A
bstract
The production of beauty and charm quarks in
ep
interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5
< Q
2
<
1000 GeV
2
using an integrated ...luminosity of 354 pb
−1
. The beauty and charm content in events with at least one jet have been 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
Q
2
, Bjorken
x
, jet trans- verse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of
x
and
Q
2
. The running beauty-quark mass,
m
b
at the scale
m
b
, was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be
m
b
(
m
b
) = 4.07 ± 0.14 (fit)
− 0.07
+ 0.01
(mod.)
− 0.00
+ 0.05
(param.)
− 0.05
+ 0.08
(theo.) GeV.
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.
Measurements of open charm production cross sections in deep-inelastic
ep
scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections
for charm production are obtained ...in the kinematic range of photon virtuality 2.5≤
Q
2
≤2000 GeV
2
and Bjorken scaling variable 3⋅10
−5
≤
x
≤5⋅10
−2
. The combination method accounts for the correlations of the systematic uncertainties among the different data sets. The combined charm data together with the combined inclusive deep-inelastic scattering cross sections from HERA are used as input for a detailed NLO QCD analysis to study the influence of different heavy flavour schemes on the parton distribution functions. The optimal values of the charm mass as a parameter in these different schemes are obtained. The implications on the NLO predictions for
W
±
and
Z
production cross sections at the LHC are investigated. Using the fixed flavour number scheme, the running mass of the charm quark is determined.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The production of charm and beauty quarks in
ep
interactions has been measured with the ZEUS detector at HERA for squared four-momentum exchange
Q
2
>20 GeV
2
, using an integrated luminosity of ...126 pb
−1
. Charm and beauty quarks were identified through their decays into muons. Differential cross sections were measured for muon transverse momenta
and pseudorapidities −1.6<
η
μ
<2.3, as a function of
,
η
μ
,
Q
2
and Bjorken
x
. The charm and beauty contributions to the proton structure function
F
2
were also extracted. The results agree with previous measurements based on independent techniques and are well described by QCD predictions.
The production of beauty quarks in
ep
interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared
Q
2
>10 GeV
2
, using an integrated luminosity of 363 pb
−1
. ...The beauty events were identified using electrons from semileptonic
b
decays with a transverse momentum
GeV 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
.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 120 pb
−1
. The hadronic decay channels
D
+
→
K
S
0
π
+
, Λ
c
+
→
pK
S
...0
and Λ
c
+
→ Λ
π
+
, and their charge conjugates, were reconstructed. The presence of a neutral strange hadron in the final state reduces the combinatorial background and extends the measured sensitivity into the low transverse momentum region. The kinematic range is 0
< p
T
(
D
+
, Λ
c
+
) < 10 GeV, |
η
(
D
+
, Λ
c
+
)| < 1
.
6, 1.5 <
Q
2
< 1000 GeV
2
and 0
.
02 <
y
< 0.7. Inclusive and differential cross sections for the production of
D
+
mesons are compared to next-to-leading-order QCD predictions. The fraction of
c
quarks hadronising into Λ
c
+
baryons is extracted.
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.
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.
A
bstract
The production of beauty and charm quarks in
ep
interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5
< Q
2
<
1000 GeV
2
using an integrated ...luminosity of 354 pb
−1
. The beauty and charm content in events with at least one jet have been 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
Q
2
, Bjorken
x
, jet trans- verse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of
x
and
Q
2
. The running beauty-quark mass,
m
b
at the scale
m
b
, was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be
m
b
(
m
b
) = 4.07 ± 0.14 (fit)
− 0.07
+ 0.01
(mod.)
− 0.00
+ 0.05
(param.)
− 0.05
+ 0.08
(theo.) GeV.
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