Over the past 20 years, the INFN Section of Ferrara has developed a solid and acknowledged experience in the design and construction of storage cells for gaseous targets. The use of this technology has had a significant impact in the field of experimental hadronic physics. Examples of the application of this technology are the target of the HERMES experiment at HERA (DESY), operated from 1995 to 2007, that of the OLYMPUS experiment at DORIS (DESY), operated in the period 2012-2013, and that of the PAX/JEDI experiment, currently in operation at COSY (Forschungszentrum Julich). The storage cell, typically made of a 50-200 mm thick layer of aluminum with cylindrical geometry, is placed inside the beam-pipe of the accelerator, coaxially with the beam. The latter then intercepts directly the target gas contained into the cell, without interacting with other materials, as in the case of solid targets. Furthermore, with respect to the more traditional gaseous jet targets, the use of a storage cell allows to reach areal densities of the order of 10¹³-10¹⁴ atoms/cm², i.e. up to two orders of magnitude higher. The experience acquired by the Ferrara Section in the framework of CSN3 experiments, has recently allowed to develop a storage cell for the LHCb experiment (SMOG2 project). Starting from RUN3 (2021), LHCb will therefore be the only LHC experiment to be provided with two distinct interaction points and the possibility of operating simultaneously in two collision modes: collider and fixed-target mode. The beam-gas collisions will occur at a center-of-mass energy of 115 GeV for proton beams and 72 GeV for lead beams. SMOG2 will allow to carry out precision studies in the field of QCD and astroparticle physics in essentially unexplored kinematic regions.

Find more details in: http://w3.lnf.infn.it/un-bersaglio-fisso-per-lhc/.

 Left: The HERMES storage cell. Right: Half of the LHCb storage cell.

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 p_T. 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:

https://home.cern/news/news/physics/cern-collaborations-present-new-results-particles-charm-quarks

Further reading:

D meson anisotropy in Pb-Pb collisions:

https://arxiv.org/pdf/2005.11131.pdf

J/ψ meson anisotropy in Pb-Pb collisions:

https://arxiv.org/pdf/2005.14518.pdf

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:

https://home.cern/news/news/physics/fresh-antimatter-study-alice-collaboration-will-help-search-dark-matter

Further reading:

Measurement of the low-energy antideuteron inelastic cross section:

https://arxiv.org/pdf/2005.11122.pdf

(Anti-)Deuteron production in pp collisions at √ s = 13 TeV:

https://arxiv.org/pdf/2003.03184.pdf

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.