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A. Chakrabarti

Publications and source records attributed to A. Chakrabarti.

At least 19 recordsLinked to original sources
arXiv2026

Demonstrating CBM Capabilities by $Λ$ Baryon Reconstruction in Ni+Ni Collisions with the mCBM Experiment at SIS18 of GSI/FAIR

The Compressed Baryonic Matter (CBM) experiment at the upcoming Facility for Antiproton and Ion Research (FAIR) is a high-rate fixed-target experiment designed to investigate nuclear matter at extreme baryon densities in relativistic nucleus-nucleus collisions. To enable high-statistics measurements of rare probes, CBM is designed to operate at event rates up to 10 MHz. This necessitates the development of fast and radiation-tolerant detectors, self-triggered front-end electronics, a free-streaming data acquisition architecture, and real-time event reconstruction capabilities. Prototype versions and pre-series productions of the CBM detector systems have been deployed in the mini-CBM demonstrator setup mCBM - an experimental precursor comprising sub-components of all major CBM systems, installed at the SIS18 facility of GSI/FAIR within the FAIR Phase-0 program. In 2024, Ni+Ni collisions at a kinetic beam energy of 1.93 AGeV and an average interaction rate of about 250 kHz were successfully recorded. This dataset enables a detailed evaluation of the operational performance of the detector systems as well as the complete CBM data chain, while the reconstruction of rare $Λ$ baryons serves as a natural benchmark. This paper presents the first results on $Λ$ signal reconstruction with the mCBM experiment, demonstrating the readiness of the detector technologies and the data chain for the upcoming full-scale CBM experiment.

physics.ins-det↗
arXiv2018

Mass distribution in 36.2 MeV alpha induced fission of 232Th

Mass distribution of fission products has been determined in (alpha+232Th) reaction at Elab=36.2 MeV using alpha particles from the cyclotron at the Variable Energy Cyclotron Centre (VECC), Kolkata. Yields of 69 fission products having half-lives in the range of about ~1 min to several days have been measured using gamma ray spectrometry of fission products. The mass distribution obtained on the basis of the yields shows a clear triple humped structure showing the contribution from both asymmetric and symmetric modes of fission. Comparison of the experimental mass distribution with the prediction based on the GEF code, which takes into account multi-chance fission, shows that the simulation based on GEF reasonably reproduces asymmetric component arising from standard I mode of fission, but underestimate the contribution from Standard II fission mode. Also, the peak like structure in the symmetric region could not be reproduced.

nucl-ex↗
arXiv2017

Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR

Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.

nucl-ex↗
arXiv2015

Wetting and phase separation in soft adhesion

In the classic theory of solid adhesion, surface energy drives deformation to increase contact area while bulk elasticity opposes it. Recently, solid surface stress has been shown also to play an important role in opposing deformation of soft materials. This suggests that the contact line in soft adhesion should mimic that of a liquid droplet, with a contact angle determined by surface tensions. Consistent with this hypothesis, we observe a contact angle of a soft silicone substrate on rigid silica spheres that depends on the surface functionalization but not the sphere size. However, to satisfy this wetting condition without a divergent elastic stress, the gel separates from its solvent near the contact line. This creates a four-phase contact zone with two additional contact lines hidden below the surface of the substrate. While the geometries of these contact lines are independent of the size of the sphere, the volume of the phase-separated region is not, but rather depends on the indentation volume. These results indicate that theories of adhesion of soft gels need to account for both the compressibility of the gel network and a non-zero surface stress between the gel and its solvent.

cond-mat.soft↗
arXiv2013

Nanopattern on Carbon and by Carbon

We have reported nanopattern formation on carbon thin film and Si(100) surfaces by low energy inert and carbon ion beams. It is interesting to observe the role of carbon as target as well as projectile for nano patterning. Using carbon thin film as target, nano patterns of carbon are formed by inert (Ar+) and self (C+) ion bombardment, whereas carbon ion beam is used to form well ordered Si nano ripple structure in a cost effective way where implanted carbon plays an important role to form Si ripple in relatively lower fluence than the inert projectile.

cond-mat.mtrl-sci↗
arXiv2013

Antiferromagnetic Exchange Interactions in Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ ferromagnetic Heusler alloy

Magnetism in Ni-Mn-Z (Z = Ga,In,Sn,Sb) Heusler alloys has so far been predominantly attributed to Rudermann-Kittel-Kasuya-Yoshida type interactions between Mn atoms. We investigate magnetic interactions in one such alloy, Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ and attempt to explain the origin of antiferromagnetic (AFM) interactions that coexist with ferromagnetic ones. Through the combination of x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD), we find that Ni plays an important role along with Mn in the overall magnetism. A significant hybridization that develops between Mn and Ni orbitals results in a small antiferromagnetic moment at Ni sites. The shift in the XMCD hysteresis loops in the martensitic phase suggests that antiferromagnetism results from superexchange like interactions between Mn atoms mediated by Ni.

