6,266 research outputs found
Decays of b hadrons and a possible new four-quark interaction
A possibility is considered of explaining the low experimental value of the
ratio of the lifetimes tau(Lambda_b)/tau(B_d) by a new `centiweak' four-quark
interaction, i.e with a strength on the order of 10^{-2}G_F. It is noted that
the considered interaction can also improve agreement with the data on low
semileptonic branching ratio B_{sl}(B) in B meson decays with a simultaneous
slight decrease in the prediction for the average charm yield in those decays.
The proposed new interaction modifies within the present experimental limits
the predictions for differences of lifetimes among B mesons, and can thus be
probed by more precise data on these differences. A sample model is briefly
discussed, where the new interaction arises through a weak SU(2) singlet scalar
field with quantum numbers of a diquark.Comment: 10 page
Non-factorizable terms, heavy quark masses, and semileptonic decays of D and B mesons
The non-factorizable terms in the operator product expansion have been
recognized as one of theoretical obstacles for precision determination of the
mixing parameter from semileptonic B decays. It is pointed out here
that the recent CLEO data on the parameters of the heavy quark expansion
and , combined with a theoretical bound on
strongly favor the existence of a sizeable contribution of
non-factorizable terms in semileptonic decays of mesons. Thus these terms
are likely to solve the long-standing problem of the deficit of semileptonic
decay rate of the mesons, and with better data their magnitude can be
determined and used in studies of the parameter .Comment: 7 pages, 1 figur
On the Parity Degeneracy of Baryons
The gross features of the observed baryon excitation spectrum below 2 GeV are
well explained if the spectrum generating algebra of its intrinsic orbital
angular momentum states is o(4)*su(2)_I. The spins of the resonances are
obtained through the coupling of a Lorentz bi-spinor (1/2,0)+ (0,1/ 2) to a
multiplet of the type (j,j) in its O(4)/O(3) reduction. The parities of the
resonances follow from those of the O(3) members of the (j,j) multiplets. In
this way relativistic SL(2,C) representations are constructed. For example, the
first S11, P11, and D13 states with masses around 1500 MeV fit into the (1/2,
1/2)* [(1/2,0)+(0,1/2)] representation. The observed parities of the resonances
correspond to natural parities of the (1/2,1/2) states. The second P11, S11,
D13- together with the first P13, F15, D15, and (a predicted) F17 -resonances,
centered around 1700 MeV, are organized into the (3/2,3/2)*[(1/2,0)+(0,1/2)]
representation. I argue that the members of the (3/2,3/2) multiplet carry
unnatural parities and that in this region chiral symmetry is restored. In the
N(939)- N(1650) transition the chiral symmetry mode is changed, and therefore,
a chiral phase transition is predicted to take place.Comment: 9 pages, LaTex, 1 figure; published in Mod.Phys.Lett. A12 (1997)
2373; minor misprints corrected, no statement change
The form factors from analyticity and unitarity
We study the shape parameters of the scalar and vector form factors
using as input dispersion relations and unitarity for the moments of suitable
heavy-light correlators evaluated with Operator Product Expansions, including
terms in perturbative QCD. For the scalar form factor, a low
energy theorem and phase information on the unitarity cut are implemented to
further constrain the shape parameters. We finally determine points on the real
axis and isolate regions in the complex energy plane where zeros of the form
factors are excluded.Comment: 6 pages, 4 figures; Seminar given at DAE-BRNS Workshop on Hadron
Physics Bhabha Atomic Research Centre, Mumbai, India, October 31-November 4,
2011, submitted to Proceeding
Rapidity particle spectra in sudden hadronization of QGP
We show that the remaining internal longitudinal flow of colliding quarks in
nuclei offers a natural explanation for the diversity of rapidity spectral
shapes observed in Pb--Pb 158AGeV nuclear collisions. Thus QGP sudden
hadronization reaction picture is a suitable approach to explain the rapidity
spectra of hadrons produced.Comment: 3 pages including 2 figure
Jets associated with Z^0 boson production in heavy-ion collisions at the LHC
The heavy ion program at the LHC will present unprecedented opportunities to
probe hot QCD matter, that is, the quark gluon plasma (QGP). Among these
exciting new probes are high energy partons associated with the production of a
Z^0 boson, or Z^0 tagged jets. Once produced, Z^0 bosons are essentially
unaffected by the strongly interacting medium produced in heavy-ion collisions,
and therefore provide a powerful signal of the initial partonic energy and
subsequent medium induced partonic energy loss. When compared with theory,
experimental measurements of Z^0 tagged jets will help quantify the jet
quenching properties of the QGP and discriminate between different partonic
energy loss formalisms. In what follows, I discuss the advantages of tagged
jets over leading particles, and present preliminary results of the production
and suppression of Z^0 tagged jets in relativistic heavy-ion collisions at LHC
energies using the Guylassy-Levai-Vitev (GLV) partonic energy loss formalism.Comment: To appear in the proceedings of the 2010 Winter Workshop on Nuclear
Dynamics, which was held in Ocho Rios, Jamaica, mon
decays revisited: branching ratios and T-odd momenta correlations
We calculate the branching ratios of the decays, and the T-odd triple momenta correlations
, due to the
electromagnetic final state interaction, in these processes. The contributions
on the order of and to the corresponding amplitudes
are treated exactly. For the branching ratios, the corrections on the order of
are estimated and demonstrated to be small. We compare the results
with those of other authors. In some cases our results differ considerably from
the previous ones.Comment: 13 pages, 11 figures; references adde
Simple Classification of Light Baryons
We introduce a classification number which describes the baryon mass
information in a fuzzy manner. According to and of baryons, we put
all known light baryons in a simple table in which some baryons with same (,
) are classified as members of known octets or decuplets. Meanwhile, we
predict two new possible octets.Comment: 5 latex pages, 5 tables, no figur
A (p/E) Calculation of Strong Pionic Decays of Baryons
Strong pionic decays of baryons are studied in a non-relativistic quark model
framework via a convergent (p/E) expansion of the transition operator. Results
are compared to the ones obtained within a more conventional (p/m) expansion.Comment: 16 pages, LaTeX, using amssymb.st
Upper Bound on the Mass of the Type III Seesaw Triplet in an SU(5) Model
We investigate correlation between gauge coupling unification, fermion mass
spectrum, proton decay, perturbativity and ultraviolet cutoff within an SU(5)
grand unified theory with minimal scalar content and an extra adjoint
representation of fermions. We find strong correlation between the upper bound
on the mass of both the bosonic and fermionic SU(2) triplets and the cutoff.
The upper bound on the mass of fermionic triplet responsible for Type III
seesaw mechanism is 10^{2.1} GeV for the Planck scale cutoff. In that case both
the idea of grand unification and nature of seesaw mechanism could be tested at
future collider experiments through the production of those particles.
Moreover, the prediction for the proton decay lifetime is at most an order of
magnitude away from the present experimental limits. If the cutoff is lowered
these predictions change significantly. In the most general scenario, if one
does (not) neglect a freedom in the quark and lepton mixing angles, the upper
bound on the fermionic triplet mass is at 10^{5.4} GeV (10^{10} GeV). Since the
predictions of the model critically depend on the presence of the
higher-dimensional operators and corresponding cutoff we address the issue of
their possible origin and also propose alternative scenarios that implement the
hybrid seesaw framework of the original proposal.Comment: 13 pages, 2 figures, minor changes introduced to match the JHEP
versio
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