arXiv subjects

I. Ahmed

Publications and source records attributed to I. Ahmed.

13 recordsLinked to original sources

arXiv2026

Measurement of isolated prompt photon production in $p$+$p$ collisions at $\sqrt{s} = 200$ GeV with the sPHENIX detector

The differential cross section of isolated prompt photon production is measured as a function of photon transverse energy ($E_{\mathrm{T}}^{\gamma}$) in proton--proton ($p$+$p$) collisions at $\sqrt{s} = 200$ GeV. The data were recorded in $2024$ with the sPHENIX detector at the Relativistic Heavy Ion Collider. Photons are reconstructed in $|\eta^{\gamma}| < 0.7$ and $12 < E_{\mathrm{T}}^{\gamma} < 32$ GeV using the electromagnetic calorimeter, and an isolation requirement is imposed using both the electromagnetic and hadronic calorimeters. The measured cross section is compared with the PYTHIA Monte Carlo event generator and perturbative quantum chromodynamics (pQCD) calculations at next-to-leading and next-to-next-to-leading order. The pQCD calculations are consistent with the result within the quoted uncertainties. This measurement provides a test of pQCD calculations for a process with sensitivity to the gluon parton distribution function of the proton and establishes the $p$+$p$ baseline for forthcoming sPHENIX measurements of isolated prompt photons in heavy-ion collisions.

nucl-ex↗

arXiv2026

Measurement of dijet transverse momentum imbalance and azimuthal acoplanarity in $p$+$p$ collisions at $\sqrt{s} = 200$ GeV with the sPHENIX detector

This Letter reports on measurements of dijet transverse momentum ($p_\mathrm{T}$) imbalance and azimuthal acoplanarity in proton-proton collisions at $\sqrt{s} = 200$~GeV, using data recorded by the sPHENIX detector at the Relativistic Heavy Ion Collider corresponding to an integrated luminosity of $41$~pb$^{-1}$. Jets are reconstructed using the anti-$k_t$ algorithm with radius parameters $R = 0.3$ to $0.8$ from electromagnetic and hadronic calorimeter energy deposits. The jet $p_\mathrm{T}$ resolution is determined directly in data using two independent methods. The dijet $p_\mathrm{T}$ imbalance is characterized by the ratio $x_\mathrm{J} = p_\mathrm{T,2}/p_\mathrm{T,1}$ where $p_\mathrm{T,1(2)}$ is the highest (second-highest) jet $p_\mathrm{T}$ in the event. The dijet azimuthal acoplanarity $\Delta\phi = |\phi_1 - \phi_2|$ is also reported. Results are reported for different $p_\mathrm{T,1}$ selections and jet radius parameters, normalized per dijet pair, and compared to the results of \textsc{Pythia} and \textsc{Herwig} Monte Carlo event generators. These measurements provide a stringent quantitative test of the modeling of QCD parton shower and hadronization dynamics, place important constraints on event-generator descriptions at RHIC energies, and establish a comprehensive proton-proton baseline for forthcoming measurements of jet modification in heavy ion collisions.

nucl-ex↗

arXiv2025

Future Circular Collider Feasibility Study Report: Volume 1, Physics, Experiments, Detectors

Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model. The report reviews the experimental opportunities offered by the staged implementation of FCC, beginning with an electron-positron collider (FCC-ee), operating at several centre-of-mass energies, followed by a hadron collider (FCC-hh). Benchmark examples are given of the expected physics performance, in terms of precision and sensitivity to new phenomena, of each collider stage. Detector requirements and conceptual designs for FCC-ee experiments are discussed, as are the specific demands that the physics programme imposes on the accelerator in the domains of the calibration of the collision energy, and the interface region between the accelerator and the detector. The report also highlights advances in detector, software and computing technologies, as well as the theoretical tools /reconstruction techniques that will enable the precision measurements and discovery potential of the FCC experimental programme. This volume reflects the outcome of a global collaborative effort involving hundreds of scientists and institutions, aided by a dedicated community-building coordination, and provides a targeted assessment of the scientific opportunities and experimental foundations of the FCC programme.

hep-ex↗

arXiv2025

Future Circular Collider Feasibility Study Report: Volume 2, Accelerators, Technical Infrastructure and Safety

In response to the 2020 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) Feasibility Study was launched as an international collaboration hosted by CERN. This report describes the FCC integrated programme, which consists of two stages: an electron-positron collider (FCC-ee) in the first phase, serving as a high-luminosity Higgs, top, and electroweak factory; followed by a proton-proton collider (FCC-hh) at the energy frontier in the second phase. FCC-ee is designed to operate at four key centre-of-mass energies: the Z pole, the WW production threshold, the ZH production peak, and the top/anti-top production threshold - delivering the highest possible luminosities to four experiments. Over 15 years of operation, FCC-ee will produce more than 6 trillion Z bosons, 200 million WW pairs, nearly 3 million Higgs bosons, and 2 million top anti-top pairs. Precise energy calibration at the Z pole and WW threshold will be achieved through frequent resonant depolarisation of pilot bunches. The sequence of operation modes remains flexible. FCC-hh will operate at a centre-of-mass energy of approximately 85 TeV - nearly an order of magnitude higher than the LHC - and is designed to deliver 5 to 10 times the integrated luminosity of the HL-LHC. Its mass reach for direct discovery extends to several tens of TeV. In addition to proton-proton collisions, FCC-hh is capable of supporting ion-ion, ion-proton, and lepton-hadron collision modes. This second volume of the Feasibility Study Report presents the complete design of the FCC-ee collider, its operation and staging strategy, the full-energy booster and injector complex, required accelerator technologies, safety concepts, and technical infrastructure. It also includes the design of the FCC-hh hadron collider, development of high-field magnets, hadron injector options, and key technical systems for FCC-hh.

