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S. B. Gerasimov

Publications and source records attributed to S. B. Gerasimov.

17 recordsLinked to original sources
arXiv2007

On a possible origin of a resonance-like structure in the two-photon invariant mass spectrum of the reaction pp->ppgg

We show that the resonance-like structure found by the \emph{CELSIUS-WASA Collaboration} in the two-photon invariant mass spectrum of the reaction $pp \to pp γγ$ is rather a signature of the $NN$-decoupled dibaryon resonance $d^\star_1$(1956) that is produced in the radiative process $pp \to γd^\star_1$ and then undergoes radiative decay into two protons $d^\star_1 \to pp γ$. It is found that a contribution of the dibaryon mechanism $pp \to γd^\star_1 \to pp γγ$ of the reaction $pp \to pp γγ$ to the invariant mass spectrum of its photon pairs can reasonably well reproduce the experimentally observed spectrum in the vicinity of the resonance-like structure.

hep-ph↗
arXiv2007

Dispersion total photoproduction sum rules for nucleons and few-body nuclei revisited

The questions on the presense and quantitative role of the constant terms in the real part of the high-energy photon-nucleon and photon-nucleus amplitudes representing the contribution of the non-Regge (the fixed j=0-pole) singularities in the finite-energy sum rules (FESR) for the photoabsorption cross sections on nucleons and the lightest atomic nuclei are discussed and new testable relations are presented for relevant combinations of the Compton scattering amplitudes.

hep-ph↗
arXiv2005

On the relations between two-photon and leptonic widths of low-lying S-wave states of charmonium

The relation between the ratio Gamma_{ee}(psi')/Gamma_{ee}(J/psi) and Gamma_{2gamma}(eta_{c}')/Gamma_{2gamma}(eta_{c}), expressed in terms of the configuration mixing amplitudes induced by the contact spin-spin interaction of quarks in the ground and radial excitation states, is shown to give, after the inclusion of the newly derived relativistic corrections, the radiative eta_{c}'- and η_c-width ratio in fair accord with recent experiments. The dynamical model is proposed to derive the ratio of relative probability of the ground (eta_{c}(2980))- and first radial excitation (eta_{c}'(3640))-state formation in gamma-gamma collisions followed by their decay into the pi\bar{K}K and p\bar{p} channels.

hep-ph↗
arXiv2005

Is isospin I=2 assignment preferable for d_1^*(1956) resonance candidate seen in reaction pp-> 2 gamma X below pion threshold ?

We compare the virtues of two options for the isospin (I=1 or 2) of the apparently exotic dibarion resonance d_1^*(1956), as it is noticed by the DIB2gamma Collaboration (JINR) in the reaction pp -> 2 gamma X below the pion threshold, and using recent results following from the RMC Collaboration (TRIUMF) measurement of the relative probability of the double-photon pion capture in the pi-mesic deuterium atoms.

nucl-th↗
arXiv2004

Further remarks on electroweak moments of baryons and manifestations of broken SU(3)

The role of nonvalence, {\it e.g.} sea quarks and/or meson degrees of freedom in static and quasistatic baryon electroweak observables, is discussed within the phenomenological sum rule approach. The inclusion of nonvalence degrees of freedom in the analysis of baryon magnetic moments explains extremely strong violation of the standard SU(6) symmetry-based quark-model prediction for the magnetic moment ratio $R_{Σ/Λ}=(Σ^{+} + 2Σ^{-})/(-Λ) \simeq .23$, while the value $R_{Σ/Λ}(SU(6))= 1$ corresponds to the nonrelativistic quark model. We also obtain $F/D=.72$ for the quark-current-baryon coupling $SU(3)_{f}$ ratio. The implications for the "strangeness" magnetism of the nucleon and for weak axial-to-vector coupling constant relations measured in the lowest octet baryon $β$-decays are discussed. The latter shows up the possible role of the induced second-class form factor (the "weak- electricity", or pseudotensor form factor) in the extraction of the $(g_1/f_1)$-values from the hyperon's $β$-decay data.

hep-ph↗
arXiv2003

On radiative widths and a pattern of quark-diquark-gluon configuration mixing in low-lying scalar mesons

The earlier suggested and developed idea of quark-hadron duality, underlying "bremsstrahlung-weighted" sum rules for total or polarized photon interaction cross sections, is applied to the description of excitation of light scalar mesons in gamma-gamma interactions. The emphasis is put on the discussion of a role of the scalar diquark cluster degrees of freedom in the radiative formation of light scalar mesons.

hep-ph↗
arXiv2001

Search for NN-decoupled dibaryons using the process $pp \to γγX$ below the pion production threshold

The energy spectrum for high energy $γ$-rays ($E_γ\geq 10$ MeV) from the process $pp \to γγX$ emitted at $90^0$ in the laboratory frame has been measured at an energy below the pion production threshold, namely, at 216 MeV. The resulting photon energy spectrum extracted from $γ-γ$ coincidence events consists of a narrow peak at a photon energy of about 24 MeV and a relatively broad peak in the energy range of (50 - 70) MeV. The statistical significances for the narrow and broad peaks are 5.3$σ$ and 3.5$σ$, respectively. This behavior of the photon energy spectrum is interpreted as a signature of the exotic dibaryon resonance $d^\star_1$ with a mass of about 1956 MeV which is assumed to be formed in the radiative process $pp \to γd^\star_1$ followed by its electromagnetic decay via the $d^\star_1 \to pp γ$ mode. The experimental spectrum is compared with those obtained by means of Monte Carlo simulations.

