arXiv subjects

J. Bok

Publications and source records attributed to J. Bok.

At least 19 recordsLinked to original sources

arXiv2026

ePIC Early Science Report

This Early Science Report from the ePIC Collaboration outlines the compelling physics program achievable during the first years of operation of the Electron-Ion Collider (EIC), prior to the establishment of the full design luminosity and energy range. The analyses are based on realistic early-running beam configurations and detailed Geant4 ePIC detector simulations, hit digitization and data reconstruction. The projected studies from the physics working groups of ePIC span inclusive, semi-inclusive, exclusive, diffractive and tagging, as well as jet and heavy flavor measurements in both electron-proton and electron-ion collisions. Even before the collider reaches its full design performance, these measurements will constrain parton distribution functions in nucleons and nuclei, access transverse-momentum-dependent and spin-dependent observables, probe gluon dynamics in nuclei, and initiate a program of imaging of quarks and gluons. Each measurement is directly connected to the core science pillars of the EIC, identified in the 2018 report by the National Academy of Sciences: understanding the origin of the nucleon mass, unraveling the spin structure of the nucleon, and exploring the emergent properties of dense gluonic matter. The results presented here provide examples that demonstrate that the early years of EIC running with ePIC will deliver novel world-leading insights into Quantum Chromodynamics. In addition, the early science program will establish measurement and analysis methodologies that will pave the way to the subsequent full EIC physics program.

nucl-ex↗

arXiv2024

Performance of the prototype beam drift chamber for LAMPS at RAON with proton and Carbon-12 beams

Beam Drift Chamber (BDC) is designed to reconstruct the trajectories of incident rare isotope beams provided by RAON (Rare isotope Accelerator complex for ON-line experiments) into the experimental target of LAMPS (Large Acceptance Multi-Purpose Spectrometer). To conduct the performance test of the BDC, the prototype BDC (pBDC) is manufactured and evaluated with the high energy ion beams from HIMAC (Heavy Ion Medical Accelerator in Chiba) facility in Japan. Two kinds of ion beams, 100 MeV proton, and 200 MeV/u $^{12}$C, have been utilized for this evaluation, and the track reconstruction efficiency and position resolution have been measured as the function of applied high voltage. This paper introduces the construction details and presents the track reconstruction efficiency and position resolution of pBDC.

physics.ins-det↗

arXiv2021

First demonstration of in-beam performance of bent Monolithic Active Pixel Sensors

A novel approach for designing the next generation of vertex detectors foresees to employ wafer-scale sensors that can be bent to truly cylindrical geometries after thinning them to thicknesses of 20-40$μ$m. To solidify this concept, the feasibility of operating bent MAPS was demonstrated using 1.5$\times$3cm ALPIDE chips. Already with their thickness of 50$μ$m, they can be successfully bent to radii of about 2cm without any signs of mechanical or electrical damage. During a subsequent characterisation using a 5.4GeV electron beam, it was further confirmed that they preserve their full electrical functionality as well as particle detection performance. In this article, the bending procedure and the setup used for characterisation are detailed. Furthermore, the analysis of the beam test, including the measurement of the detection efficiency as a function of beam position and local inclination angle, is discussed. The results show that the sensors maintain their excellent performance after bending to radii of 2cm, with detection efficiencies above 99.9% at typical operating conditions, paving the way towards a new class of detectors with unprecedented low material budget and ideal geometrical properties.

physics.ins-det↗

arXiv2020

Space charge formation in chromium compensated GaAs radiation detectors

Space charge formation in chromium-compensated GaAs sensors is investigated by the laser-induced transient current technique applying pulsed and DC bias. Formation of non-standard space charge manifested by an appearance of both negatively and positively charged regions in DC biased sensors was revealed during 5 ms after switching bias. Using Monte Carlo simulations of current transients we determined enhanced electron lifetime τ = 150 ns and electron drift mobility μd = 3650 cm2/Vs. We developed and successfully applied theoretical model based on fast hole trapping in the system with spatially variable hole conductivity.

physics.app-ph↗

arXiv2015

Cross Section and Transverse Single-Spin Asymmetry of $η$ Mesons in $p^{\uparrow}+p$ Collisions at $\sqrt{s}=200$ GeV at Forward Rapidity

We present a measurement of the cross section and transverse single-spin asymmetry ($A_N$) for $η$ mesons at large pseudorapidity from $\sqrt{s}=200$~GeV $p^{\uparrow}+p$ collisions. The measured cross section for $0.5<p_T<5.0$~GeV/$c$ and $3.0<|η|<3.8$ is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries $A_N$ have been measured as a function of Feynman-$x$ ($x_F$) from $0.2<|x_{F}|<0.7$, as well as transverse momentum ($p_T$) from $1.0<p_T<4.5$~GeV/$c$. The asymmetry averaged over positive $x_F$ is $\langle{A_{N}}\rangle=0.061{\pm}0.014$. The results are consistent with prior transverse single-spin measurements of forward $η$ and $π^{0}$ mesons at various energies in overlapping $x_F$ ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in $p^{\uparrow}+p$ collisions.

