71 research outputs found
Search for Doubly-Charged Higgs Boson Production at HERA
A search for the single production of doubly-charged Higgs bosons H^{\pm \pm}
in ep collisions is presented. The signal is searched for via the Higgs decays
into a high mass pair of same charge leptons, one of them being an electron.
The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment
at HERA. No evidence for doubly-charged Higgs production is observed and mass
dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs
boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only
decays into an electron and a muon via a coupling of electromagnetic strength
h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the
H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged
Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3,
masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl
Study of Charm Fragmentation into D^{*\pm} Mesons in Deep-Inelastic Scattering at HERA
The process of charm quark fragmentation is studied using meson
production in deep-inelastic scattering as measured by the H1 detector at HERA.
Two different regions of phase space are investigated defined by the presence
or absence of a jet containing the meson in the event. 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
mesons.Comment: 33 pages, submitted to EPJ
Jet production in ep collisions at high Q(2) and determination of alpha(s)
The production of jets is studied in deep-inelastic e(+/-) p scattering at large negative four momentum transfer squared 150 LT Q(2) LT 15000 GeV2 using HERA data taken in 1999-2007, corresponding to an integrated luminosity of 395 pb(-1). Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q(2), jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurement
Search for Contact Interactions in Collisions at HERA
A search for physics beyond the Standard Model in neutral current deep
inelastic scattering at high negative four-momentum transfer squared Q^2 is
performed in e^{\pm}p collisions at HERA. The differential cross section
ds/dQ^2, measured using the full H1 data sample corresponding to an integrated
luminosity of 446 pb^{-1}, is compared to the Standard Model prediction. No
significant deviation is observed. Limits on various models predicting new
phenomena at high Q^2 are derived. For general four-fermion eeqq contact
interaction models, lower limits on the compositeness scale Lambda are set in
the range 3.6 TeV to 7.2 TeV. Leptoquarks with masses M_{LQ} and couplings
lambda are constrained to M_{LQ}/lambda > 0.41-1.86 TeV and limits on squarks
in R-parity violating supersymmetric models are derived. A lower limit on the
gravitational scale in (4+n) dimensions of M_{S} > 0.9 TeV is established for
low-scale quantum gravity effects in models with large extra dimensions. For
the light quark radius an upper bound of R_q< 0.65 10^{-18} m is determined.Comment: 20 pages, 6 figures and 5 table
Search for First Generation Leptoquarks in Collisions at HERA
A search for first generation scalar and vector leptoquarks produced in ep
collisions is performed by the H1 experiment at HERA. The full H1 data sample
is used in the analysis, corresponding to an integrated luminosity of 446
pb^-1. No evidence for the production of leptoquarks is observed in final
states with a large transverse momentum electron or with large missing
transverse momentum, and constraints on leptoquark models are derived. For
leptoquark couplings of electromagnetic strength lambda=0.3, first generation
leptoquarks with masses up to 800 GeV are excluded at 95% confidence level.Comment: Revised version, accepted by Journal. 18 pages, 5 figures, 1 tabl
Measurement of Leading Neutron Production in Deep-Inelastic Scattering at HERA
The production of leading neutrons, where the neutron carries a large
fraction x_L of the incoming proton's longitudinal momentum, is studied in
deep-inelastic positron-proton scattering at HERA. The data were taken with the
H1 detector in the years 2006 and 2007 and correspond to an integrated
luminosity of 122 pb^{-1}. The semi-inclusive cross section is measured in the
phase space defined by the photon virtuality 6 < Q^2 < 100 GeV^2, Bjorken
scaling variable 1.5x10^{-4} < x < 3x10^{-2}, longitudinal momentum fraction
0.32 < x_L < 0.95 and neutron transverse momentum p_T < 0.2 GeV. The leading
neutron structure function, F_2^{LN(3)}(Q^2,x,x_L), and the fraction of
deep-inelastic scattering events containing a leading neutron are studied as a
function of Q^2, x and x_L. Assuming that the pion exchange mechanism dominates
leading neutron production, the data provide constraints on the shape of the
pion structure function.Comment: 30 pages, 9 figure
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