-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
N. Pavel, [......],
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
M. Soares,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: A search for stop production in R-parity-violating supersymmetry has been performed in e+p interactions with the ZEUS detector at HERA, using an integrated luminosity of 65pb-1. At HERA, the R-parity-violating coupling λ’ allows resonant squark production, e+d®[(q)\tilde]e^+d\to\tilde{q}. Since the lowest-mass squark state in most supersymmetry models is the light stop, [(t)\tilde]\tilde{t}, this search concentrated on production of [(t)\tilde]\tilde{t}, followed either by a direct R-parity-violating decay, or by the gauge decay to b[(c)\tilde]+1b\tilde{\chi}^+_{1}. No evidence for stop production was found and limits were set on λ’131 as a function of the stop mass in the framework of the minimal supersymmetric standard model. The results have also been
interpreted in terms of constraints on the parameters of the minimal supergravity model.
European Physical Journal C 04/2012; 50(2):269-281. · 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, [......],
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
-
S Chekanov,
M Derrick,
S Magill,
B Musgrave,
D Nicholass,
J Repond,
R Yoshida,
M C K Mattingly,
P Antonioli,
G Bari, [......],
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: Inclusive K_{S};{0}K_{S};{0} production in ep collisions at the DESY ep collider HERA was studied with the ZEUS detector using an integrated luminosity of 0.5 fb;{-1}. Enhancements in the mass spectrum were observed and are attributed to the production of f_{2}(1270)/a_{2};{0}(1320), f_{2};{'}(1525) and f_{0}(1710). Masses and widths were obtained using a fit which takes into account theoretical predictions based on SU(3) symmetry arguments, and are consistent with the Particle Data Group values. The f_{0}(1710) state, which has a mass consistent with a glueball candidate, was observed with a statistical significance of 5 standard deviations. However, if this state is the same as that seen in gammagamma-->K_{S};{0}K_{S};{0}, it is unlikely to be a pure glueball state.
Physical Review Letters 09/2008; 101(11):112003. · 7.37 Impact Factor
-
S. Chekanov,
M. Derrick,
S. Magill,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
M. Jechow,
N. Pavel, [......],
H. Wolfe,
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity
of 77.2pb-1. The measurements were made in the kinematic range Q2 < 1GeV2, 0.20<y<0.85 and xIP<0.025, where Q2 is the photon virtuality, y is the inelasticity and xIP is the fraction of the proton momentum taken by the diffractive exchange. The two jets with the highest transverse energy,
ET
jet, were required to satisfy ET
jet>7.5 and 6.5GeV, respectively, and to lie in the pseudorapidity range -1.5<ηjet<1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive
parton distributions of the proton.
European Physical Journal C 04/2008; 55(2):177-191. · 3.63 Impact Factor
-
S. Chekanov, M. Derrick, S. Magill, B. Musgrave, D. Nicholass,
M. C. K. Mattingly,
N. Pavel M. Jechow,
S. Antonelli,
P. Antonioli,
G. Bari,
M. Basile,
L. Bellagamba,
M. Bindi,
D. Boscherini, [......],
M. Rosin,
E. Brownson, T. Danielson, A. Everett, D. Kçira, D. D. Reeder,
S. Bhadra,
C. D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: The cross section for high-ET dijet production in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 81.8 pb-1. The events were required to have a virtuality of the incoming photon, Q2, of less than 1 GeV2 and a photon-proton center-of-mass energy in the range 142<Wγp<293 GeV. Events were selected if at least two jets satisfied the transverse-energy requirements of ETjet1>20 GeV and ETjet2>15 GeV and pseudorapidity (with respect to the proton beam direction) requirements of -1<ηjet1,2<3, with at least one of the jets satisfying -1<ηjet<2.5. The measurements show sensitivity to the parton distributions in the photon and proton and to effects beyond next-to-leading order in QCD. Hence these data can be used to constrain further the parton densities in the proton and photon.
Phys. Rev. D. 10/2007; 76(7).
