The production of excited charm,
D
1
(2420)
0
and
D
2
*
(2460)
0
, and charm-strange,
D
s
1
(2536)
±
, mesons in
ep
collisions was measured with the ZEUS detector at HERA using an integrated ...luminosity of 126 pb
−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
s
1
(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.
The production of D±- and D0-mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb−1. The measurements cover the kinematic range 5<Q2<1000 GeV2, ...0.02<y<0.7, 1.5<pTD<15 GeV and |ηD|<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, \(F_{2}^{c\bar{c}}\), to the proton structure function, F2.
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.
Photoproduction of beauty and charm quarks in events with at least two jets has been measured with the ZEUS detector at HERA using an integrated luminosity of 133 pb
−1
. The fractions of jets ...containing
b
and
c
quarks were 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 jet transverse momentum,
, and pseudorapidity,
η
jet
, were measured. The data are compared with previous measurements and are well described by next-to-leading-order QCD predictions.
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.
The exclusive photoproduction reaction gamma p arrow right Upsilon ( 1 S ) 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 - 1.3 + 2.0 ( stat . ) - 0.6 + 0.5 ( syst . ) GeV - 2 . This constitutes the first measurement of the t dependence of the gamma p arrow right Upsilon ( 1 S ) p cross section.
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 V
2
. 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 γ
p
system,
W
, are presented and interpreted in the context of the hypothesis of limiting fragmentation.
Subjet distributions were measured in neutral current deep inelastic
ep
scattering with the ZEUS detector at HERA using an integrated luminosity of 81.7 pb
−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
. Measurements of subjet distributions for jets with exactly two subjets for
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.
Study of taupair production at HERA Aggarwal, R.; Antonelli, S.; Antonov, A. ...
The journal of high energy physics,
02/2011, Letnik:
2011, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A study of events containing two tau leptons with high transverse momentum has been performed with the ZEUS detector at HERA, using a data sample corresponding to an integrated luminosity of 0.33 fb
...−1
. The tau candidates were identified from their decays into electrons, muons or hadronic jets. The number of tau-pair candidates has been compared with the prediction from the Standard Model, where the largest contribution is expected from Bethe-Heitler processes. The total visible cross section was extracted. Standard Model expectations agree well with the measured distributions, also at high invariant mass of the tau pair.
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