3,748 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
Isotope fractionation and sulfur metabolism by pure and enrichment cultures of elemental sulfur-disproportionating bacteria
We have explored the sulfur metabolism and accompanying fractionation of sulfur isotopes during the disproportionation of elemental sulfur by seven different enrichments and three pure bacterial cultures. Cultures were obtained from both marine and freshwater environments. In all cases appreciable fractionation accompanied elemental sulfur disproportionation, with two ranges of fractionation observed. All cultures except Desulfobulbus propionicus produced sulfide depleted in S-34 by between 5.5 and 6.9 per mil (avg of 6.3 per mi) and sulfate enriched in S-34 by between 17.1 and 20.2 per mil (avg of 18.8 per ml). The narrow range of fractionations suggests a conserved biochemistry for the disproportionation of elemental sulfur by many different marine and freshwater bacteria. Fractionations accompanying elemental sulfur disproportionation by Db. propionicus were nearly twice as great as the others, suggesting a different cellular level pathway of sulfur processing by this organism. In nearly every case pyrite formation accompanied the disproportionation of elemental sulfur. By using sulfur isotopes as a tracer of sulfur source, we could identify that pyrite formed both by the addition of elemental sulfur to FeS and from reaction between FeS and H2S. Both processes were equally fast and up to 10(4)-10(5) times faster than expected from the reported kinetics of inorganic pyrite-formation reactions. We speculate that bacteria may have enhanced rates of pyrite formation in our experimental systems. The organisms explored here have different strategies for growth and survival, and they may be active in environments ranging from dissolved sulfide-poor suboxic sediments to interfaces supporting steep opposing gradients of oxygen and sulfide. A large environmental range, combined with high bacterial numbers, significant isotope fractionations, and a possible role in pyrite formation, make elemental sulfur-disproportionating bacteria potentially significant actors in the sedimentary cycling of sulfur compounds
Relativistic effects in proton-induced deuteron break-up at intermediate energies with forward emission of a fast proton pair
Recent data on the reaction pD -> (pp) n with a fast forward pp pair with
very small excitation energy is analyzed within a covariant approach based on
the Bethe-Salpeter formalism. It is demonstrated that the minimum
non-relativistic amplitude is completely masked by relativistic effects, such
as Lorentz boost and the negative-energy P components in the 1S_0
Bethe-Salpeter amplitude of the pp pair
Weak Phase From Ratio of Rates
The ratio of partial decay rates for charged and neutral mesons to final states provides information on the weak phase when augmented with information on the CP-violating asymmetry
in the mode. The requirements for a useful determination of
are examined in the light of present information about the decays , , and the corresponding charge-conjugate
modes. The effects of electroweak penguins and rescattering corrections are
noted, and proposals are made for estimating and measuring their importance.Comment: 16 pages, latex, 3 figures, revised version sent to Phys. Rev.
Final State Radiative Effects for the Exact O(alpha) YFS Exponentiated (Un)Stable W+W- Production At and Beyond LEP2 Energies
We present the LL final state radiative effects for the exact O(alpha) YFS
exponentiated (un)stable WW pair production at LEP2/NLC energies using Monte
Carlo event generator methods. The respective event generator, version 1.12 of
the program YFSWW3, wherein both Standard Model and anomalous triple gauge
boson couplings are allowed, generates n(\gamma) radiation both from the
initial state and from the intermediate W+ W- and generates the LL final state
W decay radiative effects. Sample Monte Carlo data are illustrated.Comment: 16 pages, 8 figures, 2 table
Relativistic description of electron scattering on the deuteron
Within a quasipotential framework a relativistic analysis is presented of the
deuteron current. Assuming that the singularities from the nucleon propagators
are important, a so-called equal time approximation of the current is
constructed. This is applied to both elastic and inelastic electron scattering.
As dynamical model the relativistic one boson exchange model is used.
Reasonable agreement is found with a previous relativistic calculation of the
elastic electromagnetic form factors of the deuteron. For the unpolarized
inelastic electron scattering effects of final state interactions and
relativistic corrections to the structure functions are considered in the
impulse approximation. Two specific kinematic situations are studied as
examples.Comment: (19 pages in revtex + 15 figures not included, available upon
request.) report THU-93-10
Precision Predictions for (Un)Stable W+W- Pair Production At and Beyond LEP2 Energies Beyond LEP2 Energies
We present precision calculations of the processes e+e- -> 4-fermions in
which the double resonant W+W- intermediate state occurs. Referring to this
latter intermediate state as the 'signal process', we show that, by using the
YFS Monte Carlo event generators YFSWW3-1.14 and KORALW1.42 in an appropriate
combination, we achieve a physical precision on the signal process, as isolated
with LEP2 MC Workshop cuts, below 0.5 per cent. We stress the full gauge
invariance of our calculations and we compare our results with those of other
authors where appropriate. In particular, sample Monte Carlo data are
explicitly illustrated and compared with the results of the program RacoonWW of
Dittmaier {\it et al.}. In this way, we show that the total (physical plus
technical) precision tag for the WW signal process cross section is 0.4 per
cent for 200 GeV, for example. Results are also given for 500 GeV with an eye
toward the LC.Comment: 19 pages, 2 figs;corrected Tab. 3;improved refs.,figs.,text;improved
refs.,text;improved tex
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.
Rescattering Information from Decays
Rescattering effects can modify the dependence on the weak phase of the ratio of rates for and . A test for these effects based on the
processes has been suggested. It is pointed out that the
rates for the processes , which are expected to be {\it
dominated} by rescattering and for which considerably better experimental
bounds exist, are likely to provide a more stringent constraint on these
effects.Comment: 22 pages, latex, 7 figures, to be published in Phys. Rev. D. Minor
corrections and addition
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
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