An important observable to understand the properties of the matter produced in heavy-ion collisions is its strangeness content. Recent experimental results show that in semi-central collisions, the Λ ...and
global polarization show differences that increase at low energies. This behaviour has been described using a model where these particles may be produced from two distinct density zones in the collision region: the core and the corona where QGP processes and
p
+
p
like reactions, respectively, are mainly at work. Using this idea, the polarization can be influenced by the relative abundance of these particles coming from either regions. In this work we show how to test this model in the MPD experiment.
We present results for time resolution studies performed on three different scintillating plastics and two silicon photo-multipliers. These studies are intended to determine whether scintillating ...plastic/silicon photo-multiplier systems can be employed to provide a fast trigger signal for NICA's Multi Purpose Detector (MPD). Our results show that such a system made of cells with transverse dimensions of order of a few cm, coupled to silicon photo-multipliers, provides a time resolution of about 50 ps, which can be even further improved to attain the MPD trigger requirements of 20 ps.
We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of Standard Model (SM) extensions. LLPs are a common prediction of a wide range of ...theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). In most cases the LLP lifetime can be treated as a free parameter from the \(\mu\)m scale up to the Big Bang Nucleosynthesis limit of \(\sim 10^7\)m. Neutral LLPs with lifetimes above \(\sim\) 100m are particularly difficult to probe, as the sensitivity of the LHC main detectors is limited by challenging backgrounds, triggers, and small acceptances. MATHUSLA is a proposal for a minimally instrumented, large-volume surface detector near ATLAS or CMS. It would search for neutral LLPs produced in HL-LHC collisions by reconstructing displaced vertices (DVs) in a low-background environment, extending the sensitivity of the main detectors by orders of magnitude in the long-lifetime regime. In this white paper we study the LLP physics opportunities afforded by a MATHUSLA-like detector at the HL-LHC. We develop a model-independent approach to describe the sensitivity of MATHUSLA to BSM LLP signals, and compare it to DV and missing energy searches at ATLAS or CMS. We then explore the BSM motivations for LLPs in considerable detail, presenting a large number of new sensitivity studies. While our discussion is especially oriented towards the long-lifetime regime at MATHUSLA, this survey underlines the importance of a varied LLP search program at the LHC in general. By synthesizing these results into a general discussion of the top-down and bottom-up motivations for LLP searches, it is our aim to demonstrate the exceptional strength and breadth of the physics case for the construction of the MATHUSLA detector.
An important observable to understand the properties of the matter produced in heavy-ion collisions is its strangeness content. Recent experimental results show that in semi-central collisions, the ...\(\Lambda\) and \(\bar{\Lambda}\) global polarization show differences that increase at low energies. This behaviour has been described using a model where these particles may be produced from two distinct density zones in the collision region: the core and the corona where QGP processes and p + p like reactions, respectively, are mainly at work. Using this idea, the polarization can be influenced by the relative abundance of these particles coming from either regions. In this work we show how to test this model in the MPD experiment.
During the 2011 Pb-Pb run, dedicated triggers were used by the ALICE Collaboration to enrich ultra-peripheral collisions (UPC) to measure the J/psi roduction cross section and its rapidity dependence ...at a centre of mass energy of 2.76 TeV per nucleon pair. In this article, the ongoing studies on J/psi photoproduction in UPC events are presented.
The silicon photo-multipliers (SiPMs) are commonly used in the construction of radiation detectors such as those used in high energy experiments and its applications, where an excellent time ...resolution is required for triggering. In most of this cases, the trigger systems electric charge information is discarded due to limitations in data acquisition. In this work we propose a method using a simple radiation detector based on an organic plastic scintillator \(2\times2\times0.3\)~cm\(^3\) size, to estimate the electric charge obtained from the acquisition of the fast output signal of a SensL SiPM model C-60035-4P-EVB. Our results suggest a linear relation between the reconstructed electric charge from the fast output of the SiPM used with respect to the one reconstructed with its standard signal output. Using our electric charge reconstruction method, we compared the sensitivity of two plastic scintillators, BC404 and BC422Q, under the presence of Sr90, Cs137, Co60, and Na22 radiation sources.
Two modules of the AD detector have been studied with the test beam at the T10 facility at CERN. The AD detector is made of scintillator pads read out by wave-length shifters (WLS)coupled to clean ...fibres that carry the produced light to photo-multiplier tubes (PMTs). In ALICE the AD is used to trigger and study the physics of diffractive and ultra-peripheral collisions as well as for a variety of technical tasks like beam-gas background monitoring or as a luminometer. The position dependence of the modules' efficiency has been measured and the effect of hits on the WLS or PMTs has been evaluated. The charge deposited by pions and protons has been measured at different momenta of the test beam. The time resolution is determined as a function of the deposited charge. These results are important ingredients to better understand the AD detector, to benchmark the corresponding simulations, and very importantly they served as a baseline for a similar device, the Forward Diffractive Detector (FDD), being currently built and that will be in operation in ALICE during the LHC Runs 3 and 4.
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![J/[psi] photoproduction in ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2100-014X/small "J/[psi] photoproduction in ultra-peripheral heavy ion collisions with the ALICE experiment")