A simultaneous fit of parton distribution functions (PDFs) and electroweak parameters to HERA data on deep inelastic scattering is presented. The input data are the neutral current and charged ...current inclusive cross sections which were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In addition, the polarization of the electron beam was taken into account for the ZEUS data recorded between 2004 and 2007. Results on the vector and axial-vector couplings of the Z boson to u- and d-type quarks, on the value of the electroweak mixing angle and the mass of the W boson are presented. The values obtained for the electroweak parameters are in agreement with Standard Model predictions.
A
bstract
The production of beauty and charm quarks in
ep
interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5
< Q
2
<
1000 GeV
2
using an integrated ...luminosity of 354 pb
−1
. The beauty and charm content in events with at least one jet have been extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of
Q
2
, Bjorken
x
, jet trans- verse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of
x
and
Q
2
. The running beauty-quark mass,
m
b
at the scale
m
b
, was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be
m
b
(
m
b
) = 4.07 ± 0.14 (fit)
− 0.07
+ 0.01
(mod.)
− 0.00
+ 0.05
(param.)
− 0.05
+ 0.08
(theo.) GeV.
Production of exclusive dijets in diffractive deep inelastic Formula omitted scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb Formula omitted. The ...measurement was performed for Formula omitted-p centre-of-mass energies in the range Formula omitted and for photon virtualities Formula omitted. Energy flows around the jet axis are presented. The cross section is presented as a function of Formula omitted and Formula omitted, where Formula omitted, x is the Bjorken variable and Formula omitted is the proton fractional longitudinal momentum loss. The angle Formula omitted is defined by the Formula omitted-dijet plane and the Formula omitted- Formula omitted plane in the rest frame of the diffractive final state. The Formula omitted cross section is measured in bins of Formula omitted. The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Single- and double-differential inclusive dijet cross sections in neutral current deep inelastic
ep
scattering have been measured with the ZEUS detector using an integrated luminosity of 374 pb
−1
. ...The measurement was performed at large values of the photon virtuality,
Q
2
, between 125 and 20 000 GeV
2
. The jets were reconstructed with the
k
T
cluster algorithm in the Breit reference frame and selected by requiring their transverse energies in the Breit frame,
, to be larger than 8 GeV. In addition, the invariant mass of the dijet system,
, was required to be greater than 20 GeV. The cross sections are described by the predictions of next-to-leading-order QCD.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A measurement is presented, using data taken with the H1 detector at HERA, of the contribution of diffractive interactions to deep-inelastic electron-proton (
ep) scattering in the kinematic range ...8.5 <
Q
2 < 50GeV
2, 2.4 × 10
−4 < Bjorken-
x < 0.0133, and 3.7 × 10
−4 <
χ
p
< 0.043. The diffractive contribution to the proton structure function
F
2(
x,
Q
2) is evaluated as a function of the appropriate deep-inelastic scattering variables
χ
p
,
Q
2,
β (=
χ
χ
p
)
using a class of deep-inelastic
ep scattering events with no hadronic energy flow in an interval of pseudo-rapidity adjacent to the proton beam direction. the dependence of this contribution on
χ
p
is measured to be
χ
p
−
n
with
n = 1.19 ± 0.06 (stat.) ± 0.07 (syst.) independent of β and
Q
2, which is consistent with both a diffractive interpretation and a factorisable
ep diffractive cross section. A first measurement of the deep-inelastic structure of the pomeron in the form of the
Q
2 and β dependences of a factorised structure function is presented. For all measured β, this structure function is observed to be consistent with scale invariance.
The azimuthal correlation angle, \(\Delta\phi\), between the scattered lepton and the leading jet in deep inelastic \(e^{\pm}p\) scattering at HERA has been studied using data collected with the ZEUS ...detector at a centre-of-mass energy of \(\sqrt{s} = 318 \;\mathrm{GeV}\), corresponding to an integrated luminosity of \(326 \;\mathrm{pb}^{-1}\). A measurement of jet cross sections in the laboratory frame was made in a fiducial region corresponding to photon virtuality \(10 \;\mathrm{GeV}^2 < Q^2 < 350 \;\mathrm{GeV}^2\), inelasticity \(0.04 < y < 0.7\), outgoing lepton energy \(E_e > 10 \;\mathrm{GeV}\), lepton polar angle \(140^\circ < \theta_e < 180^\circ\), jet transverse momentum \(2.5 \;\mathrm{GeV} < p_\mathrm{T,jet} < 30 \;\mathrm{GeV}\), and jet pseudorapidity \(-1.5 < \eta_\mathrm{jet} < 1.8\). Jets were reconstructed using the \(k_\mathrm{T}\) algorithm with the radius parameter \(R = 1\). The leading jet in an event is defined as the jet that carries the highest \(p_\mathrm{T,jet}\). Differential cross sections, \(d\sigma/d\Delta\phi\), were measured as a function of the azimuthal correlation angle in various ranges of leading-jet transverse momentum, photon virtuality and jet multiplicity. Perturbative calculations at \(\mathcal{O}(\alpha_{s}^2)\) accuracy successfully describe the data within the fiducial region, although a lower level of agreement is observed near \(\Delta\phi \rightarrow \pi\) for events with high jet multiplicity, due to limitations of the perturbative approach in describing soft phenomena in QCD. The data are equally well described by Monte Carlo predictions that supplement leading-order matrix elements with parton showering.
A new measurement of inclusive-jet cross sections in the Breit frame in neutral current deep inelastic scattering using the ZEUS detector at the HERA collider is presented. The data were taken in the ...years 2004 to 2007 at a centre-of-mass energy of \(318\,\text{GeV}\) and correspond to an integrated luminosity of \(347\,\text{pb}^{-1}\). Massless jets, reconstructed using the \(k_t\)-algorithm in the Breit reference frame, have been measured as a function of the squared momentum transfer, \(Q^2\), and the transverse momentum of the jets in the Breit frame, \(p_{\perp,\text{Breit}}\). The measured jet cross sections are compared to previous measurements and to perturbative QCD predictions. The measurement has been used in a next-to-next-to-leading-order QCD analysis to perform a simultaneous determination of parton distribution functions of the proton and the strong coupling, resulting in a value of \(\alpha_s(M_Z^2) = 0.1142 \pm 0.0017~\text{(experimental/fit)}\) \({}^{+0.0006}_{-0.0007}~\text{(model/parameterisation)}\) \({}^{+0.0006}_{-0.0004}~\text{(scale)}\), whose accuracy is improved compared to similar measurements. In addition, the running of the strong coupling is demonstrated using data obtained at different scales.
The evolution of the logarithmic scaled energy spectra with energy scale, in the framework of the modified leading logarithmic approximation (MLLA), is investigated. The behaviour of the higher order ...moments of HERA deep inelastic scattering data are compared with the analytic predictions of MLLA.
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