803 research outputs found
Nonleptonic Weak Decays of Bottom Baryons
Cabibbo-allowed two-body hadronic weak decays of bottom baryons are analyzed.
Contrary to the charmed baryon sector, many channels of bottom baryon decays
proceed only through the external or internal W-emission diagrams. Moreover,
W-exchange is likely to be suppressed in the bottom baryon sector.
Consequently, the factorization approach suffices to describe most of the
Cabibbo-allowed bottom baryon decays. We use the nonrelativistic quark model to
evaluate heavy-to-heavy and heavy-to-light baryon form factors at zero recoil.
When applied to the heavy quark limit, the quark model results do satisfy all
the constraints imposed by heavy quark symmetry. The decay rates and up-down
asymmetries for bottom baryons decaying into and
are calculated. It is found that the up-down asymmetry is negative except for
decay and for decay modes with in the final
state. The prediction for
is consistent with the recent CDF measurement. We also present
estimates for decays and compare with various model
calculations.Comment: 24 pages, to appear in Phys. Rev. Uncertainties with form factor q^2
dependence are discusse
Hamiltonian Formalism of the de-Sitter Invariant Special Relativity
Lagrangian of the Einstein's special relativity with universal parameter
() is invariant under Poincar\'e transformation which preserves
Lorentz metric . The has been extended to be
one which is invariant under de Sitter transformation that preserves so called
Beltrami metric . There are two universal parameters and in
this Special Relativity (denote it as ). The
Lagrangian-Hamiltonian formulism of is formulated in this
paper. The canonic energy, canonic momenta, and 10 Noether charges
corresponding to the space-time's de Sitter symmetry are derived. The canonical
quantization of the mechanics for -free particle is
performed. The physics related to it is discussed.Comment: 24 pages, no figur
Light-Front Approach for Heavy Pentaquark Transitions
Assuming the two diquark structure for the pentaquark state as advocated in
the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and
parity-odd triplet heavy pentaquark baryons. The theoretical estimate of
charmed and bottom pentaquark masses is quite controversial and it is not clear
whether the ground-state heavy pentaquark lies above or below the strong-decay
threshold. We study the weak transitions of heavy pentaquark states using the
light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark
transition form factors can be expressed in terms of three Isgur-Wise
functions: two of them are found to be normalized to unity at zero recoil,
while the third one is equal to 1/2 at the maximum momentum transfer, in
accordance with the prediction of the large-Nc approach or the quark model.
Therefore, the light-front model calculations are consistent with the
requirement of heavy quark symmetry. Numerical results for form factors and
Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to
Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to
Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q,
Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light
octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and
Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+
pi- are estimated to be at the level of 10^{-3} and a few percents,
respectively.Comment: 33 pages, 3 figures, version to be published in Phys. Rev.
Light-Front Approach for Pentaquark Strong Decays
Assuming the two diquark structure for the pentaquark state as advocated in
the Jaffe-Wilczek model, we study the strong decays of light and heavy
parity-even pentaquark states using the light-front quark model in conjunction
with the spectator approximation. The narrowness of the Theta width is ascribed
to the p-wave configuration of the diquark pair. Taking the Theta width as a
benchmark, we estimate the rates of the strong decays Xi_{3/2}-- to Xi- pi-,
Sigma- K-, Sigma_{5c}0 to D_s- p, D_{s0}*- p and Xi_{5c}0 to D_s- Sigma+,
D_{s0}^{*-} Sigma+ with Sigma_{5c} Xi_{5c} being antisextet charmed pentaquarks
and D_{s0}* a scalar strange charmed meson. The ratio of Gamma(P_c to Baryon
D_{s0}*)/Gamma(P_c to Baryon D_s) is very useful for verifying the parity of
the antisextet charmed pentaquark P_c. It is expected to be of order unity for
an even parity P_c and much less than one for an odd parity pentaquark.Comment: 24 pages, 2 figure
Numerical Simulation of the Thermomechanical Behavior of a Hot Stamping Die
For studying the temperature field of hot stamping, the effect of the distance between cooling pipes, the distance between the cooling pipe and mold surface, and the water cooling pipe diameter were evaluated with ANSYS software. The results showed that the maximum temperature was about 50°C, and the maximum temperature difference of hot stamping was less than 35°C. The maximum temperature and the uniformity of stamping temperature can be improved by controlling the size and spacing of cooling pipes.Определен эффект расстояния между трубами охлаждения, расстояния между трубой охлаждения и поверхностью формы и диаметра трубы водяного охлаждения на температурное поле горячей штамповки с использованием программного обеспечения ANSYS. Показано, что максимальная температура составляет примерно 50°С, а максимальный перепад температуры горячей штамповки менее 35°С. Регулирование размеров и расстояния между трубами охлаждения позволяет увеличить максимальную температуру и равномерность распределения
температуры штамповки
CKM Favored Semileptonic Decays of Heavy Hadrons at Zero Recoil
We study the properties of Cabibbo-Kobayashi-Maskawa (CKM) favored
semileptonic decays of mesons and baryons containing a heavy quark at the point
of no recoil. We first use a diagrammatic analysis to rederive the result
observed by earlier authors that at this kinematic point the meson decays
via transitions can only produce a or meson. The result is
generalized to include photon emissions which violate heavy quark flavor
symmetry. We show that photons emitted by the heavy quarks and the charged
lepton are the only light particles that can decorate the decays at zero recoil, and the similar processes of heavy baryons.
