3,121 research outputs found
Controlling Molecular Scattering by Laser-Induced Field-Free Alignment
We consider deflection of polarizable molecules by inhomogeneous optical
fields, and analyze the role of molecular orientation and rotation in the
scattering process. It is shown that molecular rotation induces spectacular
rainbow-like features in the distribution of the scattering angle. Moreover, by
preshaping molecular angular distribution with the help of short and strong
femtosecond laser pulses, one may efficiently control the scattering process,
manipulate the average deflection angle and its distribution, and reduce
substantially the angular dispersion of the deflected molecules. We provide
quantum and classical treatment of the deflection process. The effects of
strong deflecting field on the scattering of rotating molecules are considered
by the means of the adiabatic invariants formalism. This new control scheme
opens new ways for many applications involving molecular focusing, guiding and
trapping by optical and static fields
In Pursuit of New Physics with B_s Decays
The presence of a sizeable CP-violating phase in B_s^0-B_s^0-bar mixing would
be an unambiguous signal of physics beyond the Standard Model. We analyse
various possibilities to detect such a new phase considering both tagged and
untagged decays. The effects of a sizeable width difference Delta Gamma between
the B_s mass eigenstates, on which the untagged analyses rely, are included in
all formulae. A novel method to find this phase from simple measurements of
lifetimes and branching ratios in untagged decays is proposed. This method does
not involve two-exponential fits, which require much larger statistics. For the
tagged decays, an outstanding role is played by the observables of the
time-dependent angular distribution of the B_s -> J/psi [-> l^+ l^-] \phi [->
K^+K^-] decay products. We list the formulae needed for the angular analysis in
the presence of both a new CP-violating phase and a sizeable Delta Gamma, and
propose methods to remove a remaining discrete ambiguity in the new phase. This
phase can therefore be determined in an unambiguous way.Comment: minor changes, lattice prediction of Delta Gamma updated, appears in
PR
Exploring CP Violation with Decays
We point out that the pure ``tree'' decays are
particularly well suited to extract the CKM angle through amplitude
relations. In contrast to conceptually similar strategies using or decays, the advantage of the approach is that
the corresponding triangles have three sides of comparable length and do not
involve small amplitudes. Decays of the type -- the
-spin counterparts of -- can be added to the
analysis, as well as channels, where the - and -mesons are
replaced by higher resonances.Comment: 9 pages, LaTeX, 3 figures, reference adde
Extracting gamma and Penguin Topologies through CP Violation in B_s^0 -> J/psi K_S
The B_s^0 -> J/psi K_S decay has recently been observed by the CDF
collaboration and will be of interest for the LHCb experiment. This channel
will offer a new tool to extract the angle gamma of the unitarity triangle and
to control doubly Cabibbo-suppressed penguin corrections to the determination
of sin(2beta) from the well-known B_d^0 -> J/psi K_S mode with the help of the
U-spin symmetry of strong interactions. While any competitive determination of
gamma is interesting, the latter aspect is particularly relevant as LHCb will
enter a territory of precision which makes the control of doubly
Cabibbo-suppressed Standard-Model corrections mandatory. Using the data from
CDF and the e^+e^- B factories as a guideline, we explore the sensitivity for
gamma and the penguin parameters and point out that the B_s^0-\bar B_s^0 mixing
phase phi_s, which is only about -2 deg in the Standard Model but may be
enhanced through new physics, is a key parameter for these analyses. We find
that the mixing-induced CP violation S(B_s^0 -> J/psi K_S) shows an interesting
correlation with sin(phi_s), which serves as a target region for the first
measurement of this observable at LHCb.Comment: 20 pages, 8 figure
Exploring CP Violation through Correlations in B --> pi K, B_d --> pi^+pi^-, B_s --> K^+K^- Observable Space
We investigate allowed regions in observable space of B --> pi K, B_d -->
pi^+pi^- and B_s --> K^+K^- decays, characterizing these modes in the Standard
Model. After a discussion of a new kind of contour plots for the
system, we focus on the mixing- induced and direct CP asymmetries of the decays
B_d --> pi^+pi^- and B_s--> K^+K^-. Using experimental information on the
CP-averaged B_d --> pi^{+/-}K^{+/-} and B_d --> pi^+pi^- branching ratios, the
relevant hadronic penguin parameters can be constrained,implying certain
allowed regions in observable space. In the case of B_d --> pi^+pi^-, an
interesting situation arises now in view of the recent B-factory measurements
of CP violation in this channel, allowing us to obtain new constraints on the
CKM angle gamma as a function of the B^0_d--\bar{B^0_d} mixing phase
phi_d=2beta, which is fixed through A_{CP}^{mix}(B_d --> J/psi K_S) up to a
twofold ambiguity. If we assume that A_{CP}^{mix}(B_d --> pi^+pi^-) is
positive, as indicated by recent Belle data, and that phi_d is in agreement
with the ``indirect'' fits of the unitarity triangle, also the corresponding
values for gamma around 60 degrees can be accommodated. On the other hand, for
the second solution of phi_d, we obtain a gap around gamma ~ 60 degrees. The
allowed region in the space of A_{CP}^{mix}(B_s --> K^+K^-) and
A_{CP}^{dir}(B_s --> K^+K^-) is very constrained in the Standard Model, thereby
providing a narrow target range for run II of the Tevatron and the experiments
of the LHC era.Comment: 34 pages, LaTeX, 12 figures. More detailed introduction and a few
Comments added, conclusions unchanged. To appear in Phys. Rev.
