Modern gas detectors for detection of particles require F-based gases for optimal performance. Recent regulations demand the use of environmentally unfriendly F-based gases to be limited or banned. This review studies properties of potential eco-friendly gas candidate replacements.
The RPC muon detector of the CMS experiment at the LHC (CERN, Geneva, Switzerland) is equipped with a Gas Gain Monitoring (GGM) system. A report on the stability of the system during the 2011-2012 data taking run is given, as well as the observation
of an effect which suggests a novel method for the monitoring of gas mixture composition.
Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Lambda-Hypernuclei (A = 5-16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced decay widths, Gamma_2N/Gamma_p, are obtained
from single proton spectra, Gamma_2N/Gamma_p = 0.50 +/- 0.24, and from neutron and proton coincidence spectra, Gamma_2N/Gamma_p = 0.36 +/- 0.14stat +0.05sys -0.04sys , in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Lambda decay width, Gamma_p/Gamma_Lambda, without resorting to Intra Nuclear Cascade models but by exploiting only experimental data, under the assumption of a linear dependence on A of the Final State Interaction contribution. This is the first systematic determination ever done and it agrees within the errors with recent theoretical calculations.
Search for the neutron-rich hypernucleus 9LHe is reported by the FINUDA experiment at DAFNE, INFN-LNF, studying (pi+, pi-) pairs in coincidence from the K-stop + 9Be --> 9LHe + pi+ production reaction followed by 9LHe --> 9Li + pi- weak decay. An upp
er limit of the production rate of 9LHe undergoing this two-body pi- decay is determined to be (2.3 +/- 1.9) 10-6/K-stop at 90% confidence level.
Resistive Plate Counters (RPC) detectors at the Large Hadron Collider (LHC) experiments use gas recirculation systems to cope with large gas mixture volumes and costs. In this paper a long-term systematic study about gas purifiers, gas contaminants a
nd detector performance is discussed. The study aims at measuring the lifetime of purifiers with unused and used cartridge material along with contaminants release in the gas system. During the data-taking the response of several RPC double-gap detectors was monitored in order to characterize the correlation between dark currents, filter status and gas contaminants.
The Gas Gain Monitoring (GGM) system of the Resistive Plate Chamber (RPC) muon detector in the Compact Muon Solenoid (CMS) experiment provides fast and accurate determination of the stability in the working point conditions due to gas mixture changes
in the closed loop recirculation system. In 2011 the GGM began to operate using a feedback algorithm to control the applied voltage, in order to keep the GGM response insensitive to environmental temperature and atmospheric pressure variations. Recent results are presented on the feedback method used and on alternative algorithms.
Three candidate events of the neutron-rich hypernucleus 6{Lambda}H were uniquely identified in the FINUDA experiment at DA{Phi}NE, Frascati, by observing {pi}+ mesons from the (K-stop,{pi}+) production reaction on 6Li targets, in coincidence with {pi
}-mesons from 6{Lambda}H rightarrow 6He+{pi}- weak decay. Details of the experiment and the analysis of its data are reported, leading to an estimate of (2.9pm2.0)cdot10-6/K- stop for the 6{Lambda}H production rate times the two-body {pi}- weak decay branching ratio. The 6{Lambda}H binding energy with respect to 5H + {Lambda} was determined jointly from production and decay to be B{Lambda} = (4.0 pm 1.1) MeV, assuming that 5H is unbound with respect to 3H + 2n by 1.7 MeV. The binding energy determined from production is higher, in each one of the three events, than that determined from decay, with a difference of (0.98 pm 0.74) MeV here assigned to the 0+g.s. rightarrow 1+ excitation. The consequences of this assignment to {Lambda} hypernuclear dynamics are briefly discussed.
Evidence for the neutron-rich hypernucleus 6{Lambda}H is presented from the FINUDA experiment at DA{Phi}NE, Frascati, studying ({pi}+, {pi}-) pairs in coincidence from the K- +6Li rightarrow 6 H+{pi}+ production reaction followed by 6{Lambda}H righta
rrow 6He + {pi}- weak decay. The production rate of 6{Lambda}H undergoing this two-body {pi}- decay is determined to be (2.9pm2.0)cdot10-6/K-. Its binding energy, evaluated jointly from production and decay, is B{Lambda}(6{Lambda}H) = (4.0pm1.1) MeV with respect to 5H+{Lambda}. A systematic difference of (0.98 pm 0.74) MeV between B{Lambda} values derived separately from decay and from production is tentatively assigned to the 6{Lambda}H 0+g.s. rightarrow 1+ excitation.
The decay of $Lambda$-hypernuclei without pion emission, known as Non Mesonic Weak Decay (NMWD), gives an effective tool to investigate $Delta$S=1 four-baryon interactions. It was theoretically suggested that the two-nucleon induced mechanism could p
lay a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of $Gamma_{2N}$/$Gamma_{NMWD}$=0.24$pm$${0.03_{stat}}^{+0.03_{sys}}_{{-{0.02_{sys}}}}$ has been deduced, with an error reduced by a factor more than two compared with the previous assessment.
The CMS RPC muon detector utilizes a gas recirculation system called closed loop (CL) to cope with large gas mixture volumes and costs. A systematic study of CL gas purifiers has been carried out over 400 days between July 2008 and August 2009 at CER
N in a low-radiation test area, with the use of RPC chambers with currents monitoring, and gas analysis sampling points. The study aimed to fully clarify the presence of pollutants, the chemistry of purifiers used in the CL, and the regeneration procedure. Preliminary results on contaminants release and purifier characterization are reported.
