arXiv subjects

D. Banerjee

Publications and source records attributed to D. Banerjee.

At least 19 recordsLinked to original sources

arXiv2026

Observation of multipartite spin entanglement in a cuprate chain

Quantum materials are believed to host highly entangled states of matter, but probing and quantifying such entanglement has long remained experimentally elusive. Here, we use resonant inelastic X-ray scattering (RIXS) as a probe of multipartite spin entanglement. By projecting the RIXS cross section onto the appropriate spin excitation channel, we show that the Quantum Fisher Information can be extracted directly from the measured spin fluctuation spectrum. We detect at least 7-partite spin entanglement in the model one-dimensional cuprate Sr$_2$CuO$_3$, revealing one of the largest entanglement depths yet reported in a solid. The observed entanglement depth agrees with Hubbard-model expectations and persists to elevated temperatures. Our results establish RIXS as an experimental probe of many-body spin entanglement and provide a platform for extensions to charge and orbital sectors and nonequilibrium settings.

cond-mat.str-el↗

arXiv2026

Low lying excitations in $^{150}$Pm

The low lying excitations in odd-odd $^{150}$Pm have been studied through proton induced reaction with an array of five Compton suppressed Clover HPGe and one segmented planar Ge detectors. The relative excitation functions for the observed $\gamma$ rays have been studied using singles data at two beam energies of 8~MeV and 9~MeV. 16 new $\gamma$ rays and 15 new levels have been placed in the level scheme of $^{150}$Pm based on $\gamma-\gamma$ coincidence data. The relative intensities for the observed $\gamma$ rays have been determined using total and gated projections. Tentative spin-parity assignments were made to few low lying excitations of $^{150}$Pm, using limited angular distribution data and other information. Lifetimes were estimated for two excited levels in this nucleus using using generalized centroid difference analysis, applied in the nanosecond range, with Ge detectors. Large basis shell model and projected shell model calculation were performed to interpret the experimentally observed levels. The present work indicates 1$^-$ ground state, a 2$^-$ state close to the ground state ($\sim$50~keV) and a low lying 6$^-$ isomeric state in this odd-odd nucleus along with emerging band structures developed with two quasiparticle configurations.

nucl-ex↗

arXiv2026

Improved limits on a new $Z'$ in $B-L$ scenarios with the NA64 experiment at CERN

Extensions of the Standard Model featuring an additional $U(1)_{B-L}$ gauge symmetry provide a compelling framework linking the origin of neutrino masses to possible dark matter candidates. The associated gauge boson, $Z'$, couples directly to Standard Model fermions and can be produced in fixed-target experiments through electron-nucleus interactions. In this work, we present new constraints on the coupling constant $g_{B-L}$ obtained with the NA64 experiment using the full electron-beam dataset collected between 2016 and 2022, corresponding to $(9.4\pm0.5)\times10^{11}$ electrons on target. The analysis includes the resonant $e^{+}e^{-}$ annihilation production channel, which enhances sensitivity in the mass range $m_{Z'}\in[200,300]$ MeV. The larger dataset provides approximately three times the statistics of previous analyses, thereby improving sensitivity. For the unbroken $U(1)_{B-L}$ case, the new limits exceed those from dedicated neutrino-scattering experiments, providing the most stringent laboratory bounds on $g_{B-L}$ for sub-GeV masses of the new boson. In scenarios where the $Z'$ couples to dark matter, the decay width is dominated by invisible channels, and the corresponding exclusion limits can be directly derived from the NA64 invisible-mode analysis.

hep-ex↗

arXiv2026

Hindered $\Delta K=1$ Dipole Strength in octupole bands in $N=90$ $^{154}$Gd from Lifetime Measurements with $\gamma-\gamma$ fast timing technique

The lifetimes of the low-lying negative-parity $1^-$ state at 1414~keV and $2^-$ state at 1398~keV in $^{154}$Gd have been measured using the $\gamma$--$\gamma$ fast-timing technique with the VENTURE array at VECC, Kolkata. The states were populated through the $\beta$ decay of $^{154}$Tb, produced in proton-induced reactions at the K130 cyclotron. From the measured lifetimes, absolute $B(E1)$ transition strengths were deduced. The extracted $B(E1)$ values are compared with those of neighboring Gd isotopes and with Gogny-HFB-based $sdf$-IBM calculations. The results show that the measured $E1$ strengths from these states are strongly hindered compared with the corresponding $\Delta K=0$ transitions, providing evidence for weak $\Delta K=1$ dipole strength in $^{154}$Gd.

