arXiv subjects

Swapan Das

Publications and source records attributed to Swapan Das.

24 records · Page 2Linked to original sources

arXiv2011

Low energy ω(\to π^0 γ) meson photoproduction in the nucleus

The $π^0 γ$ invariant mass distribution spectra in the $ (γ, π^0γ) $ reaction were measured by TAPS/ELSA collaboration to look for the hadron parameters of the $ω$ meson in Nb nucleus. We study the mechanism for this reaction, where we consider that the elementary reaction in Nb nucleus proceeds as $ γN \to ωN; ~ ω\to π^0γ$. The $ω$ meson photoproduction amplitude for this reaction is extracted from the measured four momentum transfer distribution in the $ γp \to ωp $ reaction. The propagation of the $ω$ meson and the distorted wave function for the $π^0$ meson in the final state are described by the eikonal form. The $ω$ and $π^0$ mesons nucleus optical potentials, appearing in the $ω$ meson propagator and $π^0$ meson distorted wave function respectively, are estimated using the "$t\varrho$" approximation. The effects of pair correlation and color transparency are also studied. The calculated results do not show medium modification for the $ω$ meson produced in the nucleus for its momentum greater than 200 MeV. It occurs since the $ω$ meson dominantly decays outside the nucleus. The dependence of the cross section on the final state interaction is also investigated. The broadening of the $ω$ meson mass distribution spectra is shown to occur due to the large resolution width associated with the detector used in the experiment.

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arXiv2011

$ρN$ resonance dynamics in the proton nucleus reaction

The strong coupling of rho meson to the nucleon produces $s$ and $p$ wave rho meson nucleon $(ρN)$ resonances. In a nucleus, the $ρN$ resonance-hole polarization generates the optical potential or self-energy for the rho meson. The scattering of rho meson due to this potential provides valuable informations about the $ρN$ resonance dynamics in a nucleus. To investigate it, we use this potential to calculate the mass distribution spectrum for the $ρ$ meson produced coherently in the proton nucleus reaction. The cross sections arising due to $s$ and $p$ wave $ρN$ resonances have been presented. The coherent and incoherent contributions to the cross sections due to these resonances are compared. In addition, the calculated results due to non-relativistic and relativistic $ρ$ meson self-energy are illustrated.

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arXiv2010

$ ω(\to π^+π^-π^0) $ meson photoproduction on proton

The cross section is estimated for the $π^+π^-π^0$ invariant mass distribution in the $γp$ reaction in the GeV region. This reaction is assumed to proceed through the formation of the $ω$ meson in the intermediate state, since the production cross section for this meson in the $γp$ reaction in GeV region is significant and it has large branching ratio (88.8%) in the $π^+π^-π^0$ channel. The cross sections for this reaction have been calculated using the energy dependent reaction amplitude, i.e., $f_{γp \to ωp}(0)$, extracted from the latest $ω$ meson photoproduction data. We use established procedure to calculate other factors, like width and propagator of the $ω$ meson, so that our calculation can provide reliable cross section. The calculated results reproduce the measured $π^+π^-π^0$ invariant mass distribution spectra in the $γp$ reaction.

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arXiv2009

$π^0γ$ invariant mass distribution in the low energy $γp \to ωp$ reaction

We study the reaction mechanism for the correlated $π^0γ$ emission in the photon induced reaction on the proton target. Since this reaction is studied in the GeV region, we assume that it proceeds through the formation of the vector meson in the intermediate state. The vector meson, being an unstable particle, decays into $π^0γ$ bosons after propagating certain distance. Our analysis shows that the $π^0γ$ event seen in coincidence in the final state dominantly arises due to the decay of $ω$ meson. The calculated results reproduce the measured $π^0γ$ invariant mass distribution spectra very well.

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arXiv2006

$π^+π^-$ Emission from Coherent $ρ^0$ Propagation in Nuclei

Cross sections for the $π^+π^-$ events arising due to the decay of $ρ^0$ meson have been calculated. This rho meson is considered to produce coherently in the $(p,p^\prime)$ reaction on a nucleus. The distorted wave functions for the continuum particles and the rho meson propagator are described by the eikonal form. The sensitivity of the cross section on the pion emission angle as well as on the beam energy has been investigated. The cross sections for the $ρ^0$ decaying inside and outside the nucleus are compared. In addition, the coherent and incoherent contributions to the cross section due to $ρ^0$ inside and outside decay amplitudes are presented. The initial and final state interactions for this reaction have been studied. The nuclear medium effect on the $ρ^0$ propagation through the nucleus is also explored.

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arXiv2000

Exploring vector meson masses in nuclear collisions

The formalism developed earlier by us for the propagation of a resonance in the nuclear medium in proton-nucleus collisions has been modified to the case of vector boson production in heavy-ion collisions. The first part of the talk describes this formalism. The formalism includes coherently the contribution to the observed di-lepton production from the decay of a vector boson inside as well as outside the nuclear medium. The calculated invariant rho mass distributions are presented for the $ρ$-meson production using optical potentials estimated within the VDM and the resonance model. In the second part of the talk we write a formalism for coherent rho production in proton nucleus collisions and explore the sensitivity of the (p,p$^\prime ρ^0$) reaction cross section to medium mass modification of the rho meson.

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