A high-pressure hydrogen time projection chamber for the MuCap experiment

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.Comment: 15 pages, 13 figures, to be submitted to Eur. Phys. J. A; clarified section 3.1.2 and made minor stylistic corrections for Eur. Phys. J. A requirement

Measurement of Muon Capture on the Proton to 1% Precision and Determination of the Pseudoscalar Coupling g_P

The MuCap experiment at the Paul Scherrer Institute has measured the rate L_S of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1%. A muon beam was stopped in a time projection chamber filled with 10-bar, ultra-pure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. L_S is determined from the difference between the mu- disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of 1.2 10^10 mu- decays, from which we extract the capture rate L_S = (714.9 +- 5.4(stat) +- 5.1(syst)) s^-1 and derive the proton's pseudoscalar coupling g_P(q^2_0 = -0.88 m^2_mu) = 8.06 +- 0.55.Comment: Updated figure 1 and small changes in wording to match published versio

Measurement of the Rate of Muon Capture in Hydrogen Gas and Determination of the Proton's Pseudoscalar Coupling gPg_P

The rate of nuclear muon capture by the proton has been measured using a new experimental technique based on a time projection chamber operating in ultra-clean, deuterium-depleted hydrogen gas at 1 MPa pressure. The capture rate was obtained from the difference between the measured $\mu^-$ disappearance rate in hydrogen and the world average for the $\mu^+$ decay rate. The target's low gas density of 1% compared to liquid hydrogen is key to avoiding uncertainties that arise from the formation of muonic molecules. The capture rate from the hyperfine singlet ground state of the $\mu p$ atom is measured to be $\Lambda_S=725.0 \pm 17.4 s^{-1}$, from which the induced pseudoscalar coupling of the nucleon, $g_P(q^2=-0.88 m_\mu^2)=7.3 \pm 1.1$, is extracted. This result is consistent with theoretical predictions for $g_P$ that are based on the approximate chiral symmetry of QCD.Comment: submitted to Phys.Rev.Let

Peptic ulcer: the current state of the problem

Peptic ulcer disease (PUD) is a chronic polyetiological recurrent disease of gastroduodenal region. In most cases, the pathogenesis of PU is caused by imbalance between the aggressive factors and protective factors of the gastric or duodenal mucosa. Helicobacter pylori (H. pylori) infection and the use of non-steroidal anti-inflammatory drugs (NSAIDs), including aspirin, are the major causative factors leading to PUD development. 65% of gastric ulcers and 80% of duodenal ulcers were found to be associated with H. pylori infection. In turn, NSAIDs account for 30% of gastric ulcers and 15% of duodenal ulcers. About 0.1–1% of  all PUs are caused by Zollinger-Ellison syndrome. Abdominal pain is the leading symptom in the clinical findings of patients with exacerbation of PUD. Dyspeptic syndrome (vomiting, nausea, belching, abnormal bowel pattern) is much less common in   patients with PUD. Endoscopic examination of the upper gastrointestinal tract is currently the gold standard test used in   the  diagnosis of PUD and is recommended for all patients suspected of having this disease (unless contraindicated). Antisecretory therapy including proton pump inhibitors is the main approach to the treatment of PUD, as well as the prevention of its complications. Integral to the treatment of patients with H. pylori-associated PU is the eradication therapy of the infection. It is  reasonable to use a cytoprotector rebamipide, which accelerates ulcer healing and improves the resulting scar quality, as part of the pharmacotherapy of PUD. In addition, the use of rebamipide in H. pylori eradication therapy regimens contributes to increased efficiency of elimination of the microorganisms

Performance of the Muon Identification at LHCb

The performance of the muon identification in LHCb is extracted from data using muons and hadrons produced in J/\psi->\mu\mu, \Lambda->p\pi and D^{\star}->\pi D0(K\pi) decays. The muon identification procedure is based on the pattern of hits in the muon chambers. A momentum dependent binary requirement is used to reduce the probability of hadrons to be misidentified as muons to the level of 1%, keeping the muon efficiency in the range of 95-98%. As further refinement, a likelihood is built for the muon and non-muon hypotheses. Adding a requirement on this likelihood that provides a total muon efficiency at the level of 93%, the hadron misidentification rates are below 0.6%.Comment: 17 pages, 10 figure

Performance of the LHCb muon system with cosmic rays

The LHCb Muon system performance is presented using cosmic ray events collected in 2009. These events allowed to test and optimize the detector configuration before the LHC start. The space and time alignment and the measurement of chamber efficiency, time resolution and cluster size are described in detail. The results are in agreement with the expected detector performance.Comment: Submitted to JINST and accepte

Measurement of the front-end dead-time of the LHCb muon detector and evaluation of its contribution to the muon detection inefficiency

A method is described which allows to deduce the dead-time of the front-end electronics of the LHCb muon detector from a series of measurements performed at different luminosities at a bunch-crossing rate of 20 MHz. The measured values of the dead-time range from 70 ns to 100 ns. These results allow to estimate the performance of the muon detector at the future bunch-crossing rate of 40 MHz and at higher luminosity

Performance of the LHCb muon system

The performance of the LHCb Muon system and its stability across the full 2010 data taking with LHC running at ps = 7 TeV energy is studied. The optimization of the detector setting and the time calibration performed with the first collisions delivered by LHC is described. Particle rates, measured for the wide range of luminosities and beam operation conditions experienced during the run, are compared with the values expected from simulation. The space and time alignment of the detectors, chamber efficiency, time resolution and cluster size are evaluated. The detector performance is found to be as expected from specifications or better. Notably the overall efficiency is well above the design requirementsComment: JINST_015P_1112 201