893 research outputs found
Note on new interesting baryon channels to measure the photon polarization in b -> s gamma
At LHC a large number of b-flavored baryons will be produced. In this note we
propose new baryon modes to determine the photon helicity of the penguin
transition . The decay has the
drawback that the , being neutral and long-lived, will escape
detection most of the time. To overcome this difficulty, transitions of the
type have been proposed, where
denotes an excited state decaying strongly within the detector into the clean
mode . The doublet , that decays weakly, has a number of good
features. The charged baryon will decay into the mode ,
where the ground state hyperon , although it will decay most of the time
outside the detector, can be detected because it is charged. We consider also
the decay of into , where a higher mass state
can decay strongly within the detector. We point out that the initial
transverse polarization of has to be known in all cases. To determine
this parameter through the transition , we distinguish
between different cases, and underline that in some situations one needs {\it
theoretical input} on the asymmetry parameter of the primary
decay. {\it A fortiori} the same considerations apply to the case of the
Bound on the curvature of the Isgur-Wise function of the baryon semileptonic decay Lambda_b -> Lambda_c + l + nu
In the heavy quark limit of QCD, using the Operator Product Expansion, the
formalism of Falk for hadrons or arbitrary spin, and the non-forward amplitude,
as proposed by Uraltsev, we formulate sum rules involving the Isgur-Wise
function of the baryon transition , where the light cloud has for both
initial and final baryons. We recover the lower bound for the slope
obtained by Isgur et al., and we
generalize it by demonstrating that the IW function is an
alternate series in powers of , i.e. . Moreover, exploiting systematically the sum rules, we get an improved
lower bound for the curvature in terms of the slope, . This
bound constrains the shape of the Isgur-Wise function and it will be compelling
in the analysis of future precise data on the differential rate of the baryon
semileptonic decay , that
has a large measured branching ratio, of about 5%.Comment: 16 page
Time-Efficient Read/Write Register in Crash-prone Asynchronous Message-Passing Systems
The atomic register is certainly the most basic object of computing science.
Its implementation on top of an n-process asynchronous message-passing system
has received a lot of attention. It has been shown that t \textless{} n/2
(where t is the maximal number of processes that may crash) is a necessary and
sufficient requirement to build an atomic register on top of a crash-prone
asynchronous message-passing system. Considering such a context, this paper
visits the notion of a fast implementation of an atomic register, and presents
a new time-efficient asynchronous algorithm. Its time-efficiency is measured
according to two different underlying synchrony assumptions. Whatever this
assumption, a write operation always costs a round-trip delay, while a read
operation costs always a round-trip delay in favorable circumstances
(intuitively, when it is not concurrent with a write). When designing this
algorithm, the design spirit was to be as close as possible to the one of the
famous ABD algorithm (proposed by Attiya, Bar-Noy, and Dolev)
Sum rules for leading and subleading form factors in Heavy Quark Effective Theory using the non-forward amplitude
Within the OPE, we the new sum rules in Heavy Quark Effective Theory in the
heavy quark limit and at order 1/m_Q, using the non-forward amplitude. In
particular, we obtain new sum rules involving the elastic subleading form
factors chi_i(w) (i = 1,2, 3) at order 1/m_Q that originate from the L_kin and
L_mag perturbations of the Lagrangian. To the sum rules contribute only the
same intermediate states (j^P, J^P) = ((1/2)^-, 1^-), ((3/2)^-, 1^-) that enter
in the 1/m_Q^2 corrections of the axial form factor h_(A_1)(w) at zero recoil.
This allows to obtain a lower bound on -delta_(1/m^2)^(A_1) in terms of the
chi_i(w) and the shape of the elastic IW function xi(w). An important
theoretical implication is that chi'_1(1), chi_2(1) and chi'_3(1) (chi_1(1) =
chi_3(1) = 0 from Luke theorem) must vanish when the slope and the curvature
attain their lowest values rho^2->3/4, sigma^2->15/16. These constraints should
be taken into account in the exclusive determination of |V_(cb)|.Comment: Invited talk to the International Workshop on Quantum Chromodynamics
: Theory and Experiment, Conversano (Bari, Italy), 16-20 June 200
- âŠ