-
ZEUS collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
O. Zabiegalov, A. F. Żarnecki,
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
A. Zichichi,
Z. Zolkapli,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: The production of Z0 bosons in the reaction ep -> eZ0p*, where p* stands for
a proton or a low-mass nucleon resonance, has been studied in ep collisions at
HERA using the ZEUS detector. The analysis is based on a data sample collected
between 1996 and 2007, amounting to 496 pb-1 of integrated luminosity. The Z0
was measured in the hadronic decay mode. The elasticity of the events was
ensured by a cut on eta_max < 3.0, where eta_max is the maximum pseudorapidity
of energy deposits in the calorimeter defined with respect to the proton beam
direction. A signal was observed at the Z0 mass. The cross section of the
reaction ep -> eZ0p* was measured to be sigma(ep -> eZ0p*) = 0.13 +/- 0.06
(stat.) +/- 0.01 (syst.) pb, in agreement with the Standard Model prediction of
0.16 pb. This is the first measurement of Z0 production in ep collisions.
10/2012;
-
ZEUS Collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
M. Zolko,
D. S. Zotkin
-
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo,
O. Arslan, [......], A. F. Żarnecki,
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: A search for first-generation leptoquarks was performed in electron-proton and positron-proton collisions recorded with the ZEUS detector at HERA in 2003–2007 using an integrated luminosity of 366 pb-1. Final states with an electron and jets or with missing transverse momentum and jets were analyzed, searching for resonances or other deviations from the standard model predictions. No evidence for any leptoquark signal was found. The data were combined with data previously taken at HERA, resulting in a total integrated luminosity of 498 pb-1. Limits on the Yukawa coupling, λ, of leptoquarks were set as a function of the leptoquark mass for different leptoquark types within the Buchmüller-Rückl-Wyler model. Leptoquarks with a coupling λ=0.3 are excluded for masses up to 699 GeV.
Phys. Rev. D. 07/2012; 86(1).
-
The ZEUS collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
M. Zolko,
D. S. Zotkin,
Z. Zulkapli
[show abstract]
[hide abstract]
ABSTRACT: Measurements of the cross sections for charged current deep inelastic scattering in e
+
p collisions with a longitudinally polarised positron beam are presented. The measurements are based on a data sample with
an integrated luminosity of 132pb−1 collected with the ZEUS detector at HERA at a centre-of-mass energy of 318GeV. The total cross section is presented at positive
and negative values of the longitudinal polarisation of the positron beams. The single-differential cross-sections dσ/dQ
2, dσ/dx and dσ/dy are presented for Q
2>200GeV2. The reduced cross-section [(s)\tilde]\tilde{\sigma} is presented in the kinematic range 200<Q
2<60 000GeV2 and 0.006<x<0.562. The measurements agree well with the predictions of the Standard Model. The results are used to determine a lower
limit on the mass of a hypothetical right-handed W boson.
European Physical Journal C 04/2012; 70(4):945-963. · 3.63 Impact Factor
-
ZEUS Collaboration,
S. Chekanov,
M. Derrick,
S. Magill,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M. C. K. Mattingly,
P. Antonioli, [......],
E. Brownson,
D. D. Reeder,
A. A. Savin,
W. H. Smith,
H. Wolfe,
S. Bhadra,
C. D. Catterall,
G. Hartner,
U. Noor,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: The proton-dissociative diffractive photoproduction of J/ψ mesons has been studied in ep collisions with the ZEUS detector at HERA using an integrated luminosity of 112 pb−1. The cross section is presented as a function of the photon-proton centre-of-mass energy and of the squared four-momentum
transfer at the proton vertex. The results are compared to perturbative QCD calculations.
KeywordsLepton-Nucleon Scattering
Journal of High Energy Physics 04/2012; 2010(5):1-36. · 5.83 Impact Factor
-
The ZEUS Collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
M. Zolko,
D. S. Zotkin,
Z. Zulkapli
[show abstract]
[hide abstract]
ABSTRACT: Beauty production in deep inelastic scattering with events in which a muon and a jet are observed in the final state has been
measured with the ZEUS detector at HERA using an integrated luminosity of 114pb−1. The fraction of events with beauty quarks in the data was determined using the distribution of the transverse momentum of
the muon relative to the jet. The cross section for beauty production was measured in the kinematic range of photon virtuality,
Q
2>2GeV2, and inelasticity, 0.05<y<0.7, with the requirement of a muon and a jet. Total and differential cross sections are presented and compared to QCD predictions.
