625 research outputs found
Hadroproduction of electroweak gauge boson plus jets and TMD parton density functions
If studies of electroweak gauge boson final states at the Large Hadron
Collider, for Standard Model physics and beyond, are sensitive to effects of
the initial state's transverse momentum distribution, appropriate
generalizations of QCD shower evolution are required. We propose a method to do
this based on QCD transverse momentum dependent (TMD) factorization at high
energy. The method incorporates experimental information from the
high-precision deep inelastic scattering (DIS) measurements, and includes
experimental and theoretical uncertainties on TMD parton density functions. We
illustrate the approach presenting results for production of W-boson + n jets
at the LHC, including azimuthal correlations and subleading jet distributions.Comment: 9 pages, 4 figures. v2: comments and references added, typos
corrected; results unchange
The CCFM uPDF evolution uPDFevolv
uPDFevolv is an evolution code for TMD parton densities using the CCFM
evolution equation. A description of the underlying theoretical model and
technical realization is given together with a detailed program description,
with emphasis on parameters the user may want to changeComment: Code and description on https://updfevolv.hepforge.org Version to be
published in EPJ
Forward Jets and Energy Flow in Hadronic Collisions
We observe that at the Large Hadron Collider, using forward + central
detectors, it becomes possible for the first time to carry out calorimetric
measurements of the transverse energy flow due to "minijets" accompanying
production of two jets separated by a large rapidity interval. We present
parton-shower calculations of energy flow observables in a high-energy
factorized Monte Carlo framework, designed to take into account QCD logarithmic
corrections both in the large rapidity interval and in the hard transverse
momentum. Considering events with a forward and a central jet, we examine the
energy flow in the interjet region and in the region away from the jets. We
discuss the role of these observables to analyze multiple parton collision
effects.Comment: 9 pages, 5 figures. Version2: added results on azimuthal
distributions and more discussion of energy flow definition using jet
clusterin
Calculation of TMD Evolution for Transverse Single Spin Asymmetry Measurements
The Sivers transverse single spin asymmetry (TSSA) is calculated and compared
at different scales using the TMD evolution equations applied to previously
existing extractions. We apply the Collins-Soper-Sterman (CSS) formalism, using
the version recently developed by Collins. Our calculations rely on the
universality properties of TMD-functions that follow from the TMD-factorization
theorem. Accordingly, the non-perturbative input is fixed by earlier
experimental measurements, including both polarized semi-inclusive deep
inelastic scattering (SIDIS) and unpolarized Drell-Yan (DY) scattering. It is
shown that recent COMPASS measurements are consistent with the suppression
prescribed by TMD evolution.Comment: 4 pages, 2 figures. Version published in Physical Review Letter
LHC sensitivity to Z'/W' states in composite Higgs models
Using the 4-Dimensional Composite Higgs Model (4DCHM) realization of the
minimal composite Higgs scenario, we discuss the Large Hadron Collider (LHC)
sensitivity to new physics signals from multiple and
broad resonances. We illustrate the role of systematic uncertainties due to QCD
effects encoded in parton distribution functions for experimental searches in
leptonic channels. We show that, by reducing this systematics through the
combination of high-precision measurements of Standard Model (SM) lepton-charge
and forward-backward asymmetries near the SM vector-boson peak, the sensitivity
to the new physics signals can be greatly enhanced.Comment: 6 pages, 1 figure, Contribution to ICHEP2022 Conference Proceedings
based on arXiv:2111.09698, arXiv:2206.1246
Flavor-singlet light-cone amplitudes and radiative Upsilon decays in SCET
We study the evolution of flavor-singlet, light-cone amplitudes in the
soft-collinear effective theory (SCET), and reproduce results previously
obtained by a different approach. We apply our calculation to the color-singlet
contribution to the photon endpoint in radiative Upsilon decay. In a previous
paper, we studied the color-singlet contributions to the endpoint, but
neglected operator mixing, arguing that it should be a numerically small
effect. Nevertheless the mixing needs to be included in a consistent
calculation, and we do just that in this work. We find that the effects of
mixing are indeed numerically small. This result combined with previous work on
the color-octet contribution and the photon fragmentation contribution provides
a consistent theoretical treatment of the photon spectrum in radiative Upsilon
decay.Comment: 19 pages with 8 figure
The CCFM Monte Carlo generator CASCADE 2.2.0
CASCADE is a full hadron level Monte Carlo event generator for ep, \gamma p
and p\bar{p} and pp processes, which uses the CCFM evolution equation for the
initial state cascade in a backward evolution approach supplemented with off -
shell matrix elements for the hard scattering. A detailed program description
is given, with emphasis on parameters the user wants to change and variables
which completely specify the generated events
The influence of long- and short-term volcanic strain on aquifer pressure:a case study from Soufrière Hills Volcano, Montserrat (W.I.)
Aquifers are poroelastic bodies that respond to strain by changes in pore pressure. Crustal deformation due to volcanic processes induces pore pressure variations that are mirrored in well water levels. Here, we investigate water level changes in the Belham valley on Montserrat over the course of two years (2004-2006). Using finite element analysis, we simulate crustal deformation due to different volcanic strain sources and the dynamic poroelastic aquifer response. While some additional hydrological drivers cannot be excluded, we suggest that a poroelastic strain response of the aquifer system in the Belham valley is a possible explanation for the observed water level changes. According to our simulations, the shallow Belham aquifer responds to a steadily increasing sediment load due to repeated lahar sedimentation in the valley with rising aquifer pressures. A wholesale dome collapse in May 2006 on the other hand induced dilatational strain and thereby a short-term water level drop in a deeper-seated aquifer, which caused groundwater leakage from the Belham aquifer and thereby induced a delayed water level fall in the wells. The system thus responded to both gradual and rapid transient strain associated with the eruption of Soufrière Hills Volcano (Montserrat). This case study gives field evidence for theoretical predictions on volcanic drivers behind hydrological transients, demonstrating the potential of hydrological data for volcano monitoring. Interrogation of such data can provide valuable constraints on stress evolution in volcanic systems and therefore complement other monitoring systems. The presented models and inferred results are conceptually applicable to volcanic areas worldwide
Surprises from Quarkonium Decay into Photons
The perturbative QCD approach to quarkonium decay into a photon and hadrons
is reconsidered. It is shown that a consistent treatment within perturbative
QCD calls for the introduction of a fragmentation contribution which has been
neglected so far. The ensuing phenomenological implications are discussed, and,
in particular, the possibility of measuring the gluon fragmentation function of
the photon is addressed.
*To appear in the proceedings of the workshop QCD94, Montpellier, July '94.Comment: 4 pages + 3 figures, uuencoded postscript, Cambridge preprint
Cavendish-HEP-94/0
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