CP violation and CKM phases from angular distributions for decays into admixtures of CP eigenstates
We investigate the time-evolutions of angular distributions for decays
into final states that are admixtures of CP-even and CP-odd configurations. A
sizable lifetime difference between the mass eigenstates allows a probe
of CP violation in time-dependent untagged angular distributions. Interference
effects between different final state configurations of , determine the Wolfenstein parameter from
untagged data samples, or -- if one uses as an additional
input -- the notoriously difficult to measure CKM angle . Another
determination of is possible by using isospin symmetry of strong
interactions to relate untagged data samples of
and . We note that the untagged angular
distribution for provides interesting information about
electroweak penguins.Comment: 19 pages, LaTeX, no figure
Localized modes in nonlinear photonic kagome nanoribbons
We examine localization of light in nonlinear (Kerr) kagome lattices in the
shape of narrow strips of varying width. For the narrowest ribbon, the band
structure features a flat band leading to linear dynamical trapping of an
initially localized excitation. We also find a geometry-induced bistability of
the nonlinear modes as the width of the strip is changed. A crossover from one
to two dimensions localization behavior is observed as the width is increased,
attaining two-dimensional behavior for relatively narrow ribbons.Comment: 4 pages, 8 figures, submitted for publicatio
Using B_s^0 Decays to Determine the CP Angles \alpha and \gamma
Dighe, Gronau and Rosner have shown that, by assuming SU(3) flavor symmetry
and first-order SU(3) breaking, it is possible to extract the CP angles \alpha
and \gamma from measurements of the decay rates of B_d^0(t) --> \pi^+\pi^-,
B_d^0 --> \pi^- K^+ and B^+ --> \pi^+ K^0, along with their charge-conjugate
processes. We extend their analysis to include the SU(3)-related decays B_s^0
--> \pi^+ K^-, B_s^0(t) --> K^+ K^- and B_s^0 --> K^0 {\bar K^0}. There are
several advantages to this extension: discrete ambiguities are removed, fewer
assumptions are necessary, and the method works even if all strong phases
vanish. In addition, we show that \gamma can be obtained cleanly, with no
penguin contamination, by using the two decays B_s^0(t) --> K^+ K^- and B_s^0
--> K^0 {\bar K^0}.Comment: 28 pages, LaTe
A Simple Approximation of the One-Loop Corrected Cross Section for at LEP 2
Using the SU(2) gauge coupling, , at the high-energy
scale of , defined by the (theoretical value of the) leptonic
W-width, rather than using the low-energy value, defined via the Fermi
coupling, , in the Born approximation, and supplementing with Coulomb
corrections and initial state radiation, errors with respect to the exact
one-loop results for the differential cross section of are
below 1% at LEP 2 energies at all production angles. A similar
procedure is suggested to incorporate leading bosonic loop effects into
four-fermion production in the fermion-loop scheme. The resulting accuracy
below 1% is sufficient for LEP 2 experiments.Comment: 12 pages, LaTeX including 1 postscript figure, submitted to Phys.
Lett.
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