Solidarity with Ukraine

We, representatives of European institutes in the HADES Collaboration Board, have met Wednesday 23 March 2022. We are deeply shocked by the invasion of Ukraine perpetrated by the Russian army. In protest to this brutal aggression against a free and democratic country, our collaboration with Russian Institutes is stopped. It was also decided to remove, until further notice, the members of Russian Institutes from all the collaboration mailing lists and from the author list of the next publications. We have been obliged to take this decision, despite our longstanding and fruitful collaboration with Russian physicists, due to the unacceptable acts of the Russian Government.

HADES Analysis Workshop 2022

XLIV HADES Collaboration Meeting

Higher order flow harmonics of protons and light nuclei in Au+Au

A new paper with HADES data has appeared in Phys. Rev. Lett. It features flow coefficients (vn) of the orders n = 1–6 for protons, deuterons, and tritons as a function of centrality, transverse momentum, and rapidity in Au+Au collisions at 1.23 AGeV.

Combining the information from the flow coefficients of all orders allows us to construct for the first time, at collision energies of a few GeV, a multidifferential picture of the angular emission pattern of these particles. It reflects the complicated interplay between the effect of the central fireball pressure on the emission of particles and their subsequent interaction with spectator matter. The high precision information on higher order flow coefficients is a major step forward in constraining the equation of state of dense baryonic matter.

Phys.Rev.Lett. 125 (2021) 26, 262301

New paper on proton number fluctuations.

HADES has published new paper in PRC: "Proton-number fluctuations in sqrt(sNN) = 2.4 GeV Au+Au collisions studied with the High-Acceptance DiElectron Spectrometer (HADES)".  Moments and cumulants up to 4th orders as a function of centrality and phase-space bins are presented.

 

The QCD critical endpoint (CEP) is a very distinct feature of the phase diagram of nuclear matter, but it can presently not be located from first-principle calculations; experimental observations are needed to constrain its position. The HADES Collaboration measured cumulants and correlators for net-proton number fluctuations, the most important observable so far to search for the CEP. This extends experimental results below the lowest beam energies available at th RHIC accelerator in Brookhaven (USA) and will be useful to discern the possibility of a critical point in the QCD phase diagram. These investigations will be continued in future experiments at FAIR.

 

 

Phys. Rev. C 102, 024914 (2020)

Probing dense baryon-rich matter with virtual photons

HADES reports on the measurement of the temperature T = 71 MeV inside the hot and dense fireball created in Au+Au collisions. Results have been published in Nature Physics.

 

HADES hunts Dark Matter

HADES has put an improved upper limit on the mixing of the photon with a hypothetical massive Dark Photon, the latter being the gauge boson mediating the interaction between Dark Matter particles.

Dark Matter in the Universe

The interpretation of current astrophysical observations results in the striking mass-energy budget of matter in the universe: ~75% Dark Energy, ~20% Dark Matter, and ~5% baryonic matter [1]. The latter number refers to stars and inter/intra-galactic gas, i.e. mainly free hydrogen. Dark Energy drives the presently observed accelerated expansion of the universe. It is homogeneously distributed and can be attributed to a cosmological constant or vacuum energy.
In extreme cases it may cause, in the future, such a sudden expansion that anything in the universe is disrupted – this would be the Big Rip. Dark Matter, in contrast, is bumpy and is needed to explain the formation of the ditribution of observed visible matter in the evolving universe, evidenced by the hierarchy of structures from (super)clusters of galaxies, galaxies, stars, planets and other compact objects such as meteorites, etc.

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