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The results of a study of the mechanism of occurrence of spontaneous self-sustaining currents in proportional chambers, operating as part of experiments at the LHC, are presented. The cathode of the proportional chamber dismantled from the LHCb detector, in which the occurrence of self-supporting spontaneous currents were regularly observed, was studied by AFM, Rutherford backscattering, and Raman spectroscopy. Nanocarbon structures and their fluorinated compounds were discovered in the zone of spontaneous currents of the cathode. Such formations are well known as low-threshold sources of the field emission of electrons.

Spontaneous self-sustained currents on the cathodes of multiwire proportional chambers pose a problem for detectors in experiments at the Large Hadron Collider with prolonged exposure to radiation. The nature of spontaneous currents is studied using samples of a chamber cathode on which such currents occurred. A set of atomic force microscopy procedures for detecting and studying point emission centers is developed.

The mechanism of occurrence of spontaneous self-sustained currents in a multiwire proportional chamber from the experiment at the Large Hadron Collider has been considered. Atomic force microscopy, Rutherford backscattering, and Raman spectroscopy on the copper foil of the chamber cathode revealed the formation of nanocarbon structures and their fluorinated compounds, which are well known as low-threshold sources of field emission of electrons.

This erratum corrects measurements of the prompt and secondary (from-b).

The MUON Detector (MD) of LHCb is one of the largest instruments of this kind worldwide, and one of the most irradiated. It has performed exceptionally well during the RUN1 and RUN2 of the LHC at an instantaneous luminosity of 4\\(\\times\\)10\\(^{32}\\) cm\\(^{-2}\\)s\\(^{-1}\\), with tracking inefficiencies at the level of 1\\(\\%\\) and 2.6\\(\\%\\), respectively. Looking forward for the future LHCb Upgrade 2 (U2) planned in 2031 and aiming in running the detector at increased luminosity by a factor \\(\\sim\\)50, and at the same time keeping a very high (\\(\\sim\\)99\\(\\%\\)) detection efficiency, an option with reuse significant part of the present Multi-Wire Proportional Chambers (MWPC) in a new Muon System is presented. In addition, the first idea of new Front End Electronics (FEE) and an existing test setup applicable for designing both: new MWPCs with a higher granularity of the cathode readout pads and new FEE are described.

Background: The rate \\lambda_pp\\mu\\ characterizes the formation of pp\\mu\\ molecules in collisions of muonic p\\mu\\ atoms with hydrogen. In measurements of the basic weak muon capture reaction on the proton to determine the pseudoscalar coupling g_P, capture occurs from both atomic and molecular states. Thus knowledge of \\lambda_pp\\mu\\ is required for a correct interpretation of these experiments. Purpose: Recently the MuCap experiment has measured the capture rate \\Lambda_S from the singlet p\\mu\\ atom, employing a low density active target to suppress pp\\mu\\ formation (PRL 110, 12504 (2013)). Nevertheless, given the unprecedented precision of this experiment, the existing experimental knowledge in \\lambda_pp\\mu\\ had to be improved. Method: The MuCap experiment derived the weak capture rate from the muon disappearance rate in ultra-pure hydrogen. By doping the hydrogen with 20 ppm of argon, a competing process to pp\\mu\\ formation was introduced, which allowed the extraction of \\lambda_pp\\mu\\ from the observed time distribution of decay electrons. Results: The pp\\mu\\ formation rate was measured as \\lambda_pp\\mu = (2.01 +- 0.06(stat) +- 0.03(sys)) 10^6 s^-1. This result updates the \\lambda_pp\\mu\\ value used in the above mentioned MuCap publication. Conclusions: The 2.5x higher precision compared to earlier experiments and the fact that the measurement was performed at nearly identical conditions to the main data taking, reduces the uncertainty induced by \\lambda_pp\\mu\\ to a minor contribution to the overall uncertainty of \\Lambda_S and g_P, as determined in MuCap. Our final value for \\lambda_pp\\mu\\ shifts \\Lambda_S and g_P by less than one tenth of their respective uncertainties compared to our results published earlier.

The MuCap experiment at the Paul Scherrer Institute performed a high-precision measurement of the rate of the basic electroweak process of nuclear muon capture by the proton, \\(\\mu^- + p \\rightarrow n + \\nu_\\mu\\). The experimental approach was based on the use of a time projection chamber (TPC) that operated in pure hydrogen gas at a pressure of 10 bar and functioned as an active muon stopping target. The TPC detected the tracks of individual muon arrivals in three dimensions, while the trajectories of outgoing decay (Michel) electrons were measured by two surrounding wire chambers and a plastic scintillation hodoscope. The muon and electron detectors together enabled a precise measurement of the \\(\\mu p\\) atom's lifetime, from which the nuclear muon capture rate was deduced. The TPC was also used to monitor the purity of the hydrogen gas by detecting the nuclear recoils that follow muon capture by elemental impurities. This paper describes the TPC design and performance in detail.

The MuCap experiment is a high-precision measurement of the rate for the basic electroweak process of muon capture, mu- + p -> n + nu . The experimental approach is based on an active target consisting of a time projection chamber (TPC) operating with pure hydrogen gas. The hydrogen has to be kept extremely pure and at a stable pressure. A Circulating Hydrogen Ultrahigh Purification System was designed at the Petersburg Nuclear Physics Institute (PNPI) to continuously clean the hydrogen from impurities. The system is based on an adsorption cryopump to stimulate the hydrogen flow and on a cold adsorbent for the hydrogen cleaning. It was installed at the Paul Scherrer Institute (PSI) in 2004 and performed reliably during three experiment runs. During several months long operating periods the system maintained the hydrogen purity in the detector on the level of 20 ppb for moisture, which is the main contaminant, and of better than 7 ppb and 5 ppb for nitrogen and oxygen, respectively. The pressure inside the TPC was stabilized to within 0.024% of 10 bar at a hydrogen flow rate of 3 standard liters per minute.

The muon detector of LHCb, which comprises 1368 multi-wire-proportional-chambers (MWPC) for a total area of 435 m2, is the largest instrument of its kind exposed to such a high-radiation environment. In nine years of operation, from 2010 until 2018, we did not observe appreciable signs of ageing of the detector in terms of reduced performance. However, during such a long period, many chamber gas gaps suffered from HV trips. Most of the trips were due to Malter-like effects, characterised by the appearance of local self-sustained high currents, presumably originating from impurities induced during chamber production. Very effective, though long, recovery procedures were implemented with a HV training of the gaps in situ while taking data. The training allowed most of the affected chambers to be returned to their full functionality and the muon detector efficiency to be kept close to 100%. The possibility of making the recovery faster and even more effective by adding a small percentage of oxygen in the gas mixture has been studied and successfully tested.

A new method has been developed to check the correct behaviour of the frontend electronics of the LHCb muon detector. This method is based on the measurement of the electronic noise rate at different thresholds of the frontend discriminator. The method was used to choose the optimal discriminator thresholds. A procedure based on this method was implemented in the detector control system and allowed the detection of a small percentage of frontend channels which had deteriorated. A Monte Carlo simulation has been performed to check the validity of the method.