nucl-ex↗

arXiv2025

Non-reciprocal circular dichroism of axial phonons coupled to ferro-rotational order

Circular dichroism (CD) in X-ray absorption, defined as the difference in absorption between opposite circular polarizations, is fundamentally enabled by the breaking of time-reversal symmetry or inversion symmetry. It is therefore sensitive to magnetism, chirality, and their interplay. In contrast, the sample symmetry alone is insufficient to determine whether CD in resonant inelastic X-ray scattering (RIXS) is allowed. Rather, RIXS-CD is governed by both the sample symmetry and the scattering geometry. Here, using RIXS, we identify circularly polarized phonons coupled to ferro-rotational order in MnTiO$_3$, which we refer to as ferro-axial phonons. Their excitations provide a direct demonstration of non-reciprocal RIXS-CD, in which the dichroic response changes upon reversing the propagation direction of the incident X-rays, although the system globally preserves both inversion and time-reversal symmetries. We propose that a condensate of these phonons, manifested as standing waves, underlies the ferro-rotational order in MnTiO$_3$. The observed non-reciprocal CD reflects the interplay among photon helicity, phonon polarization, and ferro-rotational order.

cond-mat.str-el↗

arXiv2025

Lifetimes and Transition Probabilities in $N = 76 ^{130}Xe$

Lifetimes for the ${4}_1^+$ and ${6}_1^+$ states have been directly measured using $\gamma-\gamma$ fast timing technique for low lying states of $^{130}Xe$, populated from $\beta ^-$ decay of the parent $^{130}I$ produced through $^{nat}U(\alpha,f)$ reaction at $E_{\alpha}~=~40~MeV$. VENTURE array comprising of eight fast CeBr$_3$ detectors is used for lifetime measurement. The reduced transition probabilities deduced from the measured lifetimes have been compared with theoretical values obtained from the large basis shell model calculation and the interacting boson approximation (IBM) calculation.

nucl-ex↗

arXiv2025

Properties of slow magneto-acoustic waves observed simultaneously using Hi-C 2.1 and AIA

Propagating slow magneto-acoustic waves are commonly observed in different coronal structures but are most prominent in active region fan loops. Their rapid damping with damping lengths of the order of a wavelength has been investigated in the past by several authors. Although different physical mechanisms have been proposed, significant discrepancies between the theory and observations remain. Recent high-resolution observations captured simultaneously by two different instruments reveal distinct damping lengths for slow magneto-acoustic waves although their passbands are similar. These results suggest a possible contribution of instrumental characteristics on the measurement of damping lengths. Here, we analyse the behavior of slow waves using a different pair of instruments in order to check the prevalence of such results. In particular, the cotemporal observations of active region NOAA AR12712 by the High-Resolution Coronal Imager (Hi-C 2.1) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) are utilised. The estimated oscillation periods of slow magneto-acoustic waves identified from these data are 2.7{\,}$\pm${\,}0.2{\,}min from SDO/AIA, and 2.8{\,}$\pm${\,}1.2{\,}min from Hi-C 2.1. The corresponding propagation speeds are found to be 46.0{\,}$\pm${\,}1.7{\,}km{\,}s$^{-1}$ and 48.1{\,}$\pm${\,}0.6{\,}km{\,}s$^{-1}$, respectively. Damping lengths were calculated by two different methods, the Phase Tracking Method (PTM) and the Amplitude Tracking Method (ATM). The obtained values from PTM are 4.0{\,}$\pm${\,}2.1{\,}Mm and 4.1{\,}$\pm${\,}0.3{\,}Mm while those from ATM are 3.4{\,}$\pm${\,}1.0{\,}Mm and 3.7{\,}$\pm${\,}0.1{\,}Mm, respectively, for the AIA and Hi-C data. Our results do not indicate any notable difference in damping lengths between these instruments.

astro-ph.SR↗

arXiv2025

Searching for Light Dark Matter and Dark Sectors with the NA64 experiment at the CERN SPS

