arXiv subjects

P. Singh

Publications and source records attributed to P. Singh.

At least 19 recordsLinked to original sources

arXiv2026

Characterization of CMOS SPADs for future RICH Detectors

In the planned or considered upgrades of LHCb, ALICE and Belle II experiments, the Ring imaging Cherenkov (RICH) detectors will have to be improved in order to function at increased beam interaction density. The photodetectors used in future RICH detector will have to provide high granularity, single photon sensitivity and excellent timing, while being exposed to a couple of 10$^{13}$ 1-MeV neutron equivalent/cm$^2$ of background irradiation during total experiment run time. The spadRICH project is developing a CMOS single-photon avalanche diode (SPAD) based photodetector specifically optimized for the application of the planned RICH detectors, which includes neutron radiation hardness and cryogenic operation. In this work we present recent experimental characterization studies of existing SPADs produced in 55 nm BCD and 110 nm CMOS image sensor technologies. Main results include dark count rate (DCR) measurements with SPADs irradiated up to 10$^{12}$ 1-MeV neutron equivalent/cm$^2$ and cooled down to liquid nitrogen temperature.

physics.ins-det↗

arXiv2025

Kilonova and progenitor properties of merger-driven gamma-ray bursts

Gamma-Ray Burst (GRB) prompt and afterglow emission, as well as a kilonova (KN), are the expected electromagnetic (EM) counterparts of Binary Neutron Star (BNS) and Neutron Star -- Black Hole (NSBH) mergers. We aim to infer the KN ejecta parameters and the progenitor properties by modeling merger-driven GRBs with a claim of KN, good data and robust redshift measurement. We model the afterglow and KN, and perform a Bayesian analysis, within the Nuclear physics and Multi-Messenger Astrophysics (NMMA) framework. The KN emission is modeled with the radiative transfer code POSSIS and for afterglow we use the afterglowpy library. In contrast to previous approaches, our methodology simultaneously models both afterglow and KN. We find that all GRBs in our sample have a KN, but we were unable to confirm or exclude its presence in GRB 150101B. A BNS progenitor is favored for GRB 160821B, GRB 170817A/AT2017gfo, GRB 211211A, and GRB 230307A. For GRB 150101B and GRB 191019A, we obtain a slight preference for NSBH scenario, while a BNS is also viable. For KN emission, we find that the median wind mass $\langle M_{\rm wind}\rangle=0.027^{+0.046}_{-0.019}$ $M_{\odot}$ is larger than the dynamical $\langle M_{\rm dyn}\rangle = 0.012^{+0.007}_{-0.006}$ $M_{\odot}$. We find that $M_{\rm wind}$ and the beaming corrected kinetic energy of the jet can be attributed as $log(M_{\rm wind})=-20.23+0.38\,log(E_{0,J})$. We confirm the results of numerical simulation that $\tilde\Lambda$ increases with decrease in $\mathcal{M}_{\rm \,Chirp}$. Our work shows that EM modeling can be effective for probing the progenitors, and for the first time presents the progenitor properties of a sizable sample of merger-driven GRBs.

astro-ph.HE↗

arXiv2025

Readout electronics for low occupancy High-Pressure Gas TPCs

HPgTPCs have benefits such as low energy threshold, magnetisability, and 4$\pi$ acceptance, making them ideal for neutrino experiments such as DUNE. We present the design of an FPGA-based solution optimised for ND-GAr, which is part of the Phase-II more capable near detector for DUNE. These electronics reduce the cost significantly compared to using collider readout electronics which are typically designed for much higher occupancy and therefore, for example, need much larger numbers of FPGAs and power per channel. We demonstrate the performance of our electronics with the TOAD at Fermilab in the US at a range of pressures and gas mixtures up to 4.5barA, reading out ~10000 channels from a multi-wire proportional chamber. The operation took place between April and July of 2024. We measure the noise characteristics of the system to be sufficiently low and we identify sources of noise that can be further mitigated in the next iteration. We also note that the cooling scheme used in the test requires improvement before full-scale deployment. Despite these necessary improvements, we show that the system can fulfil the needs of a HPgTPC for a fraction of the price of collider readout electronics.

