Animé par Ophélie Bugnon
jeudi 13 juin 2019 à 14:00
Quantum chromodynamics (QCD) is the theory describing the interaction between color charges, quarks and gluons (also called partons). One of its fundamental property is the confinement of the partons into hadrons, the basic components of nuclei.
Under extreme conditions, QCD predicts a phase transition between nuclear matter and a medium where the partons are free to propagate, the Quark-Gluon Plasma (QGP). This state of matter can be experimentally created in ultra-relativistic heavy-ion collisions at CERN LHC, the world's largest accelerator. A Large Ion Collider Experiment (ALICE) detector is designed to exploit the unique physics potential of LHC.
Quarkonia, bound states of heavy quarks, are ideal particles to caracterize the QGP properties. Their measurement makes it possible to estimate the initial temperature of the medium.
If nucleus-nucleus collisions lead to the formation of a deconfined medium, quarkonium production is expected to be suppressed by the presence of color charges.
To quantify the suppression mechanisms, one needs to compare the production in heavy-ion collisions with respect to proton-proton collisions at the same center-of-mass energy.
In this presentation, detailed analyses of upsilon production at 5 TeV with ALICE are reported.
The Physics program of the ALICE experiment (A Large Ion Collider Experiment) at CERN LHC (Large Hadron Collider) is mostly focused on the study of the Quark-Gluon Plasma (QGP). Following this objective, the measurements of probes for QGP such as charmonia are part of the key studies in this field. In addition, charged particle multiplicity is an interesting observable providing directly comparable measurements from one collision system to another (pp, pPb and PbPb). Here we present the ongoing study of relative production yields of J/ψ and Ψ(2S) charmonia as a function of charged particle multiplicity in proton-proton collisions at 13 TeV.
An important part of the ALICE apparatus located at forward rapidity is the muon spectrometer designed to detect the muons from heavy hadron decays and to measure the characteristics of their trajectories. The Muon spectrometer is composed of different detection systems and a front absorber close to the interaction point which function is to stop a great part of the particule flow produced in the collisions, selecting the muons (few interactions with matter). On the other hand, the resolution on the origin of the decay muon trajectories is too high to distinguish quarkonia directly produced at early stages of the collision from those produced by heavy hadron decays (prompt/non-prompt). The Muon Forward Tracker (MFT) is a silicon pixel detector designed to reconstruct the muon tracks with a spatial resolution close to 5μm (sufficient to distinguish prompt and non-prompt quarkonia). The MFT is part of the ALICE upgrade program for LHC run 3 (starting in 2021) and Subatech is strongly involved in all aspects of the project (design, simulation, electronics, mechanics, qualification, future analysis…). For the « Heures Thésard » seminar, we will present an overview of the MFT upgrade project and particularly the qualification and commissioning phase including the first beam tests for a prototype of an MFT disk, performed at CERN in June 2018.