-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
N. Pavel, [......],
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
M. Soares,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The distribution of the azimuthal angle of charged and neutral hadrons relative to the lepton plane has been studied for neutral
current deep inelastic ep scattering using an integrated luminosity of 45pb-1 taken with the ZEUS detector. The kinematic range is 100<Q2<8000GeV2, 0.2<y<0.8 and 0.01<x<0.1 where Q2 is the virtuality of the exchanged boson, y is the inelasticity and x is the Bjorken variable. The measurements were made
in the hadronic centre-of-mass system. The analysis exploits the energy-flow method, which allows the measurement to be made
over a larger range of pseudorapidity compared to previous results. The dependence of the moments of the azimuthal distributions
on the pseudorapidity and minimum transverse energy of the final-state hadrons are presented. Although the predictions from
next-to-leading-order QCD describe the data better than do the Monte Carlo models incorporating leading-logarithm parton showers,
they still fail to describe the magnitude of the asymmetries. This suggests that higher-order calculations may be necessary
to describe these data.
European Physical Journal C 06/2007; 51(2):289-299. · 3.63 Impact Factor
-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
M. Jechow, [......],
H. Wolfe,
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The production of the neutral strange hadrons K0
S, Λ and Λ̄ has been measured in ep collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative
yields of strange and charged light hadrons, Λ (Λ̄) asymmetry and polarization have been measured in three kinematic regions:
Q2 > 25GeV2; 5 < Q2 < 25GeV2; and in photoproduction (Q2≃0). In photoproduction the presence of two hadronic jets, each with at least 5GeV transverse energy, was required. The measurements
agree in general with Monte Carlo models and are consistent with measurements made at e+e- colliders, except for an enhancement of baryon relative to meson production in photoproduction.
European Physical Journal C 05/2007; 51(1):1-23. · 3.63 Impact Factor
-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
N. Pavel, [......],
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
M. Soares,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The production of beauty quarks with a D*±D^{\ast\pm} and a muon in the final state has been measured with the ZEUS detector at HERA using an integrated luminosity of 114pb-1. Low transverse-momentum thresholds for the muon and D* meson allow for a measurement of beauty production closer to the production threshold than previous measurements. The beauty
signal was extracted using the charge correlations and angular distributions of the muon with respect to the D* meson. Cross sections for photoproduction and deep inelastic scattering are somewhat higher than, but compatible with, next-to-leading-order
QCD predictions, and compatible with other measurements.
European Physical Journal C 03/2007; 50(2):299-314. · 3.63 Impact Factor
-
S. Chekanov,
M. Derrick,
S. Magill,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
M. Jechow,
N. Pavel, [......],
H. Wolfe,
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: Diffractive photoproduction of D*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6pb-1. The D* mesons were reconstructed in the kinematic range: transverse momentum pT(D*) > 1.9GeV and pseudorapidity |η(D*)|<1.6, using the decay D*+→D0π+
s followed by D0→K-π+(+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing
proton. Cross sections are reported for photon–proton centre-of-mass energies in the range 130 < W < 300GeV and for photon
virtualities Q2 < 1GeV2, in two ranges of the Pomeron fractional momentum xIP<0.035 and xIP<0.01. The relative contribution of diffractive events to the inclusive D*±(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various
parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.
European Physical Journal C 01/2007; 51(2):301-315. · 3.63 Impact Factor
-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
N. Pavel, [......],
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
M. Soares,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: A new method is employed to measure the neutral current cross section up to Bjorken-x values of one with the ZEUS detector
at HERA using an integrated luminosity of 65.1pb-1 for e+p collisions and 16.7pb-1 for e-p collisions at Ös=318GeV\sqrt{s}=318\,\mathrm{GeV} and 38.6pb-1 for e+p collisions at Ös=300GeV\sqrt{s}=300\,\mathrm{GeV}. Cross sections have been extracted for Q2≥648GeV2 and are compared to predictions using different parton density functions. For the highest x bins, the data have a tendency
to lie above the expectations using recent parton density function parametrizations.
European Physical Journal C 12/2006; 49(2):523-544. · 3.63 Impact Factor
-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
D. Nicholass,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
N. Pavel, [......],
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
M. Soares,
J. Standage,
J. Whyte,
The ZEUS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The photoproduction of prompt photons, together with an accompanying jet, has been studied in ep collisions at a centre-of-mass
energy of 318GeV with the ZEUS detector at HERA using an integrated luminosity of 77pb-1. Cross sections were measured for the transverse energy of the photon and the jet larger than 5 and 6GeV, respectively.