physics.acc-ph↗

arXiv2025

Future Circular Collider Feasibility Study Report: Volume 3, Civil Engineering, Implementation and Sustainability

Volume 3 of the FCC Feasibility Report presents studies related to civil engineering, the development of a project implementation scenario, and environmental and sustainability aspects. The report details the iterative improvements made to the civil engineering concepts since 2018, taking into account subsurface conditions, accelerator and experiment requirements, and territorial considerations. It outlines a technically feasible and economically viable civil engineering configuration that serves as the baseline for detailed subsurface investigations, construction design, cost estimation, and project implementation planning. Additionally, the report highlights ongoing subsurface investigations in key areas to support the development of an improved 3D subsurface model of the region. The report describes development of the project scenario based on the 'avoid-reduce-compensate' iterative optimisation approach. The reference scenario balances optimal physics performance with territorial compatibility, implementation risks, and costs. Environmental field investigations covering almost 600 hectares of terrain - including numerous urban, economic, social, and technical aspects - confirmed the project's technical feasibility and contributed to the preparation of essential input documents for the formal project authorisation phase. The summary also highlights the initiation of public dialogue as part of the authorisation process. The results of a comprehensive socio-economic impact assessment, which included significant environmental effects, are presented. Even under the most conservative and stringent conditions, a positive benefit-cost ratio for the FCC-ee is obtained. Finally, the report provides a concise summary of the studies conducted to document the current state of the environment.

physics.acc-ph↗

arXiv2023

High-spin spectroscopy in $^{207}$At: Evidence of a 29/2$^{+}$ isomeric state

Yrast and near-yrast states above the known 25/2$^{+}$ isomer in $^{207}$At are established for the first time. The level scheme is extended up to 47/2$\hbar$ and 6.5 MeV with the addition of about 60 new $γ$-ray transitions. The half-life of the 25/2$^{+}$ isomer is revisited and a value of $T_{1/2}$ = 107.5(9) ns is deduced. Evidence of a hitherto unobserved 29/2$^{+}$ isomer in $^{207}$At is presented. A systematic study of $B(E3)$ values for the transitions de-exciting the 29/2$^{+}$ isomer in the neighboring odd-$A$ At isotopes suggests a half-life in the 2$-$4.5 $μ$s range for this state in $^{207}$At. The experimental results are compared with large-scale shell-model calculations performed using the KHM3Y effective interaction in the $Z$ = 50$-$126, $N$ = 82$-$184 model space and an overall good agreement is noted between the theory and the experiment. A qualitative comparison of the excited states and the isomers with analogous states in neighboring nuclei provides further insight into the structure of $^{207}$At.

nucl-ex↗

arXiv2023

Coexisting single-particle excitations and octupole correlations in transitional nucleus $\mathbf{^{217}Ra}$

The level structure of the transitional nucleus $\mathrm{^{217}Ra}$ has been extended with the addition of around 20 new transitions. The discrepancies between the placements of several transitions reported in the earlier studies are resolved. The newly-established negative-parity sequence at low excitation energies hints at the expected parity-doublet structures in this nucleus. The properties of the observed simplex bands are compared with that of similar bands in neighboring nuclei. Since the presence of parity-doublet structures reflect octupole correlations, theoretical calculations using reflection-asymmetric triaxial particle rotor model (RAT-PRM) have been performed. A comparison of the observed features of the simplex bands with the predictions of the RAT-PRM calculations suggests that $\mathrm{^{217}Ra}$ exhibits an intermediate the behavior between the extremes of spherical and octupole-deformed nuclei. The termination of the simplex bands at intermediate energies and the structures lying above reflect the dominance of the single-particle excitations at higher excitation energies.

nucl-ex↗

arXiv2021

Quality Inspection Aspects of Hybrid Prototypes for the CMS Outer Tracker Upgrade at HL-LHC

At the High Luminosity LHC (HL-LHC), the CMS experiment will need to operate at up to 200 interactions per 25 ns beam crossing time and with up to 4000 fb-1 of integrated luminosity. To achieve the physics goals the experiment needs to improve the tracking resolution and the ability to selectively trigger on specific physics events. The CMS tracker upgrade requires designing a new detector to cope with the HL-LHC conditions. The new Outer Tracker is based on two types of silicon modules (strip-strip and pixel-strip). Each module type has a few types of high-density interconnect hybrid circuits which house the front-end and auxiliary electronics. This paper introduces the technological choices for modules and hybrids and presents the quality inspection aspects of the first hybrid prototypes.

