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1.
The ZEUS Collaboration S. Chekanov et al. 《The European Physical Journal C - Particles and Fields》2003,27(4):531-545
Inclusive event-shape variables have been measured in the current region of the Breit frame for neutral current deep inelastic
ep scattering using an integrated luminosity of collected with the ZEUS detector at HERA. The variables studied included thrust, jet broadening and invariant jet mass. The
kinematic range covered was 10 < Q
2
< 20 480 GeV
2
and , where Q2 is the virtuality of the exchanged boson and x is the Bjorken variable. The Q dependence of the shape variables has been used in conjunction with NLO perturbative calculations and the Dokshitzer-Webber
non-perturbative corrections (`power corrections') to investigate the validity of this approach.
Received: 13 November 2002 / Published online: 7 March 2003 相似文献
2.
The HERMES Collaboration A. Airapetian et al. 《The European Physical Journal C - Particles and Fields》2003,26(4):527-538
The Gerasimov-Drell-Hearn (GDH) sum rule connects the anomalous contribution to the magnetic moment of the target nucleus
with an energy-weighted integral of the difference of the helicity-dependent photoabsorption cross sections. Originally conceived
for real photons, the GDH integral can be generalised to the case of photons with virtuality Q2. For spin-1/2 targets such as the nucleon, it then represents the non-perturbative limit of the first moment of the spin structure function g
1
(x,Q
2
) in deep inelastic scattering (DIS). The data collected by HERMES with a deuterium target are presented together with a re-analysis
of previous measurements on the proton. This provides an unprecedented and complete measurement of the generalised GDH integral
for photon-virtuality ranging over 1.2<Q
2
<12.0 GeV2 and for photon-nucleon invariant mass squared W2 ranging over 1<W
2
<45 GeV2, thus covering simultaneously the nucleon-resonance and the deep inelastic scattering regions. These data allow the study
of the Q2-dependence of the full GDH integral, which is sensitive to both the Q2-evolution of the resonance form factors and contributions of higher twist. The contribution of the nucleon-resonance region
is seen to decrease rapidly with increasing Q2. The DIS contribution is sizeable over the full measured range, even down to the lowest measured Q2. As expected, at higher Q2 the data are found to be in agreement with previous measurements of the first moment of g1. From data on the deuteron and proton, the GDH integral for the neutron has been derived and the proton-neutron difference
evaluated. This difference is found to satisfy the fundamental Bjorken sum rule at Q
2
= 5 GeV2.
Received: 20 October 2002 / Published online: 15 January 2003 相似文献
3.
We present an estimate of the cross-section for the exclusive production of a ρL
0-meson pair in e+e- scattering, which will be studied in the future high-energy International Linear Collider. For this aim, we complete calculations
of the Born order approximation of the amplitudes γ*
L,T(Q1
2)γ*
L,T(Q2
2)→ρL
0ρL
0, for arbitrary polarization of virtual photons and longitudinally polarized mesons, in the kinematical region s≫-t,Q1
2,Q2
2. These processes are completely calculable in the hard region Q1
2,Q2
2≫Λ2
QCD, and we perform most of the calculations in an analytical way. The resulting cross-section turns out to be large enough for
this process to be measurable with foreseen luminosity and energy, for Q1
2 and Q2
2 in the range of a few GeV2. 相似文献
4.
《The European Physical Journal C - Particles and Fields》2007,51(1):1-23
The production of the neutral strange hadrons K0
S, Λ and Λ̄ has been measured in ep collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative
yields of strange and charged light hadrons, Λ (Λ̄) asymmetry and polarization have been measured in three kinematic regions:
Q2 > 25 GeV2; 5 < Q2 < 25 GeV2; and in photoproduction (Q2≃0). In photoproduction the presence of two hadronic jets, each with at least 5 GeV transverse energy, was required. The measurements
agree in general with Monte Carlo models and are consistent with measurements made at e+e- colliders, except for an enhancement of baryon relative to meson production in photoproduction. 相似文献
5.
