331 research outputs found
Scintillator counters with WLS fiber/MPPC readout for the side muon range detector (SMRD)of the T2K experiment
The T2K neutrino experiment at J-PARC uses a set of near detectors to measure
the properties of an unoscillated neutrino beam and neutrino interaction
cross-sections. One of the sub-detectors of the near-detector complex, the side
muon range detector (SMRD), is described in the paper. The detector is designed
to help measure the neutrino energy spectrum, to identify background and to
calibrate the other detectors. The active elements of the SMRD consist of 0.7
cm thick extruded scintillator slabs inserted into air gaps of the UA1 magnet
yokes. The readout of each scintillator slab is provided through a single WLS
fiber embedded into a serpentine shaped groove. Two Hamamatsu multi-pixel
avalanche photodiodes (MPPC's) are coupled to both ends of the WLS fiber. This
design allows us to achieve a high MIP detection efficiency of greater than
99%. A light yield of 25-50 p.e./MIP, a time resolution of about 1 ns and a
spatial resolution along the slab better than 10 cm were obtained for the SMRD
counters.Comment: 7 pages, 4 figures; talk at TIPP09, March 12-17, Tsukuba, Japan; to
be published in the conference proceeding
The T2K Side Muon Range Detector
The T2K experiment is a long baseline neutrino oscillation experiment aiming
to observe the appearance of {\nu} e in a {\nu}{\mu} beam. The {\nu}{\mu} beam
is produced at the Japan Proton Accelerator Research Complex (J-PARC), observed
with the 295 km distant Super- Kamiokande Detector and monitored by a suite of
near detectors at 280m from the proton target. The near detectors include a
magnetized off-axis detector (ND280) which measures the un-oscillated neutrino
flux and neutrino cross sections. The present paper describes the outermost
component of ND280 which is a side muon range detector (SMRD) composed of
scintillation counters with embedded wavelength shifting fibers and Multi-Pixel
Photon Counter read-out. The components, performance and response of the SMRD
are presented.Comment: 13 pages, 19 figures v2: fixed several typos; fixed reference
Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high
We measured the longitudinal double spin asymmetries for single
hadron muo-production off protons and deuterons at photon virtuality <
1(GeV/) for transverse hadron momenta in the range 0.7
GeV/ to 4 GeV/ . They were determined using COMPASS data taken
with a polarised muon beam of 160 GeV/ or 200 GeV/ impinging on
polarised or targets. The experimental
asymmetries are compared to next-to-leading order pQCD calculations, and are
sensitive to the gluon polarisation inside the nucleon in the range
of the nucleon momentum fraction carried by gluons
Interplay among transversity induced asymmetries in hadron leptoproduction
In the fragmentation of a transversely polarized quark several left-right
asymmetries are possible for the hadrons in the jet. When only one unpolarized
hadron is selected, it exhibits an azimuthal modulation known as Collins
effect. When a pair of oppositely charged hadrons is observed, three
asymmetries can be considered, a di-hadron asymmetry and two single hadron
asymmetries. In lepton deep inelastic scattering on transversely polarized
nucleons all these asymmetries are coupled with the transversity distribution.
From the high statistics COMPASS data on oppositely charged hadron-pair
production we have investigated for the first time the dependence of these
three asymmetries on the difference of the azimuthal angles of the two hadrons.
The similarity of transversity induced single and di-hadron asymmetries is
discussed. A new analysis of the data allows to establish quantitative
relationships among them, providing for the first time strong experimental
indication that the underlying fragmentation mechanisms are all driven by a
common physical process.Comment: 6 figure
Interplay among transversity induced asymmetries in hadron leptoproduction
In the fragmentation of a transversely polarized quark several left-right
asymmetries are possible for the hadrons in the jet. When only one unpolarized
hadron is selected, it exhibits an azimuthal modulation known as Collins
effect. When a pair of oppositely charged hadrons is observed, three
asymmetries can be considered, a di-hadron asymmetry and two single hadron
asymmetries. In lepton deep inelastic scattering on transversely polarized
nucleons all these asymmetries are coupled with the transversity distribution.
From the high statistics COMPASS data on oppositely charged hadron-pair
production we have investigated for the first time the dependence of these
three asymmetries on the difference of the azimuthal angles of the two hadrons.