The beauty contribution to the structure function F
2 was extracted and is compared to theoretical predictions.
European Physical Journal C 04/2012; 69(3):347-360. · 3.63 Impact Factor
-
The ZEUS Collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
M. Zolko,
D. S. Zotkin,
Z. Zulkapli
[show abstract]
[hide abstract]
ABSTRACT: 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 374pb−1. The measurement was performed at large values of the photon virtuality, Q
2, between 125 and 20 000GeV2. 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, EjetT,BE^{\rm jet}_{T,{\rm B}}, to be larger than 8GeV. In addition, the invariant mass of the dijet system, MjjM_{\rm jj}, was required to be greater than 20GeV. The cross sections are described by the predictions of next-to-leading-order QCD.
European Physical Journal C 04/2012; 70(4):965-982. · 3.63 Impact Factor
-
The ZEUS Collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
M. Zolko,
D. S. Zotkin,
Z. Zulkapli
[show abstract]
[hide abstract]
ABSTRACT: The production of beauty quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared Q
2>10GeV2, using an integrated luminosity of 363 pb−1. The beauty events were identified using electrons from semileptonic b decays with a transverse momentum 0.9 < pTe < 80.9 < p_{T}^{e} < 8GeV 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.
European Physical Journal C 04/2012; 71(2):1-15. · 3.63 Impact Factor
-
and ZEUS collaborations,
F. D. Aaron,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
M. Al-daya Martin,
C. Alexa,
V. Andreev,
S. Antonelli, [......],
Z. Zhang,
B. O. Zhautykov,
A. Zhokin,
C. Zhou,
A. Zichichi,
T. Zimmermann,
H. Zohrabyan,
M. Zolko,
F. Zomer,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: A combination is presented of the inclusive deep inelastic cross sections measured by the H1 and ZEUS Collaborations in neutral
and charged current unpolarised e
±
p scattering at HERA during the period 1994-2000. The data span six orders of magnitude in negative four-momentum-transfer
squared, Q
2, and in Bjorken x. The combination method used takes the correlations of systematic uncertainties into account, resulting in an improved accuracy.
The combined data are the sole input in a NLO QCD analysis which determines a new set of parton distributions, HERAPDF1.0,
with small experimental uncertainties. This set includes an estimate of the model and parametrisation uncertainties of the
fit result.
Journal of High Energy Physics 04/2012; 2010(1):1-63. · 5.83 Impact Factor
-
ZEUS collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo,
V. Aushev, [......],
R. Yoshida,
C. Youngman, A. F. Żarnecki,
O. Zenaiev,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
M. Zolko,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: Charged particle production has been studied in neutral current deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 0.44 fb−1. Distributions of scaled momenta in the Breit frame are presented for particles in the current fragmentation region. The
evolution of these spectra with the photon virtuality, Q
2, is described in the kinematic region 10 < Q
2 < 41000Ge V2. Next-to-leading-order and modified leading-log-approximation QCD calculations as well as predictions from Monte Carlo models
are compared to the data. The results are also compared to e
+
e
− annihilation data. The dependences of the pseudorapidity distribution of the particles on Q
2 and on the energy in the γp system, W, are presented and interpreted in the context of the hypothesis of limiting fragmentation.