A search for QCD-instanton-induced events in deep inelastic ep scattering has been performed with the ZEUS detector at the HERA collider, using data corresponding to an integrated luminosity of 38 pb-1. A kinematic range defined by cuts on the photon virtuality, Q2 > 120 GeV2, and on the Bjorken scaling variable, x > 10-3, has been investigated. The QCD-instanton induced events were modelled by the Monte Carlo generator QCDINS. A background-independent, conservative 95% confidence level upper limit for the instanton cross section of 26 pb is obtained, to be compared with the theoretically expected value of 8.9 pb.Received: 17 December 2003, Published online: 2 April 2004 相似文献
6.
C. Adloff et al. 《The European Physical Journal C - Particles and Fields》2002,25(4):495-509
Signals of QCD instanton-induced processes are searched for in deep-inelastic scattering (DIS) at the electron-proton collider
HERA in a kinematic region defined by the Bjorken-scaling variables x > 10-3, 0.1 < y < 0.6 and photon virtualities < 100 GeV2. Several observables characterising hadronic final state properties of QCD instanton-induced events are exploited to identify
a potentially instanton-enriched domain. While an excess of events with instanton-like topology is observed it cannot be claimed
significant given the uncertainty of the standard DIS background simulation. Upper limits on the cross-section for instanton-induced
processes of between 60 pb and 1000 pb are set dependent on the kinematic domain considered. The data do not exclude the cross-section
predicted by instanton perturbation theory for small instanton sizes. At large instanton sizes a naive extrapolation of instanton
perturbation theory yields a cross-section in the range of sensitivity of this study. Such a cross-section is not observed,
in agreement with non-perturbative lattice simulations of the QCD vacuum.
Received: 27 May 2002 / Published online: 24 September 2002 相似文献
7.
In this paper we report our calculations on several important total cross-sections (TCSs) of positron impact on isoelectronic
N2 and CO molecules, treated in the complex spherical potential formalism. Basically the total (complete) cross-section Q
T consists of elastic and inelastic contributions. Our total inelastic cross-section (Q
inel) contains ionization and electronic excitations together with positronium formation. Our goal here is to bifurcate Q
inel further to deduce total ionization cross-section, using the ‘complex scattering potential–ionization contribution’ (CSP-ic)
method of electron–atom/molecule scattering. The present range of positron energy is 15–2000 eV. All the resulting cross-sections
are in a good general accord with the existing data. This work highlights the importance of various scattering channels in
e + -N2 and e + -CO interactions at intermediate and high energies. 相似文献
8.
T. Shizuma Y. Toh M. Oshima M. Sugawara M. Matsuda T. Hayakawa M. Koizumi A. Osa Y.H. Zhang Z. Liu 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):159-165
Excited states in 187Re populated by inelastic scattering of a 500 MeV 82Se beam have been studied by means of in-beam γ-ray spectroscopy. Levels built on the 5/2+[402] and 9/2-[514] one-quasiparticle states were measured up to I
π = (21/2+) and (21/2-), respectively. In addition, several new levels including an isomer at 1682 keV with a half-life of 114(23) ns have been
found. Quasiparticle configurations of the levels and the transition rates are discussed.
Received: 12 December 2002 / Accepted: 13 March 2003 / Published online: 13 May 2003 相似文献
9.
The production rates and substructure of jets have been studied in charged current deep inelastic e
+
p scattering for Q
2 > 200 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb-1. Inclusive jet cross sections are presented for jets with transverse energies
GeV and pseudorapidities in the range
. Dijet cross sections are presented for events with a jet having
GeV and a second jet having
GeV. Measurements of the mean subjet multiplicity,
, of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-to-leading-order QCD calculations are compared to the measurements. The value of
, determined from
at
for jets with
GeV, is
. The mean subjet multiplicity as a function of Q
2 is found to be consistent with that measured in NC DIS.Received: 5 June 2003, Published online: 10 October 2003 相似文献
10.
A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e
+
e
-annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e
+
e
-and
spectral functions in the
channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and
, so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are
where the errors have been separated according to their sources: experimental, missing radiative corrections in e
+
e
-data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read
where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be
(1.9
) and
(0.7
) for the e
+
e
-- and
-based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Received: 7 September 2003, Published online: 30 October 2003 相似文献
11.
