3,187 research outputs found
Power Corrections to Fragmentation Functions in Non-Singlet Deep Inelastic Scattering
We investigate the power-suppressed corrections to the fragmentation
functions of the current jet in non-singlet deep inelastic lepton-hadron
scattering. The current jet is defined by selecting final-state particles in
the current hemisphere in the Breit frame of reference. Our method is based on
an analysis of one-loop Feynman graphs containing a massive gluon, which is
equivalent to the evaluation of leading infrared renormalon contributions. We
find that the leading corrections are proportional to , as in
annihilation, but their functional forms are different. We give quantitative
estimates based on the hypothesis of universal low-energy behaviour of the
strong coupling.Comment: 14 pages, 4 figures, LaTeX2e, uses JHEP.cls (included) and epsfi
Reconstructing particle masses from pairs of decay chains
A method is proposed for determining the masses of the new particles N,X,Y,Z
in collider events containing a pair of effectively identical decay chains Z to
Y+jet, Y to X+l_1, X to N+l_2, where l_1, l_2 are opposite-sign same-flavour
charged leptons and N is invisible. By first determining the upper edge of the
dilepton invariant mass spectrum, we reduce the problem to a curve for each
event in the 3-dimensional space of mass-squared differences. The region
through which most curves pass then determines the unknown masses. A
statistical approach is applied to take account of mismeasurement of jet and
missing momenta. The method is easily visualized and rather robust against
combinatorial ambiguities and finite detector resolution. It can be successful
even for small event samples, since it makes full use of the kinematical
information from every event.Comment: 12 pages, 5 figure
The unintegrated gluon distribution from the CCFM equation
The gluon distribution f(x, k_t^2,mu^2), unintegrated over the transverse
momentum k_t of the gluon, satisfies the angular-ordered CCFM equation which
interlocks the dependence on the scale k_t with the scale \mu of the probe. We
show how, to leading logarithmic accuracy, the equation can be simplified to a
single scale problem. In particular we demonstrate how to determine the
two-scale unintegrated distribution f(x,k_t^2,mu^2) from knowledge of the
integrated gluon obtained from a unified scheme embodying both BFKL and DGLAP
evolution.Comment: 16 pages LaTeX, 3 eps figure
Polynomials, Riemann surfaces, and reconstructing missing-energy events
We consider the problem of reconstructing energies, momenta, and masses in
collider events with missing energy, along with the complications introduced by
combinatorial ambiguities and measurement errors. Typically, one reconstructs
more than one value and we show how the wrong values may be correlated with the
right ones. The problem has a natural formulation in terms of the theory of
Riemann surfaces. We discuss examples including top quark decays in the
Standard Model (relevant for top quark mass measurements and tests of spin
correlation), cascade decays in models of new physics containing dark matter
candidates, decays of third-generation leptoquarks in composite models of
electroweak symmetry breaking, and Higgs boson decay into two tau leptons.Comment: 28 pages, 6 figures; version accepted for publication, with
discussion of Higgs to tau tau deca
QCD
We discuss QCD studies that will be possible at LEP2. We examine both
experimental and theoretical aspects of jets, fragmentation functions,
multiplicities and particle spectra.Comment: 44 pages, Latex, epsfig, 18 figures, to appear on the Report of the
Workshop on Physics at LEP2, CERN 96-01, vol. 1, 199
Space, Time and Color in Hadron Production Via e+e- -> Z0 and e+e- -> W+W-
The time-evolution of jets in hadronic e+e- events at LEP is investigated in
both position- and momentum-space, with emphasis on effects due to color flow
and particle correlations. We address dynamical aspects of the four
simultanously-evolving, cross-talking parton cascades that appear in the
reaction e+e- -> gamma/Z0 -> W+W- -> q1 q~2 q3 q~4, and compare with the
familiar two-parton cascades in e+e- -> Z0 -> q1 q~2. We use a QCD statistical
transport approach, in which the multiparticle final state is treated as an
evolving mixture of partons and hadrons, whose proportions are controlled by
their local space-time geography via standard perturbative QCD parton shower
evolution and a phenomenological model for non-perturbative parton-cluster
formation followed by cluster decays into hadrons. Our numerical simulations
exhibit a characteristic `inside-outside' evolution simultanously in position
and momentum space. We compare three different model treatments of color flow,
and find large effects due to cluster formation by the combination of partons
from different W parents. In particular, we find in our preferred model a shift
of several hundred MeV in the apparent mass of the W, which is considerably
larger than in previous model calculations. This suggests that the
determination of the W mass at LEP2 may turn out to be a sensitive probe of
spatial correlations and hadronization dynamics.Comment: 52 pages, latex, 18 figures as uu-encoded postscript fil
Colour reconnection and Bose-Einstein effects
Final-state interactions and interference phenomena that could affect the
value of the W mass reconstructed from hadronic WW decays at LEP2 are reviewed,
and possible areas for future investigation are identified.Comment: 14 pages, 5 figures, LaTeX, uses epsfig. Talk at Phenomenology
Workshop on LEP2 Physics, Oxford, April 199
COMPTEL gamma ray and neutron measurements of solar flares
COMPTEL on the Compton Gamma Ray Observatory has measured the flux of x‐rays and neutrons from several solar flares. These data have also been used to image the Sun in both forms of radiation. Unusually intense flares occurred during June 1991 yielding data sets that offer some new insight into of how energetic protons and electrons are accelerated and behave in the solar environment. We summarize here some of the essential features in the solar flare data as obtained by COMPTEL during June 1991
Determination of the QCD color factor ratio CA/CF from the scale dependence of multiplicity in three jet events
I examine the determination of the QCD color factor ratio CA/CF from the
scale evolution of particle multiplicity in e+e- three jet events. I fit an
analytic expression for the multiplicity in three jet events to event samples
generated with QCD multihadronic event generators. I demonstrate that a one
parameter fit of CA/CF yields the expected result CA/CF=2.25 in the limit of
asymptotically large energies if energy conservation is included in the
calculation. In contrast, a two parameter fit of CA/CF and a constant offset to
the gluon jet multiplicity, proposed in a recent study, does not yield
CA/CF=2.25 in this limit. I apply the one parameter fit method to recently
published data of the DELPHI experiment at LEP and determine the effective
value of CA/CF from this technique, at the finite energy of the Z0 boson, to be
1.74+-0.03+-0.10, where the first uncertainty is statistical and the second is
systematic.Comment: 20 pages including 6 figures Version 2 corrects typographical error
in equation (2
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