High Acceptance Di-Electron Spectrometer Research Articles

Targets for the electron–positron pair spectrometer HADES

For experiments performed with the HADES spectrometer (High Acceptance Di-Electron Spectrometer) [1] at GSI a very extraordinary target set-up is required. Since these experiments are strongly background-dominated the alignment and mounting of the targets is crucial for the identification of the electron–positron pairs searched for as a decay product of the vector mesons. The positioning of the numerous target discs has to be done with accuracy better than ±200μm and with a minimum of material around the targets.We describe the target design, the production of the different components and the mounting methods. Finally, an outlook on future target designs and ideas is given.

Pp and ππ intensity interferometry in collisions of Ar+KCl at 1.76A GeV

Results on pp, π+π+, and π−π− intensity interferometry are reported for collisions of Ar+KCl at 1.76A GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The experimental correlation functions as a function of the relative momentum are compared to model calculations allowing the determination of the space-time extent of the corresponding emission sources. The ππ source radii are found significantly larger than the pp emission radius. The present radii do well complement the beam-energy dependences of Gaussian source radii of the collision system of size A + A ≃ 40 + 40 . The pp source radius at fixed beam energy is found to increase linearly with the cube root of the number of participants. From this trend, a lower limit of the pp correlation radius is deduced.

TAGGING THE Λ(1405) FROM ITS DECAY INTO Σ0π0

The decay of Λ(1405) into Σ0π0 was studied in p + p collisions at EKin=3.5 GeV , measured by the High Acceptance Di-Electron Spectrometer (HADES). To extract the line shape of the Λ(1405), special techniques have been developed to describe the misidentification background and extract the contributions of different production channels.

Performance of the Low-Jitter High-Gain/Bandwidth Front-End Electronics of the HADES tRPC Wall

A front-end electronics (FEE) chain for accurate time measurements has been developed for the new Resistive Plate Chamber (RPC)-based Time-of-Flight (TOF) wall of the High Acceptance Di-Electron Spectrometer (HADES). The wall covers an area of around 8 m2, divided in 6 sectors. In total, 1122 4-gap timing RPC cells are read-out by 2244 time and charge sensitive channels. The FEE chain consists of 2 custom-made boards: a 4-channel DaughterBOard (DBO) and a 32-channel MotherBOard (MBO). The DBO uses a fast 2 GHz amplifier feeding a dual high-speed discriminator. The time and charge information are encoded, respectively, in the leading edge and the width of an LVDS signal. Each MBO houses up to 8 DBOs providing them regulated voltage supply, threshold values via DACs, test signals and, additionally, routing out a signal proportional to the channel multiplicity needed for a 1st level trigger decision. The MBO delivers LVDS signals to a multi-purpose Trigger Readout Board (TRB) for data acquisition. The FEE allows achieving a system resolution around 75 ps fulfilling comfortably the requirements of the HADES upgrade .

RPC HADES-TOF wall cosmic ray test performance

Abstract In this work we present results concerning the cosmic ray test, prior to the final installation and commissioning of the new Resistive Plate Chamber (RPC) Time of Flight (TOF) wall for the High-Acceptance DiElectron Spectrometer (HADES) at GSI. The TOF wall is composed of six equal sectors, each one constituted by 186 individual 4-gaps glass-aluminium shielded RPC cells distributed in six columns and 31 rows in two partially overlapping layers, covering an area of 1.26 m2. All sectors were tested with the final Front End Electronic (FEE) and Data AcQuisition system (DAQ) together with Low Voltage (LV) and High Voltage (HV) systems. Results confirm a very uniform average system time resolution of 77 ps sigma together with an average multi-hit time resolution of 83 ps. Crosstalk levels below 1% (in average), moderate timing tails along with an average longitudinal position resolution of 8.4 mm sigma are also confirmed.

Λ−pfemtoscopy in collisions ofAr+KClat1.76A GeV

Results on $\Lambda$p femtoscopy are reported at the lowest energy so far. At a beam energy of 1.76A~GeV, the reaction Ar+KCl was studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. A high-statistics and high-purity $\Lambda$ sample was collected, allowing for the investigation of $\Lambda$ p correlations at small relative momenta. The experimental correlation function is compared to corresponding model calculations allowing the determination of the space-time extent of the $\Lambda$p emission source. The $\Lambda$p source radius is found slightly smaller than the pp correlation radius for a similar collis ion system. The present $\Lambda$p radius is significantly smaller than that found for Au+Au/Pb+Pb collisio ns in the AGS, SPS and RHIC energy domains, but larger than that observed for electroproduction from He. Taking into account all available data, we find the $\Lambda$p source radius to increase almost linearly with the number of participants to the power of one-third.

