597 research outputs found
Soft gluons and gauge-invariant subtractions in NLO parton-shower Monte Carlo event generators
We address the problem of decomposing graphs in perturbative QCD into terms
associated with particular regions. Motivated by asking how to incorporate
next-to-leading order (NLO) QCD corrections in parton-shower algorithms, we
require that: (a) The integrand for the hard part is to be integrable even if
the corrections are applied to a process that is not infrared and collinear
safe. (b) The splitting between the terms should be defined gauge-invariantly.
(c) The dependence on cut-offs should obey homogeneous evolution equations. In
the context of one-gluon-emission graphs for deep inelastic scattering, we
explain a subtractive technique that is based on gauge-invariant Wilson-line
operators. Appropriate organization of subtractions involving the soft region
allows a connection to previous work where evolution equations with respect to
the directions of the Wilson lines have been derived.Comment: 11 pages, 2 figures; v2: comments and references added, results
unchange
Color transparency in deeply inelastic diffraction
We suggest a simple physical picture for the diffractive parton distributions
that appear in diffractive deeply inelastic scattering. In this picture,
partons impinging on the proton can have any transverse separation, but only
when the separation is small can they penetrate the proton without breaking it
up. By comparing the predictions from this picture with the diffractive data
from HERA, we determine rough values for the small separations that dominate
the diffraction process.Comment: 10 pages, 2 figures; v2: citations added, two comments revised and
expanded, results unchange
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
TMDlib and TMDplotter: library and plotting tools for transverse-momentum-dependent parton distributions
Transverse-momentum-dependent distributions (TMDs) are central in high-energy
physics from both theoretical and phenomenological points of view. In this
manual we introduce the library, TMDlib, of fits and parameterisations for
transverse-momentum-dependent parton distribution functions (TMD PDFs) and
fragmentation functions (TMD FFs) together with an online plotting tool,
TMDplotter. We provide a description of the program components and of the
different physical frameworks the user can access via the available
parameterisations.Comment: version 2, referring to TMDlib 1.0.2 - comments and references adde
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
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
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
Soft Photon Spectrum in Orthopositronium and Vector Quarkonium Decays
QED gauge invariance, when combined with analyticity, leads to constraints on
the low energy end of the emitted photon spectra. This is known as Low's
theorem. It is shown that the Ore-Powell result, as well as further
developments for the orthopositronium differential decay rate, are in
contradiction with Low's theorem, i.e. that their predicted soft photon spectra
are incorrect.
A solution to this problem is presented. The implications for the
orthopositronium lifetime puzzle, the charmonium rho-pi puzzle, the prompt
photon spectrum in inclusive quarkonium decays and the extraction of alpha_S
from quarkonium annihilation rates are briefly commented.Comment: LaTeX, 10 page
Strain field analysis on Montserrat (W.I.) as tool for assessing permeable flow paths in the magmatic system of Soufrière Hills Volcano
Strain dilatometers have been operated on the volcanic island of Montserrat (West Indies) for more than a decade and have proven to be a powerful technique to approach short-term dynamics in the deformational field in response to pressure changes in the magmatic system of the andesitic dome-building Soufrière Hills Volcano (SHV). We here demonstrate that magmatic activity in each of the different segments of the SHV magmatic system (shallow dyke-conduit, upper and lower magma chambers) generates a characteristic strain pattern that allows the identification of operating sources in the plumbing system based on a simple scheme of amplitude ratios. We use this method to evaluate strain data from selected Vulcanian explosions and gas emission events that occurred at SHV between 2003 and 2012. Our results show that the events were initiated by a short phase of contraction of either one or both magma chambers and a simultaneous inflation of the shallow feeder system. The initial phase of the events usually lasted only tens to hundreds of seconds before the explosion/gas emission started and the system recovered. The short duration of this process points at rapid transport of fluids rather than magma ascent to generate the pressure changes. We suggest the propagation of tensile hydraulic fractures as viable mechanism to provide a pathway for fluid migration in the magmatic system at the observed time scale. Fluid mobilization was initiated by a sudden destabilization of large pockets of already segregated fluid in the magma chambers. Our study demonstrates that geodetic observables can provide unprecedented insights into complex dynamic processes within a magmatic system commonly assessed by theoretical modeling and petrologic observations. Key Points Strain data analysis from explosions/degassing events at Soufriere Hills Volcano Pressure release deep within the magmatic system sec-min prior to events Rapid gas rise from magma reservoir to surface via tensile hydraulic fractures © 2014. American Geophysical Union. All Rights Reserved
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