《Physics letters. [Part B]》2001,510(1-4)
Multiplicity moments of charged particles in deep inelastic e+p scattering have been measured with the ZEUS detector at HERA using an integrated luminosity of 38.4 pb−1. The moments for Q2>1000 GeV2 were studied in the current region of the Breit frame. The evolution of the moments was investigated as a function of restricted regions in polar angle and, for the first time, both in the transverse momentum and in absolute momentum of final-state particles. Analytic perturbative QCD predictions in conjunction with the hypothesis of Local Parton–Hadron Duality (LPHD) reproduce the trends of the moments in polar-angle regions, although some discrepancies are observed. For the moments restricted either in transverse or absolute momentum, the analytic results combined with the LPHD hypothesis show considerable deviations from the measurements. The study indicates a large influence of the hadronisation stage on the multiplicity distributions in the restricted phase-space regions studied here, which is inconsistent with the expectations of the LPHD hypothesis. 相似文献
12.
Cross sections for e
+
p charged current deep inelastic scattering at a centre-of-mass energy of
have been determined with an integrated luminosity of
collected with the ZEUS detector at HERA. The differential cross sections
,
and
for
are presented. In addition,
has been measured in the kinematic range
and . The predictions of the Standard Model agree well with the measured cross sections. The mass of the W boson propagator is determined to be
from a fit to
. The chiral structure of the Standard Model is also investigated in terms of the (1-y)2 dependence of the double-differential cross section. The structure-function
has been extracted by combining the measurements presented here with previous ZEUS results from e
-
p scattering, extending the measurement obtained in a neutrino-nucleus scattering experiment to a significantly higher Q
2 region.Received: 17 July 2003, Published online: 12 November 2003
a supported by the Natural Sciences and Engineering Research Council
of Canada (NSERC)
b supported by the German
Federal Ministry for Education and Research (BMBF), under contract numbers HZ1GUA 2,
HZ1GUB 0, HZ1PDA 5, HZ1VFA 5
c supported by the
MINERVA Gesellschaft für Forschung GmbH, the Israel Science Foundation, the U.S.-Israel
Binational Science Foundation and the Benozyio Center for High Energy Physics
d supported by
the German-Israeli Foundation and the Israel Science Foundation
e supported
by the Italian National Institute for Nuclear Physics (INFN)
f supported
by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and its grants
for Scientific Research
g supported by the
Korean Ministry of Education and Korea Science and Engineering Foundation
h supported
by the Netherlands Foundation for Research on Matter (FOM)
i supported by the
Polish State Committee for Scientific Research, grant no. 620/E-77/SPUB-M/DESY/P-03/DZ 247/2000-2002
j partially
supported by the German Federal Ministry for Education and Research (BMBF)
k supported by
the Fund for Fundamental Research of Russian Ministry for Science and Education and by
the German Federal Ministry for Education and Research (BMBF)
l supported by the
Spanish Ministry of Education and Science through funds provided by CICYT
m supported by
the Particle Physics and Astronomy Research Council, UK
n supported by the
US Department of Energy
o supported by the US
National Science Foundation
p supported by the
Polish State Committee for Scientific Research, grant no. 112/E-356/SPUB-M/DESY/P-03/DZ 301/2000-2002, 2 P03B 13922
q supported by the Polish State Committee for Scientific Research, grant no. 115/E-343/SPUB-M/DESY/P-03/DZ 121/2001-2002, 2 P03B 07022 相似文献
13.
