arXiv subjects

K. P. Khemchandani

Publications and source records attributed to K. P. Khemchandani.

At least 109 records · Page 6Linked to original sources

arXiv2009

Searching for exotic states in the $N πK $ system

We study the $N πK$ system in order to investigate the possibility of existence of strangeness +1 resonance(s). The formalism consists of solving the Faddeev equations with the $N π$, $πK $ and $K N$ $t$-matrices obtained from chiral dynamics. The same formalism, which leads to the finding of several $1/2^+$ resonances in the corresponding three-body $S$ = -1 channels in the 1400-2000 MeV energy region, results into only one broad bump around 1700 MeV with isospin 0. The amplitudes in isospin 1 and 2 configuration do not have any resonant structure.

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arXiv2009

Production of the omega meson in the pd --> 3He omega reaction at 1450 MeV and 1360 MeV

The production of $ω$ mesons in the $pd \to{}^3$He$ ω$ reaction has been studied at two energies near the kinematic threshold, $T_p=1450$ MeV and $T_p=1360$ MeV. The differential cross section was measured as a function of the $ω$ cm angle at both energies over the whole angular range. Whereas the results at 1360 MeV are consistent with isotropy, strong rises are observed near both the forward and backward directions at 1450 MeV. Calculations made using a two-step model with an intermediate pion fail to reproduce the shapes of the measured angular distributions and also underestimate the total cross sections.

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arXiv2008

X(2175) as a resonant state of the $ϕK \bar{K}$ system

We perform a Faddeev calculation for the three mesons system, $ϕK \bar{K}$, taking the interaction between two pseudoscalar mesons and between a vector and a pseudoscalar meson from the chiral unitary approach. We obtain a neat resonance peak around a total mass of 2150 MeV and an invariant mass for the $K \bar{K}$ system around 970 MeV, very close to the $f_0(980)$ mass. The state appears in I=0 and qualifies as a $ϕf_0(980)$ resonance. We enlarge the space of states including $ϕππ$, since $ππ$ and $K \bar{K}$ build up the $f_0$ (980), and find moderate changes that serve to quantify theoretical uncertainties. No state is seen in I=1. This finding provides a natural explanation for the recent state found at BABAR and BES, the X(2175), which decays into $ϕf_0(980)$.

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arXiv2008

Study of the $η-^7Be$ Interaction Near Threshold in $p-^6Li$ Fusion

We present a calculation for $η$ production in the $p-^6Li$ fusion near threshold including the $η-^7Be$ final state interaction (FSI). We consider the $^6Li$ and $^7Be$ nuclei as $α-d$ and $α-^3He$ clusters respectively. The calculations are done for the lowest states of $^7Be$ with $J = ({3\over2}^-, {1\over2}^-)$ resulting from the $L = $1 radial wave function. The $η-^7Be$ interaction is incorporated through the $η-^7Be$ $T-$matrix, constructed from the medium modified matrices for the $η-^3He$ and $η-α$ systems. These medium modified matrices are obtained by solving few body equations, where the scattering in nuclear medium is taken into account.

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arXiv2008

Chiral Unitary Dynamics of Hadrons and Hadrons in a Nuclear Medium

In this talk I summarize recent findings around the description of axial vector mesons as dynamically generated states from the interaction of pseudoscalar mesons and vector mesons, dedicating some attention to the two $K_1(1270)$ states. Then I review the generation of open and hidden charm scalar and axial states, and how some recent experiment supports the existence of the new hidden charm scalar state predicted. I present recent results showing that the low lying $1/2^+$ baryon resonances for S=-1 can be obtained as bound states or resonances of two mesons and one baryon in coupled channels. Then show the differences with the S=0 case, where the $N^*(1710)$ appears also dynamically generated from the two pion one nucleon system, but the $N^*(1440)$ does not appear, indicating a more complex structure of the Roper resonance. Finally I shall show how the state X(2175), recently discovered at BABAR and BES, appears naturally as a resonance of the $ϕK \bar{K}$ system.

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arXiv2008

Three-body hadronic structure of low-lying $1/2^+$ $Σ$ and $Λ$ resonances

We discuss the dynamical generation of some low-lying $1/2^+$ $Σ$'s and $Λ$'s in two-meson one-baryon systems. These systems have been constructed by adding a pion in $S$-wave to the $\bar{K} N$ pair and its coupled channels, where the $1/2^-$ $Λ$(1405)-resonance gets dynamically generated. We solve Faddeev equations in the coupled-channel approach to calculate the $T$-matrix for these systems as a function of the total energy and the invariant mass of one of the meson-baryon pairs. This squared $T$-matrix shows peaks at the energies very close to the masses of the strangeness -1, $1/2^+$ resonances listed in the particle data book.