physics.ins-det↗

arXiv2024

The puzzling long GRB 191019A: Evidence for Kilonova Light

GRB 191019A was a long Gamma-ray burst (GRB) lasting about 65 s and, as such, originally thought to be linked to a core-collapse supernova. However, even though follow-up observations identified the optical counterpart close to the bright nucleus of a nearby ancient galaxy (z=0.248), no associated supernova was found. This led to the suggestion that the burst was caused by the merger of two compact stellar objects, likely in a dense circumnuclear environment. By using a recently developed diagnostic tool based on prompt emission temporal properties, we noticed that GRB 191019A falls among those long GRBs which are associated with compact mergers and with evidence of kilonova light. We thus re-analyzed unpublished GROND multi-color (g'r'i'z'JHK_s) data obtained between 0.4 and 15 days post trigger. Image subtraction confirmed the optical counterpart in all four optical bands, with GROND tracking its fading until 1.5 days post-burst. Incorporating publicly available Swift-XRT data, a joint fit of an afterglow plus a kilonova model revealed a better match than an afterglow-only scenario. The resulting kilonova properties resemble those of AT2017gfo associated with the binary neutron star merger GW170817, with a total ejected mass of about 0.06 solar mass. Contrary to previous findings inferring a high-density circumburst environment (n0=10^7-10^8 cm^-3), our analysis finds standard conditions (n0 = 1 cm^-3), suggesting the long duration of GRB 191019A was intrinsic rather than due to jet interaction with a dense external medium.

astro-ph.HE↗

arXiv2024

Learning efficient and provably convergent splitting methods

Splitting methods are widely used for solving initial value problems (IVPs) due to their ability to simplify complicated evolutions into more manageable subproblems which can be solved efficiently and accurately. Traditionally, these methods are derived using analytic and algebraic techniques from numerical analysis, including truncated Taylor series and their Lie algebraic analogue, the Baker--Campbell--Hausdorff formula. These tools enable the development of high-order numerical methods that provide exceptional accuracy for small timesteps. Moreover, these methods often (nearly) conserve important physical invariants, such as mass, unitarity, and energy. However, in many practical applications the computational resources are limited. Thus, it is crucial to identify methods that achieve the best accuracy within a fixed computational budget, which might require taking relatively large timesteps. In this regime, high-order methods derived with traditional methods often exhibit large errors since they are only designed to be asymptotically optimal. Machine Learning techniques offer a potential solution since they can be trained to efficiently solve a given IVP with less computational resources. However, they are often purely data-driven, come with limited convergence guarantees in the small-timestep regime and do not necessarily conserve physical invariants. In this work, we propose a framework for finding machine learned splitting methods that are computationally efficient for large timesteps and have provable convergence and conservation guarantees in the small-timestep limit. We demonstrate numerically that the learned methods, which by construction converge quadratically in the timestep size, can be significantly more efficient than established methods for the Schr\"{o}dinger equation if the computational budget is limited.

math.NA↗

arXiv2024

Shape evolution in even-mass $^{98-104}$Zr isotopes via lifetime measurements using the $\gamma\gamma$-coincidence technique

The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first $2^+$ state and the increase in the transition strength B(E2; $2_1^\rightarrow 0_1^+$ going from $^{98}$Zr to $^{100}$Zr has been the first example of "quantum phase transition" in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the $\gamma\gamma$-coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in $^{98-104}$Zr carried out to extract reduced transition probabilities. The new lifetime values in $\gamma\gamma$-coincidence and $\gamma$-single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree-Fock-Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.

nucl-ex↗

arXiv2023

A Hubble Space Telescope Search for r-Process Nucleosynthesis in Gamma-ray Burst Supernovae