Since its approval in 2016, NA64 has pioneered light dark matter (LDM) searches with electron, positron, muon, and hadron beams. The experiment has successfully met its primary objectives, as outlined in the EPPS input (2018), and even exceeded them, producing results that demonstrate its ability to operate in a near-background-free environment. The Physics Beyond Collider (PBC) initiative at CERN recognizes NA64's contributions as complementary and worthy of continued exploration. Its key advantage over beam-dump approaches is that the signal rate scales as the square of the coupling rather than the fourth power, reducing the required number of beam particles for the same sensitivity. To fully exploit the NA64 physics potential, an upgrade during LS3 will enable the experiment to run in background-free mode at higher SPS beam rates. Planned upgrades include: (a) improved detector hermeticity with a new veto hadron calorimeter, (b) enhanced particle identification with a synchrotron radiation detector, and (c) increased beam rates via upgraded electronics. With the recently strengthened NA64 collaboration, stable operations and timely data analysis are planned for LHC Run 4. The expected beam exposures are approximately 1e13 electrons, 1e11 positrons (at 40 and 60 GeV), and 2e13 muons on target. This will allow NA64 to explore new LDM parameter space, with the potential for discovery or conclusive exclusion of many well-motivated models.

hep-ex↗

arXiv2025

Summary Report of the Physics Beyond Colliders Study at CERN

The Physics Beyond Collider (PBC) Study Group was initially mandated by the CERN Management to prepare the previous European Particle Physics Strategy Update for CERN projects other than the high-energy frontier colliders. The main findings were summarized in an PBC Summary Report submitted to the Strategy Update. Following the Update process, the PBC Study Group was confirmed on a permanent basis with an updated mandate taking into account the strategy recommendations. The Study Group is now in charge of supporting the proponents of new ideas to address the technical issues and physics motivation of the projects ahead of their review by the CERN Scientific Committees and decision by the Management. The present document updates the previous PBC summary report to inform the new ongoing European Particle Physics Strategy Update process, taking into account the evolution of the CERN and worldwide landscapes and the new projects under consideration within the Study Group.

hep-ex↗

arXiv2025

High efficiency veto hadron calorimeter in the NA64 experiment at CERN

NA64 is a fixed-target experiment at the CERN SPS designed to search for Light particle Dark Matter (LDM) candidates with masses in the sub-GeV range. During the 2016-2022 runs, the experiment obtained the world-leading constraints, leaving however part of the well-motivated region of parameter space suggested by benchmark LDM models still unexplored. To further improve sensitivity, as part of the upgrades to the setup of NA64 at the CERN SPS H4 beamline, a prototype veto hadron calorimeter (VHCAL) was installed in the downstream region of the experiment during the 2023 run. The VHCAL, made of Cu-Sc layers, was expected to be an efficient veto against upstream electroproduction of large-angle hadrons or photon-nuclear interactions, reducing the background from secondary particles escaping the detector acceptance. With the collected statistics of $4.4\times10^{11}$ electrons on target (EOT), we demonstrate the effectiveness of this approach by rejecting this background by more than an order of magnitude. This result provides an essential input for designing a full-scale optimized VHCAL to continue running background-free during LHC Run 4, when we expect to collect $10^{13}$ EOT. Furthermore, this technique combined with improvements in the analysis enables us to decrease our missing energy threshold from 50 GeV to 40 GeV thereby enhancing the signal sensitivity of NA64.

hep-ex↗

arXiv2025

Proof of principle for a light dark matter search with low-energy positron beams at NA64

Thermal light dark matter (LDM) with particle masses in the 1 MeV - 1 GeV range could successfully explain the observed dark matter abundance as a relic from the primordial Universe. In this picture, a new feeble interaction acts as a "portal" between the Standard Model and LDM particles, allowing for the exploration of this paradigm at accelerator experiments. In the last years, the "missing energy" experiment NA64e at CERN SPS (Super Proton Synchrotron) has set world-leading constraints in the vector-mediated LDM parameter space, by exploiting a 100 GeV electron beam impinging on an electromagnetic calorimeter, acting as an active target. In this paper, we report a detailed description of the analysis of a preliminary measurement with a 70 GeV positron beam at NA64e, performed during summer 2023 with an accumulated statistic of 1.6 x 10^10 positrons on target. This data set was analyzed with the primary aim of evaluating the performance of the NA64e detector with a lower energy positron beam, towards the realization of the post-LS3 program. The analysis results, other than additionally probing unexplored regions in the LDM parameter space, provide valuable information towards the future NA64e positron campaign.

