2,027 research outputs found
Charge asymmetry in W + jets production at the LHC
The charge asymmetry in W + jets production at the LHC can serve to calibrate
the presence of New Physics contributions. We study the ratio {\sigma}(W^+ + n
jets)/{\sigma}(W^- + n jets) in the Standard Model for n <= 4, paying
particular attention to the uncertainty in the prediction from higher-order
perturbative corrections and uncertainties in parton distribution functions. We
show that these uncertainties are generally of order a few percent, making the
experimental measurement of the charge asymmetry ratio a particularly useful
diagnostic tool for New Physics contributions.Comment: 13 pages, 7 figures. Reference added. Slightly modified tex
Use of W-Boson Longitudinal-Transverse Interference in Top Quark Spin-Correlation Functions: II
This continuation of the derivation of general beam-referenced stage-two
spin-correlation functions is for the analysis of top-antitop pair-production
at the Tevatron and at the Large Hadron Collider. Both the gluon-production and
the quark-production contributions are included for the
charged-lepton-plus-jets reaction p p or p bar{p} --> t bar{t} --> (W^+ b)(W^-
bar{b}) --> (l^{+} nu b)(W^- bar{b}). There is a simple 4-angle beam-referenced
spin-correlation function for determination of the relative sign of, or for
measurement of a possible non-trivial phase between the two dominant helicity
amplitudes for t --> W^{+} b decay. There is an analogous function and tests
for bar{t} --> W^{-} bar{b} decay. This signature requires use of the (t
bar{t}) c.m.-energy of the hadronically decaying W-boson, or the kinematically
equivalent cosine of the polar-angle of W-boson emission in the anti-top (top)
decay frame. Spinors and their outer-products are constructed so that the
helicity-amplitude phase convention of Jacob & Wick can be used throughout for
the fixing of the signs associated with this large W-boson
longitudinal-transverse interference effect.Comment: Continuation of hep-ph/0506240 to include gluon-production
contribution; 3 "postscript" figures. Equation numbers as in
published-on-line EPJ
Squark Mixing in Electron-Positron Reactions
Squark mixing plays a large role in the phenomenology of the minimal
supersymmetric standard model, determining the mass of the lightest Higgs boson
and the electroweak interactions of the squarks themselves. We examine how
mixing may be investigated in high energy reactions, both at LEP-II
and the proposed linear collider. In particular, off-diagonal production of one
lighter and one heavier squark allows one to measure the squark mixing angle,
and would allow one to test the mass relations for the light Higgs boson. In
some cases off-diagonal production may provide the best prospects to discover
supersymmetry. In the context of the light bottom squark scenario, we show that
existing data from LEP-II should show definitive evidence for the heavier
bottom squark provided that its mass GeV.Comment: 22 pages, latex, 6 figure
Soft gluons and superleading logarithms in QCD
After a brief introduction to the physics of soft gluons in QCD we present a
surprising prediction. Dijet production in hadron-hadron collisions provides
the paradigm, i.e. h_1 +h_2 \to jj+X. In particular, we look at the case where
there is a restriction placed on the emission of any further jets in the region
in between the primary (highest p_T) dijets. Logarithms in the ratio of the jet
scale to the veto scale can be summed to all orders in the strong coupling.
Surprisingly, factorization of collinear emissions fails at scales above the
veto scale and triggers the appearance of double logarithms in the hard
sub-process. The effect appears first at fourth order relative to the leading
order prediction and is subleading in the number of colours.Comment: Talk presented at the workshop "New Trends in HERA Physics", Ringberg
Castle, Tegernsee, 5-10 October 200
Phase Transition Study of Superconducting Microstructures
The presented results are part of a feasibility study of superheated
superconducting microstructure detectors. The microstructures (dots) were
fabricated using thin film patterning techniques with diameters ranging from
m up to m and thickness of m. We used arrays and single
dots to study the dynamics of the superheating and supercooling phase
transitions in a magnetic field parallel to the dot surface. The phase transi-
tions were produced by either varying the applied magnetic field strength at a
constant temperature or changing the bath temperature at a constant field.
