A Circulating Hydrogen Ultra-High Purification System for the MuCap Experiment

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.Comment: submitted to Nucl. Instr. Methods Phys. Res.

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

Immediate cortical adaptation in visual and non-visual areas functions induced by monovision

Key points: Monovision is an optical correction for presbyopes that consists of correcting one eye for far distance and the other for near distance, creating a superimposition of an in-focus with a blurred image. Brain adaptation to monovision was studied in unexperienced observers by measuring visual evoked potentials from 64-channels. The first clear effect of monovision on visual evoked potentials was the C1 amplitude reduction, indicating that the unilateral blurring induced by monovision reduces feed-forward activity in primary visual area. Monovision led also to an increased amplitude of the P1 and pP1 components, with the latter originating in prefrontal regions. This effect probably works as an attentional compensatory activity used to compensate for the degraded V1 signal. A common and often successful option to correct presbyopia with contact lenses is monovision. This is an unbalanced correction across the two eyes where one eye is corrected for far vision and the other eye is corrected for near vision. Monovision is therefore a form of acquired anisometropia that causes a superimposition of an in-focus image with a blurred image. In spite of this visual anisometropia, monovision has been successfully used for many decadesl however the brain mechanism supporting monovision is not well understood. The present study aimed to measure the visual evoked potentials with a high-density electrode array (64-channel) in a group of presbyopes and to provide a detailed spatiotemporal analysis of the cortical activity after a short period of adaptation to monovision with contact lenses. When compared with a balanced eye near correction, monovision produced both a clear reduction of the earliest visual evoked potential components, the C1 and the N1, and an amplitude increase of the P1 and pP1. These results indicate that the unilateral blurring induced by wearing monovision contact lenses reduces feed-forward activity in the primary visual area and feedback activity in extrastriate areas (C1 and N1 reduction). Interestingly, other brain activities in both extrastriate visual areas (the P1 component) and in the anterior insula (the pP1 component) appear to compensate for this dysfunction, increasing their activity during monovision. These changes confirm the presence of fluid brain adaptation in visual and non-visual areas during monocular interferences

Study of aging properties of a wire chamber operating with high-pressure hydrogen

The project for a precision measurement of the µp-capture rate (µCAP experiment) is based on an application of a multi-wire proportional chamber (MWPC) operating in ultra-pure hydrogen at 10 bar pressure. A special test setup was constructed at PNPI to investigate the MWPC performance under the expected experimental conditions. The aging studies of the MWPCs were performed with intense irradiation from an alpha-source (Am 241 ) and a beta-source (Sr 90 ). After 45 days of continuous irradiation by alpha-particles no changes in the currents, in the signal shapes, and in the counting rates were observed. It was demonstrated that the MWPCs can operate without degradation at least up to accumulated charges of 0.1 C/cm wire. These irradiation conditions are much more severe than in the real experiment. During the study of the MWPC we have observed an appearance of short duration signals with amplitudes an order of magnitude larger than those of normal signals from the alpha-particles. The number of such signals ("streamers") strongly depend on HV. We shall continue these tests in the future with the goal of obtaining more detailed information about aging properties of MWPCs operating with high-pressure hydrogen

Study of aging properties of a wire chamber operating with high-pressure hydrogen

Abstract The project for a precision measurement of the mp-capture rate (mCAP experiment) is based on an application of a multi-wire proportional chamber (MWPC) operating in ultra-pure hydrogen at 10 bar pressure. A special test setup was constructed at PNPI to investigate the MWPC performance under the expected experimental conditions. The aging studies of the MWPCs were performed with intense irradiation from an a-source ð 241 AmÞ and a b-source ð 90 SrÞ: After 45 days of continuous irradiation by a-particles no changes in the currents, in the signal shapes, and in the counting rates were observed. It was demonstrated that the MWPCs can operate without degradation at least up to accumulated charges of 0:1 C=cm wire. These irradiation conditions are much more severe than in the real experiment. During the study of the MWPC we have observed an appearance of short duration signals with amplitudes an order of magnitude larger than those of normal signals from the a-particles. The number of such signals (''streamers'') strongly depend on HV. We shall continue these tests in the future with the goal of obtaining more detailed information about aging properties of MWPCs operating with high-pressure hydrogen.

Heart Rate Variability Characteristics in a Large Group of Active-Duty Marines and Relationship to Posttraumatic Stress

OBJECTIVE: Heart rate variability (HRV), thought to reflect autonomic nervous system function, is lowered in conditions such as posttraumatic stress disorder (PTSD). The potential confounding effects of traumatic brain injury (TBI) and depression in the relationship between HRV and PTSD have not been elucidated in a large cohort of military service members. Here we describe HRV associations with stress disorder symptoms in a large study of Marines, while accounting for well-known covariates of HRV and PTSD including TBI and depression. METHODS: Four battalions of male active-duty Marines (N=2430) were assessed 1-2 months prior to a combat deployment. HRV was measured during 5 minutes of rest. Depression and PTSD were assessed using the Beck Depression Inventory and Clinician Administered PTSD scale respectively. RESULTS: After accounting for covariates including TBI, a regression indicated that lower levels of high frequency (HF) HRV were associated with a diagnosis of PTSD (beta = -.20, p=.035). Depression and PTSD severity were correlated (r= .49, p <.001), however participants with PTSD but relatively low depression scores exhibited reduced HF compared to controls (p=.012). Marines with deployment experience (n=1254) had lower HRV than those with no experience (p = .033). CONCLUSIONS: This cross-sectional analysis of a large cohort supports associations between PTSD and reduced HRV when accounting for TBI and depression symptoms. Future post-deployment assessments will be used to determine whether pre-deployment HRV can predict vulnerability and resilience to the serious psychological and physiological consequences of combat exposure