hep-ex↗

arXiv2024

Shedding light on Dark Sectors with high-energy muons at the NA64 experiment at the CERN SPS

A search for Dark Sectors is performed using the unique M2 beam line at the CERN Super Proton Synchrotron. New particles ($X$) could be produced in the bremsstrahlung-like reaction of high energy 160 GeV muons impinging on an active target, $\mu N\rightarrow\mu NX$, followed by their decays, $X\rightarrow\text{invisible}$. The experimental signature would be a scattered single muon from the target, with about less than half of its initial energy and no activity in the sub-detectors located downstream the interaction point. The full sample of the 2022 run is analyzed through the missing energy/momentum channel, with a total statistics of $(1.98\pm0.02)\times10^{10}$ muons on target. We demonstrate that various muon-philic scenarios involving different types of mediators, such as scalar or vector particles, can be probed simultaneously with such a technique. For the vector-case, besides a $L_\mu-L_\tau$ $Z'$ vector boson, we also consider an invisibly decaying dark photon ($A'\rightarrow\text{invisible}$). This search is complementary to NA64 running with electrons and positrons, thus, opening the possibility to expand the exploration of the thermal light dark matter parameter space by combining the results obtained with the three beams.

hep-ex↗

arXiv2024

On the formation height of low-corona and chromospheric channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO)

The multi-wavelength data from the Solar Dynamics Observatory (SDO) is extensively used in studying the physics of the Sun and its atmosphere. In this study, we estimate the formation heights of low-corona and chromospheric channels of the Atmospheric Imaging Assembly (AIA) over the atmospheres of sunspot umbrae during the quiet condition period within 20 different active regions. The upward propagating slow magnetoacoustic waves (slow MAWs) of 3-min period, which are perpetually present in sunspots, are utilized for this purpose. Employing a cross-correlation technique, the most frequent time lag between different channel pairs is measured. By combining this information with the local sound speed obtained from the characteristic formation temperatures of individual channels, we estimate the respective formation heights. The median values of formation heights obtained across all active regions in our sample are 356, 368, 858, 1180, and 1470 km, respectively, for the AIA 1600 {\AA}, 1700 {\AA}, 304 {\AA}, 131 {\AA}, and 171 {\AA} channels. The corresponding ranges in the formation heights are 247 $\--$ 453, 260 $\--$ 468, 575 $\--$ 1155, 709 $\--$ 1937, and 909 $\--$ 2585 km, respectively. These values are measured with respect to the HMI continuum. We find the formation height of UV channels is quite stable (between 250 $\--$ 500 km) and displays only a marginal difference between the AIA 1600 {\AA} and 1700 {\AA} during quiet conditions. On the other hand, the formation height of coronal channels is quite variable.

astro-ph.SR↗

arXiv2024

Reflectivity Studies and Production of New Flat Mirrors for the Cherenkov Threshold Detectors at CERN

Cherenkov threshold detectors (XCET) are used for identifying particles in the experimental areas at CERN. These detectors observe Cherenkov light emitted by charged particles travelling inside a pressurized gas vessel. A key component of the XCET detector is the 45-degree flat mirror reflecting the Cherenkov light towards the photomultiplier (PMT). A thorough analysis and optimization was conducted on the design and materials of this mirror, along with the surface coatings and coating techniques. A suitable manufacturing process was selected, and the first mirror prototype was produced, installed, and tested in the East Area at CERN. Experimental data obtained during beam tests is presented to assess the efficiency of the new coating and materials used.

hep-ex↗

arXiv2024

50 GeV $\pi^-$ in, nothing out: a sensitive probe of invisible $\eta$ and $\eta'$ decays with NA64h

We present the first results from a proof-of-concept search for dark sectors via invisible decays of pseudoscalar $\eta$ and $\eta'$ mesons in the NA64h experiment at the CERN SPS. Our novel technique uses the charge-exchange reaction of 50 GeV $\pi^-$ on nuclei of an active target as the source of neutral mesons. The $\eta, \eta' \to invisible$ events would exhibit themselves via a striking signature - the complete disappearance of the incoming beam energy in the detector. No evidence for such events has been found with $2.9\times10^{9}$ pions on target accumulated during one day of data taking. This allows us to set a stringent limit on the branching ratio ${\rm Br}(\eta' \to invisible) < 2.1 \times 10^{-4}$ improving the current bound by a factor of $\simeq3$. We also set a limit on ${\rm Br}(\eta \to invisible) < 1.1 \times 10^{-4}$ comparable with the existing one. These results demonstrate the great potential of our approach and provide clear guidance on how to enhance and extend the sensitivity for dark sector physics from future searches for invisible neutral meson decays.

