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S. Bhattacharyya

Publications and source records attributed to S. Bhattacharyya.

At least 91 records · Page 5Linked to original sources
arXiv2011

On Production of Hadrons in Proton-Proton Collisions at RHIC and LHC Energies and an Approach

From the very early days of Particle Physics, both experimental and theoretical studies on proton-proton collisions had occupied the center-stage of attention for very simple and obvious reasons. And this intense interest seems now to be at peak value with the onset of the Large Hadron Collider (LHC)-studies at TeV ranges of energies. In this work, we have chosen to analyse the inclusive cross-sections, the rapidity density, the $K/π$ and $p/π$-ratio behaviours and the $ $-values, in the light of the Sequential Chain Model (SCM). And the limited successes of the model encourage us to take up further studies on several other aspects of topmost importance in particle physics with the same approach.

hep-ph↗
arXiv2011

On Production of `Soft' Particles in Au+Au and Pb+Pb Collisions at High Energies

Production of low-$p_T$ (soft) hadronic particles in high energy collisions constitutes a significant corner of special interests and problems, as the perturbative quantum chromodynamics (pQCD) does not work in this region. We have probed here into the nature of the light particle production in two symmetric nuclear collisions at two neighbouring energies with the help of two non-standard models. The results are found to be in good agreement with data. Despite this, as the models applied here are not intended to provide deep insights into the actual physical processes involved in such collisions, the phenomenological bounds and constraints which cannot be remedied for the present continue to exist.

hep-ph↗
arXiv2011

Evidence for a spin-aligned neutron-proton paired phase from the level structure of $^{92}$Pd

The general phenomenon of shell structure in atomic nuclei has been understood since the pioneering work of Goeppert-Mayer, Haxel, Jensen and Suess.They realized that the experimental evidence for nuclear magic numbers could be explained by introducing a strong spin-orbit interaction in the nuclear shell model potential. However, our detailed knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers ($N = Z$), the unique nature of the atomic nucleus as an object composed of two distinct types of fermions can be expressed as enhanced correlations arising between neutrons and protons occupying orbitals with the same quantum numbers. Such correlations have been predicted to favor a new type of nuclear superfluidity; isoscalar neutron-proton pairing, in addition to normal isovector pairing (see Fig. 1). Despite many experimental efforts these predictions have not been confirmed. Here, we report on the first observation of excited states in $N = Z = 46$ nucleus $^{92}$Pd. Gamma rays emitted following the $^{58}$Ni($^{36}$Ar,2$n$)$^{92}$Pd fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution γ-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. The strong isoscalar neutron- proton correlations in these $N = Z$ nuclei are predicted to have a considerable impact on their level structures, and to influence the dynamics of the stellar rapid proton capture nucleosynthesis process.

nucl-ex↗
arXiv2010

Rapidity Spectra of Heavy Baryons in Nuclear Collisions at Various Energies : A Systematic Approach

This study aims at understanding the nature of measured data on the rapidity spectra of some heavy baryons [$Λ$, $Λ$bar, $Ξ^-$ & $Ξ$bar$^+$] produced in the nuclear collisions at some modestly high energies. Furthermore, our objective is also to build up a comprehensive and consistent methodology to analyze the data on this specific observable which has a very important place in the domain of High Energy Physics (HEP). On an overall basis, our target here attains a moderate degree of success even for production of such rare secondaries. In addition to this, the limitations of such an approach have also been pointed out.

hep-ph↗
arXiv2010

On Relativistic Disk Spectroscopy in Compact Objects with X-ray CCD Cameras

X-ray charge-coupled devices (CCDs) are the workhorse detectors of modern X-ray astronomy. Typically covering the 0.3-10.0 keV energy range, CCDs are able to detect photoelectric absorption edges and K shell lines from most abundant metals. New CCDs also offer resolutions of 30-50 (E/dE), which is sufficient to detect lines in hot plasmas and to resolve many lines shaped by dynamical processes in accretion flows. The spectral capabilities of X-ray CCDs have been particularly important in detecting relativistic emission lines from the inner disks around accreting neutron stars and black holes. One drawback of X-ray CCDs is that spectra can be distorted by photon "pile-up", wherein two or more photons may be registered as a single event during one frame time. We have conducted a large number of simulations using a statistical model of photon pile-up to assess its impacts on relativistic disk line and continuum spectra from stellar-mass black holes and neutron stars. The simulations cover the range of current X-ray CCD spectrometers and operational modes typically used to observe neutron stars and black holes in X-ray binaries. Our results suggest that severe photon pile-up acts to falsely narrow emission lines, leading to falsely large disk radii and falsely low spin values. In contrast, our simulations suggest that disk continua affected by severe pile-up are measured to have falsely low flux values, leading to falsely small radii and falsely high spin values. The results of these simulations and existing data appear to suggest that relativistic disk spectroscopy is generally robust against pile-up when this effect is modest.

