A
bstract
The exclusive photoproduction reactions
γp
→
J/ψ
(1
S
)
p
and
γp
→
ψ
(2
S
)
p
have been measured at an
ep
centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated ...luminosity of 373 pb
−
1
. The measurement was made in the kinematic range 30
< W <
180 GeV,
Q
2
<
1 GeV
2
and |
t
|
<
1 GeV
2
, where
W
is the photon-proton centre-of-mass energy,
Q
2
is the photon virtuality and
t
is the squared four-momentum transfer at the proton vertex. The decay channels used were
J/ψ
(1
S
)
→ μ
+
μ
−
,
ψ
(2
S
)
→ μ
+
μ
−
and
ψ
(2
S
)
→ J/ψ
(1
S
)
π
+
π
−
with subsequent decay
J/ψ
(1
S
)
→ μ
+
μ
−
. The ratio of the production cross sections,
R
=
σ
ψ
(2
S
)
/σ
J/ψ
(1
S
)
, has been measured as a function of
W
and |
t
| and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.
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.
Lorentz and CPT symmetry in the quark sector of the Standard Model are studied in the context of an effective field theory using ZEUS \(e^{\pm} p\) data. Symmetry-violating effects can lead to ...time-dependent oscillations of otherwise time-independent observables, including scattering cross sections. An analysis using five years of inclusive neutral-current deep inelastic scattering events corresponding to an integrated HERA luminosity of \(372\; \text{pb}^{-1}\) at \(\sqrt{s} = 318\) Gev has been performed. No evidence for oscillations in sidereal time has been observed within statistical and systematic uncertainties. Constraints, most for the first time, are placed on 42 coefficients parameterising dominant CPT-even dimension-four and CPT-odd dimension-five spin-independent modifications to the propagation and interaction of light quarks.
The high-precision HERA data allows searches up to TeV scales for beyond the Standard Model contributions to electron–quark scattering. Combined measurements of the inclusive deep inelastic cross ...sections in neutral and charged current ep scattering corresponding to a luminosity of around 1 fb−1 have been used in this analysis. A new approach to the beyond the Standard Model analysis of the inclusive ep data is presented; simultaneous fits of parton distribution functions together with contributions of “new physics” processes were performed. Results are presented considering a finite radius of quarks within the quark form-factor model. The resulting 95% C.L. upper limit on the effective quark radius is 0.43⋅10−16 cm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Charm production in charged current deep inelastic scattering has been measured for the first time in \(e^{\pm}p\) collisions, using data collected with the ZEUS detector at HERA, corresponding to an ...integrated luminosity of \(358 pb^{-1}\). Results are presented separately for \(e^{+}p\) and \(e^{-}p\) scattering at a centre-of-mass energy of \(\sqrt{s} = 318 GeV\) within a kinematic phase-space region of \(200 GeV^{2}<Q^{2}<60000 GeV^{2}\) and \(y<0.9\), where \(Q^{2}\) is the squared four-momentum transfer and \(y\) is the inelasticity. The measured cross sections of electroweak charm production are consistent with expectations from the Standard Model within the large statistical uncertainties.
Isolated photons with high transverse energy have been studied in deep inelastic \(ep\) scattering with the ZEUS detector at HERA, using an integrated luminosity of \(326\,\) pb\(^{-1}\) in the range ...of exchanged-photon virtuality \(10 - 350\) GeV\(^2\). Outgoing isolated photons with transverse energy \(4<E_T^\gamma< 15\) GeV and pseudorapidity \(-0.7 <\eta^\gamma< 0.9\) were measured with accompanying jets having transverse energy and pseudorapidity \(2.5 <E_T^{jet}<35\) GeV and \(-1.5<\eta^{jet}< 1.8\), respectively. Differential cross sections are presented for the following variables: the fraction of the incoming photon energy and momentum that is transferred to the outgoing photon and the leading jet; the fraction of the incoming proton energy transferred to the photon and leading jet; the differences in azimuthal angle and pseudorapidity between the outgoing photon and the leading jet and between the outgoing photon and the scattered electron. Comparisons are made with theoretical predictions: a leading-logarithm Monte Carlo simulation, a next-to-leading-order QCD prediction, and a prediction using the \(k_T\)-factorisation approach.
The exclusive deep inelastic electroproduction of \(\psi(2S)\) and \(J/\psi(1S)\) at an \(ep\) centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range ...\(2 < Q^2 < 80\) GeV\(^2\), \(30 < W < 210\) GeV and \(|t| < 1\) 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 data for \(2 < Q^2 < 5\) GeV\(^2\) were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb\(^{-1}\). The data for \(5 < Q^2 < 80\) GeV\(^2\) are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb\(^{-1}\). The decay modes analysed were \(\mu^+\mu^-\) and \(J/\psi(1S) \pi^+\pi^-\) for the \(\psi(2S)\) and \(\mu^+\mu^-\) for the \(J/\psi(1S)\). The cross-section ratio \(\sigma_{\psi(2S)}/\sigma_{J/\psi(1S)}\) has been measured as a function of \(Q^2, W\) and \(t\). The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.
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 polarisation 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.
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