1,773 research outputs found
Soft Gluon Logarithmic Resummation and Hadron Mass Effects in Single Hadron Inclusive Production
We define a general scheme for the evolution of fragmentation functions which
resums soft gluon logarithms in a manner consistent with fixed order evolution.
We present an explicit example of our approach in which double logarithms are
resummed using the Double Logarithmic Approximation. We show that this scheme
reproduces the Modified Leading Logarithm Approximation in certain limits, and
find that after using it to fit quark and gluon fragmentation functions to
experimental data,a good description of the data from the largest x values to
the peak region in ln (1/x) is obtained. In addition, we develop a treatment of
hadron mass effects which gives additional improvements at small x.Comment: Prepared for Ringberg Workshop: New Trends in HERA Physics 2005,
October 2 - 7, 200
The non-singlet kaon fragmentation function from e^+e^- kaon production
We perform fits to the available charged and neutral kaon production data in
, , and determine the non-singlet
combination of kaon fragmentation functions in a
model independent way and without any correlations to the other fragmentation
functions. Only nuclear isospin invariance is assumed. Working with
non-singlets allows us to include the data at very low momentum fractions,
which have so far been excluded in global fits, and to perform a first NNLO fit
to fragmentation functions. We find that the kaon non-singlet fragmentation
function at large is larger than that obtained by the other collaborations
from global fit analysis and differs significantly at low
Constraints on SUSY Seesaw from Leptogenesis and LFV
We study constraints on the fundamental parameters of supersymmetric type I
seesaw models imposed by neutrino data, charged lepton flavor violation,
thermal leptogenesis and perturbativity of the neutrino Yukawa couplings.Comment: 4 pages, 2 figures, to appear in Proceedings of SUSY06, the 14th
International Conference on Supersymmetry and the Unification of Fundamental
Interactions, UC Irvine, California, 12-17 June 200
Fully double-logarithm-resummed cross sections
We calculate the complete double logarithmic contribution to cross sections
for semi-inclusive hadron production in the modified minimal-subtraction scheme
by applying dimensional regularization to the double logarithm approximation.
The full double logarithmic contribution to the coefficient functions for
inclusive hadron production in electron-positron annihilation is obtained in
this scheme for the first time. Our result agrees with all fixed order results
in the literature, which extend to next-next-to-leading order.Comment: To appear in Nuclear Physics
Unifying the Fixed Order Evolution of Fragmentation Functions with the Modified Leading Logarithm Approximation
An approach which unifies the Double Logarithmic Approximation at small x and
the leading order DGLAP evolution of fragmentation functions at large x is
presented. This approach reproduces exactly the Modified Leading Logarithm
Approximation, but is more complete due to the degrees of freedom given to the
quark sector and the inclusion of the fixed order terms. We find that data from
the largest x values to the peak region can be better fitted than with other
approaches
Factorization breaking in high-transverse-momentum charged-hadron production at the Tevatron?
We compare the transverse momentum (p_T) distribution of inclusive
light-charged-particle production measured by the CDF Collaboration at the
Fermilab Tevatron with the theoretical prediction evaluated at next-to-leading
order in quantum chromodynamics (QCD) using fragmentation functions recently
determined through a global data fit. While, in the lower p_T range, the data
agree with the prediction within the theoretical error or slightly undershoot
it, they significantly exceed it in the upper p_T range, by several orders of
magnitude at the largest values of p_T, where perturbation theory should be
most reliable. This disagreement is too large to be remedied by introducing
additional produced particles into the calculation, and potentially challenges
the validity of the factorization theorem on which the parton model of QCD
relies. Clearly, a breakdown of the factorization theorem, being a fundamental
property of QCD, would be extremely difficult to understand.Comment: 9 pages, 5 figures; discussion extended, references added; accepted
for publication in Physical Review Letter
Medium-modified DGLAP evolution of fragmentation functions from large to small x
The unified description of fragmentation function evolution from large to
small x which was developed for the vacuum in previous publications is now
generalized to the medium, and is studied for the case in which the complete
contribution from the largest class of soft gluon logarithms, the double
logarithms, are accounted for and with the fixed order part calculated to
leading order. In this approach it proves possible to choose the remaining
degrees of freedom related to the medium such that the distribution of produced
hadrons is suppressed at large momenta while the production of soft
radiation-induced charged hadrons at small momenta is enhanced, in agreement
with experiment. Just as for the vacuum, our approach does not require further
assumptions concerning fragmentation and is more complete than previous
computations of evolution in the medium
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