Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity of 77.2 pb
-1
. The measurements were made in the kinematic range Q
2
...< 1 GeV
2
, 0.20<y<0.85 and x
IP
<0.025, where Q
2
is the photon virtuality, y is the inelasticity and x
IP
is the fraction of the proton momentum taken by the diffractive exchange. The two jets with the highest transverse energy, E
T
jet
, were required to satisfy E
T
jet
>7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range -1.5<η
jet
<1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive parton distributions of the proton.
The ZEUS detector has been used to study dissociation of virtual photons in events with a leading proton, \(\gamma^{*} p \to X p\), in e + p collisions at HERA. The data cover photon virtualities in ...two ranges, 0.03 < Q2 < 0.60 GeV2 and 2 < Q2 < 100 GeV2, with MX > 1.5 GeV, where MX is the mass of the hadronic final state, X. Events were required to have a leading proton, detected in the ZEUS leading proton spectrometer, carrying at least 90% of the incoming proton energy. The cross section is presented as a function of t, the squared four-momentum transfer at the proton vertex, \(\Phi\), the azimuthal angle between the positron scattering plane and the proton scattering plane, and Q2. The data are presented in terms of the diffractive structure function, \(F_2^{\smasht{D(3)}}\). A next-to-leading-order QCD fit to the higher-Q2 data set and to previously published diffractive charm production data is presented.
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.
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.
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.
Exclusive electroproduction of two pions at HERA Abramowicz, H.; Aggarwal, R.; Antonov, A. ...
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
−
.
We present the first X-ray spectrum obtained by the Low-Energy Transmission Grating Spectrometer (LETGS) aboard the Chandra X-Ray Observatory. The spectrum is of Capella and covers a wavelength range ...of 5-175 Å (2.5-0.07 keV). The measured wavelength resolution, which is in good agreement with ground calibration, is Deltalambda approximately 0.06 Å (FWHM). Although in-flight calibration of the LETGS is in progress, the high spectral resolution and unique wavelength coverage of the LETGS are well demonstrated by the results from Capella, a coronal source rich in spectral emission lines. While the primary purpose of this Letter is to demonstrate the spectroscopic potential of the LETGS, we also briefly present some preliminary astrophysical results. We discuss plasma parameters derived from line ratios in narrow spectral bands, such as the electron density diagnostics of the He-like triplets of carbon, nitrogen, and oxygen, as well as resonance scattering of the strong Fe xvii line at 15.014 Å.
The production of beauty quarks in
ep
interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared
Q
2
>10 GeV
2
, using an integrated luminosity of 363 pb
−1
. ...The beauty events were identified using electrons from semileptonic
b
decays with a transverse momentum
GeV and pseudorapidity |
η
e
|<1.5. Cross sections for beauty production were measured and compared with next-to-leading-order QCD calculations. The beauty contribution to the proton structure function
F
2
was extracted from the double-differential cross section as a function of Bjorken-
x
and
Q
2
.
A
bstract
In this extended analysis using the ZEUS detector at HERA, the photoproduction of isolated photons together with a jet is measured for different ranges of the fractional photon energy,
x
γ
...meas
, contributing to the photon-jet final state. Cross sections are evaluated in the photon transverse-energy and pseudorapidity ranges 6
< E
T
γ
<
15 GeV and −0
.
7
< η
γ
<
0
.
9, and for jet transverse-energy and pseudorapidity ranges 4
< E
T
jet
<
35 GeV and −1
.
5
< η
jet
<
1
.
8, for an integrated luminosity of 374 pb
−1
. The kinematic observables studied comprise the transverse energy and pseudorapidity of the photon and the jet, the azimuthal difference between them, the fraction of proton energy taking part in the interaction, and the difference between the pseudorapidities of the photon and the jet. Higher-order theoretical calculations are compared to the results.
Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 120 pb
−1
. The hadronic decay channels
D
+
→
K
S
0
π
+
, Λ
c
+
→
pK
S
...0
and Λ
c
+
→ Λ
π
+
, and their charge conjugates, were reconstructed. The presence of a neutral strange hadron in the final state reduces the combinatorial background and extends the measured sensitivity into the low transverse momentum region. The kinematic range is 0
< p
T
(
D
+
, Λ
c
+
) < 10 GeV, |
η
(
D
+
, Λ
c
+
)| < 1
.
6, 1.5 <
Q
2
< 1000 GeV
2
and 0
.
02 <
y
< 0.7. Inclusive and differential cross sections for the production of
D
+
mesons are compared to next-to-leading-order QCD predictions. The fraction of
c
quarks hadronising into Λ
c
+
baryons is extracted.
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