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arXiv2008

The $σK$ coupling in the chiral unitary approach and the isoscalar $\bar{K}N$, $\bar{K}A$ interaction

We evaluate the "$σ$" exchange contribution to the $\bar{K}N\to\bar{K}N$ scattering within a chiral unitary approach. We show that the chiral transition potentials for $ππ\to K \bar{K}$ in the $t$-channel lead to a "$σ$" contribution that vanishes in the $\bar{K}$ forward direction and, hence, would produce a null "$σ$" exchange contribution to the $K^-$ optical potential in nuclear matter in a simple impulse approximation. This is a consequence of the fact that the leading order chiral Lagrangian gives an I=0 $ππ\to K\bar{K}$ amplitude proportional to the squared momentum transfer, $q^2$. This finding poses questions on the meaning or the origin of "$σ$" exchange potentials used in relativistic mean field approaches to the $K^-$ nuclear selfenergy. This elementary "$σ$" exchange potential in $\bar{K}N\to\bar{K}N$ is compared to the Weinberg-Tomozawa term and is found to be smaller than present theoretical uncertainties but will be relevant in the future when aiming at fitting increasingly more accurate data.

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arXiv2008

The $N^*(1710)$ as a resonance in the $ππN$ system

We study the $ππN$ system by solving the Faddeev equations, for which the input two-body $t$-matrices are obtained by solving the Bethe-Salpeter equation in the coupled channel formalism. The potentials for the $ππ$, $πN$ sub-systems and their coupled channels are obtained from chiral Lagrangians, which have been earlier used to study resonances in these systems successfully. In this work, we find a resonance in the $ππN$ system with a mass of $1704 - i 375/2$ MeV and with quantum numbers $I=1/2$, $J^π=1/2^+$. We identify this state with the $N^*(1710)$. This peak is found where the energies of the $ππ$ sub-system fall in the region of the $σ$ resonance. We do not find evidence for the Roper resonance in our study indicating a more complex structure for this resonance, nor for any state with total isospin $I=3/2$ or $5/2$.

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arXiv2008

Three body resonances in two meson-one baryon systems

We report four $Σ$'s and three $Λ$'s, in the 1500 - 1800 MeV region, as two meson - one baryon S-wave $(1/2)^+$ resonances. We solve Faddeev equations in the coupled channel approach. The invariant mass of one of the meson-baryon pairs and that of the three particles have been varied and peaks in the squared three body $T$-matrix have been found very close to the existing $S$ = -1, $J^P= 1/2^+$ low lying baryon resonances. The input two-body $t$-matrices for meson-meson and meson-baryon interaction have been calculated by solving the Bethe-Salpeter equation with the potentials obtained in the chiral unitary approach.

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arXiv2007

Recent Developments in Chiral Unitary Dynamics of Resonances

In this talk I summarize recent findings made on the description of axial vector mesons as dynamically generated states from the interaction of peseudoscalar mesons and vector mesons, dedicating some attention to the two $K_1(1270)$ states. Then I review the generation of open and hidden charm scalar and axial states. Finally, I present recent results showing that the low lying $1/2^+$ baryon resonances for S=-1 can be obtained as bound states or resonances of two mesons and one baryon in coupled channels dynamics.

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arXiv2007

Comment on "Hadronic $^3$He$η$ production near threshold"

Measurements of the differential and total cross sections for the $p d \to ^3$He $η$ reaction at five energies were recently reported [Phys. Rev. C {\bf 75}, 014004 (2007)] and comparisons with theoretical models were made. We point out that these comparisons involved a model based on ad hoc assumptions and hence the conclusions regarding the reaction mechanism as well as the role of the higher partial waves drawn in the above work are misleading. Revised conclusions based on better model calculations are presented.

