10,209 research outputs found
Drell-Yan Lepton Angular Distribution at Small Transverse Momentum
We investigate the dependence of the Drell-Yan cross section on lepton polar
and azimuthal angles, as generated by the lowest-order QCD annihilation and
Compton processes. We focus in particular on the azimuthal-angular
distributions, which are of the form cos(phi) and cos(2phi). At small
transverse momentum q_T of the lepton pair, q_T << Q, with Q the pair mass,
these terms are known to be suppressed relative to the phi-independent part of
the Drell-Yan cross section by one or two powers of the transverse momentum.
Nonetheless, as we show, like the phi-independent part they are subject to
large logarithmic corrections, whose precise form however depends on the
reference frame chosen. These logarithmic contributions ultimately require
resummation to all orders in the strong coupling. We discuss the potential
effects of resummation on the various angular terms in the cross section and on
the Lam-Tung relation.Comment: 13 pages, 2 figures; reference added, minor other changes, matches
version to be published in PR
Theoretical study of the synthesis of superheavy nuclei with Z= 119 and 120 in heavy-ion reactions with trans-uranium targets
By using a newly developed di-nuclear system model with a dynamical potential
energy surface---the DNS-DyPES model, hot fusion reactions for synthesizing
superheavy nuclei (SHN) with the charge number Z = 112-120 are studied. The
calculated evaporation residue cross sections are in good agreement with
available data. In the reaction 50Ti+249Bk -> (299-x)119 + xn, the maximal
evaporation residue (ER) cross section is found to be about 0.11 pb for the
4n-emission channel. For projectile-target combinations producing SHN with
Z=120, the ER cross section increases with the mass asymmetry in the incident
channel increasing. The maximal ER cross sections for 58Fe+244Pu and 54Cr +
248Cm are relatively small (less than 0.01 pb) and those for 50Ti+249Cf and
50Ti+251Cf are about 0.05 and 0.25 pb, respectively.Comment: 6 pages, 5 figures; Phys. Rev. C, in pres
Formation of superheavy nuclei in cold fusion reactions
Within the concept of the dinuclear system (DNS), a dynamical model is
proposed for describing the formation of superheavy nuclei in complete fusion
reactions by incorporating the coupling of the relative motion to the nucleon
transfer process. The capture of two heavy colliding nuclei, the formation of
the compound nucleus and the de-excitation process are calculated by using an
empirical coupled channel model, solving a master equation numerically and
applying statistical theory, respectively. Evaporation residue excitation
functions in cold fusion reactions are investigated systematically and compared
with available experimental data. Maximal production cross sections of
superheavy nuclei in cold fusion reactions with stable neutron-rich projectiles
are obtained. Isotopic trends in the production of the superheavy elements
Z=110, 112, 114, 116, 118 and 120 are analyzed systematically. Optimal
combinations and the corresponding excitation energies are proposed.Comment: 18 pages, 8 figure
The group approach to AdS space propagators: A fast algorithm
In this letter we show how the method of [4] for the calculation of two-point
functions in d+1-dimensional AdS space can be simplified. This results in an
algorithm for the evaluation of the two-point functions as linear combinations
of Legendre functions of the second kind. This algorithm can be easily
implemented on a computer. For the sake of illustration, we displayed the
results for the case of symmetric traceless tensor fields with rank up to l=4.Comment: 14 pages, comment adde
Neutrinoless Double Beta Decay and Future Neutrino Oscillation Precision Experiments
We discuss to what extent future precision measurements of neutrino mixing
observables will influence the information we can draw from a measurement of
(or an improved limit on) neutrinoless double beta decay. Whereas the Delta m^2
corresponding to solar and atmospheric neutrino oscillations are expected to be
known with good precision, the parameter theta_{12} will govern large part of
the uncertainty. We focus in particular on the possibility of distinguishing
the neutrino mass hierarchies and on setting a limit on the neutrino mass. We
give the largest allowed values of the neutrino masses which allow to
distinguish the normal from the inverted hierarchy. All aspects are discussed
as a function of the uncertainty stemming from the involved nuclear matrix
elements. The implications of a vanishing, or extremely small, effective mass
are also investigated. By giving a large list of possible neutrino mass
matrices and their predictions for the observables, we finally explore how a
measurement of (or an improved limit on) neutrinoless double beta decay can
help to identify the neutrino mass matrix if more precise values of the
relevant parameters are known.Comment: 35 pages, 12 figures. Comments and references added. To appear in PR
A Unified Picture for Single Transverse-Spin Asymmetries in Hard Processes
Using Drell-Yan pair production as an example, we explore the relation
between two well-known mechanisms for single transverse-spin asymmetries in
hard processes: twist-three quark-gluon correlations when the pair's transverse
momentum is large, , and time-reversal-odd and
transverse-momentum-dependent parton distributions when is much less
than the pair's mass. We find that although the two mechanisms have their own
domain of validity, they describe the same physics in the kinematic region
where they overlap. This unifies the two mechanisms and imposes an important
constraint on phenomenological studies of single spin asymmetries.Comment: 4 pages, 3 figure
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