The differential γ+jet cross sections were reconstructed as functions of the transverse energy, pseudorapidity and xγ
obs, the fraction of the incoming photon momentum taken by the photon-jet system. Predictions based on leading-logarithm parton-shower
Monte Carlo models and next-to-leading-order (NLO) QCD generally underestimate the cross sections for the transverse energies
of prompt photons below 7GeV, while the kT-factorisation QCD calculation agrees with the data better. When the minimum transverse energy of prompt photons is increased
to 7GeV, both NLO QCD and the kT-factorisation calculations are in good agreement with the data.
European Physical Journal C 12/2006; 49(2):511-522. · 3.63 Impact Factor
-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
N. Pavel,
A.G. Yagües Molina, [......],
S. Dhawan,
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
M. Soares,
J. Standage,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: Differential inclusive jet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector using an integrated luminosity of 38.7 pb−1. The jets have been identified using the kT cluster algorithm in the longitudinally invariant inclusive mode in the laboratory frame; they have been selected with jet transverse energy, above 6 GeV and jet pseudorapidity, ηjet, between −1 and 3. Measurements of cross sections as functions of , Björken x and the photon virtuality, Q2, are presented. Three phase-space regions have been selected in order to study parton dynamics from the most global to the most restrictive region of forward-going (close to the proton-beam direction) jets at low x, where the effects of BFKL evolution might be present. The measurements have been compared to the predictions of leading-logarithm parton-shower Monte Carlo models and fixed-order perturbative QCD calculations. In the forward region, QCD calculations underestimate the data up to an order of magnitude at low x. An improved description of the data in this region is obtained by including QCD corrections, which account for the lowest-order -channel gluon-exchange diagrams, highlighting the importance of such terms in the parton dynamics at low x.
Physics Letters B.
-
S. Chekanov,
M. Derrick,
S. Magill,
S. Miglioranzi,
B. Musgrave,
J. Repond,
R. Yoshida,
M.C.K. Mattingly,
N. Pavel,
A.G. Yagües Molina, [......],
S. Dhawan,
S. Bhadra,
C.D. Catterall,
Y. Cui,
G. Hartner,
S. Menary,
U. Noor,
M. Soares,
J. Standage,
J. Whyte
[show abstract]
[hide abstract]
ABSTRACT: A search for pentaquarks decaying to Ξ−π− (Ξ−π+) and corresponding antiparticles has been performed with the ZEUS detector at HERA. The data sample consists of deep inelastic ep scattering events at centre-of-mass energies of 300 and 318 GeV, and corresponds to 121 pb−1 of integrated luminosity. A clear signal for Ξ0(1530)→Ξ−π+ was observed. However, no signal for any new baryonic state was observed at higher masses in either the Ξ−π− or Ξ−π+ channels. The searches in the antiparticle channels were also negative. Upper limits on the ratio of a possible () signal to the Ξ0(1530) signal were set in the mass range 1650–2350 MeV.
Physics Letters B.
-
H Abramowicz,
DESY Forschung Hochenergiephysik,
I Abt,
L Adamczyk,
M Adamus,
P.D. Allfrey,
S. Antonelli,
P. Antonioli,
A. Antonov,
M Arneodo, [......],
R Yoshida,
C Youngman,
M. Zambrana,
A.F. \.Zarnecki,
L Zawiejski,
W Zeuner,
B.O. Zhautykov,
C Zhou,
A. Zichichi,
D.S. Zotkin
Phys. Rev. D 78(2008),072001.
-
H Abramowicz,
I Abt,
L Adamczyk,
M Adamus,
V Adler,
P.D. Allfrey,
S. Antonelli,
P. Antonioli,
A. Antonov,
M Arneodo, [......],
R Yoshida,
C Youngman,
M. Zambrana,
A.F. \.Zarnecki,
L Zawiejski,
B.O. Zhautykov,
C Zhou,
A. Zichichi,
D.S. Zotkin,
S.A. Zotkin
Red Report (2007),.
-
H Abramowicz,
I Abt,
L Adamczyk,
M Adamus,
V Adler,
P.D. Allfrey,
S. Antonelli,
P. Antonioli,
A. Antonov,
M Arneodo, [......],
C Youngman,
M. Zambrana,
A.F. \.Zarnecki,
L Zawiejski,
W Zeuner,
B.O. Zhautykov,
C Zhou,
A. Zichichi,
D.S. Zotkin,
S.A. Zotkin
Red Report (2007),10.1016/j.nuclphysb.2007.08.021.