astro-ph.HE↗
arXiv2010

Understanding the Characteristics of Multiple Production of Light Hadrons in Cu + Cu Interactions at Various RHIC Energies: A Model-based Analysis

Experiments involving copper-copper collisions at the RHIC-BNL (USA) at energies $\sqrt{s_{NN}}$ = 22.5, 62 and 200 GeV have produced a vast amount of high-precision data which are to be analysed in the light of various competing models in the domain of multiparicle production scenario. We have chosen to analyse here the measured data on the $p_T$ -spectra of various light and non-strange secondaries at various energies mentioned above, some of their very important ratio-behaviours at the various centralities of the collisions and the nuclear modification factors $R_{AA}$ and $R_{CP}$ in the light of a version of the Sequential Chain Model (SCM). The agreements between the measured data and model-based results are generally found to be modestly satisfactory. Besides, our obtained results have also been compared with results based upon two approaches with strong standard model flavour, of which one is purely pQCD-oriented and is forwarded by Vitev.

hep-ph↗
arXiv2010

Relativistic Lines and Reflection from the Inner Accretion Disks Around Neutron Stars

A number of neutron star low-mass X-ray binaries have recently been discovered to show broad, asymmetric Fe K emission lines in their X-ray spectra. These lines are generally thought to be the most prominent part of a reflection spectrum, originating in the inner part of the accretion disk where strong relativistic effects can broaden emission lines. We present a comprehensive, systematic analysis of Suzaku and XMM-Newton spectra of 10 neutron star low-mass X-ray binaries, all of which display broad Fe K emission lines. Of the 10 sources, 4 are Z sources, 4 are atolls and 2 are accreting millisecond X-ray pulsars (also atolls). The Fe K lines are well fit by a relativistic line model for a Schwarzschild metric, and imply a narrow range of inner disk radii (6 - 15 GM/c^2) in most cases. This implies that the accretion disk extends close to the neutron star surface over a range of luminosities. Continuum modeling shows that for the majority of observations, a blackbody component (plausibly associated with the boundary layer) dominates the X-ray emission from 8 - 20 keV. Thus it appears likely that this spectral component produces the majority of the ionizing flux that illuminates the accretion disk. Therefore, we also fit the spectra with a blurred reflection model, wherein a blackbody component illuminates the disk. This model fits well in most cases, supporting the idea that the boundary layer is illuminating a geometrically thin disk.

astro-ph.HE↗
arXiv2010

On the Nature of the Rapidity-Spectra at RHIC and Some Other Energies

On the basis of the Grand Combinational Model (GCM) outlined and somewhat detailed in the text, we have attempted to capture here the several interesting assorted characteristics of the rapidity-spectra of the major varieties of secondaries produced in diverse nuclear reactions at various energies, though the main thrust of our work lies on addressing the data-trends from RHIC-BNL experiments. Obviously the core of the present approach is purely phenomenological. Still, the method and the model address the features of the data modestly well. And the method appears to have the rich potentiality, if the systematic sets of data for rapidity-studies at gradually increasing energies were available.

hep-ph↗
arXiv2010

New X-ray observations of the Geminga pulsar wind nebula

Previous observations of the middle-aged pulsar Geminga with XMM-Newton and Chandra have shown an unusual pulsar wind nebula (PWN), with a 20" long central (axial) tail directed opposite to the pulsar's proper motion and two 2' long, bent lateral (outer) tails. Here we report on a deeper (78 ks) Chandra observation and a few additional XMM-Newton observations of the Geminga PWN. The new Chandra observation has shown that the axial tail, which includes up to three brighter blobs, extends at least 50" (i.e., 0.06 d_{250} pc) from the pulsar. It also allowed us to image the patchy outer tails and the emission in the immediate vicinity of the pulsar with high resolution. The PWN luminosity, L_{0.3-8 keV} ~ 3\times 10^{29} d_{250}^2 erg/s, is lower than the pulsar's magnetospheric luminosity by a factor of 10. The spectra of the PWN elements are rather hard (photon index ~ 1). Comparing the two Chandra images, we found evidence of PWN variability, including possible motion of the blobs along the axial tail. The X-ray PWN is the synchrotron radiation from relativistic particles of the pulsar wind; its morphology is connected with the supersonic motion of Geminga. We speculate that the outer tails are either (1) a sky projection of the limb-brightened boundary of a shell formed in the region of contact discontinuity, where the wind bulk flow is decelerated by shear instability, or (2) polar outflows from the pulsar bent by the ram pressure from the ISM. In the former case, the axial tail may be a jet emanating along the pulsar's spin axis, perhaps aligned with the direction of motion. In the latter case, the axial tail may be the shocked pulsar wind collimated by the ram pressure.