KeywordsLepton-Nucleon Scattering
Journal of High Energy Physics 04/2012; 2010(6):1-42. · 5.83 Impact Factor
-
The and ZEUS collaborations,
F. D. Aaron,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
M. Aldaya Martin,
C. Alexa,
V. Andreev,
S. Antonelli, [......],
B. O. Zhautykov,
A. Zhokin,
C. Zhou,
A. Zichichi,
T. Zimmermann,
H. Zohrabyan,
M. Zolko,
F. Zomer,
D. S. Zotkin,
R. Zus
[show abstract]
[hide abstract]
ABSTRACT: A search for events containing an isolated electron or muon and missing transverse momentum produced in e
±
p collisions is performed with the H1 and ZEUS detectors at HERA. The data were taken in the period 1994–2007 and correspond
to an integrated luminosity of 0.98 fb−1. The observed event yields are in good overall agreement with the Standard Model prediction, which is dominated by single
W production. In the e
+
p data, at large hadronic transverse momentum P
T
X
> 25GeV, a total of 23 events are observed compared to a prediction of 14.0 ± 1.9. The total single W boson production cross section is measured as 1.06 ± 0.16 (stat.) ± 0.07 (sys.) pb, in agreement with an Standard Model (SM)
expectation of 1.26 ± 0.19 pb.
KeywordsLepton-Nucleon Scattering
Journal of High Energy Physics 04/2012; 2010(3):1-19. · 5.83 Impact Factor
-
ZEUS Collaboration,
S. Chekanov,
M. Derrick,
S. Magill,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M. C. K. Mattingly,
P. Antonioli, [......],
W. H. Smith,
H. Wolfe,
S. Bhadra,
C. D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: The production of excited charm, D
1(2420)0 and D
2*(2460)0, and charm-strange, D
s1(2536)±, mesons in ep collisions was measured with the ZEUS detector at HERA using an integrated luminosity of 126pb−1. Masses, widths and helicity parameters were determined. The measured yields were converted to the rates of c quarks hadronising as a given excited charm meson and to the ratios of the dominant D
2*(2460)0 and D
s1(2536)± branching fractions. A search for the radially excited charm meson, D
*′(2640)±, was also performed. The results are compared with those measured previously and with theoretical expectations.
European Physical Journal C 04/2012; 60(1):25-45. · 3.63 Impact Factor
-
The ZEUS Collaboration,
S. Chekanov,
M. Derrick,
S. Magill,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M. C. K. Mattingly,
P. Antonioli, [......],
W. H. Smith,
H. Wolfe,
S. Bhadra,
C. D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: 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 318GeV. 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 GeV2. The double-differential cross-section d
2
σ/dxdQ
2 is presented in the kinematic range 280<Q
2<30 000 GeV2 and 0.015<x<0.65. The measured cross sections are compared with the predictions of the Standard Model.
European Physical Journal C 04/2012; 61(2):223-235. · 3.63 Impact Factor
-
The ZEUS Collaboration,
S. Chekanov,
M. Derrick,
S. Magill,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M. C. K. Mattingly,
P. Antonioli, [......],
W. H. Smith,
H. Wolfe,
S. Bhadra,
C. D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: 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
x[(F3)\tilde]x\tilde{F_{3}}
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.
European Physical Journal C 04/2012; 62(4):625-658. · 3.63 Impact Factor
-
The ZEUS Collaboration,
S. Chekanov,
M. Derrick,
S. Magill,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M. C. K. Mattingly,
P. Antonioli, [......],
W. H. Smith,
H. Wolfe,
S. Bhadra,
C. D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: The production of D
±- and D
0-mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6pb−1. The measurements cover the kinematic range 5<Q
2<1000 GeV2, 0.02<y<0.7, 1.5<p
T
D
<15 GeV and |η
D
|<1.6. Combinatorial background to the D-meson signals is reduced by using the ZEUS microvertex detector to reconstruct displaced secondary vertices. Production cross
sections are compared with the predictions of next-to-leading-order QCD, which is found to describe the data well. Measurements
are extrapolated to the full kinematic phase space in order to obtain the open-charm contribution,
F2c[`(c)]F_{2}^{c\bar{c}}
, to the proton structure function,F
2.
