779 research outputs found
Radiative quarkonium decays and the NMSSM Higgs interpretation of the HyperCP Sigma+ --> p mu+mu- events
We study the potential of radiative decays of the Upsilon(1S) and of the phi
mesons to search for a light pseudoscalar Higgs boson, proposed as a possible
interpretation of Sigma+ --> p mu+mu- events observed by the HyperCP
collaboration at Fermilab. We conclude that the detection of this signal should
certainly be possible with the current CLEO Upsilon(1S) data, and is within the
reach of KLOE in at least part of the range of couplings suggested by the
HyperCP findings.Comment: 6 pages, no figure
Is There a Significant Excess in Bottom Hadroproduction at the Tevatron?
We discuss the excess in the hadroproduction of B mesons at the Tevatron. We
show that an accurate use of up-to-date information on the B fragmentation
function reduces the observed excess to an acceptable level. Possible
implications for experimental results reporting bottom quark cross sections,
also showing an excess with respect to next-to-leading order theoretical
predictions, are discussed.Comment: 5 pages, Latex, 4 figures. Submitted to Phys. Rev. Let
The Photon Content of the Proton
The photon PDF of the proton is needed for precision comparisons of LHC cross
sections with theoretical predictions. In a recent paper, we showed how the
photon PDF could be determined in terms of the electromagnetic proton structure
functions and measured in electron-proton scattering experiments,
and gave an explicit formula for the PDF including all terms up to
next-to-leading order. In this paper we give details of the derivation. We
obtain the photon PDF using the factorisation theorem and applying it to
suitable BSM hard scattering processes. We also obtain the same PDF in a
process-independent manner using the usual definition of PDFs in terms of
light-cone Fourier transforms of products of operators. We show how our method
gives an exact representation for the photon PDF in terms of and ,
valid to all orders in QED and QCD, and including all non-perturbative
corrections. This representation is then used to give an explicit formula for
the photon PDF to one order higher than our previous result. We also generalise
our results to obtain formul\ae\ for the polarised photon PDF, as well as the
photon TMDPDF. Using our formula, we derive the subset of DGLAP
splitting functions to order and , which agree with
known results. We give a detailed explanation of the approach that we follow to
determine a photon PDF and its uncertainty within the above framework.Comment: 75 pages, 25 figures, data files corresponding to the figures
available at http://doi.org/10.5281/zenodo.837233, LUXqed17 PDF files
available in LHAPDF, references added in v
Heavy flavour mass corrections to the longitudinal and transverse cross sections in e^+e^- - collisions
The sentence, 7th line below Eq. (28), starting with "Further we exclude all
interference terms ...." is wrong and has been corrected. Eq. (33) :
f_k^{l,(i)} -> h_k^{l,(i)} i=0,1 Second line below Eq. (33) m_bar(m)=m is
replaced by m_bar(\mu_0)=\mu_0 with \mu_0=4.10 GeV and \mu_0=166.1 GeV for
bottom and top respectively. The numbers in the third column of tables 1 and 2
are a little bit changed.Comment: 8 pages Latex, all compressed by uufile
Functional equations for one-loop master integrals for heavy-quark production and Bhabha scattering
The method for obtaining functional equations, recently proposed by one of
the authors, is applied to one-loop box integrals needed in calculations of
radiative corrections to heavy-quark production and Bhabha scattering. We
present relationships between these integrals with different arguments and box
integrals with all propagators being massless. It turns out that functional
equations are rather useful for finding imaginary parts and performing analytic
continuations of Feynman integrals. For the box master integral needed in
Bhabha scattering, a new representation in terms of hypergeometric functions
admitting one-fold integral representation is derived. The hypergeometric
representation of a master integral for heavy-quark production follows from the
functional equation.Comment: 14 pages, 3 figure
Inclusive B-Meson Production at the LHC in the GM-VFN Scheme
We calculate the next-to-leading-order cross section for the inclusive
production of B mesons in pp collisions in the general-mass
variable-flavor-number scheme, an approach which takes into account the finite
mass of the b quarks. We use realistic evolved non-perturbative fragmentation
functions obtained from fits to e+e- data and compare results for the
transverse-momentum and rapidity distributions at a center-of-mass energy of 7
TeV with recent data from the CMS Collaboration. We find good agreement, in
particular at large values of pT.Comment: Minor changes to the text, accepted for publication in Phys. Rev.
