Nuclear and Quark Matter Seminar 2021

Dates:
20.01. | 21.04. | 25.08. | 15.12. |

Previous years: 2020 | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 | 2013

• 20 January 2021, 13:30 - online only
  
  Ignazio Bombaci - University of Pisa and INFN, Pisa, Italy
  The hyperon puzzle in neutron stars
  
  Abstract
  The so called hyperon puzzle in neutron stars, the difficulty to reconcile the measured masses of neutron stars with the presence of hyperons in their interiors, is one of the hot topics in astrophysics which is stimulating copious experimental and theoretical research in hypernuclear physics and dense matter physics. After illustrating the origin of the hyperon puzzle, I will discuss some of its possible solutions, and particularly those related to the role of hyperonic two- and three-body interactions on the equation of state of dense matter. Afterward, I will discuss a possibility to circumvent the hyperon puzzle allowing for the presence of strangeness in neutron stars in the form of deconfined strange quark matter, and thus considering the so called quark stars, i.e. hybrid stars or strange stars. Finally I will discuss the astrophysical consequences of the possible conversion process of an hadronic star to a quark star.
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• 21 April 2021, 13:30 - online only
  
  Marina Kozhevnikova - JINR, Dubna, Russia
  Update of the Three-fluid Hydrodynamics-based Event Simulator (THESEUS) and light-nuclei production in heavy-ion collisions
  
  Abstract
  We present an updated event generator THESEUS, based on the three-fluid dynamics (3FD), complemented by UrQMD cascade for the late stage of the nuclear collision. The generator is extended to simulate light-nuclei production in relativistic heavy-ion collisions via thermal mechanism, on the same basis as hadrons. We present the rapidity, transverse momentum spectra, first v1 flow harmonics of deuterons, tritons, He at different collision energies and impact parameters. The results are compared with experimental data from NA49 and STAR. We show that anti-deuteron spectra from THESEUS are in agreement with STAR data. We demonstrate the contributions from the excited states of Helium to the yields of deuteron, triton and He. The reproduction is achieved without any extra parameters, while the original coalescence approach in 3FD requires a tuning of the coalescence coefficients for each light nucleus separately.
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• 25 August 2021, 13:30 - EMMI/KBW Lecture Hall (1.17)
  
  Mandatory registration for the seminar is available here
  
  Valentina Zaccolo - University and INFN, Trieste, Italy
  Soft-QCD physics at the LHC
  
  Abstract
  The hadronic interactions are accurately described when the perturbative QCD approach is used. This is true for hard processes with large momentum transfer compared to the QCD scale. However, perturbative QCD fails to describe hadronic interactions when the effective strong coupling constant is large, i.e. for processes at low transverse momentum called soft. Multiple Parton Interactions (MPI) are composed of semi-hard parton interactions. Their contribution becomes more relevant at high centre-of-mass energy of the colliding hadrons. However, the non-perturbative component of MPI cannot be trivially separated from products of initial and final state soft radiation and beam remnants from the proton break up. Therefore, experimentally, one attempts to topologically separate the partons produced in the hardest scattering from the softer part, called the Underlying Event. In this seminar, some of the newest results about soft QCD at LHC will be discussed. The focus will be on the characterisation of the event based on topological constraints and on how these techniques can bring minimum-bias and identified-particles studies to the precision era.
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• 15 December 2021, 13:30 - online only
  
  Igor Altsybeev - St. Petersburg State University, Russia
  Suppressing volume fluctuations with strongly-intensive observables: recent experimental results and future prospects
  
  Abstract
  In relativistic heavy-ion collisions, properties of the initial state and effects arising during evolution of the medium, such as a transition between the hadronic and partonic phases, should reflect themselves in event-by-event fluctuations of various quantities, like particle number and particle mean transverse momentum. However, many observables used for these studies are trivially affected by the fluctuations of system volume from one event to another. This undesired effect can be eliminated if one uses a special class of observables - the so-called strongly intensive quantities. In this talk, recent measurements of several strongly intensive observables in ALICE and NA61/SHINE experiments are discussed, and problems revealed. It is shown that interpretation of the acceptance-integrated observables is often challenging, and more differential analysis is required. Thus, a set of new differential strongly intensive observables is proposed. One of these observables is the correlation coefficient between ratios of identified particle yields measured in two angular acceptance intervals. Similarly to the integrated observable ν_dyn, this coefficient is independent of the volume fluctuations, but allows one to separate short-range effects from the underlying patterns of global fluctuations. In particular, correlations between kaon-to-pion ratios (K/π - K/π) probe the pattern of canonical strangeness suppression along rapidity. Similarly, proton-to-pion rapidity correlations (p/π - p/π) are sensitive to canonical ensemble effects for baryons. Behaviour of these quantities in various models (event generators, thermal model) is demonstrated.
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