54 research outputs found
A fast and accurate method for perturbative resummation of transverse momentum-dependent observables
We propose a novel strategy for the perturbative resummation of transverse
momentum-dependent (TMD) observables, using the spectra of gauge bosons
(, Higgs) in collisions in the regime of low (but perturbative)
transverse momentum as a specific example. First we introduce a scheme to
choose the factorization scale for virtuality in momentum space instead of in
impact parameter space, allowing us to avoid integrating over (or cutting off)
a Landau pole in the inverse Fourier transform of the latter to the former. The
factorization scale for rapidity is still chosen as a function of impact
parameter , but in such a way designed to obtain a Gaussian form (in ) for the exponentiated rapidity evolution kernel, guaranteeing convergence
of the integral. We then apply this scheme to obtain the spectra for
Drell-Yan and Higgs production at NNLL accuracy. In addition, using this scheme
we are able to obtain a fast semi-analytic formula for the perturbative
resummed cross sections in momentum space: analytic in its dependence on all
physical variables at each order of logarithmic accuracy, up to a numerical
expansion for the pure mathematical Bessel function in the inverse Fourier
transform that needs to be performed just once for all observables and
kinematics, to any desired accuracy.Comment: 60 pages + Appendices, 16 Figures v.2, Accepted in JHEP, discussion
added on low-qT limit, other minor clarifications made and typos correcte
Analytic Calculation of 1-Jettiness in DIS at
We present an analytic calculation of cross sections
in deep inelastic scattering (DIS) dependent on an event shape, 1-jettiness,
that probes final states with one jet plus initial state radiation. This is the
first entirely analytic calculation for a DIS event shape cross section at this
order. We present results for the differential and cumulative 1-jettiness cross
sections, and express both in terms of structure functions dependent not only
on the usual DIS variables , but also on the 1-jettiness .
Combined with previous results for log resummation, predictions are obtained
over the entire range of the 1-jettiness distribution.Comment: 40 pages, 8 figure
Using Line Shapes to Discriminate between Binding Mechanisms for the X(3872)
We construct line shapes for the X(3872) that generalize the Flatte and
zero-range line shapes that have been considered previously. These line shapes
are associated with scattering amplitudes that are exactly unitary for real
values of the interaction parameters and can be derived from a renormalizable
quantum field theory. The new line shapes can be used to discriminate between
the alternative binding mechanisms in which the X(3872) is generated either
dynamically by charm meson interactions or by a resonance near the D^{*0}
Dbar^0 threshold. If the resonance is identified with the P-wave charmonium
state chi'_{c1}, the interaction parameters can be constrained by using
charmonium phenomenology. We analyze data on the X(3872) and also data from the
Belle and Babar Collaborations on the invariant mass distribution of the charm
mesons from the decay B -> K + D^{*0} Dbar^0 up to 4000 MeV. Our analysis is
compatible with the mechanism for the X(3872) being either a fine-tuning of
charm meson interactions or the fine-tuning of the chi'_{c1} to the D^{*0}
Dbar^0 threshold. In particular, the data do not exclude a separate chi'_{c1}
resonance between the D^{*+} D^- threshold and 4000 MeV.Comment: 50 pages, 5 figures, 2 tables. Version published in Physical Review
Efimov Physics in Atom-Dimer Scattering of Lithium-6 Atoms
Lithium-6 atoms in the three lowest hyperfine states display universal
properties when the S-wave scattering length between each pair of states is
large. Recent experiments reported four pronounced features arising from Efimov
physics in the atom-dimer relaxation rate, namely two resonances and two local
minima. We use the universal effective field theory to calculate the atom-dimer
relaxation rate at zero temperature. Our results describe the four features
qualitatively and imply there is a hidden local minimum. In the vicinity of the
resonance at 685 G, we perform a finite temperature calculation which improves
the agreement of theory and experiment. We conclude that finite temperature
effects cannot be neglected in the analysis of the experimental data.Comment: 13 pages, 5 figures, final versio
Transverse Vetoes with Rapidity Cutoff in SCET
We consider di-jet production in hadron collisions where a transverse veto is
imposed on radiation for (pseudo-)rapidities in the central region only, where
this central region is defined with rapidity cutoff. For the case where the
transverse measurement (e.g., transverse energy or min for jet veto) is
parametrically larger relative to the typical transverse momentum beyond the
cutoff, the cross section is insensitive to the cutoff parameter and is
factorized in terms of collinear and soft degrees of freedom. The virtuality
for these degrees of freedom is set by the transverse measurement, as in
typical transverse-momentum dependent observables such as Drell-Yan, Higgs
production, and the event shape broadening. This paper focuses on the other
region, where the typical transverse momentum below and beyond the cutoff is of
similar size. In this region the rapidity cutoff further resolves soft
radiation into (u)soft and soft-collinear radiation with different rapidities
but identical virtuality. This gives rise to rapidity logarithms of the
rapidity cutoff parameter which we resum using renormalization group methods.
We factorize the cross section in this region in terms of soft and collinear
functions in the framework of soft-collinear effective theory, then further
refactorize the soft function as a convolution of the (u)soft and
soft-collinear functions. All these functions are calculated at one-loop order.
As an example, we calculate a differential cross section for a specific
partonic channel, , for the jet shape angularities and show that
the refactorization allows us to resum the rapidity logarithms and
significantly reduce theoretical uncertainties in the jet shape spectrum
Optimal spin-quantization axes for the polarization of dileptons with large transverse momentum
The leading-order parton processes that produce a dilepton with large
transverse momentum predict that the transverse polarization should increase
with the transverse momentum for almost any choice of the quantization axis for
the spin of the virtual photon. The rate of approach to complete transverse
polarization depends on the choice of spin quantization axis. We propose axes
that optimize that rate of approach. They are determined by the momentum of the
dilepton and the direction of the jet that provides most of the balancing
transverse momentum.Comment: 4 pages, 1 figure, minor corrections, version published in Phys. Rev.
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