2,994 research outputs found
Separating Electroweak and Strong interactions in Drell-Yan processes at LHC: leptons angular distributions and reference frames
Among the physics goals of LHC experiments, precision tests of the Standard
Model in the Strong and Electroweak sectors play an important role. Because of
nature of the proton-proton processes, observables based on the measurement of
the direction and energy of leptons provide the most precise signatures. In the
present paper, we concentrate on the angular distribution of Drell-Yan process
leptons, in the lepton-pair rest-frame. The vector nature of the intermediate
state imposes that distributions are to a good precision described by spherical
polynomials of at most second order.
We show that with the proper choice of the coordinate frames, only one
coefficient in this polynomial decomposition remains sizable, even in the
presence of one or two high jets. The necessary stochastic choice of the
frames relies on probabilities independent from any coupling constants.
This remains true when one or two partons accompany the lepton pairs. In this
way electroweak effects can be better separated from strong interaction ones
for the benefit of the interpretation of the measurements.
Our study exploits properties of single gluon emission matrix elements which
are clearly visible if a conveniently chosen form of their representation is
used. We rely also on distributions obtained from matrix element based Monte
Carlo generated samples of events with two leptons and up to two additional
partons in test samples. Incoming colliding protons' partons are distributed
accordingly to PDFs and are strictly collinear to the corresponding beams.Comment: 22 pages 9 figure
Trefoil knot and ad-hoc classification of elementary fields in the Standard Model
We present an arbitrary model based on the trefoil knot to construct objects
of the same spectrum as that of elementary particles. It includes `waves' and
three identical sets of sources. Due to Lorentz invariance, `waves' group into
3 types of 1, 3 and 8 objects and `sources' consists of 3 identical sets of
30+2 elements, which separate into: 1 * 1 * 2 + 1 * 2 * 2 + 3 * 2 * 2 + 3 * 1 *
2 + 3 * 1 * 2 and another 1 * 1 * 2 group (which does not match classification
of the Standard Model fields). On the other hand, there is no room in this
construction for objects directly corresponding to Higgs-like degrees of
freedom.Comment: uuencoded and gtar: was.tex was1.eps was2.eps. Use latex; in total 8
pages including front and 2 figure page
Spin polarization and the Einstein--Podolsky--Rosen paradox in the Monte Carlo event records
In the future high energy physics experiments, the question of properly
matching the phenomenological programs that describe different parts of the
physics processes (such as hard scattering, hadronization, decay of resonances,
detector response, etc.) is very important. In the past, FORTAN common blocks
filled with lists of objects (particles, strings, clusters, etc.) of defined
properties, origins and descendants were in use. Similar structures are now
envisaged, for future programs, to be written in languages such as C++ or Java.
From the physics point of view such an approach is not correct, since this
kind of data structures impose certain approximations on the physics content.
In the present paper, we will explore their limits, using examples from the
physics of W's, tau's and the Higgs boson, still to be discovered.Comment: latex 10 pages, including 10 attachments in postscript forma
The tauola-photos_F environment for versioning the TAUOLA and PHOTOS packages
We present the system for versioning two packages: the TAUOLA of tau lepton
decay and PHOTOS for radiative corrections in decays. The following features
can be chosen in automatic or semi-automatic way: (1) format of the common
block HEPEVT; (2) version of the physics input (for TAUOLA): as published, as
initialized by CLEO collaboration, as initialized by ALEPH collaboration (it is
suggested to use this version only with the help of the collaboration advice);
(3) type of application: stand-alone, universal interface through HEPEVT,
interface for KKMC Monte Carlo; (4) random number generators; (5) compiler
options.Comment: nine pages, late
How to Generate Four-Fermion Phase Space
We present a scheme for integrating the matrix element of an arbitrary
e^+e^-\to f_1f_2\bar f_3\bar f_4 process over the complete four-fermion phase
space, or its any part, by means of the Monte Carlo technique. The presented
algorithm has been successfully implemented in the KORALW Monte Carlo code.Comment: 16 page
Next to Leading Logarithms and the PHOTOS Monte Carlo
With the approaching start-up of the experiments at LHC, the urgency to
quantify systematic uncertainties of the generators, used in the interpretation
of the data, is becoming pressing. The PHOTOS Monte Carlo program is often used
for the simulationof experimental, selection-sensitive, QED radiative
corrections in decays of Z bosons and other heavy resonances and particles.