Preliminary results on the dynamics of the phase transitions of arrays and
single indium dots will be reported.Comment: 7pages in LaTex format, five figures available upon request by
[email protected], preprint Bu-He 93/
W^+W^+ plus dijet production in the POWHEGBOX
We present an implementation of the calculation of the production of W^+W^+
plus two jets at hadron colliders, at next-to-leading order (NLO) in QCD, in
the POWHEG framework, which is a method that allows the interfacing of NLO
calculations to shower Monte Carlo programs. This is the first 2 -> 4 process
to be described to NLO accuracy within a shower Monte Carlo framework. The
implementation was built within the POWHEGBOX package. We discuss a few
technical improvements that were needed in the POWHEGBOX to deal with the
computer intensive nature of the NLO calculation, and argue that further
improvements are possible, so that the method can match the complexity that is
reached today in NLO calculations. We have interfaced our POWHEG implementation
with PYTHIA and HERWIG, and present some phenomenological results, discussing
similarities and differences between the pure NLO and the POWHEG+PYTHIA
calculation both for inclusive and more exclusive distributions. We have made
the relevant code available at the POWHEGBOX web site.Comment: 16 pages, 5 figure
The Pomeron In Exclusive Vector Meson Production
An earlier developed model for vector meson photoproduction, based on a
dipole Pomeron exchange, is extended to electroproduction. Universality of the
non linear Pomeron trajectory is tested by fitting the model to ZEUS and H1
data as well as to CDF data on elastic scattering.Comment: 12 pages, 13 figure
Differential Cross Section for Higgs Boson Production Including All-Orders Soft Gluon Resummation
The transverse momentum distribution is computed for inclusive Higgs
boson production at the energy of the CERN Large Hadron Collider. We focus on
the dominant gluon-gluon subprocess in perturbative quantum chromodynamics and
incorporate contributions from the quark-gluon and quark-antiquark channels.
Using an impact-parameter -space formalism, we include all-orders
resummation of large logarithms associated with emission of soft gluons. Our
resummed results merge smoothly at large with the fixed-order
expectations in perturbative quantum chromodynamics, as they should, with no
need for a matching procedure. They show a high degree of stability with
respect to variation of parameters associated with the non-perturbative input
at low . We provide distributions for Higgs boson masses
from to 200 GeV. The average transverse momentum at zero rapidity
grows approximately linearly with mass of the Higgs boson over the range ~GeV. We provide analogous results
for boson production, for which we compute GeV. The
harder transverse momentum distribution for the Higgs boson arises because
there is more soft gluon radiation in Higgs boson production than in
production.Comment: 42 pages, latex, 26 figures. All figures replaced. Some changes in
wording. Published in Phys. Rev. D67, 034026 (2003
Thickness Estimation of Epitaxial Graphene on SiC using Attenuation of Substrate Raman Intensity
A simple, non-invasive method using Raman spectroscopy for the estimation of
the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is
presented, enabling simultaneous determination of thickness, grain size and
disorder using the spectra. The attenuation of the substrate Raman signal due
to the graphene overlayer is found to be dependent on the graphene film
thickness deduced from X-ray photoelectron spectroscopy and transmission
electron microscopy of the surfaces. We explain this dependence using an
absorbing overlayer model. This method can be used for mapping graphene
thickness over a region and is capable of estimating thickness of multilayer
graphene films beyond that possible by XPS and Auger electron spectroscopy
(AES).Comment: 14 pages, 9 figure
Likelihood Functions for Supersymmetric Observables in Frequentist Analyses of the CMSSM and NUHM1
On the basis of frequentist analyses of experimental constraints from
electroweak precision data, g-2, B physics and cosmological data, we
investigate the parameters of the constrained MSSM (CMSSM) with universal soft
supersymmetry-breaking mass parameters, and a model with common non-universal
Higgs masses (NUHM1). We present chi^2 likelihood functions for the masses of
supersymmetric particles and Higgs bosons, as well as b to s gamma, b to mu mu
and the spin-independent dark matter scattering cross section. In the CMSSM we
find preferences for sparticle masses that are relatively light. In the NUHM1
the best-fit values for many sparticle masses are even slightly smaller, but
with greater uncertainties. The likelihood functions for most sparticle masses
are cut off sharply at small masses, in particular by the LEP Higgs mass
constraint. Both in the CMSSM and the NUHM1, the coannihilation region is
favoured over the focus-point region at about the 3-sigma level, largely but
not exclusively because of g-2. Many sparticle masses are highly correlated in
both the CMSSM and NUHM1, and most of the regions preferred at the 95% C.L. are
accessible to early LHC running. Some slepton and chargino/neutralino masses
should be in reach at the ILC. The masses of the heavier Higgs bosons should be
accessible at the LHC and the ILC in portions of the preferred regions in the
(M_A, tan beta) plane. In the CMSSM, the likelihood function for b to mu mu is
peaked close to the Standard Model value, but much larger values are possible
in the NUHM1. We find that values of the DM cross section > 10^{-10} pb are
preferred in both the CMSSM and the NUHM1. We study the effects of dropping the
g-2, b to s gamma, relic density and M_h constraints.Comment: 34 pages, 24 figure
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