Hadron identification with the HERMES RICH Hommez, B.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2003, Letnik:
502, Številka:
1
Journal Article
Recenzirano
The HERMES experiment has upgraded its spectrometer in 1998 with a ring imaging Cherenkov (RICH) detector to allow the identification of pions, kaons and protons over practically the entire momentum ...range of HERMES, by using two radiators, silica aerogel and C4F10 gas. The identification of the different hadrons in the HERMES RICH detector is based on two different methods: the inverse ray tracing method (IRT) and the direct ray tracing method (DRT). Both methods use a likelihood analysis to select the most probable particle type. The IRT and DRT method exist in parallel; a decision network chooses the optimal method for a certain event topology. Details on the IRT and DRT methods will be presented as well as the development of an “unfolding program” which allows to extract true (π,K,p) momentum distributions from the measured ones.
Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized ...deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.
Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The ...asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.
Longitudinal double-spin asymmetries of charged hadrons with high transverse momentum
p
T
have been measured in electroproduction using the H
ermes
detector at H
era
. Processes involving gluons in ...the nucleon have been enhanced relative to others by selecting hadrons with
p
T
typically above 1 GeV. In this kinematic domain the gluon polarization has been extracted in leading order making use of the model embedded in the Monte Carlo Generator P
ythia
6.2. The gluon polarization obtained from single inclusive hadrons in the
p
T
range 1 GeV <
p
T
< 2.5 GeV using a deuterium target is
at a scale
and
. For different final states and kinematic domains, consistent values of
have been found within statistical uncertainties using hydrogen and deuterium targets.
A search for diffuse neutrinos with energies in excess of 10 super(5) GeV is conducted with AMANDA-II data recorded between 2000 and 2002. Above 10 super(7) GeV, the Earth is essentially opaque to ...neutrinos. This fact, combined with the limited overburden of the AMANDA-II detector (roughly 1.5 km), concentrates these ultra-high-energy neutrinos at the horizon. The primary background for this analysis is bundles of downgoing, high-energy muons from the interaction of cosmic rays in the atmosphere. No statistically significant excess above the expected background is seen in the data, and an upper limit is set on the diffuse all-flavor neutrino flux of image GeV cm super(-2) s super(-1) sr super(-1) valid over the energy range of image to 10 super(9) GeV. A number of models that predict neutrino fluxes from active galactic nuclei are excluded at the 90% confidence level.
The optical properties of silica aerogel tiles with a refractive index of 1.03 and dimensions
11×11×1
cm
3
, produced by the Matsushita Electric Works (Japan), have been measured in the wavelength ...range from 200 to 900 nm. The tiles are used as one of the two radiators of the ring imaging Cherenkov counter of the HERMES experiment at DESY-HERA. The transmittance of light has been measured on 200 tiles by means of a double beam spectrophotometer. The light transflectance and reflectance have been measured on one tile by means of a single-beam spectrophotometer and an integrating reflecting sphere. Typical values of the measured transmittances at a wavelength
λ=400 nm are around 0.67. The measured transflectance increases almost linearly from 0.4 to 0.96 in the interval 200–300 nm, and remains nearly constant at the value 0.95 in the complementary
λ-range. The measured reflectance, mostly confined below 400 nm, is completely interpretable as backscattering from inside the aerogel, revealing an absence of light reflection at the aerogel surfaces. The transmittance data have been fitted with the Hunt formula, whose parameters have been used to evaluate the number of unscattered and scattered Cherenkov photons produced by aerogel. For stacks of 5 tiles and quantum efficiencies of phototubes with bialkali photocathodes, rings with up to 19 photoelectrons/event can be expected for
β=1 particles.
The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a ...negligible residual vector polarization enabled the first measurement of the tensor asymmetry A(d)zz and the tensor structure function b(d)1 for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV2 < <5 GeV2. The quantities A(d)zz and b(d)1 are found to be nonzero. The rise of b(d)1 for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.
The HERMES hydrogen and deuterium nuclear-polarized gas targets have been in use since 1996 with the polarized electron beam of HERA at DESY to study the spin structure of the nucleon. Polarized ...atoms from a Stern–Gerlach Atomic Beam Source are injected into a storage cell internal to the HERA electron ring. Atoms diffusing from the center of the storage cell into a side tube are analyzed to determine the atomic fraction and the atomic polarizations. The atoms have a nuclear polarization, the axis of which is defined by an external magnetic holding field. The holding field was longitudinal during 1996–2000, and was changed to transverse in 2001. The design of the target is described, the method for analyzing the target polarization is outlined, and the performance of the target in the various running periods is presented.
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