Thanks to its complete phase-space coverage it is possible, with no
approximations for any decay channel, to implement the matrix-element. The
present paper will be devoted to those parts of the next-to-leading order
corrections for Z decays which are normally missing in PHOTOS. The analytical
form of the exact and truncated (standard) kernel used in PHOTOS will be
explicitly given. The correction, being the ratio of the exact to the
approximate kernel, can be activated as an optional contribution to the
internal weight of PHOTOS.
To calculate the weight, the information on the effective Born-level Z/gamma*
couplings and even directions of the incoming beams, is needed. A universal
implementation would have made the PHOTOS solution less modular and less
convenient for the users. That is why, for the time being, we will keep the
correcting weight as an extra option, available for special tests only.
We will quantify the numerical effect of the approximation with the help of a
multitude of distributions. The numerical size of the effect is in general
below 0.1%; however, in some corners of the phase-space (well defined and
contributing less than 0.5% to the total rate), it may reach up to about 20% of
their relative size.Comment: 23+1 pages 6 groups of figure
Inclusion of tau anomalous magnetic and electric dipole moments in the KORALZ Monte Carlo
We describe modifications made to KORALZ version 4.03 in order to allow for
anomalous magnetic and electric dipole moments of the tau. We discuss the
verification of the method at LEP 1 energies.Comment: 14 pages, 9 figure
How to use SANC to improve the PHOTOS Monte Carlo simulation of bremsstrahlung in leptonic W-Boson decays
Using the SANC system we study the one-loop electroweak standard model
predictions, including virtual and real photon emission, for the decays of the
on-shell vector boson, W --> L ANTI-NU (GAMMA). The complete one-loop
corrections and exact photon emission matrix element are taken into account.
For the phase-space integration, the Monte Carlo technique is used. This
provides a useful element, first for the evaluation of the theoretical
uncertainty of PHOTOS. Later we analyse the source of the differences between
SANC and PHOTOS and we calculate the additional weight, which once installed,
improves predictions of PHOTOS simulations. We can conclude that, after the
correction of the weight is implemented, the theoretical uncertainty of PHOTOS
simulations due to an incomplete first-order matrix element is reduced to below
alpha/pi, for observables not tagging the photon in a direct way, and to 10%
otherwise. This is interesting for applications in the phenomenology of the
ongoing LEP2 and future LC and LHC experimental studies.Comment: Submitted to Acta Physica Polonica. 8 pages, 5 figure
tau Decays to Five Mesons in TAUOLA
The tau-decay library TAUOLA has gained popularity over the last decade.
However, with the continuously increasing precision of the data, some of its
functionality has become insufficient. One of the requirements is the
implementation of decays into five mesons plus a neutrino with a realistic
decay amplitude. This note describes a step into this direction. For the 2pi-
pi+ 2pi0 mode the three decay chains tau- --> a_1- nu --> rho- (--> pi- pi0)
omega (--> pi- pi+ pi0) nu, tau- --> a_1- nu --> a_1- (--> 2pi- pi+) f_0 (-->
2pi0) nu, and tau- --> a_1- nu --> a_1- (--> pi- 2pi0) f_0 (--> pi + pi-) nu
are introduced with simple assumptions about the couplings and propagators of
the various resonances. Similar amplitudes (without the rho omega
contributions) are adopted for the pi- 4pi0 and 3pi- 2pi+ modes.
The five-pion amplitude is thus based on a simple model, which, however, can
be considered as a first realistic example. Phase-space generation includes the
possibility of presampling the omega and a_1 resonances, in one channel only,
however. This is probably sufficient for the time being, both for physics
applications and for tests.
The technical test of the new part of the generator is performed by comparing
Monte Carlo and analytical results. To this end a non-realistic, but easy to
calculate, purely scalar amplitude for the decay into five massless pions was
used.Comment: 10 page
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