cond-mat.mtrl-sci↗
arXiv2011

Key factors of ion induced nanopatterning

We have reported the dependence of projectile mass, chemical reactivity and effect of molecular beams on the ion induced nano structure formation, when 8 keV He1+, N1+, O1+, Ar1+ atomic ions and 16 keV N21+ and O21+ molecular ions are bombarded on the Si(100) surface at an incidence angle of 60^{\circ}. Atomic force microscopy (AFM) measurement shows that the initiation and growth of ripple structures are determined not only by the collision cascades but also by the chemical reactivity and molecular state of the projectiles. This experimental investigation explores the necessary requirements for ion induced controlled nanopatterning.

cond-mat.mtrl-sci↗
arXiv2011

Kinetics of microribbon formation in a simplified model of amelogenin biomacromolecules

We show that the kinetics of microribbon formation of amelogenin molecules is well described by a combination of translational and rotational diffusion of a simplified anisotropic bipolar model consisting of hydrophobic spherical colloid particles and a point charge located on each particle surface. The colloid particles interact via a standard depletion attraction while the point charges interact through a screened Coulomb repulsion. We study the kinetics via a Brownian dynamics simulation of both translational and rotational motions and show that the anisotropy brought in by the charge dramatically affects the kinetic pathway of cluster formation and our simple model captures the main features of the experimental observations.

cond-mat.soft↗
arXiv2010

Projectile's mass, reactivity and molecular dependence on ion nanostructuring

We have reported the dependence of projectile mass along with the chemical reactivity and nonlinear effects on ion beam induced nano structure formation when 8 keV He1+, N1+, O1+, Ar1+ atomic ions and 16 keV N21+ and O21+ molecular ions are bombarded on the Si (100) surface at an incidence angle of 600. Ex situ atomic force microcopy (AFM) measurements reveals the ripple structure development of various forms and dimensions depending on the projectiles mass, chemical reactivity and molecular state. This experimental study explores the necessary requirements for ion induced nanopatterning and their control.

cond-mat.mes-hall↗
arXiv2010

Some topics in the kinetics of protein aggregation

Preliminary results are presented for the kinetics of phase separation in three distinct models of protein aggregation. The first is a model of the formation of spherical microcrystals of insulin via an initial formation of fractal clusters of insulin. The results of our Brownian dynamics study of this model are in qualitative agreement with a recent experimental study (Biophys. Jour. 89 (2005) 3424-3433) of microcrystal formation from aqueous mixtures of insulin. A second work involves a theory for the formation of metastable bundles of sickle hemoglobin from fibers, based on a recent generic theory of bundle formation (Phy. Rev. Lett. 99 (2007) 098101). We also discuss a model for the microscopic formation of these fibers. Finally, we discuss preliminary results for the kinetics of cluster formation for a six patch model of protein crystallization.

physics.bio-ph↗
arXiv2009

Coulomb explosion sputtering of selectively oxidized Si

We have studied multiply charged Arq+ ion induced potential sputtering of a unique system comprising of coexisting Silicon and Silicon oxide surfaces. Such surfaces are produced by oblique angle oxygen ion bombardment on Si(100), where ripple structures are formed and one side of each ripple gets more oxidized. It is observed that higher the potential energy of Arq+ ion, higher the sputtering yield of the non conducting (oxide) side of the ripple as compared to the semiconducting side. The results are explained in terms of Coulomb explosion model where potential sputtering depends on the conductivity of the ion impact sites.

cond-mat.mtrl-sci↗
arXiv2009

Unitary Braid Matrices: Bridge between Topological and Quantum Entanglements

Braiding operators corresponding to the third Reidemeister move in the theory of knots and links are realized in terms of parametrized unitary matrices for all dimensions. Two distinct classes are considered. Their (non-local) unitary actions on separable pure product states of three identical subsystems (say, the spin projections of three particles) are explicitly evaluated for all dimensions. This, for our classes, is shown to generate entangled superposition of four terms in the base space. The 3-body and 2-body entanglements (in three 2-body subsystems), the 3-tangles and 2-tangles are explicitly evaluated for each class. For our matrices, these are parametrized. Varying parameters they can be made to sweep over the domain (0,1).Thus braiding operators corresponding to over- and under-crossings of three braids and, on closing ends, to topologically entangled Borromean rings are shown, in another context, to generate quantum entanglements. For higher dimensions, starting with different initial triplets one can entangle by turns, each state with all the rest. A specific coupling of three angular momenta is briefly discussed to throw more light on three body entanglements.