physics.ins-det↗

arXiv2019

Fast gate-based readout of silicon quantum dots using Josephson parametric amplification

Spins in silicon quantum devices are promising candidates for large-scale quantum computing. Gate-based sensing of spin qubits offers compact and scalable readout with high fidelity, however further improvements in sensitivity are required to meet the fidelity thresholds and measurement timescales needed for the implementation of fast-feedback in error correction protocols. Here, we combine radio-frequency gate-based sensing at 622 MHz with a Josephson parametric amplifier (JPA), that operates in the 500-800 MHz band, to reduce the integration time required to read the state of a silicon double quantum dot formed in a nanowire transistor. Based on our achieved signal-to-noise ratio (SNR), we estimate that singlet-triplet single-shot readout with an average fidelity of 99.7% could be performed in 1 $μ$s, well-below the requirements for fault-tolerant readout and 30 times faster than without the JPA. Additionally, the JPA allows operation at a lower RF power while maintaining identical SNR. We determine a noise temperature of 200 mK with a contribution from the JPA (25%), cryogenic amplifier (25%) and the resonator (50%), showing routes to further increase the read-out speed.

cond-mat.mes-hall↗

arXiv2016

Exclusive J/psi and Upsilon photoproduction and the low x gluon

We discuss the potential to constrain the small-$x$ PDFs using the exclusive production of heavy vector mesons. The calculation of $J/ψ$ and $Υ$ photoproduction at NLO in collinear factorisation is described. The different behaviour of the NLO corrections for $J/ψ$ and $Υ$ is highlighted and we outline what might be expected from the inclusion of these processes in a PDF fit.

hep-ph↗

arXiv2014

Prediction of topological Nernst effect in silicene and similar 2D materials

We consider Berry phase mediated Nernst effect in silicene. The low energy band structure of silicene consists of two valleys near the Dirac points, similar to graphene. The low energy transport properties of the quasiparticles can be described as Berry phase dependent phenomena. By contrast to graphene, silicene has strong spin-orbit interaction leading to opening of the gap in the energy spectrum and spin-splitting of the bands in each valley. If an electric field is applied perpendicular to the silicene sheet, it allows tunability of the gap. \ We show that this results in Berry-phase-supported spin and valley polarized Nernst effect when the system is subjected to a temperature gradient. The Nernst response can be used to create valley and spin polarization at the transverse edges of silicene sheet. The applied electric field also allows control of valley and spin polarization in silicene. The predicted valley and spin polarized Nernst effect in silicene is more general and applies to other two-dimensional (2D) buckled Dirac Fermion systems such as 2D germanium and tin.

cond-mat.mes-hall↗

arXiv2008

Quasielastic neutron scattering of hydrated BaZr_{0.90}A_{0.10}O_{2.95} (A = Y and Sc)

Proton motions in hydrated proton conducting perovskites BaZr_{0.90}A_{0.10}O_{2.95} (A = Y and Sc) have been investigated using quasielastic neutron scattering. The results reveal a localized motion on the ps time scale and with an activation energy of ~10-30 meV, in both materials. The temperature dependence of the total mean square displacement of the protons suggests an onset of this motion at a temperature of about 300 K. Comparison of the QENS results to density functional theory calculations suggests that for both materials this motion can be ascribed to intra-octahedral proton transfers occurring close to a dopant atom. The low activation energy, more than ten times lower than the activation energy for the macroscopic proton conductivity, suggests that this motion is not the rate-limiting process for the long-range proton diffusion, i.e. it is not linked to the two materials significantly different proton conductivities.

cond-mat.mtrl-sci↗

arXiv2008

Short-range structure of proton conducting perovskite BaIn_{x}Zr_{1-x}O_{3-x/2} (x = 0-0.75)

In a systematic study we investigate the effect of dopant level and hydration on the short-range structure of the proton conducting perovskite-type oxide BaIn_{x}Zr_{1-x}O_{3-x/2} (x = 0-0.75), using infrared and Raman spectroscopy. The results show that doping leads to significant local distortions of the average cubic structure of these materials. By increasing the In concentration from x = 0 to x = 0.75 new bands appear and grow in intensity in both the IR and Raman spectra, showing that the local distortions become successively more and more pronounced. The structural distortions are largely uncorrelated to the presence of oxygen vacancies, but instead are mainly driven by the size difference between the In^{3+} and Zr^{4+} ions, which leads to displacements of the cations and to tilting of the (In/Zr)O_{6} octahedra. Based on our results, we suggest that there is a threshold between x = 0.10 and x = 0.25 where the local structural distortions propagate throughout the whole perovskite structure. Comparison of our spectroscopic data with the proton conductivity reported for the same materials indicates that the presence of extended structural distortions are favorable for fast proton transport.

cond-mat.mtrl-sci↗