hep-ex↗

arXiv2024

First constraints on the $L_\mu-L_\tau$ explanation of the muon $g-2$ anomaly from NA64-$e$ at CERN

The inclusion of an additional $U(1)$ gauge $L_\mu-L_\tau$ symmetry would release the tension between the measured and the predicted value of the anomalous muon magnetic moment: this paradigm assumes the existence of a new, light $Z^\prime$ vector boson, with dominant coupling to $\mu$ and $\tau$ leptons and interacting with electrons via a loop mechanism. The $L_\mu-L_\tau$ model can also explain the Dark Matter relic abundance, by assuming that the $Z'$ boson acts as a "portal" to a new Dark Sector of particles in Nature, not charged under known interactions. In this work we present the results of the $Z'$ search performed by the NA64-$e$ experiment at CERN SPS, that collected $\sim 9\times10^{11}$ 100 GeV electrons impinging on an active thick target. Despite the suppressed $Z'$ production yield with an electron beam, NA64-$e$ provides the first accelerator-based results excluding the $g-2$ preferred band of the $Z'$ parameter space in the 1 keV $ < m_{Z'} \lesssim 2$ MeV range, in complementarity with the limits recently obtained by the NA64-$\mu$ experiment with a muon beam.

hep-ex↗

arXiv2024

Exploration of the Muon $g-2$ and Light Dark Matter explanations in NA64 with the CERN SPS high energy muon beam

We report on a search for a new $Z'$ ($L_\mu-L_\tau$) vector boson performed at the NA64 experiment employing a high energy muon beam and a missing energy-momentum technique. Muons from the M2 beamline at the CERN Super Proton Synchrotron with a momentum of 160 GeV/c are directed to an active target. A signal event is a single scattered muon with momentum $<$ 80 GeV/c in the final state, accompanied by missing energy, i.e. no detectable activity in the downstream calorimeters. For a total statistic of $(1.98\pm0.02)\times10^{10}$ muons on target, no event is observed in the expected signal region. This allows us to set new limits on part of the remaining $(m_{Z'},\ g_{Z'})$ parameter space which could provide an explanation for the muon $(g-2)_\mu$ anomaly. Additionally, our study excludes part of the parameter space suggested by the thermal Dark Matter relic abundance. Our results pave the way to explore Dark Sectors and light Dark Matter with muon beams in a unique and complementary way to other experiments.

hep-ex↗

arXiv2023

The Fibre Resolved opticAl and Near-ultraviolet Czerny-Turner Imaging Spectropolarimeter (FRANCIS)

The solar physics community is entering a golden era that is ripe with next-generation ground- and space-based facilities. With ever-increasing resolving power stemming from the newest observational telescopes, it becomes more challenging to obtain (near-)simultaneous measurements at high spatial, temporal and spectral resolutions, while operating at the diffraction limit of these new facilities. Hence, in recent years there has been increased interest in the capabilities integral field units (IFUs) offer towards obtaining the trifecta of high spatial, temporal and spectral resolutions contemporaneously. To date, IFUs developed for solar physics research have focused on mid-optical and infrared measurements. Here, we present an IFU prototype that has been designed for operation within the near-ultraviolet to mid-optical wavelength range, hence providing additional spectral coverage to the instrument suites developed to date. The IFU was constructed as a low-budget proof-of-concept for the upcoming 2m class Indian National Large Solar Telescope and employs circular cross-section fibres to guide light into a Czerny-Turner configuration spectrograph, with the resulting spectra captured using a high quantum efficiency scientific CMOS camera. Mapping of each input fibre allows for the reconstruction of two-dimensional spectral images, with frame rates exceeding 20 per second possible while operating in a non-polarimetric configuration. The science verification data presented here highlights the suitability of fibre-fed IFUs operating at near-ultraviolet wavelengths for solar physics research. Importantly, the successful demonstration of this type of instrument paves the way for further technological developments to make a future variant suitable for upcoming ground-based and space-borne telescope facilities.

astro-ph.SR↗