astro-ph.HE↗
arXiv2010

Local Probing of Mesoscopic Physics of Ferroelectric Domain Walls

Domain wall dynamics in ferroic materials underpins functionality of data storage and information technology devices. Using localized electric field of a scanning probe microscopy tip, we experimentally demonstrate a surprisingly rich range of polarization reversal behaviors in the vicinity of the initially flat 180°ferroelectric domain wall. The nucleation bias is found to increase by an order of magnitude from a 2D nucleus at the wall to 3D nucleus in the bulk. The wall is thus significantly ferroelectrically softer than the bulk. The wall profoundly affects switching on length scales of the order of micrometers. The mechanism of correlated switching is analyzed using analytical theory and phase-field modeling. The long-range effect is ascribed to wall bending under the influence of a tip bias well below the bulk nucleation field and placed many micrometers away from the wall. These studies provide an experimental link between the macroscopic and mesoscopic physics of domain walls and atomistic models of nucleation.

cond-mat.mtrl-sci↗
arXiv2010

Understanding the New High Energy Data-sets Measured by BESS, CAPRICE and PAMELA on Antiproton Flux and $\bar{P}/P$ Ratios

Reliable data from the very recent high-precision measurements on the antiproton fluxes and the antiproton-to-proton ratios by the PAMELA Collaboration at relatively much higher energies are now available. The results with regard to antiproton production phenomena spring no special surprises; rather they are sharply in contrast with and contradiction to the case of positron production at the same energy-range. However, the totality of data on antiproton production from the past experiments to the very recent PAMELA outburst seem to be a very challenging exercise for interpretation in terms of the secondary production mechanisms alone, the galactic propagation model etc against the background of the `dark-matter'-related controversy. In the present work we assume the validity of the simple leaky box model, choose a simple particle production model and attempt at providing a comprehensive interpretation of the totality of data on both antiproton flux measurements and the $\overline{P}/P$ ratio-values for the various experiments ranging from BESS, CAPRICE to the latest PAMELA experiment. With the assumption of no contribution from the exotic sources to the antiproton production process, our model and the method describe the totality of the measured data with a fair degree of success.

astro-ph.HE↗
arXiv2009

Paradigm Shifts and a Possible Resolution of the PAMELA-Paradox in Astroparticle Physics

Very recently, PAMELA Collaboration has formally reported two sets of data on positron and antiproton flux measurements done at very high energies and with unprecedented accuracy. The reports reveal a puzzle of great topical interest and importance : it is decisively found that there is a sharp smooth rise of the positron fraction, whereas for antiproton production no such rises occur; rather the fraction either flattens, or shows signs of falling off gradually with increasing energies. The present work is just an attempt to decipher the riddle with the help of a host of radically new ideas about the particle-structure, the multiparticle-production mechanisms and the concept of nucleon break-downs into the constituent partons. The application of these ideas found remarkable successes in the past; exactly similar or more striking are the findings by the present study.

astro-ph.HE↗
arXiv2009

Analysing $j/Ψ$ Production in Various RHIC Interactions with a Version of Sequential Chain Model (SCM)

We have attempted to develop here tentatively a model for $J/Ψ$ production in p+p, d+Au, Cu + Cu and Au + Au collisions at RHIC energies on the basic ansatz that the results of nucleus-nucleus collisions could be arrived at from the nucleon-nucleon (p + p)-interactions with induction of some additional specific features of high energy nuclear collisions. Based on the proposed new and somewhat unfamiliar model, we have tried (i) to capture the properties of invariant $p_T$ -spectra for $J/Ψ$ meson production; (ii) to study the nature of centrality dependence of the $p_T$ -spectra; (iii) to understand the rapidity distributions; (iv) to obtain the characteristics of the average transverse momentum $< p_T >$ and the values of $< p_T^2 >$ as well and (v) to trace the nature of nuclear modification factor. The alternative approach adopted here describes the data-sets on the above-mentioned various observables in a fairly satisfactory manner. And, finally, the nature of $J/Ψ$-production at Large Hadron Collider(LHC)-energies deduced on the basis of our chosen model has been presented in a predictive way against the RHIC-yields, both calculated for the most central collisions and on the same model.