European Physical Journal C 04/2012; 63(2):171-188. · 3.63 Impact Factor
-
The ZEUS Collaboration,
S. Chekanov,
M. Derrick,
S. Magill,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M. C. K. Mattingly,
P. Antonioli, [......],
W. H. Smith,
H. Wolfe,
S. Bhadra,
C. D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: Subjet distributions were measured in neutral current deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 81.7pb−1. Jets were identified using the k
T
cluster algorithm in the laboratory frame. Subjets were defined as jet-like substructures identified by a reapplication of
the cluster algorithm at a smaller value of the resolution parameter ycuty_{\rm cut}. Measurements of subjet distributions for jets with exactly two subjets for ycut=0.05y_{\rm cut}=0.05 are presented as functions of observables sensitive to the pattern of parton radiation and to the colour coherence between
the initial and final states. Perturbative QCD predictions give an adequate description of the data.
European Physical Journal C 04/2012; 63(4):527-548. · 3.63 Impact Factor
-
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo,
V. Aushev, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
M. Zolko,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: Three-jet production in deep inelastic ep scattering and photoproduction was investigated with the ZEUS detector at HERA using an integrated luminosity of up to 127 pb-1. Measurements of differential cross sections are presented as functions of angular correlations between the three jets in the final state and the proton-beam direction. These correlations provide a stringent test of perturbative QCD and show sensitivity to the contributions from different color configurations. Fixed-order perturbative calculations assuming the values of the color factors CF, CA, and TF as derived from a variety of gauge groups were compared to the measurements to study the underlying gauge group symmetry. The measured angular correlations in the deep inelastic ep scattering and photoproduction regimes are consistent with the admixture of color configurations as predicted by SU(3) and disfavour other symmetry groups, such as SU(N) in the limit of large N.
Phys. Rev. D. 03/2012; 85(5).
-
ZEUS Collaboration,
H Abramowicz,
I Abt,
L Adamczyk,
M Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M Arneodo, [......],
L Zawiejski,
O. Zenaiev,
W Zeuner,
B.O. Zhautykov,
N. Zhmak,
C Zhou,
A. Zichichi,
Z. Zolkapli,
M. Zolko,
D.S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: The exclusive electroproduction of two pions in the mass range 0.4 <
M{\pi}{\pi} < 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 < Q2 < 80 GeV2, 32 < W < 180 GeV and |t| < 0.6 GeV2, where Q2 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{\pi}{\pi})|, assuming that the studied mass range includes
the contributions of the {\rho}, {\rho}' and {\rho}" vector-meson states. The
masses and widths of the resonances were obtained and the Q2 dependence of the
cross-section ratios {\sigma}({\rho}' \rightarrow {\pi}{\pi})/{\sigma}({\rho})
and {\sigma}({\rho}" \rightarrow {\pi}{\pi})/{\sigma}({\rho}) was extracted.
The pion form factor obtained in the present analysis is compared to that
obtained in e+e- \rightarrow {\pi}+{\pi}-.
11/2011;
-
ZEUS Collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
M. Zolko,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: A search for single-top production, $ep \rightarrow etX$, has been performed
with the ZEUS detector at HERA using data corresponding to an integrated
luminosity of $0.37\fbi$. No evidence for top production was found, consistent
with the expectation from the Standard Model. Limits were computed for
single-top production via flavour changing neutral current transitions. The
result was combined with a previous ZEUS result yielding a total luminosity of
0.50fb-1. A 95% credibility level upper limit of 0.13 pb was obtained for the
cross section at the centre-of-mass energy of $\sqrt{s}=315\gev$.
11/2011;
-
ZEUS collaboration,
H. Abramowicz,
I. Abt,
L. Adamczyk,
M. Adamus,
R. Aggarwal,
S. Antonelli,
P. Antonioli,
A. Antonov,
M. Arneodo, [......],
L. Zawiejski,
O. Zenaiev,
W. Zeuner,
B. O. Zhautykov,
N. Zhmak,
C. Zhou,
A. Zichichi,
Z. Zolkapli,
M. Zolko,
D. S. Zotkin
[show abstract]
[hide abstract]
ABSTRACT: The exclusive photoproduction reaction gamma p -> Upsilon(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 Q^2<1 GeV^2, where W is the photon-proton centre-of-mass energy and Q^2
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 +2.0 -1.3 (stat.) +0.5 -0.6 (syst.)
GeV^-2. This constitutes the first measurement of the t dependence of the gamma
p -> Upsilon(1S) p cross section.
11/2011;