Strangeness measurements at the HADES experiment

We report on high acceptance di-electron spectrometer (HADES) measurements of strange hadrons in the collision systems Ar(1.756 AGeV)+KCl and p+p at 3.5 GeV. Comparisons of K0s transverse mass and rapidity spectra to IQMD transport model calculations give a strong hint to a repulsive kaon–nucleon potential. The effect of the potential shows up strongest at very low transverse momenta, which were measured by HADES with high statistics. Statistical model fits show a fair agreement to the particle yields measured in the heavy-ion data, apart from the Ξ− yield which is off by more than an order of magnitude. Furthermore, first results from the Σ(1385)+ reconstruction in p+p reactions are presented, showing an excellent agreement with published data.

Investigation of the production of electron-positron pairs in nucleon-nucleon interactions with the HADES detector

The inclusive production of electron-positron pairs in proton-proton and deuteron-proton collisions at a beam kinetic energy of 1.25 GeV per nucleon was studied with the HADES (High Acceptance Dielectron Spectrometer) detector. The main objective of the deuteron-proton experiment was to investigate pair production in quasifree neutron-proton collisions. In the invariant-mass region M > 140 MeV/c 2, the invariant-mass spectrum determined in this channel shows a significant enhancement of the pair yield in relation to that in the case of proton-proton collisions.

Deep SubthresholdΞ−Production inAr+KClReactions at1.76A GeV

We report first results on a deep subthreshold production of the doubly strange hyperon Xi;{-} in a heavy-ion reaction. At a beam energy of 1.76A GeV the reaction Ar + KCl was studied with the High Acceptance Di-Electron Spectrometer at SIS18/GSI. A high-statistics and high-purity Lambda sample was collected, allowing for the investigation of the decay channel Xi;{-} --> Lambdapi;{-}. The deduced Xi;{-}/(Lambda + Sigma;{0}) production ratio of (5.6 +/- 1.2_{-1.7};{+1.8}) x 10;{-3} is significantly larger than available model predictions.

Performances of the Front-End Electronics for the HADES RPC TOF wall on a 12C beam

A Front-End Electronics (FEE) chain for timing accurate measurements has been developed for the RPC wall upgrade of the High-Acceptance DiElectron Spectrometer (HADES). The wall will cover an area of around 8 m 2 with 1122 RPC cells (2244 electronic channels). The FEE chain consists of two boards: a four-channel DaughterBOard (DBO) and a 32-channel MotherBOard (MBO). The DBO uses a fast 2 GHz amplifier feeding a discriminator. The time and the charge information are encoded in the leading and the trailing edge (by a charge to width method) of an LVDS signal. Each MBO houses up to eight DBOs providing them regulated voltage supply, threshold values via DACs, test signals and collection of their trigger outputs. The MBO delivers LVDS signals to a time-to-digital converter readout board (TRB) based on HPTDC for data acquisition. In this work, we present the performance of the FEE measured using: (a) narrow electronic test pulses and (b) real signals read out in a fully instrumented RPC sextant installed in its final position at the HADES. The detector was exposed to particles coming from reactions of a 12C beam on Be and Nb targets at 2 GeV/A kinetic energy. Results for the whole electronic chain ( DBO + MBO + TRB ) show a timing jitter of around 40 ps/channel for pulses above 100 fC and 80 ps/channel for beam data taken with the RPC.

In-beam measurements of the HADES-TOF RPC wall

A full size prototype of the new inner High-Acceptance DiElectron Spectrometer (HADES)-TOF wall based on Resistive Plate Chambers (RPCs) was mounted and exposed to secondaries from C reactions on Be and Nb targets at 2 AGeV kinetic energy and typical HADES particle fluxes. The tested sextant is constituted by 187 individual 4-gap glass–aluminium shielded RPC cells distributed in three columns and two layers, covering an area of 1.26 m 2 . An average timing resolution of 73 ps σ was measured with 99 % intrinsic efficiency, on a random location, and moderate timing tails, along with an average longitudinal position resolution of 7.7 mm σ , in the range from a few Hz / cm 2 up to 80 Hz / cm 2 without noticeable degradation of performance. Additionally, the matching efficiency was estimated using the tracking system of HADES, yielding an average value of 97.5%.

Level 3 trigger algorithm and Hardware Platform for the HADES experiment

A next generation real time trigger method to improve the enrichment of lepton events in the High Acceptance DiElectron Spectrometer (HADES) trigger system has been developed. In addition, a flexible Hardware Platform (Gigabit Ethernet-Multi-Node, GE-MN) was developed to implement and test the trigger method. The trigger method correlates the ring information of the HADES Ring Imaging Cherenkov (RICH) detector with the fired wires (drift cells) of the HADES Mini Drift Chamber (MDC) detector. It is demonstrated that this Level 3 trigger method can enhance the number of events which contain leptons by a factor of up to 50 at efficiencies above 80%. The performance of the correlation method in terms of the events analyzed per second has been studied with the GE-MN prototype in a lab test setup by streaming previously recorded experiment data to the module. This paper is a compilation from Kirschner [Level 3 trigger algorithm and Hardware Platform for the HADES experiment, Ph.D. Thesis, II. Physikalisches Institut der Justus-Liebig-Universität Gießen, urn:nbn:de:hebis:26-opus-50784, October 2007 [1]].

