The exclusive photoproduction reaction γp→ϒ(1S)p has been studied with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 468 pb−1. The measurement covers the kinematic ...range 60<W<220 GeV and Q2<1 GeV2, where W is the photon–proton centre-of-mass energy and Q2 is the photon virtuality. The exponential slope, b, of the t dependence of the cross section, where t is the squared four-momentum transfer at the proton vertex, has been measured, yielding b=4.3−1.3+2.0(stat.)−0.6+0.5(syst.) GeV−2. This constitutes the first measurement of the t dependence of the γp→ϒ(1S)p cross section.
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Newton’s Law of Gravitation has been tested at small values
a
of the acceleration, down to
a ≈
10
−10
ms
−2
, the approximate value of MOND’s constant
a
0
. Within experimental errors no deviations ...from Newton’s Law were found. A comparison with six versions of the MOND interpolation function is given. Under the assumptions made in this paper one of the versions can be excluded.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS ...collaborations at HERA for neutral and charged current ... scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb... and span six orders of magnitude in negative four-momentum-transfer squared, ..., and Bjorken x. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in ... An extraction of ... and results on electroweak unification and scaling violations are also presented.
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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.
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Exclusive electroproduction of two pions at HERA Abramowicz, H.; Aggarwal, R.; Antonov, A. ...
The European physical journal. C, Particles and fields,
01/2012, Volume:
72, Issue:
1
Journal Article
Peer reviewed
Open access
The exclusive electroproduction of two pions in the mass range 0.4<
M
ππ
<2.5 GeV has been studied with the ZEUS detector at HERA using an integrated luminosity of 82 pb
−1
. The analysis was carried ...out in the kinematic range of 2<
Q
2
<80 GeV
2
, 32<
W
<180 GeV and |
t
|<0.6 GeV
2
, where
Q
2
is the photon virtuality,
W
is the photon-proton centre-of-mass energy and
t
is the squared four-momentum transfer at the proton vertex. The two-pion invariant-mass distribution is interpreted in terms of the pion electromagnetic form factor, |
F
(
M
ππ
)|, assuming that the studied mass range includes the contributions of the
ρ
,
ρ
′ and
ρ
′′ vector-meson states. The masses and widths of the resonances were obtained and the
Q
2
dependence of the cross-section ratios
σ
(
ρ
′→
ππ
)/
σ
(
ρ
) and
σ
(
ρ
′′→
ππ
)/
σ
(
ρ
) was extracted. The pion form factor obtained in the present analysis is compared to that obtained in
e
+
e
−
→
π
+
π
−
.
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Measurements of the cross sections for charged current deep inelastic scattering in
e
−
p
collisions with longitudinally polarised electron beams are presented. The measurements are based on a data ...sample with an integrated luminosity of 175 pb
−1
collected with the ZEUS detector at HERA at a centre-of-mass energy of 318 GeV. The total cross section is given for positively and negatively polarised electron beams. The differential cross-sections
d
σ
/
dQ
2
,
d
σ
/
dx
and
d
σ
/
dy
are presented for
Q
2
>200 GeV
2
. The double-differential cross-section
d
2
σ
/
dxdQ
2
is presented in the kinematic range 280<
Q
2
<30 000 GeV
2
and 0.015<
x
<0.65. The measured cross sections are compared with the predictions of the Standard Model.
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A
bstract
The production of
D
*±
mesons in deep inelastic
ep
scattering has been measured for exchanged photon virtualities 5 <
Q
2
< 1000 GeV
2
, using an integrated luminosity of 363 pb
−1
with ...the ZEUS detector at HERA. Differential cross sections have been measured and compared to next-to-leading-order QCD calculations. The cross-sections are used to extract the charm contribution to the proton structure functions, expressed in terms of the reduced charm cross section,
. Theoretical calculations based on fits to inclusive HERA data are compared to the results.
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The production of neutrons carrying at least 20% of the proton beam energy (
x
L
>
0.2
) in
e
+
p collisions has been studied with the ZEUS detector at HERA for a wide range of
Q
2, the photon ...virtuality, from photoproduction to deep inelastic scattering. The neutron-tagged cross section,
ep→
e′
Xn, is measured relative to the inclusive cross section,
ep→
e′
X, thereby reducing the systematic uncertainties. For
x
L> 0.3, the rate of neutrons in photoproduction is about half of that measured in hadroproduction, which constitutes a clear breaking of factorisation. There is about a 20% rise in the neutron rate between photoproduction and deep inelastic scattering, which may be attributed to absorptive rescattering in the
γp system. For 0.64<
x
L<0.82, the rate of neutrons is almost independent of the Bjorken scaling variable
x and
Q
2. However, at lower and higher
x
L values, there is a clear but weak dependence on these variables, thus demonstrating the breaking of limiting fragmentation. The neutron-tagged structure function,
F
LN(3)
2(
x,
Q
2,
x
L), rises at low values of
x in a way similar to that of the inclusive
F
2(
x,
Q
2) of the proton. The total
γπ cross section and the structure function of the pion,
F
π
2(
x
π
,
Q
2) where
x
π
=
x/(1−
x
L), have been determined using a one-pion-exchange model, up to uncertainties in the normalisation due to the poorly understood pion flux. At fixed
Q
2,
F
π
2 has approximately the same
x dependence as
F
2 of the proton.
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