The existence of a secondary (in addition to compact object mergers) source of heavy element ($r$-process) nucleosynthesis, the core-collapse of rapidly-rotating and highly-magnetized massive stars, has been suggested by both simulations and indirect observational evidence. Here, we probe a predicted signature of $r$-process enrichment, a late-time ($\gtrsim 40$ days post-burst) distinct red color, in observations of GRB-supernovae (GRB-SNe) which are linked to these massive star progenitors. We present optical to near-IR color measurements of four GRB-SNe at $z \lesssim 0.4$, extending out to $> 500$ days post-burst, obtained with the Hubble Space Telescope and large-aperture ground-based telescopes. Comparison of our observations to models indicates that GRBs 030329, 100316D and 130427A are consistent with both no enrichment and producing $0.01 - 0.15 M_{\odot}$ of $r$-process material if there is a low amount of mixing between the inner $r$-process ejecta and outer SN layers. GRB 190829A is not consistent with any models with $r$-process enrichment $\geq 0.01 M_{\odot}$. Taken together the sample of GRB-SNe indicates color diversity at late times. Our derived yields from GRB-SNe may be underestimated due to $r$-process material hidden in the SN ejecta (potentially due to low mixing fractions) or the limits of current models in measuring $r$-process mass. We conclude with recommendations for future search strategies to observe and probe the full distribution of $r$-process produced by GRB-SNe.

astro-ph.HE↗

arXiv2023

NV with nitrogen

The paper highlights the difference the properties the nitrogen vacancy centre in bulk diamond containing nitrogen compared to the properties of single centres. Charge transfer between the negative and neutral charge state can occur with a tunnelling of an electron from an adjacent nitrogen atom without involving conduction or valence electrons. This contrasts with charge transfer of single sites. There are other differences for example with the intersystem crossing.

cond-mat.mtrl-sci↗

arXiv2023

First operation of an ALICE OROC operated in high pressure Ar-CO$_{2}$ and Ar-CH$_{4}$

New neutrino-nucleus interaction cross-section measurements are required to improve nuclear models sufficiently for future long-baseline neutrino experiments to meet their sensitivity goals. A time projection chamber (TPC) filled with a high-pressure gas is a promising detector to characterise the neutrino sources planned for such experiments. A gas-filled TPC is ideal for measuring low-energy particles as they travel much further in gas than solid or liquid neutrino detectors. Using a high-pressure gas increases the target density, resulting in more neutrino interactions. This paper will examine the suitability of multiwire proportional chambers (MWPCs) taken from the ALICE TPC to be used as the readout chambers of a high-pressure gas TPC. These chambers were previously operated at atmospheric pressure. We tested one such MWPC at up to almost 5 bar absolute (barA) with the UK high-pressure test stand at Royal Holloway, University of London. This paper reports the successful operation of an ALICE TPC outer readout chamber (OROC) at pressures up to 4.8 bar absolute with Ar-CH$_{4}$ mixtures with a CH$_{4}$ content between 2.8% and 5.0%, and so far up to 4 bar absolute with Ar-CO$_{2}$ (90-10). We measured the charge gain of this OROC using signals induced by an $^{55}$Fe source. The largest gain achieved at 4.8 bar was $64\pm2)\cdot10^{3}$ at stable conditions with an anode wire voltage of 2990 V in Ar-CH$_{4}$ (95.9-4.1). In Ar-CO$_{2}$ a gain of $(4.2\pm0.1)\cdot10^{3}$ was observed at an anode voltage of 2975 V at 4 barA gas pressure. Based on all our gain measurements, we extrapolate that, at the 10 barA pressure necessary to fit 1 tonne of gas into the ALICE TPC volume, a gain of 5000 in Ar-CO$_{2}$ (90-10) (10000 in Ar-CH$_{4}$ with $\sim\!$ 4% CH$_{4}$ content) may be achieved with an OROC anode voltage of 4.2 V ($\sim\!$ 3.1 kV).

