Electrical discharge propagation between GEM foils Utrobicic, A.; Kovacic, M.; Erhardt, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2021, Letnik:
989
Journal Article
Recenzirano
This paper presents the studies of fast sequential discharge formations in neighboring Gas Electron Multiplier foils (so called fast discharge propagations). We report on the characteristics of the ...time delay between the discharges, which has been shown to be of the order of tens of nanoseconds. This time delay decreases both with increasing voltage on the foil where the secondary discharge occurs as well as with decreasing distance between the neighboring foils. Optical measurements of the discharges in two- and three-stage detector setups show that the propagating discharge does not occur directly below the primary discharge, but is displaced from the shortest line between neighboring foils. This observation, together with Scanning Electron Microscope and Energy Dispersive Spectroscopy analyses of the material deposited below the position of the primary discharge provide valuable information on the time evolution of the fast discharge propagation through the detector and its formation mechanism. In the light of these findings, we propose and discuss a new hypothesis for the occurrence of the secondary discharges.
The STAR collaboration has reported precision measurements on the transverse single spin asymmetries for the production of forward π0 mesons from polarized proton collisions at √s 200 GeV. To ...disentangle the contributions to forward asymmetries, one has to look beyond inclusive π0 production to the production of forward jets or direct photons. Present forward detector capabilities are not well matched to the complete reconstruction of forward jets, but do have sufficient acceptance for "jet-like" events."Jet-like" events are the clustered response of an electromagnetic calorimeter that is primarily sensitive to incident photons, electrons and positrons. During the RHIC running in the year 2006, STAR with the Forward Pion Detector (FPD++) in place collected 6.8 pb−1 of data with an average polarization of 60 %. FPD++ was a modular detector prototype of the Forward Meson Spectrometer (FMS) that consisted of two detectors placed symmetrically with respect to the beam line at a distance of 7.4 m from the interaction point. Readout of the FPD++ was triggered when the sum of energies in the central module of the calorimeter used for π0 measurements was larger than a threshold. This trigger minimizes the bias for "jet-like" events, making it appropriate to disentangling contributions to the forward transverse spin asymmetries. We report on the status of the analysis.
The first evidence of spin alignment of vector mesons ( K*0 and ϕ ) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ρ 00 is measured at ...midrapidity ( | y | < 0.5 ) in Pb-Pb collisions at a center-of-mass energy ( √sNN ) of 2.76 TeV with the ALICE detector. ρ 00 values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum ( p T < 2 GeV / c ) for K*0 and ϕ at a level of 3 σ and 2 σ , respectively. No significant spin alignment is observed for the K0S meson ( spin = 0 ) in Pb-Pb collisions and for the vector mesons in p p collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.
This paper presents an investigation of the delayed discharge propagation (DP) to the readout electrode. After a primary discharge develops inside a GEM foil hole the DP can occur with a time delay ...in the range of 1–100μs. A single hole THGEM (THick GEM) foil that enables a controlled discharge position and the induction of primary discharge with an over-voltage in the THGEM foil has been used in the initial DP measurements. In order to justify the use of a custom-made THGEM foil, additional measurements were made with a standard GEM foil. Correlated optical (with an ordinary SLR (Single-Lens Reflex) and a high-speed camera) and electrical measurements of the delayed DP were made for a Ne–CO2-N2 (90-10-5) mixture and with different powering configurations. Measurements show that the delayed DP happens without a drift field, with an inverted induction field, inverted THGEM voltages or an inverted drift field. After the primary discharge, there is a charge transfer in the induction region at an induction field value below that of the onset field for DP. In the time between the primary discharge and the delayed DP, three different current regimes are observed, which suggests multiple charge transfer mechanisms in the induction region. High-speed camera recordings provide valuable insight into the time evolution of the primary discharge and the delayed DP, especially when correlated with electrical measurements.
We report the first measurements of the moments--mean (M), variance (σ(2)), skewness (S), and kurtosis (κ)--of the net-charge multiplicity distributions at midrapidity in Au+Au collisions at seven ...energies, ranging from sqrtsNN=7.7 to 200 GeV, as a part of the Beam Energy Scan program at RHIC. The moments are related to the thermodynamic susceptibilities of net charge, and are sensitive to the location of the QCD critical point. We compare the products of the moments, σ(2)/M, Sσ, and κσ(2), with the expectations from Poisson and negative binomial distributions (NBDs). The Sσ values deviate from the Poisson baseline and are close to the NBD baseline, while the κσ(2) values tend to lie between the two. Within the present uncertainties, our data do not show nonmonotonic behavior as a function of collision energy. These measurements provide a valuable tool to extract the freeze-out parameters in heavy-ion collisions by comparing with theoretical models.
Experimental results are presented on event-by-event net-proton fluctuation measurements in Pb–Pb collisions at sNN=2.76 TeV, recorded by the ALICE detector at the CERN LHC. These measurements have ...as their ultimate goal an experimental test of Lattice QCD (LQCD) predictions on second and higher order cumulants of net-baryon distributions to search for critical behavior near the QCD phase boundary. Before confronting them with LQCD predictions, account has to be taken of correlations stemming from baryon number conservation as well as fluctuations of participating nucleons. Both effects influence the experimental measurements and are usually not considered in theoretical calculations. For the first time, it is shown that event-by-event baryon number conservation leads to subtle long-range correlations arising from very early interactions in the collisions.
Local parity-odd domains are theorized to form inside a quark-gluon plasma which has been produced in high-energy heavy-ion collisions. The local parity-odd domains manifest themselves as charge ...separation along the magnetic field axis via the chiral magnetic effect. The experimental observation of charge separation has previously been reported for heavy-ion collisions at the top RHIC energies. In this Letter, we present the results of the beam-energy dependence of the charge correlations in Au+Au collisions at midrapidity for center-of-mass energies of 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV from the STAR experiment. After background subtraction, the signal gradually reduces with decreased beam energy and tends to vanish by 7.7 GeV. This implies the dominance of hadronic interactions over partonic ones at lower collision energies.
This paper presents a concept of a multiple channel picoammeter suitable for operation at a high voltage. To ensure floating operation, 1kHz readout rate and low battery usage, the picoammeter ...employs an optical fibre for data transmission. The analogue conditioning section consists of a transimpedance amplifier that is connected to a 16 bit ΣΔ ADC which is integrated into the microcontroller. Simultaneous reception of data sent from multiple picoammeter units is achieved using an FPGA device and a USB interface to the host PC. A prototype with a ±125nA range was constructed. The paper includes a calibration procedure of the prototype and an example of a current leakage test conducted on a 10×10cm2 GEM foil. The resolution achieved by the prototype in a 15min test at 0.5nA bias was 6.5pA FWHM.
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