HADES (High Acceptance Di-Electron Spectrometer) is located at the GSI (Helmholtzzentrum für Schwerionenforschung) Darmstadt. It is an experiment focused on the study of the hot and dense nuclear ...matter mainly via the detection of the di-lepton pairs. Electromagnetic CALorimeter (ECAL) was recently added to the HADES setup. This new subdetector allows measuring of photons from the decay of neutral mesons and resonances. It also allows to discriminate between electrons and pions in the high-momenta region over 400 MeV/c. ECAL follows same hexagonal geometry as HADES, i.e. it consists of six sectors in azimuth. The first four sectors were finished and commissioned in 2018. The first experiment with ECAL included in HADES setup took place on March 2019, investigating the Ag+Ag reaction at beam energy of 1.65 A GeV. During the commissioning, several issues popped up and they were addressed. The issues and their solution will be described in the article.
HADES is a large acceptance spectrometer operating at SIS18, GSI, Germany. It is aimed at exploration of QCD phase diagram at the ion beam energies of 1-2 AGeV in the region of high baryonic ...densities. The new segmented electromagnetic calorimeter (ECal) was built to extend experimental opportunities of the HADES detector. The electromagnetic calorimeter will allow to study new reaction channels involving the production of neutral mesons and neu-tral resonances in elementary and heavy-ion reactions via detection of their two photon decay. An additional advantage of such a device is the resulting improvement of the electron-to-pion separation at large momenta. The detector is based on 978 Cherenkov lead glass modules divided into 6 sectors, and it covers forward angles of 12° < θ < 45° and almost full azimuthal angle. Currently four out of six sectors planned are assembled in the experimental area. The first raw beam data obtained with the ECal detector in Ag+Ag reactions at 1.65 AGeV beam are presented.
HADES is a high acceptance di-electron spectrometer operating at SIS18, GSI, Germany aimed at study of hadron-proton, hadron-nucleus and nucleus-nucleus collisions at 1-4 AGeV beam energies. The new ...electromagnetic calorimeter (ECal) was added to the experimental setup in order to measure γ-quanta and thus extend its capabilities in study of π0-, η-mesons, production of neutral hyperons and to improve electron-to-hadron separation for the partcles with momenta p > 300 MeV/c. The first data taking with the ECal detector was carried out in March 2019 when Ag+Ag collisions at 1.23 AGeV and 1.58 AGeV beam energies were studied. The methods of reconstruction of the γγ invariant mass spectra from these data are discussed. The analysis includes several steps: calibration of each module of the ECal detector, identification of γ-quanta, reconstruction of γγ invariant mass spectra and subtraction of combinatorial background. The obtained results show experimental capabilities of the new detector and, after efficiency corrections, will allow to normalize yields of other particles.
The study of 3π and 4π meson production in np interactions was carried out at the momenta of incident neutrons P0 = 3.83, 4.42 and 5.20 GeV/c. The characteristics of the reactions were satisfactorily ...described by OPER model. For the better description of the reaction np → ppπ+ π− π− π0 it was necessary to take into account the production of η0 and ω0 mesons.
The global polarization of Λ hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au ...collisions at sNN=2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon's transverse momentum (pT) and rapidity (yCM) for the range of centrality 0–40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20 – 40%) collisions the polarization magnitudes are 〈PΛ〉(%)=6.8±1.3(stat.)±2.1(syst.) for Au+Au and 〈PΛ〉(%)=6.2±0.4(stat.)±0.6(syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D-fluid-dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.
The search for charged particle tracks in detectors with linear sensing elements, such as multiwire proportional drift chambers, silicon strip detectors etc., often begins with the identification of ...a straight segment of track. This can be achieved by constructing all reasonable combinations of fired detector channels. In high multiplicity environment, with many fired detector channels, this approach causes large combinatorics and significantly reduces the performance of the track finding algorithms.
We provide a method which allows to find initial approximations of straight segments of track in space using four linear sensing elements. This method is especially helpful if there are no parallel elements in the setup. The procedure can also be applied as a first approximation to the case of finding curved tracks. In general, it can be used to find a line in space which crosses the other four lines.
Flow coefficients vn of the orders n = 1 – 6 are measured with the High-Acceptance Spectrometer (HADES) at GSI for protons, deuterons, and tritons as a function of centrality, transverse momentum, ...and rapidity in Au + Au collisions at √sNN = 2.4 GeV. 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.
We present a search for the e+e− decay of a hypothetical dark photon, also named U vector boson, in inclusive dielectron spectra measured by HADES in the p(3.5 GeV) + p, Nb reactions, as well as the ...Ar (1.756 GeV/u) + KCl reaction. An upper limit on the kinetic mixing parameter squared ϵ2 at 90% CL has been obtained for the mass range MU=0.02–0.55 GeV/c2 and is compared with the present world data set. For masses 0.03–0.1 GeV/c2, the limit has been lowered with respect to previous results, allowing now to exclude a large part of the parameter region favored by the muon g−2 anomaly. Furthermore, an improved upper limit on the branching ratio of 2.3×10−6 has been set on the helicity-suppressed direct decay of the eta meson, η→e+e−, at 90% CL.
In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the ...population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπ±pdpTdy distributions of correlated π±p pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1<Minv(GeV/c2)<1.4, the yield is found to be similar for π+p and π−p pairs, and to follow a power law 〈Apart〉α, where 〈Apart〉 is the mean number of participating nucleons. The exponent α depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is α=1.5±0.08st±0.2sy.
PDF