quant-ph↗
arXiv2009

Entangled states, Lorentz transformations, Spin-precession in magnetic fields

Two positive mass, spin $\frac 12$ particles created in an entangled state are studied in the presence of a constant magnetic field inducing distinct precessions, depending on the respective momenta, of the two spins. The charge and anomalous magnetic moment of each particle is taken into account. Consequences for entanglement and, more generally, on correlations, are derived. We start, however, with a compact derivation of the effects of Lorentz transformations on such entangled states, though that has been studied by several authors. Our formalism displays conveniently the analogies and the differences between the two cases. Moreover, combining the two, one obtains the case of constant, orthogonal electric and magnetic fields. More general perspectives are evoked in the concluding remarks.

hep-th↗
arXiv2008

Multiparameter statistical models from $N^2\times N^2$ braid matrices: Explicit eigenvalues of transfer matrices ${\bf T}^{(r)}$, spin chains, factorizable scatterings for all $N$

For a class of multiparameter statistical models based on $N^2\times N^2$ braid matrices the eigenvalues of the transfer matrix ${\bf T}^{(r)}$ are obtained explicitly for all $(r,N)$. Our formalism yields them as solutions of sets of linear equations with simple constant coefficients. The role of zero-sum multiplets constituted in terms of roots of unity is pointed out and their origin is traced to circular permutations of the indices in the tensor products of basis states induced by our class of ${\bf T}^{(r)}$ matrices. The role of free parameters, increasing as $N^2$ with $N$, is emphasized throughout. Spin chain Hamiltonians are constructed and studied for all $N$. Inverse Cayley transforms of Yang-Baxter matrices corresponding to our braid matrices are obtained for all $N$. They provide potentials for factorizable $S$-matrices. Main results are summarized and perspectives are indicated in the concluding remarks.

math.QA↗
arXiv2008

A new eight vertex model and higher dimensional, multiparameter generalizations

We study statistical models, specifically transfer matrices corresponding to a multiparameter hierarchy of braid matrices of $(2n)^2\times(2n)^2$ dimensions with $2n^2$ free parameters $(n=1,2,3,...)$. The simplest, $4\times 4$ case is treated in detail. Powerful recursion relations are constructed giving the dependence on the spectral parameter $θ$ of the eigenvalues of the transfer matrix explicitly at each level of coproduct sequence. A brief study of higher dimensional cases ($n\geq 2$) is presented pointing out features of particular interest. Spin chain Hamiltonians are also briefly presented for the hierarchy. In a long final section basic results are recapitulated with systematic analysis of their contents. Our eight vertex $4\times 4$ case is compared to standard six vertex and eight vertex models.

math.QA↗
arXiv2007

Higher Dimensional Multiparameter Unitary and Nonunitary Braid Matrices: Even Dimensions

A class of $(2n)^2\times(2n)^2$ multiparameter braid matrices are presented for all $n$ $(n\geq 1)$. Apart from the spectral parameter $θ$, they depend on $2n^2$ free parameters $m_{ij}^{(\pm)}$, $i,j=1,...,n$. For real parameters the matrices $R(θ)$ are nonunitary. For purely imaginary parameters they became unitary. Thus a unification is achieved with odd dimensional multiparameter solutions presented before.

math.QA↗
arXiv2007

Higher Dimensional Unitary Braid Matrices: Construction, Associated Structures and Entanglements

We construct $(2n)^2\times (2n)^2$ unitary braid matrices $\hat{R}$ for $n\geq 2$ generalizing the class known for $n=1$. A set of $(2n)\times (2n)$ matrices $(I,J,K,L)$ are defined. $\hat{R}$ is expressed in terms of their tensor products (such as $K\otimes J$), leading to a canonical formulation for all $n$. Complex projectors $P_{\pm}$ provide a basis for our real, unitary $\hat{R}$. Baxterization is obtained. Diagonalizations and block-diagonalizations are presented. The loss of braid property when $\hat{R}$ $(n>1)$ is block-diagonalized in terms of $\hat{R}$ $(n=1)$ is pointed out and explained. For odd dimension $(2n+1)^2\times (2n+1)^2$, a previously constructed braid matrix is complexified to obtain unitarity. $\hat{R}\mathrm{LL}$- and $\hat{R}\mathrm{TT}$-algebras, chain Hamiltonians, potentials for factorizable $S$-matrices, complex non-commutative spaces are all studied briefly in the context of our unitary braid matrices. Turaev construction of link invariants is formulated for our case. We conclude with comments concerning entanglements.

math.QA↗