The production of B ± mesons in proton-proton collisions at s√ = 7 TeV is studied using 35 pb−1 of data collected by the LHCb detector. The B ± mesons are reconstructed exclusively in the B ± → J/ψK ...± mode, with J/ψ → μ + μ −. The differential production cross-section is measured as a function of the B ± transverse momentum in the fiducial region 0 < p T < 40 GeV/c and with rapidity 2.0 < y < 4.5. The total cross-section, summing up B + and B −, is measured to be σ(pp → B ± X, 0 < p T < 40 GeV/c, 2.0 < y < 4.5) = 41.4 ± 1.5 (stat.) ± 3.1 (syst.) μb.
The production of isolated high-energy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of 326 pb−1. ...Measurements were made for exchanged photon virtualities, Q2, in the range 10 to 350 GeV2. The photons were measured in the transverse-energy and pseudorapidity ranges 4<ETγ<15 GeV and −0.7<ηγ<0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5<ETjet<35 GeV and −1.5<ηjet<1.8. Differential cross sections are presented as functions of these quantities. Perturbative QCD predictions give a reasonable description of the shape of the measured cross sections over most of the kinematic range, but the absolute normalisation is typically in disagreement by 20–30%.
Inclusive-jet and dijet differential cross sections have been measured in neutral current deep inelastic
ep scattering for exchanged boson virtualities
Q
2
>
125
GeV
2
with the ZEUS detector at ...HERA using an integrated luminosity of 82 pb
−1. Jets were identified in the Breit frame using the
k
T
cluster algorithm. Jet cross sections are presented as functions of several kinematic and jet variables. The results are also presented in different regions of
Q
2
. Next-to-leading-order QCD calculations describe the measurements well. Regions of phase space where the theoretical uncertainties are small have been identified. Measurements in these regions have the potential to constrain the gluon density in the proton when used as inputs to global fits of the proton parton distribution functions.
A
bstract
The cross sections for inelastic photoproduction of
J/ψ
and
ψ
′ mesons have been measured in
ep
collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb
−1
...collected in the period 1996–2007. The
ψ
′ to
J/
ψ cross section ratio was measured in the range 0
.
55
< z <
0
.
9 and 60
< W <
190 GeV as a function of
W
,
z
and
p
T
. Here
W
denotes the photon-proton centre-of-mass energy,
z
is the fraction of the incident photon energy carried by the meson and
p
T
is the transverse momentum of the meson with respect to the beam axis. The
J/ψ
cross sections were measured for 0
.
1
< z <
0
.
9, 60
< W <
240 GeV and
p
T
>
1 GeV. Theoretical predictions within the non-relativistic QCD framework including NLO colour-singlet and colour-octet contributions were compared to the data, as were predictions based on the
k
T
-factorisation approach.
Differential inclusive-jet cross sections have been measured for different jet radii in neutral current deep inelastic ep scattering for boson virtualities Q2>125 GeV2 with the ZEUS detector at HERA ...using an integrated luminosity of 81.7 pb−1. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally inclusive mode for different values of the jet radius R. Differential cross sections are presented as functions of Q2 and the jet transverse energy, ET,Bjet. The dependence on R of the inclusive-jet cross section has been measured for Q2>125 and 500 GeV2 and found to be linear with R in the range studied. Next-to-leading-order QCD calculations give a good description of the measurements for 0.5⩽R⩽1. A value of αs(MZ) has been extracted from the measurements of the inclusive-jet cross section dσ/dQ2 with R=1 for Q2>500 GeV2: αs(MZ)=0.1207±0.0014(stat.)−0.0033+0.0035(exp.)−0.0023+0.0022(th.). The variation of αs with ET,Bjet is in a good agreement with the running of αs as predicted by QCD.
Mean values and differential distributions of event-shape variables have been studied in neutral current deep inelastic scattering using an integrated luminosity of 82.2 pb
−1 collected with the ZEUS ...detector at HERA. The kinematic range is
80
<
Q
2
<
20
480
GeV
2
and
0.0024
<
x
<
0.6
, where
Q
2
is the virtuality of the exchanged boson and
x is the Bjorken variable. The data are compared with a model based on a combination of next-to-leading-order QCD calculations with next-to-leading-logarithm corrections and the Dokshitzer–Webber non-perturbative power corrections. The power-correction method provides a reasonable description of the data for all event-shape variables studied. Nevertheless, the lack of consistency of the determination of
α
s
and of the non-perturbative parameter of the model,
α
0
¯
, suggests the importance of higher-order processes that are not yet included in the model.
Three- and four-jet final states have been measured in photoproduction at HERA using the ZEUS detector with an integrated luminosity of
121
pb
−1
. The results are presented for jets with ...transverse energy
E
T
jet
>
6
GeV
and pseudorapidity
|
η
jet
|
<
2.4
, in the kinematic region given by the virtuality of the photon
Q
2
<
1
GeV
2
and the inelasticity
0.2
⩽
y
⩽
0.85
and in two mass regions defined as
25
⩽
M
n
j
<
50
GeV
and
M
n
j
⩾
50
GeV
, where
M
n
j
is the invariant mass of the
n-jet system. The four-jet photoproduction cross section has been measured for the first time and represents the highest-order process studied at HERA. Both the three- and four-jet cross sections have been compared with leading-logarithmic parton-shower Monte Carlo models, with and without multi-parton interactions. The three-jet cross sections have been compared to an
O
(
α
α
s
2
)
perturbative QCD calculation.
A search for events with an isolated high-energy lepton and large missing transverse momentum has been performed with the ZEUS detector at HERA using a total integrated luminosity of 504 pb−1. The ...results agree well with Standard Model predictions. The cross section for production of single W bosons in electron–proton collisions with unpolarised electrons is measured to be 0.89−0.22+0.25(stat.)±0.10(syst.)pb.
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