hep-ph↗
arXiv2009

Search for TeV $γ$ -rays from H1426+428 during 2004-07 with the TACTIC telescope

The BL Lac object H1426+428 ($z\equiv 0.129$) is an established source of TeV $γ$-rays and detections of these photons from this object also have important implications for estimating the Extragalactic Background Light (EBL) in addition to the understanding of the particle acceleration and $γ$-ray production mechanisms in the AGN jets. We have observed this source for about 244h in 2004, 2006 and 2007 with the TACTIC $γ$-ray telescope located at Mt. Abu, India. Detailed analysis of these data do not indicate the presence of any statistically significant TeV $γ$-ray signal from the source direction. Accordingly, we have placed an upper limit of $\leq1.18\times10^{-12}$ $photons$ $cm^{-2}$ $s^{-1}$ on the integrated $γ$-ray flux at 3$σ$ significance level.

astro-ph.CO↗
arXiv2009

The Behavior of Matter under Extreme Conditions

The cores of neutron stars harbor the highest matter densities known to occur in nature, up to several times the densities in atomic nuclei. Similarly, magnetic field strengths can exceed the strongest fields generated in terrestrial laboratories by ten orders of magnitude. Hyperon-dominated matter, deconfined quark matter, superfluidity, even superconductivity are predicted in neutron stars. Similarly, quantum electrodynamics predicts that in strong magnetic fields the vacuum becomes birefringent. The properties of matter under such conditions is governed by Quantum Chromodynamics (QCD) and Quantum Electrodynamics (QED), and the close study of the properties of neutron stars offers the unique opportunity to test and explore the richness of QCD and QED in a regime that is utterly beyond the reach of terrestrial experiments. Experimentally, this is almost virgin territory.

astro-ph.HE↗
arXiv2008

Science with the XEUS High Time Resolution Spectrometer

XEUS has been recently selected by ESA for an assessment study. XEUS is a large mission candidate for the Cosmic Vision program, aiming for a launch date as early as 2018. XEUS is a follow-on to ESA's Cornerstone X-Ray Spectroscopy Mission (XMM-Newton). It will be placed in a halo orbit at L2, by a single Ariane 5 ECA, and comprises two spacecrafts. The Silicon pore optics assembly of XEUS is contained in the mirror spacecraft while the focal plane instruments are contained in the detector spacecraft, which is maintained at the focus of the mirror by formation flying. The main requirements for XEUS are to provide a focused beam of X-rays with an effective aperture of 5 m^2 at 1 keV, 2 m^2 at 7 keV, a spatial resolution better than 5 arcsec, a spectral resolution ranging from 2 to 6 eV in the 0.1-8 keV energy band, a total energy bandpass of 0.1-40 keV, ultra-fast timing, and finally polarimetric capabilities. The High Time Resolution Spectrometer (HTRS) is one of the five focal plane instruments, which comprises also a wide field imager, a hard X-ray imager, a cryogenic spectrometer, and a polarimeter. The HTRS is unique in its ability to cope with extremely high count rates (up to 2 Mcts/s), while providing sub-millisecond time resolution and good (CCD like) energy resolution. In this paper, we focus on the specific scientific objectives to be pursued with the HTRS: they are all centered around the key theme "Matter under extreme conditions" of the Cosmic Vision science program. We demonstrate the potential of the HTRS observations to probe strong gravity and matter at supra-nuclear densities. We conclude this paper by describing the current implementation of the HTRS in the XEUS focal plane.

astro-ph↗
arXiv2008

Very High Energy gamma-ray observations of Mrk 501 using TACTIC imaging gamma-ray telescope during 2005-06

In this paper we report on the Markarian 501 results obtained during our TeV $γ$-ray observations from March 11 to May 12, 2005 and February 28 to May 7, 2006 for 112.5 hours with the TACTIC $γ$-ray telescope. During 2005 observations for 45.7 hours, the source was found to be in a low state and we have placed an upper limit of 4.62 $\times$ 10$^{-12}$ photons cm$^{-2}$ s$^{-1}$ at 3$σ$ level on the integrated TeV $γ$-ray flux above 1 TeV from the source direction. However, during the 2006 observations for 66.8h, detailed data analysis revealed the presence of a TeV $γ$-ray signal from the source with a statistical significance of 7.5$σ$ above $E_γ\geq$ 1 TeV. The time averaged differential energy spectrum of the source in the energy range 1-11 TeV is found to match well with the power law function of the form ($dΦ/dE=f_0 E^{-Γ}$) with $f_0=(1.66\pm0.52)\times 10^{-11}cm^{-2}s^{-1}TeV^{-1}$ and $Γ=2.80\pm0.27$.

astro-ph↗