physics.ins-det↗

arXiv2022

On the creation of near-surface nitrogen-vacancy centre ensembles by implantation of type Ib diamond

Dense, near-surface (within 10 nm) ensembles of nitrogen-vacancy (NV) centres in diamond are rapidly moving into prominence as the workhorse of a variety of envisaged applications, ranging from the imaging of fast-fluctuating magnetic signals to the facilitation of nuclear hyperpolarisation. Unlike their bulk counterparts, near-surface ensembles suffer from charge stability issues and reduced NV formation efficiency due to the diamond surface's role as a vacancy sink during annealing and an electron sink afterwards. To this end, work is ongoing to determine the best methods for producing high-quality ensembles in this regime. Here we examine the prospects for creating such ensembles cost-effectively by implanting nitrogen-rich type Ib diamond with electron donors, aiming to exploit the high bulk nitrogen density to combat surface-induced band bending in the process. This approach has previously been successful at creating deeper ensembles, however we find that in the near-surface regime there are fewer benefits over nitrogen implantation into pure diamond substrates. Our results suggest that control over diamond surface termination during annealing is key to successfully creating high-yield near-surface NV ensembles generally, and implantation into type Ib diamond may be worth revisiting once that has been accomplished.

cond-mat.other↗

arXiv2022

Improved measurement of the $0_2^+\rightarrow0_1^+$ E0 transition strength for $^{72}$Se using the SPICE spectrometer

The selenium isotopes lie at the heart of a tumultuous region of the nuclear chart where shape coexistence effects grapple with neutron-proton pairing correlations, triaxiality, and the impending proton dripline. In this work a study of $^{72}$Se by internal conversion electron and $\gamma$-ray spectroscopy was undertaken with the SPICE and TIGRESS arrays. New measurements of the branching ratio and lifetime of the $0_2^+$ state were performed yielding a determination of $\rho^2(E0;0_2^+{\rightarrow}0_1^+)=29(3)$ milliunits. two state mixing calculations were performed that highlighted the importance of interpretation of such $E0$ strength values in the context of shape-coexistence.

nucl-ex↗

arXiv2022

EmProx: Neural Network Performance Estimation For Neural Architecture Search

Common Neural Architecture Search methods generate large amounts of candidate architectures that need training in order to assess their performance and find an optimal architecture. To minimize the search time we use different performance estimation strategies. The effectiveness of such strategies varies in terms of accuracy and fit and query time. This study proposes a new method, EmProx Score (Embedding Proximity Score). Similar to Neural Architecture Optimization (NAO), this method maps candidate architectures to a continuous embedding space using an encoder-decoder framework. The performance of candidates is then estimated using weighted kNN based on the embedding vectors of architectures of which the performance is known. Performance estimations of this method are comparable to the MLP performance predictor used in NAO in terms of accuracy, while being nearly nine times faster to train compared to NAO. Benchmarking against other performance estimation strategies currently used shows similar to better accuracy, while being five up to eighty times faster.

cs.LG↗

arXiv2022

The Evolution of AGN Activity in Brightest Cluster Galaxies

We present the results of an analysis of Wide-field Infrared Survey Explorer (WISE) observations on the full 2500 deg^2 South Pole Telescope (SPT)-SZ cluster sample. We describe a process for identifying active galactic nuclei (AGN) in brightest cluster galaxies (BCGs) based on WISE mid-infrared color and redshift. Applying this technique to the BCGs of the SPT-SZ sample, we calculate the AGN-hosting BCG fraction, which is defined as the fraction of BCGs hosting bright central AGNs over all possible BCGs. Assuming {\bf an evolving} single-burst stellar population model, we find statistically significant evidence (>99.9%) for a mid-IR excess at high redshift compared to low redshift, suggesting that the fraction of AGN-hosting BCGs increases with redshift over the range of 0 < z < 1.3. The best-fit redshift trend of the AGN-hosting BCG fraction has the form (1+z)^(4.1+/-1.0). These results are consistent with previous studies in galaxy clusters as well as field galaxies. One way to explain this result is that member galaxies at high redshift tend to have more cold gas. While BCGs in nearby galaxy clusters grow mostly by dry mergers with cluster members, leading to no increase in AGN activity, BCGs at high redshift could primarily merge with gas-rich satellites, providing fuel for feeding AGNs. If this observed increase in AGN activity is linked to gas-rich mergers, rather than ICM cooling, we would expect to see an increase in scatter in the P_cav vs L_cool relation at z > 1. Lastly, this work confirms that the runaway cooling phase, as predicted by the classical cooling flow model, in the Phoenix cluster is extremely rare and most BCGs have low (relative to Eddington) black hole accretion rates.

