A series of semi-inclusive deep-inelastic scattering measurements on deuterium, helium, neon, krypton, and xenon targets has been performed in order to study hadronization. The data were collected ...with the HERMES detector at the DESY laboratory using a 27.6 GeV positron or electron beam. Hadron multiplicities on nucleus
A relative to those on the deuteron,
R
A
h
, are presented for various hadrons (
π
+
,
π
−
,
π
0
,
K
+
,
K
−
,
p, and
p
¯
) as a function of the virtual-photon energy
ν, the fraction
z of this energy transferred to the hadron, the photon virtuality
Q
2
, and the hadron transverse momentum squared
p
t
2
. The data reveal a systematic decrease of
R
A
h
with the mass number
A for each hadron type
h. Furthermore,
R
A
h
increases (decreases) with increasing values of
ν (
z), increases slightly with increasing
Q
2
, and is almost independent of
p
t
2
, except at large values of
p
t
2
. For pions two-dimensional distributions also are presented. These indicate that the dependences of
R
A
π
on
ν and
z can largely be described as a dependence on a single variable
L
c
, which is a combination of
ν and
z. The dependence on
L
c
suggests in which kinematic conditions partonic and hadronic mechanisms may be dominant. The behaviour of
R
A
π
at large
p
t
2
constitutes tentative evidence for a partonic energy-loss mechanism. The
A-dependence of
R
A
h
is investigated as a function of
ν,
z, and of
L
c
. It approximately follows an
A
α
form with
α
≈
0.5
–
0.6
.
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.
The compact emulsion spectrometer Buontempo, S; Camilleri, L; Catanesi, M.G ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2001, Letnik:
457, Številka:
3
Journal Article
Recenzirano
Odprti dostop
An emulsion spectrometer has been built and tested with pion beams in a 0.7 T magnetic field. A momentum resolution, Δ
P/
P=13%±1%, has been obtained for 5 and
10
GeV/c
particles.
Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive ρ0 electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized ...hydrogen and deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted in the kinematic region 1<Q2<7 GeV2, 3.0<W<6.3 GeV, and −t<0.4 GeV2. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic dependences of all SDMEs on Q2 and t are presented, as well as the longitudinal-to-transverse ρ0 electroproduction cross-section ratio as a function of Q2. A small but statistically significant deviation from the hypothesis of s-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes; these amplitudes are naturally generated with a quark-exchange mechanism.
Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive
ρ
0
electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized ...hydrogen and deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted in the kinematic region 1<
Q
2
<7 GeV
2
, 3.0<
W
<6.3 GeV, and −
t
<0.4 GeV
2
. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic dependences of all SDMEs on
Q
2
and
t
are presented, as well as the longitudinal-to-transverse
ρ
0
electroproduction cross-section ratio as a function of
Q
2
. A small but statistically significant deviation from the hypothesis of
s
-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes; these amplitudes are naturally generated with a quark-exchange mechanism.
The HERMES silicon project—the radiation protection system van Beuzekom, M.G.; Bouhali, O.; Mexner, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2003, Letnik:
512, Številka:
1
Journal Article
Recenzirano
The HERMES-detector has recently been upgraded with a silicon detector called the Lambda Wheels. This is the first detector following the interaction region. It consists of two disks of silicon ...detectors close to the beamline. This location makes it vulnerable to increased radiation levels which may be caused by beam instabilities. The Lambda Wheel detector, therefore, contains a system to detect these instabilities. This additional system triggers a kicker which dumps the HERA-lepton beam when the radiation level becomes too high.
This contribution describes the radiation monitor which consists of two sets of three ionization chambers each, and the data-acquisition system which reads them out. The system has been installed and is operational since the summer of 2001. The HERA-accelerator was being commissioned after an upgrade during this time and several kinds of beam instabilities were observed with this protection system. The characteristics of some events will be described.
The influence of the nuclear medium on lepto-production of hadrons was studied in the HERMES experiment at DESY in semi-inclusive deep-inelastic scattering of 27.6 GeV positrons off deuterium, ...nitrogen and krypton targets. The differential multiplicity for krypton relative to that of deuterium has been measured for the first time for various identified hadrons (π+, π−, π0, K+, K−, p and p̄) as a function of the virtual photon energy ν, the fraction z of this energy transferred to the hadron, and the hadron transverse momentum squared pt2. The multiplicity ratio is strongly reduced in the nuclear medium at low ν and high z, with significant differences among the various hadrons. The distribution of the hadron transverse momentum is broadened towards high pt2 in the nuclear medium, in a manner resembling the Cronin effect previously observed in collisions of heavy ions and protons with nuclei.
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