nucl-ex↗
arXiv2000

Photoabsorption sum rules and quark structure parameters of hadrons

Following the idea of the quark-hadron duality we present, within the constituent quark model approach, the relations between different bremsstrahlung-weihgted integrals of the nucleon resonance photoexcitation cross sections and correlation functions of the quark dipole moments in the nucleon ground state. These functions are of interest for checking detailed quark-configuration structure of the nucleon state vector. Some applications of this approach in meson sector are made and the role of meson degrees of freedom in the electromagnetic baryon observables is briefly discussed.

hep-ph↗
arXiv2000

Hadron spectroscopy based on relativistic Schrödinger-like wave equations

Relativistic potential-type equations are proposed which approximately reproduce important features and constraints of field-theoretic models and can be useful tool in hadron spectroscopy. Within this approach, the Regge-trajectory parameters and some properties of hihger radial excitations in the light quark sector are discussed.

hep-ph↗
arXiv1999

Electroweak moments of baryons and hidden strangeness of the nucleon

The phenomenological sum-rule-based approach is used to discuss the quark composition dependence of some static electroweak characteristics of baryons.The role of nonvalence degrees of freedom (the sea partons and/or peripheral meson currents) is shown to be important to select and make use of the relevant symmetry parametrization of baryon observables.The implications of the baryon magnetic moment analysis for estimation of the $Δ$q values of the spin-dependent DIS on nucleons, the contribution of hidden strangeness to the nucleon magnetic moment and to the quark-line-rule violating $ϕπ$ - production in antinucleon-nucleon annihilation reaction are presented.

hep-ph↗
arXiv1999

Two-photon processes in two-nucleon systems as a tool of searching for exotic six-quark resonances

The reaction $pp \to pp2γ$, proposed earlier to probe for the NN--decoupled dibaryon resonances, has been studied by the DIB$2γ$ Collaboration (JINR) and their preliminary data seem to give evidence for the resonance effect at about 1920 MeV. We discuss some other two-photon processes: the double radiative capture reaction in pionic deuterium, photoabsorption sum rules and the nuclear Compton scattering, which we consider to be especially feasible for further test and invesigation of possible low-lying, exotic six-quark states.

nucl-th↗
arXiv1998

On Valence Gluons in Heavy Quarkonia

To include the explicit valence gluon degrees of freedom into spectroscopy of the lowest states of heavy quarkonia, we consider, within an adiabatic model, the properties of the lowest hybrid $\bar{Q}Qg$-mesons and estimate the effects of their mixing with low-lying vector $\bar{c}c$-charmonia. The perspectives of compatibility of the resulting picture with data are discussed.

hep-ph↗
arXiv1998

On Mesoatoms of the Deuterium and Possible Existence of Exotic Dibaryons

As a desirable supplement to the reaction $pp \to pp2γ$, proposed earlier (nucl-th/9712064 and references therein) to probe for the NN--decoupled dibaryon resonances we suggest to use for the same goal the radiative capture processes in mesoatoms of the deuterium which we consider to be especially feasible for further test and invesigation of possible low-lying exotic resonance states.

nucl-th↗
arXiv1997

On Electroweak Moments of Baryons and Spin-Flavour Structure of the Nucleon

The phenomenological sum-rule-based approach is used to discuss the quark composition dependence of some static and quasi-static electroweak characteristics of nucleons.The role of nonvalence degrees of freedom, the nucleon sea partons and/or peripheral meson currents, is shown to be important to select and make use of the relevant symmetry parametrization of hadron observables. With our preferable universal value of the SU(3)-symmetry parameter $α_{D}=D/F+D=.58$, taken for both magnetic moments and axial-vector constants entering into the semi-leptonic baryon decays, we obtain the following values for moments $Δq$ of the spin-dependent structure function of the proton: $Δu \simeq .84(.82), Δd \simeq -.42(-.44), Δs=-.22 \pm .05 (-.10 \pm .03)$, where the values in parentheses correspond to the widely used "standard" value of $α^{axial}_{D}=.63$. The estimations of the strange sea contributions to the nucleon magnetic moments and rms are also presented.

hep-ph↗
arXiv1997

Radiative processes of nucleon interactions and possible existence of exotic dibaryons

The cross section of the reaction $pp \to pp γγ$ is estimated and the exploration possibilities of this reaction to probe for a possible excitation of subnuclear degrees of freedom in two-nucleon systems, in particular, the production and decay of the NN-decoupled dibaryon resonances, are briefly discussed.Some arguments for and implications of the intermediate dibaryon resonance excitation are inferred from preliminary data on the two-photon yield and energy distribution observed by the DIBAR2$γ$ - Collaboration at the kinetic energy of the initial proton $T_{lab} \simeq 200 MeV$.

nucl-th↗