583 research outputs found
Design and operation of a cryogenic charge-integrating preamplifier for the MuSun experiment
The central detector in the MuSun experiment is a pad-plane time projection
ionization chamber that operates without gas amplification in deuterium at 31
K; it is used to measure the rate of the muon capture process . A new charge-sensitive preamplifier, operated at
140 K, has been developed for this detector. It achieved a resolution of 4.5
keV(D) or 120 RMS with zero detector capacitance at 1.1 s
integration time in laboratory tests. In the experimental environment, the
electronic resolution is 10 keV(D) or 250 RMS at a 0.5 s
integration time. The excellent energy resolution of this amplifier has enabled
discrimination between signals from muon-catalyzed fusion and muon capture on
chemical impurities, which will precisely determine systematic corrections due
to these processes. It is also expected to improve the muon tracking and
determination of the stopping location.Comment: 18 pages + title page, 13 figures, to be submitted to JINST; minor
corrections, added one reference, updated author lis
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, . 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 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
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
disappearance rate in hydrogen and the world average for the 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 atom is
measured to be , from which the induced
pseudoscalar coupling of the nucleon, , is
extracted. This result is consistent with theoretical predictions for
that are based on the approximate chiral symmetry of QCD.Comment: submitted to Phys.Rev.Let
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.
Correlations in STAR: interferometry and event structure
STAR observes a complex picture of RHIC collisions where correlation effects
of different origins -- initial state geometry, semi-hard scattering,
hadronization, as well as final state interactions such as quantum intensity
interference -- coexist. Presenting the measurements of flow, mini-jet
deformation, modified hadronization, and the Hanbury Brown and Twiss effect, we
trace the history of the system from the initial to the final state. The
resulting picture is discussed in the context of identifying the relevant
degrees of freedom and the likely equilibration mechanism.Comment: 8 pages, 6 figures, plenary talk at the 5th International Conference
on Physics and Astrophysics of Quark Gluon Plasma, to appear in Journal of
Physics G (http://www.iop.org
Measurements of double-helicity asymmetries in inclusive production in longitudinally polarized collisions at GeV
We report the double helicity asymmetry, , in inclusive
production at forward rapidity as a function of transverse momentum
and rapidity . The data analyzed were taken during
GeV longitudinally polarized collisions at the Relativistic Heavy Ion
Collider (RHIC) in the 2013 run using the PHENIX detector. At this collision
energy, particles are predominantly produced through gluon-gluon
scatterings, thus is sensitive to the gluon polarization
inside the proton. We measured by detecting the decay
daughter muon pairs within the PHENIX muon spectrometers in the
rapidity range . In this kinematic range, we measured the
to be ~(stat)~~(syst). The
can be expressed to be proportional to the product of the
gluon polarization distributions at two distinct ranges of Bjorken : one at
moderate range where recent RHIC data of jet and
double helicity spin asymmetries have shown evidence for significant gluon
polarization, and the other one covering the poorly known small- region . Thus our new results could be used to further
constrain the gluon polarization for .Comment: 335 authors, 10 pages, 4 figures, 3 tables, 2013 data. Version
accepted for publication by Phys. Rev. D. Plain text data tables for the
points plotted in figures for this and previous PHENIX publications are (or
will be) publicly available at http://www.phenix.bnl.gov/papers.htm
J/psi suppression at forward rapidity in Au+Au collisions at sqrt(s_NN)=39 and 62.4 GeV
We present measurements of the J/psi invariant yields in sqrt(s_NN)=39 and
62.4 GeV Au+Au collisions at forward rapidity (1.2<|y|<2.2). Invariant yields
are presented as a function of both collision centrality and transverse
momentum. Nuclear modifications are obtained for central relative to peripheral
Au+Au collisions (R_CP) and for various centrality selections in Au+Au relative
to scaled p+p cross sections obtained from other measurements (R_AA). The
observed suppression patterns at 39 and 62.4 GeV are quite similar to those
previously measured at 200 GeV. This similar suppression presents a challenge
to theoretical models that contain various competing mechanisms with different
energy dependencies, some of which cause suppression and others enhancement.Comment: 365 authors, 10 pages, 11 figures, 4 tables. Submitted to Phys. Rev.
C. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Cross Section and Transverse Single-Spin Asymmetry of Mesons in Collisions at GeV at Forward Rapidity
We present a measurement of the cross section and transverse single-spin
asymmetry () for mesons at large pseudorapidity from
~GeV collisions. The measured cross section for
~GeV/ and is well described by a
next-to-leading-order perturbative-quantum-chromodynamics calculation. The
asymmetries have been measured as a function of Feynman- () from
, as well as transverse momentum () from
~GeV/. The asymmetry averaged over positive is
. The results are consistent with prior
transverse single-spin measurements of forward and mesons at
various energies in overlapping ranges. Comparison of different particle
species can help to determine the origin of the large observed asymmetries in
collisions.Comment: 484 authors, 13 pages, 11 figures, 4 tables, 2008 data. v2 is version
accepted by Phys. Rev. D. Plain text data tables for the points plotted in
figures for this and previous PHENIX publications are (or will be)publicly
available at http://www.phenix.bnl.gov/papers.htm
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