(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Exclusive electroproduction of ... mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region ...of ... GeV..., 3.0 GeV ... 6.3 GeV, and ... GeV... Results on the angular distribution of the ... meson, including its decay products, are presented. The data were accumulated with the HERMES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of ... or ... Violation of ...-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse ... production by longitudinal and transverse virtual photons, ... and ..., is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the ... transition dominates over the two natural-parity-exchange amplitudes describing the ... and ... transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity.
Exclusive rho super(0)-meson electroproduction is studied in the HERMES experiment, using a 27.6 GeV longitudinally polarized electron/positron beam and unpolarized hydrogen and deuterium targets in ...the kinematic region 0.5 GeV super(2)<Q super(2)<7.0 GeV super(2), 3.0 GeV <W<6.3 GeV, and -t'<0.4 GeV super(2). Real and imaginary parts of the ratios of the natural-parity-exchange helicity amplitudes T sub(11) ( $\gamma*}_{T} \rightarrow\rho_{T}$ ), T sub(01) ( $\gamma*}_{T} \rightarrow \rho_{L}$ ), T sub(10) ( $\gamma*}_{L} \rightarrow\rho_{T}$ ), and T sub(1-1) ( $\gamma*}_{-T} \rightarrow\rho_{T}$ ) to T sub(00) ( $\gamma*}_{L}\rightarrow\rho_{L}$ ) are extracted from the data. For the unnatural-parity-exchange amplitude U sub(11), the ratio |U sub(11)/T sub(00)| is obtained. The Q super(2) and t' dependences of these ratios are presented and compared with perturbative QCD predictions.
Exclusive
ρ
0
-meson electroproduction is studied in the HERMES experiment, using a 27.6 GeV longitudinally polarized electron/positron beam and unpolarized hydrogen and deuterium targets in the ...kinematic region 0.5 GeV
2
<
Q
2
<7.0 GeV
2
, 3.0 GeV <
W
<6.3 GeV, and −
t
′<0.4 GeV
2
. Real and imaginary parts of the ratios of the natural-parity-exchange helicity amplitudes
T
11
(
),
T
01
(
),
T
10
(
), and
T
1−1
(
) to
T
00
(
) are extracted from the data. For the unnatural-parity-exchange amplitude
U
11
, the ratio |
U
11
/
T
00
| is obtained. The
Q
2
and
t
′ dependences of these ratios are presented and compared with perturbative QCD predictions.
In this paper we document the current analysis software training and onboarding activities in several High Energy Physics (HEP) experiments: ATLAS, CMS, LHCb, Belle II and DUNE. Fast and efficient ...onboarding of new collaboration members is increasingly important for HEP experiments as analyses and the related software become ever more complex with growing datasets. A meeting series was held by the HEP Software Foundation (HSF) in 2022 for experiments to showcase their initiatives. Here we document and analyse these in an attempt to determine a set of key considerations for future experiments.
We studied simultaneously the (4)He(e,e'p), (4)He(e,e'pp), and (4)He(e,e'pn) reactions at Q(2)=2(GeV/c)(2) and x(B)>1, for an (e,e'p) missing-momentum range of 400 to 830 MeV/c. The knocked-out ...proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum, in a region where the nucleon-nucleon (NN) force is expected to change from predominantly tensor to repulsive. The abundance of neutron-proton pairs is reduced as the nucleon momentum increases beyond ∼500 MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum. Our data are compared with calculations of two-nucleon momentum distributions in (4)He and discussed in the context of probing the elusive repulsive component of the NN force.
We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction 3)He(↑)(e,e')X on a polarized (3)He gas target. Assuming ...time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be nonzero if two-photon-exchange contributions are included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron beam, covers a range of 1.7<W<2.9 GeV, 1.0<Q(2)<4.0 GeV(2) and 0.16<x<0.65. Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-(3)He cross-section ratios. The measured neutron asymmetries are negative with an average value of (-1.09±0.38)×10(-2) for invariant mass W>2 GeV, which is nonzero at the 2.89σ level. Our measured asymmetry agrees both in sign and magnitude with a two-photon-exchange model prediction that uses input from the Sivers transverse momentum distribution obtained from semi-inclusive deep-inelastic scattering.
The beam-helicity asymmetry in associated electroproduction of real photons, ep arrow right e gamma pi N , in the Delta (1232)-resonance region is measured using the longitudinally polarized Hera ...positron beam and an unpolarized hydrogen target. Azimuthal Fourier amplitudes of this asymmetry are extracted separately for two channels, ep arrow right e gamma pi super(0) p and ep arrow right e gamma pi super(+) n, from a data set collected with a recoil detector. All asymmetry amplitudes are found to be consistent with zero.
A subset of results from the recently completed Jefferson Lab Qweak experiment are reported. This experiment, sensitive to physics beyond the Standard Model, exploits the small parity-violating ...asymmetry in elastic e→p$\vec e{\rm{p}}$ scattering to provide the first determination of the proton’s weak charge Qwp$Q_w^p$. The experiment employed a 180 μA longitudinally polarized 1.16 GeV electron beam on a 35 cm long liquid hydrogen target. Scattered electrons in the angular range 6° < θ < 12° corresponding to Q2 = 0.025 GeV2 were detected in eight Cerenkov detectors arrayed symmetrically around the beam axis. The goals of the experiment were to provide a measure of e→p$\vec e{\rm{p}}$ to 4.2% (combined statisstatistical and systematic error), which implies a measure of sin2(θw) at the level of 0.3%, and to help constrain the vector weak quark charges C1u and C1d. The experimental method is described, with particular focus on the challenges associated with the world’s highest power LH2 target. The new constraints on C1u and C1d provided by the subset of the experiment’s data analyzed to date will also be shown, together with the extracted weak charge of the neutron.
The beam-helicity asymmetry in associated electroproduction of real photons, eparrow righteγpiN , in the Delta(1232)-resonance region is measured using the longitudinally polarized Hera positron beam ...and an unpolarized hydrogen target. Azimuthal Fourier amplitudes of this asymmetry are extracted separately for two channels, eparrow righteγpi^sup 0^ p and eparrow righteγpi^sup +^ n, from a data set collected with a recoil detector. All asymmetry amplitudes are found to be consistent with zero.
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