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arXiv2007

A study of the $p d \to p d η$ reaction

A study of the $p d \to p d η$ reaction in the energy range where the recent data from Uppsala are available, is done in the two-step model of $η$ production including the final state interaction. The $η-d$ final state interaction is incorporated through the solution of the Lippmann Schwinger equation using an elastic scattering matrix element, $T_{ηd \to ηd}$, which is required to be half off-shell. It is written in a factorized form, with an off-shell form factor multiplying an on-shell part given by an effective range expansion up to the fourth power in momentum. The parameters of this expansion have been taken from an existing recent relativistic Faddeev equation solution for the $ηNN$ system corresponding to different $η-N$ scattering amplitudes. Calculations have also been done using few body equations within a finite rank approximation (FRA) to generate $T_{ηd \to ηd}$. The $p-d$ final state interaction is included in the spirit of the Watson-Migdal prescription by multiplying the matrix element by the inverse of the Jost function. The $η-d$ interaction is found to be dominant in the region of small invariant $η-d$ mass, $M_{ηd}$. The $p-d$ interaction enhances the cross section in the whole region of $M_{ηd}$, but is larger for large $M_{ηd}$. We find nearly isotropic angular distributions of the proton and the deuteron in the final state. All the above observations are in agreement with data. The production mechanism for the entire range of the existing data on the $p d \to p d η$ reaction seems to be dominated by the two-step model of $η$ production.

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arXiv2006

Small eta-N scattering lengths favour eta-d and eta-alpha states

Unstable states of the eta meson and the 3He nucleus predicted using the time delay method were found to be in agreement with a recent claim of eta-mesic 3He states made by the TAPS collaboration. Here, we extend this method to a speculative study of the unstable states occurring in the eta-d and eta-4He elastic scattering. The T-matrix for eta-4He scattering is evaluated within the Finite Rank Approximation (FRA) of few body equations. For the evaluation of time delay in the eta-d case, we use a parameterization of an existing Faddeev calculation and compare the results with those obtained from FRA. With an eta-N scattering length, $a_{ηN} = (0.42, 0.34)$ fm, we find an eta-d unstable bound state around -16 MeV, within the Faddeev calculation. A similar state within the FRA is found for a low value of $a_{ηN}$, namely, $a_{ηN} = (0.28, 0.19)$ fm. The existence of an eta-4He unstable bound state close to threshold is hinted by $a_{ηN} = (0.28, 0.19)$ fm, but is ruled out by large scattering lengths.

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arXiv2006

Possible eta-mesic 3He states within the finite rank approximation

We extend the method of time delay proposed by Eisenbud and Wigner, to search for unstable states formed by eta mesons and the 3He nucleus. Using few body equations to describe eta-3He elastic scattering, we predict resonances and unstable bound states within different models of the eta-N interaction. The eta-3He states predicted within this novel approach are in agreement with the recent claim of the evidence of eta-mesic 3He made by the TAPS collaboration.

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arXiv2004

Hidden evidence of non-exponential nuclear decay

The framework to describe natural phenomena at their basics being quantum mechanics, there exist a large number of common global phenomena occurring in different branches of natural sciences. One such global phenomenon is spontaneous quantum decay. However, its long time behaviour is experimentally poorly known. Here we show, that by combining two genuine quantum mechanical results, it is possible to infer on this large time behaviour, directly from data. Specifically, we find evidence for non-exponential behaviour of alpha decay of 8Be at large times from experiments.

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arXiv2004

Evidence of Pentaquark States from K+ N Scattering Data?

Motivated by the recent experimental evidence of the exotic B = S = +1 baryonic state Theta(1540), we examine the older existing data on K+ N elastic scattering through the time delay method. We find positive peaks in time delay around 1.545 and 1.6 GeV in the D03 and P01 partial waves of K+ N scattering respectively, in agreement with experiments. We also find an indication of the J=3/2 Theta* spin-orbit partner to the Theta, in the P03 partial wave at 1.6 GeV. We discuss the pros and contras of these findings in support of the interpretation of these peaks as possible exotics.

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arXiv2004

Time Delay Plots of Unflavoured Baryons

We explore the usefulness of the existing relations between the $S$-matrix and time delay in characterizing baryon resonances in pion-nucleon scattering. We draw attention to the fact that the existence of a positive maximum in time delay is a necessary criterion for the existence of a resonance and should be used as a constraint in conventional analyses which locate resonances from poles of the $S$-matrix and Argand diagrams. The usefulness of the time delay plots of resonances is demonstrated through a detailed analysis of the time delay in several partial waves of $πN$ elastic scattering.

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arXiv2003

Three-body mechanism of $η$ production

The usefulness of the three-body mechanism of $η$-meson production is tested by extending to high energies a recently developed two step model of the $p d \to ^3$He $η$ reaction by us, which was successful in reproducing the energy dependence of the data near threshold. The $η$ production in this model, proceeds in two steps via the $p p \to πd$ and $πN \to ηp$ reactions with the intermediate particles being off-shell. The final state interaction(FSI) is incorporated through a $T$-matrix for $η^3$He elastic scattering constructed using few body equations. In a comparison of the calculated angular distributions with some recently available data, we discover the limitations of the model at high energies.

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