Electroweak Corrections using Effective Field Theory: Applications to the LHC
Electroweak Sudakov logarithms at high energy, of the form alpha/sin^2
theta_W^n log^m s/M_{Z,W}^2, are summed using effective theory (EFT) methods.
The exponentiation of Sudakov logarithms and factorization is discussed in the
EFT formalism. Radiative corrections are computed to scattering processes in
the standard model involving an arbitrary number of external particles. The
computations include non-zero particle masses such as the t-quark mass,
electroweak mixing effects which lead to unequal W and Z masses and a massless
photon, and Higgs corrections proportional to the top quark Yukawa coupling.
The structure of the radiative corrections, and which terms are summed by the
EFT renormalization group is discussed in detail. The omitted terms are smaller
than 1%. We give numerical results for the corrections to dijet production,
dilepton production, t-\bar t production, and squark pair production. The
purely electroweak corrections are significant -- about 15% at 1 TeV,
increasing to 30% at 5 TeV, and they change both the scattering rate and
angular distribution. The QCD corrections (which are well-known) are also
computed with the EFT. They are much larger -- about a factor of four at 1 TeV,
increasing to a factor of thirty at 5 TeV. Mass effects are also significant;
the q \bar q -> t \bar t rate is enchanced relative to the light-quark
production rate by 40%.Comment: Additional details added on exponentiation, and the form of the
Sudakov series. Figures darkened to print better. 40 pages, 40 figure
Tau Neutrino Astronomy in GeV Energies
We point out the opportunity of the tau neutrino astronomy for the neutrino
energy E ranging between 10 GeV and 10^3 GeV. In this energy range, the
intrinsic tau neutrino production is suppressed relative to the intrinsic muon
neutrino production. Any sizable tau neutrino flux may thus arise because of
the \nu_{\mu}\to \nu_{\tau} neutrino oscillations only. It is demonstrated
that, in the presence of the neutrino oscillations, consideration of the
neutrino flavor dependence in the background atmospheric neutrino flux leads to
the drastically different prospects between the observation of the
astrophysical muon neutrinos and that of the astrophysical tau neutrinos.
Taking the galactic-plane neutrino flux as the targeted astrophysical source,
we have found that the galactic-plane tau neutrino flux dominates over the
atmospheric tau neutrino flux for E > 10 GeV. Hence, the galactic-plane can at
least in principle be seen through the tau neutrinos with energies just greater
than 10 GeV. In a sharp contrast, the galactic-plane muon neutrino flux is
overwhelmed by its atmospheric background until E > 10^6 GeV.Comment: major revision of text and two new figures, to appear in PR
Top-Quark Pair Production Beyond Next-to-Leading Order
We report on recent calculations of the differential cross section for
top-quark pair production at hadron colliders. The results are differential
with respect to the top-pair invariant mass and to the partonic scattering
angle. In these calculations, which were carried out by employing
soft-collinear effective theory techniques, we resummed threshold logarithms up
to next-to-next-to-leading logarithmic order. Starting from the differential
cross section, it is possible to obtain theoretical predictions for the
invariant-mass distribution and the total cross section. We summarize here our
results for these observables, and we compare them with the results obtained
from different calculational methods.Comment: Talk presented at Loops and Legs in Quantum Field Theory 2010,
Woerlitz, Germany, April 25-30, 2010. 6 page
NLO Higgs boson production via vector-boson fusion matched with shower in POWHEG
We present a next-to-leading order calculation of Higgs boson production in
vector-boson fusion processes interfaced to shower Monte Carlo programs,
implemented according to the POWHEG method.Comment: 16 pages, 9 figures. A few references and a new figure adde
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