astro-ph.GA↗

arXiv2021

Unraveling the reaction mechanism for large alpha production and incomplete fusion in reactions involving weakly bound stable nuclei

The origin of the large $\alpha$ particle production and incomplete fusion in reactions involving weakly-bound $\alpha$+$x$ cluster nuclei still remains unresolved. While the (two-step) process of breakup followed by capture of the ``free" complementary fragment ($x$) is widely believed to be responsible, a few recent studies suggest the dominant role of (direct) cluster stripping. To achieve an unambiguous experimental discrimination between these two processes, a coincidence measurement between the outgoing $\alpha$ particles and $\gamma$ rays from the heavy residues has been performed for the $^7$Li($\alpha$+triton)+$^{93}$Nb system. Proper choice of kinematical conditions allowed for the first time a significant population of the region accessible only to the direct triton stripping process and not to breakup followed by the capture of the ``free'' triton (from the three-body continuum). This result, also supported by a cluster-transfer calculation, clearly establishes the dominance of the direct cluster-stripping mechanism in the large alpha production.

nucl-ex↗

arXiv2021

High temperature oxidation behavior of disordered (Ti0.5Zr0.5)2AlC MAX phase via a Machine Learning-Augmented DFT Approach

The Zr-based MAX phases have attracted considerable attention for their outstanding irradiation behavior and high neutron transparency relevant to nuclear power generation technologies. In spite of increased understanding of physical behavior crystalline MAX phases, the high-temperature oxidation behavior and reaction mechanism of disordered MAX phases both from theory and experiments are not well understood due to increased system complexity. Here, we present a detailed comparative assessment of high-temperature thermodynamic-stability and oxidation behavior (reaction-products and chemical activity) of ordered Ti2AlC and disordered (Ti0.5Zr0.5)2AlC. We believe that the new insights will enhance our understanding of oxidation process in disordered MAX phases.

cond-mat.mtrl-sci↗

arXiv2021

Exploring the contamination of the DES-Y1 Cluster Sample with SPT-SZ selected clusters

We perform a cross validation of the cluster catalog selected by the red-sequence Matched-filter Probabilistic Percolation algorithm (redMaPPer) in Dark Energy Survey year 1 (DES-Y1) data by matching it with the Sunyaev-Zel'dovich effect (SZE) selected cluster catalog from the South Pole Telescope SPT-SZ survey. Of the 1005 redMaPPer selected clusters with measured richness $\hat\lambda>40$ in the joint footprint, 207 are confirmed by SPT-SZ. Using the mass information from the SZE signal, we calibrate the richness--mass relation using a Bayesian cluster population model. We find a mass trend $\lambda\propto M^{B}$ consistent with a linear relation ($B\sim1$), no significant redshift evolution and an intrinsic scatter in richness of $\sigma_{\lambda} = 0.22\pm0.06$. At low richness SPT-SZ confirms fewer redMaPPer clusters than expected. We interpret this richness dependent deficit in confirmed systems as due to the increased presence at low richness of low mass objects not correctly accounted for by our richness-mass scatter model, which we call contaminants. At a richness $\hat \lambda=40$, this population makes up $>$12$\%$ (97.5 percentile) of the total population. Extrapolating this to a measured richness $\hat \lambda=20$ yields $>$22$\%$ (97.5 percentile). With these contamination fractions, the predicted redMaPPer number counts in different plausible cosmologies are compatible with the measured abundance. The presence of such a population is also a plausible explanation for the different mass trends ($B\sim0.75$) obtained from mass calibration using purely optically selected clusters. The mean mass from stacked weak lensing (WL) measurements suggests that these low mass contaminants are galaxy groups with masses $\sim3$-$5\times 10^{13} $ M$_\odot$ which are beyond the sensitivity of current SZE and X-ray surveys but a natural target for SPT-3G and eROSITA.

