Abstract: This paper presents measurements of charged-hadron spectra obtained in pp, p+Pb, and Pb+Pb collisions at root s or root s(NN) = 5.02TeV, and in Xe+Xe collisions at root s(NN) = 5.44TeV. The data recorded by the ATLAS detector at the LHC have total integrated luminosities of 25 pb(-1), 28 nb(-1), 0.50 nb(-1), and 3 μb(-1), respectively. The nuclear modification factors RpPb and R-AA are obtained by comparing the spectra in heavy-ion and pp collisions in a wide range of charged-particle transverse momenta and pseudorapidity. The nuclear modification factor RpPb shows a moderate enhancement above unity with a maximum at p(T) approximate to 3 GeV; the enhancement is stronger in the Pb-going direction. The nuclear modification factors in both Pb+Pb and Xe+Xe collisions feature a significant, centrality-dependent suppression. They show a similar distinct p(T)-dependence with a local maximum at p(T) approximate to 2 GeV and a local minimum at p(T) approximate to 7 GeV. This dependence is more distinguishable in more central collisions. No significant eta |-dependence is found. A comprehensive comparison with several theoretical predictions is also provided. They typically describe RAA better in central collisions and in the pT range from about 10 to 100 GeV.

Abstract: We evaluate ratios of the chi(c1) decay rates to eta (eta', K-) and one of the f(0) (1370), f(0) (1710), f(2) (1270), f(2)'(1525), K-2*(1430) resonances, which in the local hidden gauge approach are dynamically generated from the vector-vector interaction. With the simple assumption that the chi(c1) is a singlet of SU(3), and the input from the study of these resonances as vector-vector molecular states, we describe the experimental ratio B(chi(c1)-> eta f(2) (1270))/B(chi(c1) -> eta'f(2)' (1525)) and make predictions for six more ratios that can be tested in future experiments.

Abstract: We study the nonconservation of the chiral charge of Dirac fields between past and future null infinity due to the Adler-Bell-Jackiw chiral anomaly. In previous investigations [A. del Rio, Phys. Rev. D 104, 065012 (2021)], we found that this charge fails to be conserved if electromagnetic sources in the bulk emit circularly polarized radiation. In this article, we unravel yet another contribution coming from the nonzero, infrared “soft” charges of the external, electromagnetic field. This new contribution can be interpreted as another manifestation of the ordinary memory effect produced by transitions between different infrared sectors of Maxwell theory, but now on test quantum fields rather than on test classical particles. In other words, a flux of electromagnetic waves can leave a memory on quantum fermion states in the form of a permanent, net helicity. We elaborate this idea in both 1 + 1 and 3 + 1 dimensions. We also show that, in sharp contrast, gravitational infrared charges do not contribute to the fermion chiral anomaly.

Abstract: We report on the thermal neutron flux measurements carried out at the Laboratorio Subterraneo de Canfranc (LSC) with two commercial 2 '' x 2 '' CLYC detectors. The measurements were performed as part of an experimental campaign at LSC with He-3 detectors, for establishing the sensitivity limits and use of CLYCs in low background conditions. Acareful characterization of the intrinsic alpha and gamma-ray background in the detectors was required and done with dedicated measurements. It was found that the alpha activities in the two CLYC crystals differ by a factor of three, and the use of Monte Carlo simulations and a Bayesian unfolding method allowed us to determine the specific alpha activities from the U-238 and Th-232 decay chains. The simulations and unfolding also revealed that the gamma-ray background registered in the detectors is dominated by the intrinsic activity of the components of the detector such as the aluminum housing and photo-multiplier and that the activity within the crystal is low in comparison. The data from the neutron flux measurements with the two detectors were analyzed with different methodologies: one based on an innovative alpha/neutron pulse shape discrimination method and one based on the subtraction of the intrinsic alpha background that masks the neutron signals in the region of interest. The neutron sensitivity of the CLYCs was calculated by Monte Carlo simulations with MCNP6 and GEANT4. The resulting thermal neutron fluxes are in good agreement with complementary flux measurement performed with He-3 detectors, but close to the detection limit imposed by the intrinsic a activity.

Abstract: The success of the Belle II experiment in Japan relies on the very high instantaneous luminosity, close to 6x1035 cm-2 s-1, expected from the SuperKEKB collider. The corresponding beam conditions at such luminosity levels generate large rates of background particles and creates stringent constraints on the vertex detector, adding to the physics requirements. Current prospects for the occupancy rates in the present vertex detector (VXD) at full luminosity fall close to the acceptable limits and bear large uncertainties. In this context, the Belle II collaboration is considering the possibility to install an upgraded VXD system around 2027 to provide a sufficient safety margin with respect to the expected background rate and possibly enhance tracking and vertexing performance. The VTX collaboration has started the design of a fully pixelated VXD, called VTX, based on fast and highly granular Depleted Monolithic Active Pixel Sensors (DMAPS) integrated on light support structures. The two main technical features of the VTX proposal are the usage of a single sensor type over all the layers of the system and the overall material budget below 2% of radiation length, compared to the current VXD which has two different sensor technologies and about 3% of radiation length. A dedicated sensor (OBELIX), taylored to the specific needs of Belle II, is under development, evolving from the existing TJ-Monopix2 sensor. The time-stamping precision below 100 ns will allow all VTX layers to take part in the track finding strategy contrary to the current situation. The first two detection layers are designed according to a self-supported all-silicon ladder concept, where 4 contiguous sensors are diced out of a wafer, thinned and interconnected with post-processed redistribution layers. The outermost detection layers follow a more conventional approach with a cold plate and carbon fibre support structure, and light flex cables interconnecting the sensors. This document will review the context, technical details and development status of the proposed Belle II VTX.