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Ya. Azimov

Publications and source records attributed to Ya. Azimov.

13 recordsLinked to original sources
arXiv2013

What is the real meaning of the Froissart theorem ?

The Froissart bounds for amplitudes and cross sections are explained and reconsidered to clarify the role of different assumptions. It is the physical conditions of unitarity and of no massless exchanges, together with mathematical properties of the Legendre functions, that imply much softer high-energy asymptotics for elastic amplitudes at physical angles than for the same amplitudes at nonphysical angles. The canonical log-squared boundary for σ_{tot} appears only under the additional hypothesis that the amplitude at any nonphysical angle cannot grow faster than some power of energy. The Froissart results are further shown to admit some reinforcement. Comparison of the familiar and new Froissart-like restrictions with the existing data on σ_{tot} and diffraction slope at all available energies (including LHC) does not allow yet to unambiguously determine the asymptotic behavior of σ_{tot}, but shows that its current increase cannot be saturated (i.e., maximally rapid).

hep-ph↗
arXiv2012

Observation of a narrow structure in p(gamma,K_s)X via interference with phi-meson production

We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The observed structure may be due to the interference between a strange (or anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L) photoproduction leading to the same final state. The statistical significance of the observed excess of events estimated as the log likelihood ratio of the resonant signal+background hypothesis and the phi-production based background only hypothesis corresponds to 5.3 sigma.

hep-ex↗
arXiv2011

How Robust is the Froissart Bound?

Proof of the Froissart theorem is reconsidered in a different way to extract its necessary conditions. Two physical inputs, unitarity and absence of massless intermediate hadrons, are indisputable. Also important are mathematical properties of the Legendre functions. Assumptions on dispersion relations, single or double, appear to be excessive. Instead, one should make assumptions on possible high-energy asymptotics of the amplitude in nonphysical configurations, which have today no firm basis. Asymptotics for the physical amplitude always appear essentially softer than for the nonphysical one. Froissart's paper explicitly assumed the hypothesis of power behavior and obtained asymptotic bound for total cross sections $\sim \log^2{(s/s_0)}$ with some constant $s_0$. Our bounds are slightly stronger than original Froissart ones. They show that the scale $s_0$ should itself slowly grow with $s$. Under different assumptions about asymptotic behavior of nonphysical amplitudes, the total cross section could grow even faster than $\log^2{s}$. The problem of correct asymptotics might be clarified by precise measurements at the LHC and higher energies.

hep-ph↗
arXiv2010

Quantum interference of particles and resonances

Though the phenomenon of quantum-mechanical interference has been known for many years, it still has many open questions. The present review discusses specifically how the interference of resonances may and does work. We collect data on the search for rare decay modes of well-known resonances that demonstrate a wide variety of possible different manifestations of interference. Some special kinds of resonance interference, not yet sufficiently studied and understood, are also briefly considered. The interference may give useful experimental procedures to search for new resonances with arbitrary quantum numbers, even with exotic ones, and to investigate their properties.

hep-ph↗
arXiv2007

How is Exotics Produced ? Where to Search for it ?

On the basis of existing data, we suggest such a mechanism of production for exotic hadrons that can explain, at least qualitatively, why the Theta+-baryon is seen in some experiments and not in others. With our hypothesis, production of exotic hadrons is a new kind of hard processes. We also can propose new experiments to check (and confirm?) existence of exotics and to provide new important information about both exotic and conventional hadrons [The talk is based on the papers by Ya. Azimov, K. Goeke, and I. Strakovsky, Phys Rev D 76, 074013 (2007)]

hep-ph↗
arXiv2007

A possible explanation why the Theta+ is seen in some experiments and not in others

To understand the whole set of positive and null data on the Theta+(1530)-production, we suggest the hypothesis that multiquark hadrons are mainly generated from many-quark states, which emerge either as short-term hadron fluctuations, or as hadron remnants in hard processes. This approach allows us to describe both non-observation of the Theta+ in current null experiments and peculiar features of its production in positive experiments. Further, we are able to propose new experiments that might be decisive for the problem of the Theta+ existence. Distributions of the Theta+ in such experiments can give important information both on higher Fock components of conventional hadrons and about structure and hadronization properties of hadron remnants produced in hard processes. We also explain that description of multiquark hadrons may require a modified form of the constituent quark model, with quark masses and couplings being intermediate between their values for the familiar constituent quarks and the current ones.

hep-ph↗
arXiv2007

K*-couplings for the antidecuplet excitation

We estimate the coupling of the K* vector meson to the N-->Theta+ transition employing unitary symmetry, vector meson dominance, and results from the GRAAL Collaboration for eta photoproduction off the neutron. Our small numerical value for the coupling constant is consistent with the non-observation of the Theta+ in recent CLAS searches for its photoproduction. We also estimate the K*-coupling for the N-->Sigma* excitation, with Sigma* being the Sigma-like antidecuplet partner of the Theta+-baryon.

hep-ph↗
arXiv2005

Extraction of radiative decay width for the non-strange partner of Theta^+

Using the results of the GRAAL collaboration on the \eta photoproduction from the neutron target, we attempt to extract the partial radiative width of the possible new nucleon resonance N^*(1675). The obtained estimates support this resonance to be a very attractive candidate for the non-strange member of the exotic antidecuplet of baryons -- a partner of the \Theta^+ pentaquark. Our phenomenological value for the transition magnetic moment \mu(n^* n), appears to be in good agreement with predictions of the Chiral Quark Soliton Model.

hep-ph↗
arXiv1999

Phenomenology of Neutral D-meson Decays and Double-Flavor Oscillations

Decays of neutral D-mesons are considered phenomenologically without invoking any particular models. Special attention is given to cascade decays with intermediate neutral kaons where coherent double-flavor oscillations (CDFO) become possible. We show necessity and unique possibilities of experiments on CDFO. They allow to relate with each other widths and masses of D-meson eigenstates, to separate interference effects due to $D^0 - \bar D^0$ mixing and/or Cabibbo-favored vs. doubly-suppressed transitions. Such experiments provide the only known ways to unambiguous model-independent measurements of all CP-violating parameters and of Cabibbo-doubly-suppressed amplitudes, where the New Physics may have more prominent manifestations. Similar experiments would be useful and interesting also for charged $D$-meson decays to neutral kaons.

hep-ph↗
arXiv1997

Double-Flavor Oscillations and Properties of Heavy Mesons

Phenomenon of coherent double-flavor oscillations is discussed. They can arise when heavy flavored neutral mesons decay with production of neutral kaons. The oscillations may be used to study detailed properties of the heavy mesons and their decays. They may give new insight into the problem of CP-violation. In particular, they provide the only known way to the complete unambiguous measurements of CP-violating parameters for neutral B-meson decays. The corresponding experiments seem to be hard, but possible at hadron facilities.

hep-ph↗
arXiv1996

Hara's Theorem and W-exchange in Hyperon Weak Radiative Decays

We reconsider Hara's theorem in its relation to the well-known properties of beta-decay. All assumptions necessary for the theorem to be true are explicitly formulated. Further, we study the W-exchange contribution to weak radiative decays and show that it does not violate Hara's theorem. However, this contribution reveals the essential role of particle mixing in symmetry considerations and some peculiar features of gauge-invariant amplitudes under perturbative expansion. Together they explain an effect, which was treated as contradicting Hara's theorem, without any violation. The properties of W-exchange we describe here may have more general importance and should be taken into account in further detailed calculations of weak processes.

hep-ph↗