We present results of dc magnetization and magnetic relaxation study showing the kinetic arrest of a first order ferromagnetic to antiferromagnetic transition in Ce(Fe$_{0.96}$Ru$_{0.04}$)$_2$. This leads to the formation of a non-ergodic glass-like magnetic state. The onset of the magnetic-glass transformation is tracked through the slowing down of the magnetization dynamics. This glassy state is formed with the assistance of an external magnetic field and this is distinctly different from the well known 'spin-glass' state.

M. K. Chattopadhyay S. B. Roy P. Chaddah

Superheated drops are known to vaporise when exposed to energetic nuclear radiation since the discovery of bubble chamber. As the degree of superheat increases in a given liquid, less and less energetic neutrons are required to cause nucleation. This property of superheated liquids are being utilised to develope the neutron spectromer. A new principle of neutron spectrometry using Superheated liquid are developed and the developed principle has been tested by Am-Be neutron source.

Mala Das B. K. Chatterjee B. Roy S. C. Roy

The mixed state of type II superconductors has magnetic flux penetrating the sample in the form of vortices, with each vortex carrying an identical quantum of flux. These vortices generally form a triangular lattice under weak mutually repulsive forces; the lattice spacing can be easily varied over many orders of magnitude by varying the external magnetic field. The elastic moduli of this lattice are small and this soft vortex matter can undergo phase transitions like normal matter, but with thermal fluctuations and underlying defects playing an important role. We discuss experimental studies on vortex matter phase transitions, with some emphasis on DC magnetisation measurements investigating the nature of the phase transition.

P. Chaddah S. B. Roy

We present results of dc magnetisation study showing that the low temperature antiferromagnetic state in various CeFe$_2$-based pseudobinary alloys can be transformed into ferromagnetic state through a magnetic field induced phase transition. We highlight the presence of hysteresis and phase coexistence across this metamagnetic transition and argue that the observed phase transition is of first order in nature.

Meghmalhar Manekar Sujeet Chaudhary M. K. Chattopadhyay Kanwal Jeet Singh S. B. Roy P. Chaddah

Solid solution between nonmagnetic narrow gap semiconductor FeSi and diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with long-range helical magnetic ordering, for a wide range of intermediate concentration. We report various interesting magnetic properties of these alloys, including low temperature re-entrant spin-glass like behaviour and a novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya interaction in the magnetic response of these non-centrosymmetric alloys is discussed.

M. K. Chattopadhyay S. B. Roy Sujeet Chaudhary

Neutron detection efficiency of superheated drops of Freon22 for neutrons obtained from a 3Ci Am-Be neutron source has been reported in this paper. Neutron detection efficiency of both F-22 and F-12 have been determined from the measured nucleation rate using the volumetric method developed in our lab. The result shows that the neutron detection efficiency of F-22 for the energy spectrum obtained from Am-Be is almost double, while the life time is 58.6% smaller than that of F-12, for a particular neutron flux of that source.

Mala Das B. Roy B. K. Chatterjee S. C. Roy

Superheated drops are known to detect neutrons through the nucleation caused by the recoil nuclei produced by the interactions of neutrons with the atoms constituting the superheated liquid molecule. A novel method of finding the neutron energy from the temperature dependence response of SDD has been developed. From the equivalence between the dependence of threshold energy for nucleation on temperature of SDD and the dependence of dE/dx of the recoil ions with the energy of the neutron, a new method of finding the neutron energy spectrum of a polychromatic as well as monochromatic neutron source has been developed.

Mala Das B. K. Chatterjee B. Roy S. C. Roy

We correct erroneous conclusions from Ref.[1] regarding the values of various critical exponents, calculated to the two-loop order, and argue that $\epsilon$-expansion near two spatial dimension, with $\epsilon=d-2$ may not be reliable to address the critical properties of disorder driven Dirac semimetal-metal quantum phase transition in $d=3$.

Bitan Roy S. Das Sarma

The radiative decays of $b$-baryons facilitate the direct measurement of photon helicity in $b\to s\gamma$ transitions thus serving as an important test of physics beyond the Standard Model. In this paper we analyze the complete angular distribution of ground state $b$-baryon ($\Lambda_{b}^{0}$ and $\Xi_{b}^{-}$) radiative decays to multibody final states assuming an initially polarized $b$-baryon sample. Our sensitivity study suggests that the photon polarization asymmetry can be extracted to a good accuracy along with a simultaneous measurement of the initial $b$-baryon polarization. With higher yields of $b$-baryons, achievable in subsequent runs of the Large Hadron Collider (LHC), we find that the photon polarization measurement can play a pivotal role in constraining different new physics scenarios.

Luis Miguel García Martín Brij Jashal Fernando Martínez Vidal Arantza Oyanguren Shibasis Roy Ria Sain Rahul Sinha

Within the framework of a dynamical and physically transparent model developed earlier, we study the time evolution of various quark flavours in the baryon-free region in ultrarelativistic heavy ion collisions. We show that even under optimistic conditions, the quark-gluon system fails to achieve chemical equilibrium.

J. Alam P. Roy S. Sarkar S. Raha B. Sinha