Implications for the determinations of the CKM parameter are
discussed. Also studied in this paper is the connection between our
diagrammatic analysis of suppression of particle emission and the formal
observation based on weak currents at zero recoil being generators of heavy
quark symmetry. We show that the two approaches can be unified by considering
the Isgur-Wise function in the presence of an external source.Comment: 27 pages, including 11 figures using macros FEYNMAN.te
Phosphoproteins and protein-kinase activity in isolated envelopes of pea (Pisum sativum L.) chloroplasts
A protein kinase was found in envelope membranes of purified pea (Pisum sativum L.) chloroplasts. Separation of the two envelope membranes showed that most of the enzyme activity was localized in the outer envelope. The kinase was activated by Mg2+ and inhibited by ADP and pyrophosphate. It showed no response to changes in pH in the physiological range (pH 7-8) or conventional protein substrates. Up to ten phosphorylated proteins could be detected in the envelope-membrane fraction. The molecular weights of these proteins, as determined by polyacrylamide-gel electrophoresis were: two proteins higher than 145 kDa, 97, 86, 62, 55, 46, 34 and 14 kDa. The 86-kDa band being the most pronounced. Experiments with separated inner and outer envelopes showed that most labeled proteins are also localized in the outer-envelope fraction. The results indicate a major function of the outer envelope in the communication between the chloroplast and the parent cell
Vector and pseudoscalar charm meson radiative decays
Combining heavy quark effective theory and the chiral Lagrangian approach we
investigate radiative decays of pseudoscalar mesons. We first reanalyse
decays within the effective Lagrangian approach
using heavy quark spin symmetry, chiral symmetry Lagrangian, but including also
the light vector mesons. We then investigate decays
and calculate the and partial widths and branching ratios.Comment: 21 pages Latex, no figures, IJS-TP-94/19, TUM-31-62/94, NUHEP-TH-94-
Nonresonant Three-body Decays of D and B Mesons
Nonresonant three-body decays of D and B mesons are studied. It is pointed
out that if heavy meson chiral perturbation theory (HMChPT) is applied to the
heavy-light strong and weak vertices and assumed to be valid over the whole
kinematic region, then the predicted decay rates for nonresonant charmless
3-body B decays will be too large and especially B^- --> pi^- K^+ K^- greatly
exceeds the current experimental limit. This can be understood as chiral
symmetry has been applied there twice beyond its region of validity. If HMChPT
is applied only to the strong vertex and the weak transition is accounted for
by the form factors, the dominant B^* pole contribution to the tree-dominated
direct three-body B decays will become small and the branching ratio will be of
order 10^{-6}. The decay modes B^- --> (K^- h^+ h^-)_{NR} and bar{B}^0 -->
(bar{K}^0 h^+h^-)_{NR} for h = pi, K are penguin dominated. We apply HMChPT in
two different cases to study the direct 3-body D decays and compare the results
with experiment. Theoretical uncertainties are discussed.Comment: 24 pages, 2 figures. New experimental results of direct 3-body D
decays as Reported at ICHEP2002 are included. To appear in Phys. Re
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