《The European Physical Journal C - Particles and Fields》2007,51(2):289-299
The distribution of the azimuthal angle of charged and neutral hadrons relative to the lepton plane has been studied for neutral
current deep inelastic ep scattering using an integrated luminosity of 45 pb-1 taken with the ZEUS detector. The kinematic range is 100<Q2<8000 GeV2, 0.2<y<0.8 and 0.01<x<0.1 where Q2 is the virtuality of the exchanged boson, y is the inelasticity and x is the Bjorken variable. The measurements were made
in the hadronic centre-of-mass system. The analysis exploits the energy-flow method, which allows the measurement to be made
over a larger range of pseudorapidity compared to previous results. The dependence of the moments of the azimuthal distributions
on the pseudorapidity and minimum transverse energy of the final-state hadrons are presented. Although the predictions from
next-to-leading-order QCD describe the data better than do the Monte Carlo models incorporating leading-logarithm parton showers,
they still fail to describe the magnitude of the asymmetries. This suggests that higher-order calculations may be necessary
to describe these data. 相似文献
14.
《The European Physical Journal C - Particles and Fields》2007,52(4):813-832
The production of dijets in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an
integrated luminosity of 61 pb-1. The dijet cross section has been measured for virtualities of the exchanged virtual photon, 5 < Q2 < 100 GeV2, and γ*p centre-of-mass energies, 100 < W < 250 GeV. The jets, identified using the inclusive kT algorithm in the γ*p frame, were required to have a transverse energy E*
T,jet > 4 GeV and the jet with the highest transverse energy was required to have E*
T,jet > 5 GeV. All jets were required to be in the pseudorapidity range -3.5<η*
jet<0. The differential cross sections are compared to leading-order predictions and next-to-leading-order QCD calculations based
on recent diffractive parton densities extracted from inclusive diffractive deep inelastic scattering data. 相似文献
15.
K. Terasaki 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):676-678
Although assigning D
s0
+(2317) to the I
3 = 0 component
of iso-triplet four-quark mesons is favored by experiments, its neutral and doubly charged partners have not yet been observed.
It is discussed why they were not observed in inclusive e
+
e
-→cˉ experiment and that they can be observed in B decays. 相似文献
16.
《The European Physical Journal C - Particles and Fields》2009,62(4):625-658
Measurements of the neutral current cross sections for deep inelastic scattering in e
−
p collisions at HERA with a longitudinally polarised electron beam are presented. The single-differential cross-sections d
σ/dQ
2, d
σ/dx and d
σ/dy and the double-differential cross sections in Q
2 and x are measured in the kinematic region y<0.9 and Q
2>185 GeV
2 for both positively and negatively polarised electron beams and for each polarisation state separately. The measurements
are based on an integrated luminosity of 169.9 pb
−1 taken with the ZEUS detector in 2005 and 2006 at a centre-of-mass energy of 318 GeV. The structure functions
and xF
3
γ
Z
are determined by combining the e
−
p results presented in this paper with previously measured e
+
p neutral current data. The asymmetry parameter A
− is used to demonstrate the parity violating effects of electroweak interactions at large spacelike photon virtuality. The
measurements agree well with the predictions of the Standard Model. 相似文献
17.
We extract the neutron charge form factor G
n
E(Q
2) from the charge form factor of deuteron G
d
C(Q
2) obtained from T
20(Q
2) data at 0≤Q
2≤ 1.717 (GeV/c)2. The extraction is based on the relativistic impulse approximation in the instant form of the relativistic Hamiltonian dynamics.
Our results (12 new points) are compatible with existing values of the neutron charge form factor of other authors. We propose
a fit for the whole set (36 points) taking into account the data for the slope of the form factor at Q
2 = 0.
Received: 26 July 2002 / Accepted: 18 September 2002 / Published online: 4 February 2003
RID="a"
ID="a"e-mail: krutov@ssu.samara.ru
RID="b"
ID="b"e-mail: troitsky@theory.sinp.msu.ru
Communicated by V.V. Anisovich 相似文献
18.
19.
20.
《The European Physical Journal C - Particles and Fields》2007,49(2):523-544
A new method is employed to measure the neutral current cross section up to Bjorken-x values of one with the ZEUS detector
at HERA using an integrated luminosity of 65.1 pb-1 for e+p collisions and 16.7 pb-1 for e-p collisions at and 38.6 pb-1 for e+p collisions at . Cross sections have been extracted for Q2≥648 GeV2 and are compared to predictions using different parton density functions. For the highest x bins, the data have a tendency
to lie above the expectations using recent parton density function parametrizations. 相似文献