How sensitive are di-leptons from ρ mesons to the high baryon density region?

We show that the measurement of dileptons might provide only a restricted view into the most dense stages of heavy-ion reactions. Thus, possible studies of meson and baryon properties at high baryon densities, as, e.g., done at the GSI High Acceptance DiElectron Spectrometer (HADES) and envisioned for the Facility for Antiproton and Ion Research (FAIR) compressed baryonic matter experiments, might observe weaker effects than currently expected in certain approaches. We argue that the strong absorption of resonances in the high-baryon-density region of the heavy-ion collision masks information from the early hot and dense phase due to a strong increase of the total decay width because of collisional broadening. To obtain additional information, we also compare the currently used approaches to extract dileptons from transport simulations, i.e., shining, only vector mesons from final baryon resonance decays and instant emission of dileptons and find a strong sensitivity on the method employed in particular at FAIR and the CERN Super Proton Synchrotron energies. It is shown explicitly that a restriction to \ensuremath{\rho} meson (and therefore dilepton) production only in final-state baryon resonance decays provide a strong bias toward rather low baryon densities. The results presented are obtained from ultrarelativistic quantum molecular dynamics v2.3 calculations using the standard setup.

Dilepton production in pp and CC collisions with HADES

e + e - production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2GeV kinetic beam energy, the exclusive η production and the Dalitz decay η→γe + e - have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e + e - invariant-mass spectrum from the 12C + 12C reaction at 2AGeV is presented and compared with a simplified thermal model.

DIELECTRON PRODUCTION IN C + C AND p + p COLLISIONS WITH HADES

The High Acceptance Di-Electron Spectrometer HADES1 has been constructed at the SIS accelerator (GSI Darmstadt) to investigate electron-positron pairs produced in proton, pion and heavy ion induced reactions. The main goal of these studies is to explore properties of hadrons in nuclear matter. The apparatus and the experimental results from C + C at 2.0 AGeV and 1.0 AGeV and p + p at 2.2 GeV compared with Monte-Carlo events from a generator based on known cross-sections and branching ratios are presented.

Di-electron production in C+C and p+p collisions with HADES

The High Acceptance Di-Electron Spectrometer HADES at GSI, Darmstadt, has been designed for systematic studies of hadron properties inside nuclear matter. First measured mass and momentum distributions of e+e- pairs produced in 12C+12C collisions at 1 and 2 AGeV are presented and compared with p+p collisions at 2.2 GeV incident energy. The spectrometer set-up and the analysis methods are briefly outlined and a comparison of the data with Monte-Carlo events from a generator based on known production cross-sections and branching ratios is shown and discussed.

Measurement of the di-electron mass spectrum in 12C+ 12C collisions at 2 AGeV by HADES

The physics program of the High Acceptance Di-Electron Spectrometer HADES at GSI is largely motivated by the aim to study medium modifications of hadrons predicted by many theoretical approaches, as well as by the need to shed light on the still unexplained results of the former DLS experiment. In this contribution the HADES experiment is outlined and first results obtained in 12C+12C collisions at 2 AGeV are presented.

Di-electron measurements in C+C reactions at [formula omitted] with HADES

The High Acceptance DiElectron Spectrometer HADES has been recently commissioned at GSI, Darmstadt. It has been designed for systematic studies of hadron properties inside nuclear matter. We report first preliminary results on invariant masses e + e - -pairs which were measured in 12 C + 12 C collisions at E kin = 2 GeV ⋅ A . The analysis methods are briefly outlined and a comparison with detailed Monte-Carlo simulations is shown.

Dilepton analysis in the HADES spectrometer for C+C at 2 A GeV

The high-acceptance dielectron spectrometer (HADES) has become operational at GSI Darmstadt. The primary physics programme is to study in-medium changes of light vector mesons via their e+e− decays. The methods of dilepton signal reconstruction in the HADES spectrometer and preliminary dilepton spectra for C+C reactions at 2 A GeV are presented. In the signal reconstruction, particularly important is the reduction of the huge combinatorial background arising from e+e− combinations of leptons from gamma conversion in materials with other leptons in the collision. The purity of the dilepton signal is determined by using GEANT simulations with the full HADES geometry and a realistic detector response.

Probing of in-medium hadron structure with HADES

The High Acceptance DiElectron Spectrometer (HADES) has been recently commissioned at GSI Darmstadt. It has been designed to study hadron properties inside nuclear matter via measurements of dielectron decays in proton, pion and heavy ion induced reactions in 1−2 AGeV energy range. We report first preliminary results on invariant masses of e+e− pairs measured in 12C + 12C collisions at E=2 AGeV and compare them to simulations based on UrQMD transport model. In summary we present and discuss planned experiments.