Measurements are presented of single and double-differential dijet cross sections in diffractive photoproduction based on a data sample with an integrated luminosity of 47 pb
−1
. The events are of ...the type
ep
→
eXY
, where the hadronic system
X
contains at least two jets and is separated by a large rapidity gap from the system
Y
, which consists of a leading proton or low-mass proton excitation. The dijet cross sections are compared with QCD calculations at next-to-leading order and with a Monte Carlo model based on leading order matrix elements with parton showers. The measured cross sections are smaller than those obtained from the next-to-leading order calculations by a factor of about 0.6. This suppression factor has no significant dependence on the fraction
x
γ
of the photon four-momentum entering the hard subprocess. Ratios of the diffractive to the inclusive dijet cross sections are measured for the first time and are compared with Monte Carlo models.
Signals of QCD instanton-induced processes are searched for in neutral current deep-inelastic scattering at the electron-proton collider HERA in the kinematic region defined by the Bjorken-scaling ...variable $x > 10^{-3}$, the inelasticity $0.2< y < 0.7$ and the photon virtuality $150 < Q^2 < 15000$ GeV$^2$. The search is performed using H1 data corresponding to an integrated luminosity of ~$351$ pb$^{-1}$. No evidence for the production of QCD instanton-induced events is observed. Upper limits on the cross section for instanton-induced processes between $1.5$~pb and $6$~pb, at $95\%$~ confidence level, are obtained depending on the kinematic domain in which instantons could be produced. Compared to earlier publications, the limits are improved by an order of magnitude and for the first time are challenging theory predictions.
The asymmetric synthesis of novel non-proteinogenic β-heterocyclic α-amino acids via the diastereoselective conjugate addition of heterocyclic nucleophiles to the dehydroalanine moiety of chiral ...Ni(II) complexes has been studied. The complexes were formed from the Schiff base of dehydroalanine using (S)-2-N-(N-benzylprolyl)aminobenzophenone as a chiral auxiliary. After decomposition of the complexes, the α-amino acids were isolated with 30–99% ee.
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.
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.
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.
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.
Measurements of cross sections for events with charm and beauty jets in deep inelastic scattering at HERA are presented. Events with jets of transverse energy
GeV and pseudorapidity −1.0<
η
jet
<1.5 ...in the laboratory frame are selected in the kinematic region of photon virtuality
Q
2
>6 GeV
2
and inelasticity variable 0.07<
y
<0.625. Measurements are also made requiring a jet in the Breit frame with
GeV. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189 pb
−1
. The numbers of charm and beauty jets are determined using variables reconstructed using the H1 vertex detector with which the impact parameters of the tracks to the primary vertex and the position of secondary vertices are measured. The measurements are compared with QCD predictions and with previous measurements where heavy flavours are identified using muons.
Events with high energy isolated electrons, muons or tau leptons and missing transverse momentum are studied using the full
e
±
p
data sample collected by the H1 experiment at HERA, corresponding to ...an integrated luminosity of 474 pb
−1
. Within the Standard Model, events with isolated leptons and missing transverse momentum mainly originate from the production of single
W
bosons. The total single
W
boson production cross section is measured as 1.14±0.25 (
stat
.)±0.14 (
sys
.) pb, in agreement with the Standard Model expectation. The data are also used to establish limits on the
WW
γ
gauge couplings and for a measurement of the
W
boson polarisation.
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