The similarity of transversity induced single and di-hadron asymmetries is
discussed. A new analysis of the data allows to establish quantitative
relationships among them, providing for the first time strong experimental
indication that the underlying fragmentation mechanisms are all driven by a
common physical process.Comment: 6 figure
Resonance Production and S-wave in at 190 GeV/c
The COMPASS collaboration has collected the currently largest data set on
diffractively produced final states using a negative pion
beam of 190 GeV/c momentum impinging on a stationary proton target. This data
set allows for a systematic partial-wave analysis in 100 bins of three-pion
mass, GeV/c , and in 11 bins of the reduced
four-momentum transfer squared, (GeV/c) . This
two-dimensional analysis offers sensitivity to genuine one-step resonance
production, i.e. the production of a state followed by its decay, as well as to
more complex dynamical effects in nonresonant production. In this paper,
we present detailed studies on selected partial waves with , , , , and . In these waves, we observe
the well-known ground-state mesons as well as a new narrow axial-vector meson
decaying into . In addition, we present the results
of a novel method to extract the amplitude of the subsystem with
in various partial waves from the
data. Evidence is found for correlation of the and
appearing as intermediate isobars in the decay of the known
and .Comment: 96 page
Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data
Using a novel analysis technique, the gluon polarisation in the nucleon is
re-evaluated using the longitudinal double-spin asymmetry measured in the cross
section of semi-inclusive single-hadron muoproduction with photon virtuality
. The data were obtained by the COMPASS experiment at
CERN using a 160 GeV/ polarised muon beam impinging on a polarised LiD
target. By analysing the full range in hadron transverse momentum ,
the different -dependences of the underlying processes are separated
using a neural-network approach. In the absence of pQCD calculations at
next-to-leading order in the selected kinematic domain, the gluon polarisation
is evaluated at leading order in pQCD at a hard scale of . It is determined in three intervals
of the nucleon momentum fraction carried by gluons, , covering the
range ~ and does not exhibit a significant
dependence on . The average over the three intervals, at
, suggests that the gluon polarisation
is positive in the measured range.Comment: 14 pages, 6 figure
Measurement of the charged-pion polarisability
The COMPASS collaboration at CERN has investigated pion Compton scattering,
, at centre-of-mass energy below 3.5 pion
masses. The process is embedded in the reaction
, which is initiated by
190\,GeV pions impinging on a nickel target. The exchange of quasi-real photons
is selected by isolating the sharp Coulomb peak observed at smallest momentum
transfers, \,(GeV/). From a sample of 63\,000 events the
pion electric polarisability is determined to be $\alpha_\pi\ =\ (\,2.0\ \pm\
0.6_{\mbox{\scriptsize stat}}\ \pm\ 0.7_{\mbox{\scriptsize syst}}\,) \times
10^{-4}\,\mbox{fm}^3\alpha_\pi=-\beta_\pi$, which
relates the electric and magnetic dipole polarisabilities. It is the most
precise measurement of this fundamental low-energy parameter of strong
interaction, that has been addressed since long by various methods with
conflicting outcomes. While this result is in tension with previous dedicated
measurements, it is found in agreement with the expectation from chiral
perturbation theory. An additional measurement replacing pions by muons, for
which the cross-section behavior is unambigiously known, was performed for an
independent estimate of the systematic uncertainty.Comment: Published version: 9 pages, 3 figures, 1 tabl
The Spin Structure Function of the Proton and a Test of the Bjorken Sum Rule
New results for the double spin asymmetry and the proton
longitudinal spin structure function are presented. They were
obtained by the COMPASS collaboration using polarised 200 GeV muons scattered
off a longitudinally polarised NH target. The data were collected in 2011
and complement those recorded in 2007 at 160\,GeV, in particular at lower
values of . They improve the statistical precision of by
about a factor of two in the region . A next-to-leading order
QCD fit to the world data is performed. It leads to a new determination
of the quark spin contribution to the nucleon spin, ranging
from 0.26 to 0.36, and to a re-evaluation of the first moment of .
The uncertainty of is mostly due to the large uncertainty in
the present determinations of the gluon helicity distribution. A new evaluation
of the Bjorken sum rule based on the COMPASS results for the non-singlet
structure function yields as ratio of the axial and
vector coupling constants , which validates the sum rule to an accuracy of about
9\%.Comment: 19 pages, 8 figures and table
Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised proton
Measurements of the Collins and Sivers asymmetries for charged pions and
charged and neutral kaons produced in semi-inclusive deep-inelastic scattering
of high energy muons off transversely polarised protons are presented. The
results were obtained using all the available COMPASS proton data, which were
taken in the years 2007 and 2010. The Collins asymmetries exhibit in the
valence region a non-zero signal for pions and there are hints of non-zero
signal also for kaons. The Sivers asymmetries are found to be positive for
positive pions and kaons and compatible with zero otherwise.Comment: 15 pages, 13 figures and 1 tabl
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