, , Λ, Ξ) at midrapidity in high-multiplicity pp collisions at = 13 TeV were obtained with the ALICE apparatus. The transverse spherocity estimator categorizes events by their azimuthal topology. Utilizing narrow selections on , it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The estimator is found to effectively constrain the hardness of the events when the midrapidity (|η| < 0.8) estimator is used.The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced.The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of .[graphic not available: see fulltext
The state of the dark energy equation of state circa 2023
No full textWe critically examine the state of current constraints on the dark energy (DE) equation of state (EoS) w. Our study is motivated by the observation that, while broadly consistent with the cosmological constant value w = -1, several independent probes appear to point towards a slightly phantom EoS (w ∼ -1.03) which, if confirmed, could have important implications for the Hubble tension. We pay attention to the apparent preference for phantom DE from Planck Cosmic Microwave Background (CMB) data alone, whose origin we study in detail and attribute to a wide range of (physical and geometrical) effects. We deem the combination of Planck CMB, Baryon Acoustic Oscillations, Type Ia Supernovae, and Cosmic Chronometers data to be particularly trustworthy, inferring from this final consensus dataset w = -1.013, in excellent agreement with the cosmological constant value. Overall, despite a few scattered hints, we find no compelling evidence forcing us away from the cosmological constant (yet)