26 research outputs found
How to Run the Coupling in the Dipole Approach to the BFKL Equation
We use the dipole expansion to provide a systematic way of including the
running coupling into the BFKL equation. In terms of a Borel representation, we
obtain an expression for the kernel of the BFKL equation.Comment: 10 pages, latex, 1 figure, included. LaTeX2e compatibility problems
fixed: no changes in content
Bi-local baryon interpolating fields with two flavours
We construct bi-local interpolating field operators for baryons consisting of
three quarks with two flavors, assuming good isospin symmetry. We use the
restrictions following from the Pauli principle to derive relations/identities
among the baryon operators with identical quantum numbers. Such relations that
follow from the combined spatial, Dirac, color, and isospin Fierz
transformations may be called the (total/complete) Fierz identities. These
relations reduce the number of independent baryon operators with any given spin
and isospin. We also study the Abelian and non-Abelian chiral transformation
properties of these fields and place them into baryon chiral multiplets. Thus
we derive the independent baryon interpolating fields with given values of spin
(Lorentz group representation), chiral symmetry ( group
representation) and isospin appropriate for the first angular excited states of
the nucleon.Comment: 15 pages, 4 tables, accepted by EPJ
The resummation of inter-jet energy flow for gaps-between-jets processes at HERA
We calculate resummed perturbative predictions for gaps-between-jets
processes and compare to HERA data. Our calculation of this non-global
observable needs to include the effects of primary gluon emission (global
logarithms) and secondary gluon emission (non-global logarithms) to be correct
at the leading logarithm (LL) level. We include primary emission by calculating
anomalous dimension matrices for the geometry of the specific event definitions
and estimate the effect of non-global logarithms in the large limit. The
resulting predictions for energy flow observables are consistent with
experimental data.Comment: 31 pages, 4 figures, 2 table
Dijet Rapidity Gaps in Photoproduction from Perturbative QCD
By defining dijet rapidity gap events according to interjet energy flow, we
treat the photoproduction cross section of two high transverse momentum jets
with a large intermediate rapidity region as a factorizable quantity in
perturbative QCD. We show that logarithms of soft gluon energy in the interjet
region can be resummed to all orders in perturbation theory. The resummed cross
section depends on the eigenvalues of a set of soft anomalous dimension
matrices, specific to each underlying partonic process, and on the
decomposition of the scattering according to the possible patterns of hard
color flow. We present a detailed discussion of both. Finally, we evaluate
numerically the gap cross section and gap fraction and compare the results with
ZEUS data. In the limit of low gap energy, good agreement with experiment is
obtained.Comment: 37 pages, Latex, 17 figure
Measuring Parton Densities in the Pomeron
We present a program to measure the parton densities in the pomeron using
diffractive deep inelastic scattering and diffractive photoproduction, and to
test the resulting parton densities by applying them to other processes such as
the diffractive production of jets in hadron-hadron collisions. Since QCD
factorization has been predicted NOT to apply to hard diffractive scattering,
this program of fitting and using parton densities might be expected to fail.
Its success or failure will provide useful information on the space-time
structure of the pomeron.Comment: Contains revisions based on Phys. Rev. D referee comments. RevTeX
version 3, epsf, 31 pages. Uuencoded compressed postscript figures appended.
Uncompressed postscript files available at
ftp://ftp.phys.psu.edu/pub/preprint/psuth136
Perturbative QCD Analysis of Meson Decays
Resummation of large QCD radiative corrections, including leading and
next-to-leading logarithms, in pion electromagnetic form factor is reviewed.
Similar formalism is applied to exclusive processes involving heavy mesons, and
leads to Sudakov suppression for the semi-leptonic decay . It is
found that, with the inclusion of Sudakov effects, perturbative QCD analysis of
this decay is possible for the energy fraction of the pion above 0.3. By
combining predictions from the soft pion theorems, we estimate that the upper
limit of the KM matrix element is roughly 0.003.Comment: 26 pages in latex, figures are available for reques
A Critical Analysis of the Proton Form Factor with Sudakov Suppression and Intrinsic Transverse Momentum
The behavior of the proton magnetic form factor is studied within the
modified hard scattering picture, which takes into account gluonic radiative
corrections in terms of transverse separations. We parallel the analysis given
previously by Li and make apparent a number of serious objections. The
appropriate cut-off needed to render the form-factor calculation finite is both
detailed and analyzed by considering different cut-off prescriptions. The use
of the maximum interquark separation as a common infrared cut-off in the
Sudakov suppression factor is proposed, since it avoids difficulties with the
-singularities and yields a proton form factor insensitive to the
inclusion of the soft region which therefore can be confidently attributed to
perturbative QCD. Results are presented for a variety of proton wave functions
including also their intrinsic transverse momentum. It turns out that the
perturbative contribution, although theoretically self-consistent for
larger than about ~GeV to ~GeV, is too small compared to
the data.Comment: 31 pages (RevTex) + 6 figures in PS-file; preprint BUGH Wuppertal
WU-B-94-06, preprint Ruhr-Universit\"at Bochum RUB-TPII-01/9
Rho GTPase function in flies: insights from a developmental and organismal perspective.
Morphogenesis is a key event in the development of a multicellular organism and is reliant on coordinated transcriptional and signal transduction events. To establish the segmented body plan that underlies much of metazoan development, individual cells and groups of cells must respond to exogenous signals with complex movements and shape changes. One class of proteins that plays a pivotal role in the interpretation of extracellular cues into cellular behavior is the Rho family of small GTPases. These molecular switches are essential components of a growing number of signaling pathways, many of which regulate actin cytoskeletal remodeling. Much of our understanding of Rho biology has come from work done in cell culture. More recently, the fruit fly Drosophila melanogaster has emerged as an excellent genetic system for the study of these proteins in a developmental and organismal context. Studies in flies have greatly enhanced our understanding of pathways involving Rho GTPases and their roles in development
Performance of the CMS Level-1 trigger in proton-proton collisions at √s = 13 TeV
At the start of Run 2 in 2015, the LHC delivered proton-proton collisions at a center-of-mass energy of 13\TeV. During Run 2 (years 2015–2018) the LHC eventually reached a luminosity of 2.1× 10 cms, almost three times that reached during Run 1 (2009–2013) and a factor of two larger than the LHC design value, leading to events with up to a mean of about 50 simultaneous inelastic proton-proton collisions per bunch crossing (pileup). The CMS Level-1 trigger was upgraded prior to 2016 to improve the selection of physics events in the challenging conditions posed by the second run of the LHC. This paper describes the performance of the CMS Level-1 trigger upgrade during the data taking period of 2016–2018. The upgraded trigger implements pattern recognition and boosted decision tree regression techniques for muon reconstruction, includes pileup subtraction for jets and energy sums, and incorporates pileup-dependent isolation requirements for electrons and tau leptons. In addition, the new trigger calculates high-level quantities such as the invariant mass of pairs of reconstructed particles. The upgrade reduces the trigger rate from background processes and improves the trigger efficiency for a wide variety of physics signals