astro-ph.CO↗

arXiv2020

Metric-driven search for structurally stable inorganic compounds

We report a facile `metric' for the identification of structurally and dynamically (positive definite phonon structure) stable inorganic compounds. The metric considers charge-imbalance within the local substructures in crystalline compounds calculated using first-principles density-functional theory. To exemplify, we chose carbon-based nitrides as it provides a large pool of structurally stable and unstable phases. We showcase how local structural information related to Wyckoff symmetry uniquely identifies four new carbon-nitride phases. The metric predicts three new structurally stable phases of 4 (C)$:$3 (N) stoichiometry, i.e., C$_{4}$N$_{3}$, which is further confirmed by direct phonon calculations. The structurally stable phases also satisfy the thermodynamic stability and mechanical stability criteria. New phases possess extraordinary mechanical properties, similar to diamond, and show insulating bandgap ranging from optimal, 1.45 eV (optimal) to 5.5 eV (large gap). The structural, electronic, and optical properties of Pm(1)-C$_{4}$N$_{3}$, discussed in detail, indicate possible application in optoelectronic and photovoltaic technologies. The way metric is design, it can be used to predict stability of any material with three-dimensional bonding network. The metric was also able to predict structural stability of other nitride polymorphs with 100$\%$ accuracy. We believe that the proposed `Metric' will accelerate the search of unknown and unexplored inorganic compounds by quick filtering of dynamically stable phases without expensive density-functional theory calculations.

cond-mat.mtrl-sci↗

arXiv2020

Cosmological Constraints from DES Y1 Cluster Abundances and SPT Multi-wavelength data

We perform a joint analysis of the counts of redMaPPer clusters selected from the Dark Energy Survey (DES) Y1 data and multi-wavelength follow-up data collected within the 2500 deg$^2$ South Pole Telescope (SPT) SZ survey. The SPT follow-up data, calibrating the richness--mass relation of the optically selected redMaPPer catalog, enable the cosmological exploitation of the DES cluster abundance data. To explore possible systematics related to the modeling of projection effects, we consider two calibrations of the observational scatter on richness estimates: a simple Gaussian model which account only for the background contamination (BKG), and a model which further includes contamination and incompleteness due to projection effects (PRJ). Assuming either a $\Lambda$CDM+$\sum m_\nu$ or $w$CDM+$\sum m_\nu$ cosmology, and for both scatter models, we derive cosmological constraints consistent with multiple cosmological probes of the low and high redshift Universe, and in particular with the SPT cluster abundance data. This result demonstrates that the DES Y1 and SPT cluster counts provide consistent cosmological constraints, if the same mass calibration data set is adopted. It thus supports the conclusion of the DES Y1 cluster cosmology analysis which interprets the tension observed with other cosmological probes in terms of systematics affecting the stacked weak lensing analysis of optically--selected low--richness clusters. Finally, we analyse the first combined optically-SZ selected cluster catalogue obtained by including the SPT sample above the maximum redshift probed by the DES Y1 redMaPPer sample. Besides providing a mild improvement of the cosmological constraints, this data combination serves as a stricter test of our scatter models: the PRJ model, providing scaling relations consistent between the two abundance and multi-wavelength follow-up data, is favored over the BKG model.

astro-ph.CO↗