Inclusive jet production is studied in neutral current deep-inelastic positron-proton scattering at large four momentum transfer squared Q(2) > 150 GeV2 with the H1 detector at HERA. Single and ...double differential inclusive jet cross sections are measured as a function of Q(2) and of the transverse energy E-T of the jets in the Breit frame. The measurements are found to be well described by calculations at next-to-leading order in perturbative QCD. The running of the strong coupling is demonstrated and the value of alpha(s)(M-Z) is determined. The ratio of the inclusive jet cross section to the inclusive neutral current cross section is also measured and used to extract a precise value for ces (M-Z) = 0.1193 +/- 0.0014(exp.)(-0.0030)(+0.0047) (th.) +/- 0.0016(pdf). (c) 2007 Elsevier BX All rights reserved.
The cross section for
in photoproduction is measured with the H1 detector at the
ep
-collider HERA. The decay channel
is selected by identifying the semi-electronic decays of the
b
-quarks. The total ...production cross section is measured in the kinematic range given by the photon virtuality
Q
2
≤1 GeV
2
, the inelasticity 0.05≤
y
≤0.65 and the pseudorapidity of the
b
-quarks
. The differential production cross section is measured as a function of the average transverse momentum of the beauty quarks 〈
P
T
(
b
)〉 down to the threshold. The results are compared to next-to-leading-order QCD predictions.
Charged particle production in deep-inelastic
ep
scattering is measured with the H1 detector at HERA. The kinematic range of the analysis covers low photon virtualities, 5<
Q
2
<100 GeV
2
, and small ...values of Bjorken-
x
, 10
−4
<
x
<10
−2
. The analysis is performed in the hadronic centre-of-mass system. The charged particle densities are measured as a function of pseudorapidity (
η
∗
) and transverse momentum (
) in the range 0<
η
∗
<5 and
in bins of
x
and
Q
2
. The data are compared to predictions from different Monte Carlo generators implementing various options for hadronisation and parton evolutions.
A search for excited electrons is performed using the full e±p data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb−1. The electroweak decays of excited ...electrons e∗→eγ, e∗→eZ and e∗→νW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e∗ production cross sections and on the ratio f/Λ of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e∗ production via contact interactions is also addressed for the first time in ep collisions.
A search for second and third generation scalar and vector leptoquarks produced in ep collisions via the lepton flavour violating processes ep→μX and ep→τX is performed by the H1 experiment at HERA. ...The full data sample taken at a centre-of-mass energy s=319 GeV is used for the analysis, corresponding to an integrated luminosity of 245 pb−1 of e+p and 166 pb−1 of e−p collision data. No evidence for the production of such leptoquarks is observed in the H1 data. Leptoquarks produced in e±p collisions with a coupling strength of λ=0.3 and decaying with the same coupling strength to a muon–quark pair or a tau–quark pair are excluded at 95% confidence level up to leptoquark masses of 712 GeV and 479 GeV, respectively.
Deep-inelastic positron-proton scattering events at low photon virtuality,
Q
2
, with a forward jet, produced at small angles with respect to the proton beam, are measured with the H1 detector at ...HERA. A subsample of events with an additional jet in the central region is also studied. For both samples, differential cross sections and normalised distributions are measured as a function of the azimuthal angle difference, Δ
ϕ
, between the forward jet and the scattered positron in bins of the rapidity distance,
Y
, between them. The data are compared to predictions of Monte Carlo generators based on different evolution approaches as well as to next-to-leading order calculations in order to test the sensitivity to QCD evolution mechanisms.
Cross sections for elastic photoproduction of
J/
ψ and
ϒ mesons are presented. For
J/
ψ mesons the dependence on the photon-proton centre-of-mass energy
W
γp
is analysed in an extended range with ...respect to previous measurements of
26≤W
γp≤285
GeV
. The measured energy dependence is parameterized as
σ
γp
∝
W
γp
δ
with
δ=0.83±0.07. The differential cross section
dσ/
dt for
J/
ψ mesons is derived, its dependence on
W
γp
and on
t is analysed and the effective trajectory (in terms of Regge theory) is determined to be
α(
t)=(1.27±0.05)+(0.08±0.17)·
t/GeV
2. Models based on perturbative QCD and on pomeron exchange are compared to the data.
The process of charm quark fragmentation is studied using
D
* ±
meson production in deep-inelastic scattering as measured by the H1 detector at HERA. The parameters of fragmentation functions are ...extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution of partons together with string fragmentation and particle decays. Additionally, they are determined for a next-to-leading order QCD calculation in the fixed flavour number scheme using the independent fragmentation of charm quarks to
D
* ±
mesons. Two different regions of phase space are investigated defined by the presence or absence of a jet containing the
D
* ±
meson in the event. The fragmentation parameters extracted for the two phase space regions are found to be different.
Inclusive jet, dijet and trijet differential cross sections are measured in neutral current deep-inelastic scattering for exchanged boson virtualities ... using the H1 detector at HERA. The data were ...taken in the years 2003 to 2007 and correspond to an integrated luminosity of ... Double differential Jet cross sections are obtained using a regularised unfolding procedure. They are presented as a function of ... and the transverse momentum of the jet, ..., and as a function of ... and the proton's longitudinal momentum fraction, ..., carried by the parton participating in the hard interaction. In addition normalised double differential jet cross sections are measured as the ratio of the jet cross sections to the inclusive neutral current cross sections in the respective ... bins of the jet measurements. Compared to earlier work, the measurements benefit from an improved reconstruction and calibration of the hadronic final state. The cross sections are compared to perturbative QCD calculations in next-to-leading order and are used to determine the running coupling and the value of the strong coupling constant as ...
Measurements are presented of diffractive open charm production at HERA. The event topology is given by ep→eXY where the system X contains at least one charmed hadron and is well separated by a large ...rapidity gap from a leading low-mass proton remnant system Y. Two analysis techniques are used for the cross section measurements. In the first, the charm quark is tagged by the reconstruction of a D*±(2010) meson. This technique is used in deep-inelastic scattering (DIS) and photoproduction (γp). In the second, a method based on the displacement of tracks from the primary vertex is used to measure the open charm contribution to the inclusive diffractive cross section in DIS. The measurements are compared with next-to-leading order QCD predictions based on diffractive parton density functions previously obtained from a QCD analysis of the inclusive diffractive cross section at H1. A good agreement is observed in the full kinematic regime, which supports the validity of QCD factorization for open charm production in diffractive DIS and γp.
PDF
