ALICE studies the quark-gluon plasma expansion with charm quarks
Charm quarks serve as probes of the quark-gluon plasma (QGP) formed when lead nuclei collide in the LHC. When lead nuclei do not collide head on, the QGP system is elongated and the expansion leads to a dominant elliptical modulation - elliptic flow v2 - in the momentum distribution of hadrons.
The ALICE Collaboration recently measured, using the large lead-lead sample collected in 2018, the elliptic flow of hadrons containing charm quarks, either bound to a light quark (D meson) or in charm-anticharm pairs (J/ψ). The results are shown in the figure as a function of transverse momentum pT. At low momentum, the elliptic flow of D mesons is not as large as that of pions (that contain only light quarks), while the elliptic flow of J/ψ is lower than both, but distinctly observed. This pattern indicates that the heavy charm quarks are dragged with the QGP expansion, but likely to a lesser extent than light quarks, and that both D mesons and J/ψ at low momentum are in part formed by the binding (recombination) of flowing quarks.
The INFN groups played a central role for achievement of these results.
CERN Media Update:
D meson anisotropy in Pb-Pb collisions:
J/ψ meson anisotropy in Pb-Pb collisions:
ALICE studies of antinuclei at the LHC help Dark Matter searches in space
Dark Matter (DM) is thought to account for approximately 80% of the matter in the Universe and is searched for in several experiments on Earth and in space (including AMS-02 and GAPS). The detection of low-energy antinuclei is a promising signal in the DM searches in space. Yet, in order to interpret a possible observation, a quantitative understanding of the antinuclei production and annihilation mechanisms within the interstellar medium is mandatory. These mechanisms can be studied using the LHC as an antimatter factory and the ALICE experiment as an antimatter detector. The INFN groups play an important role in these studies. The ALICE collaboration has recently published a measurement of the production of (anti)deuterons in proton-proton collisions, as well as in other colliding systems, providing strong constraints to the production models, shown as overlaid curves in the left panel of the figure, which can then be used to predict the antinuclei fluxes in space. The Collaboration has also measured for the first time the antideuteron inelastic cross section at low energy (right panel), using the ALICE detector as an absorber. The momentum range covered in this measurement is of particular relevance to interpret observations in space in terms of DM candidates. Additionally, these measurements help understanding the low-energy antimatter-matter annihilation processes.
CERN Media Update:
Measurement of the low-energy antideuteron inelastic cross section:
(Anti-)Deuteron production in pp collisions at √ s = 13 TeV:
2019 CNAF report published online: the contribution of experiments in CSN3
The annual CNAF report, for 2019, is online at this link. Previous editions are available at this link. Three experiments belonging to the CSN3 contributed to this edition, with the following reports:
- ALICE computing at the INFN CNAF Tier1
- From experimental nuclear astrophysics to nucleosynthesis simulations with ASFIN
- The NEWCHIM activity at CNAF for the CHIMERA and FARCOS devices
In 2019, the ASFIN, FOOT, FAMU, NUCLEX, GAMMA, n-TOF and NEWCHIM experiments benefited from the calculation resources offered by CNAF, for a total of about 9400 HS06, 150 TB of disk and 1900 TB of tape. To these must be added the ALICE experiment with about 60000 HS06, 6000 TB of disk and 12000 TB of tape.
"The Third Meeting on Physics with Heavy Ions at High Energies" has been postponed. The new dates will be announced as soon as possible. The Organizing Committee has decided to pospone the meeting because of the Covid-19 restrictions.
Web page https://agenda.infn.it/event/21267/
The new portal created by the External Funds Division (DFE) has been online since 15 April to optimize the search for information on funding opportunities offered by the various funding institutions, events and training opportunities, with direct links to research tools, including "Research Professional". The website allows one to access a public database that collects all the projects with funding received from the INFN on external funds.