How Sensitive Global Observables are to the Event Topology in Heavy-ion Collisions at the Large Hadron Collider: A Case Study

Particle production and event topology are very strongly correlated in high-energy hadronic and nuclear collisions. Event topology is decided by the underlying particle production dynamics and medium effects. Transverse spherocity is an event shape observable, which has been used in pp and heavy-ion collisions to separate the events based on their geometrical shapes. It has the unique capability to distinguish between jetty and isotropic events. In this work, we have implemented transverse spherocity in Pb-Pb collisions at √ sNN = 5.02 TeV using A Multi-Phase Transport Model (AMPT). While awaiting for experimental explorations, we perform a feasibility study of dependence of transverse spherocity on some of the global observables in heavy-ion collisions at the Large Hadron Collider energies. These global observables include the Bjorken energy density (εBj), speed of sound (cs2) in the medium and the kinetic freeze-out properties for different collision centralities. The present study reveals about the usefulness of event topology dependent measurements in heavy-ion collisions in contrast to proton-proton collisions.

First observation of a tau neutrino charged current interaction with charm production in the OPERA experiment

An event topology with two secondary vertices compatible with the decay of short-lived particles was found in the analysis of neutrino interactions in the OPERA target. The observed topology is compatible with tau neutrino charged current (CC) interactions with charm production and neutrino neutral current (NC) interactions with $$c\overline{c}$$cc¯ pair production. However, other processes can mimic this topology. A dedicated analysis was implemented to identify the underlying process. A Monte Carlo simulation was developed and complementary procedures were introduced in the kinematic reconstruction. A multivariate analysis technique was used to achieve an optimal separation of signal from background. Most likely, this event is a $$\nu _{\tau }$$ντ CC interaction with charm production, the tau and charm particle decaying into 1 prong and 2 prongs, respectively. The significance of this observation is evaluated.

NEXT: Searching for the ββ0νDecay at the LSC

The goal of the NEXT collaboration is the sensitive search of the neutrino-less double beta decay ([Formula: see text]) of [Formula: see text]Xe at the LSC. After a successful R&D phase, a first large-scale prototype of a high-pressure gas-Xenon electroluminescent TPC (NEW) is being operated at LSC since 2016. NEW is a 10-kg radiopure detector meant to understand the relevant backgrounds for the [Formula: see text]search and to perform a measurement of the two neutrino mode of the double beta decay ([Formula: see text]). The first phase of the NEW physics program comprises the commissioning of the detector and the data taking with calibration sources. This phase has allowed to understand the detector capabilities in terms of energy resolution and event topology reconstruction. The operation of NEW is setting the grounds for the construction of the NEXT-100 detector: a TPC holding 100 kg of [Formula: see text]Xe and reaching a sensitivity to the [Formula: see text]half-life of [Formula: see text] y after 3 years of data taking. The latest results of the NEW detector as well as the status of the NEXT-100 project are presented.

Latest results on diffraction at HERA

Recent results on diffraction from the H1 and ZEUS experiments at HERA are presented. Measurement of open charm production in diffractive DIS has been performed by the H1 experiment using the event topology, given by ep → eXY, where the system X, containing at least one D*(2010) meson, is separated from a leading low-mass proton dissociative system Y by a large rapidity gap. The photoproduction of isolated photons is measured using diffractive events recorded by the ZEUS experiment. Cross sections are evaluated in the photon transverse-energy and pseudorapidity ranges 5 < EγT < 15 GeV and -0:7 < ηγ < 0:9, inclusively and with a jet with transverse-energy and pseudorapidity in the ranges 4 < EjetT < 35 GeV and -1:5 < ηjet < 1:8. The exclusive deep inelastic electroproduction and photoproduction of Ψ(2S ) and J=Ψ(1S) mesons has been also studied by ZEUS. The cross-section ratio σ(Ψ(2S))=σ(J=Ψ(1S)) has been measured as a function of Q2, W and t. The results are compared to several predictions of QCD-inspired models, providing tests of the models in a region of soft to hard diffraction.