hep-ex↗

arXiv2015

Search for dark photons from neutral meson decays in $p$$+$$p$ and $d$$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV

The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment $(g-2)_μ$ deviates from SM calculations by 3.6$σ$. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, $U$, in $π^0,η\rightarrow γe^+e^-$ decays and obtained upper limits of $\mathcal{O}(2\times10^{-6})$ on $U$-$γ$ mixing at 90% CL for the mass range $30<m_U<90$ MeV/$c^2$. Combined with other experimental limits, the remaining region in the $U$-$γ$ mixing parameter space that can explain the $(g-2)_μ$ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of $29<m_U<32$ MeV/$c^2$ remaining.

nucl-ex↗

arXiv2015

An Upgrade Proposal from the PHENIX Collaboration

In this document the PHENIX collaboration proposes a major upgrade to the PHENIX detector at the Relativistic Heavy Ion Collider. This upgrade, sPHENIX, enables an extremely rich jet and beauty quarkonia physics program addressing fundamental questions about the nature of the strongly coupled quark-gluon plasma (QGP), discovered experimentally at RHIC to be a perfect fluid. The startling dynamics of the QGP on fluid-like length scales is an emergent property of quantum chromodynamics (QCD), seemingly implicit in the Lagrangian but stubbornly hidden from view. QCD is an asymptotically free theory, but how QCD manifests as a strongly coupled fluid with specific shear viscosity near $T_C$, as low as allowed by the uncertainty principle, is as fundamental an issue as that of how confinement itself arises.

nucl-ex↗

arXiv2014

Low-mass vector-meson production at forward rapidity in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low mass vector meson, $ω$, $ρ$, and $ϕ$, production through the dimuon decay channel at forward rapidity ($1.2<|y|<2.2$) in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV. The differential cross sections for these mesons are measured as a function of both $p_T$ and rapidity. We also report the integrated differential cross sections over $1<p_T<7$ GeV/$c$ and $1.2<|y|<2.2$: $dσ/dy(ω+ρ\rightarrowμμ) = 80 \pm 6 \mbox{(stat)} \pm 12 \mbox{(syst)}$ nb and $dσ/dy(ϕ\rightarrowμμ) = 27 \pm 3 \mbox{(stat)} \pm 4 \mbox{(syst)}$ nb. These results are compared with midrapidity measurements and calculations.

hep-ex↗

arXiv2014

Measurement of $K_S^0$ and $K^{*0}$ in $p$$+$$p$, $d$$+$Au, and Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=200$ GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of $K_S^0$ and $K^{*0}$ meson production at midrapidity in $p$$+$$p$, $d$$+$Au, and Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The $K_S^0$ and $K^{*0}$ mesons are reconstructed via their $K_S^0 \rightarrow π^0(\rightarrow γγ)π^0(\rightarrowγγ)$ and $K^{*0} \rightarrow K^{\pm}π^{\mp}$ decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of $K_S^0$ and $K^{*0}$ mesons in $d$$+$Au and Cu$+$Cu collisions at different centralities. In the $d$$+$Au collisions, the nuclear modification factor of $K_S^0$ and $K^{*0}$ mesons is almost constant as a function of transverse momentum and is consistent with unity showing that cold-nuclear-matter effects do not play a significant role in the measured kinematic range. In Cu$+$Cu collisions, within the uncertainties no nuclear modification is registered in peripheral collisions. In central collisions, both mesons show suppression relative to the expectations from the $p$$+$$p$ yield scaled by the number of binary nucleon-nucleon collisions in the Cu$+$Cu system. In the $p_T$ range 2--5 GeV/$c$, the strange mesons ($K_S^0$, $K^{*0}$) similarly to the $ϕ$ meson with hidden strangeness, show an intermediate suppression between the more suppressed light quark mesons ($π^0$) and the nonsuppressed baryons ($p$, $\bar{p}$). At higher transverse momentum, $p_T>5$ GeV/$c$, production of all particles is similarly suppressed by a factor of $\approx$ 2.

nucl-ex↗

arXiv2014

Comparison of the space-time extent of the emission source in $d$$+$Au and Au$+$Au collisions at $\sqrt{s_{NN}}=200$ GeV

Two-pion interferometry measurements in $d$$+$Au and Au$+$Au collisions at $\sqrt{s_{NN}}=200$ GeV are used to extract and compare the Gaussian source radii R$_{\rm out}$, R$_{\rm side}$, and R$_{\rm long}$, which characterize the space-time extent of the emission sources. The comparisons, which are performed as a function of collision centrality and the mean transverse momentum for pion pairs, indicate strikingly similar patterns for the $d$$+$Au and Au$+$Au systems. They also indicate a linear dependence of R$_{\rm side}$ on the initial transverse geometric size $\bar{R}$, as well as a smaller freeze-out size for the $d$$+$Au system. These patterns point to the important role of final-state rescattering effects in the reaction dynamics of $d$$+$Au collisions.

nucl-ex↗

arXiv2014

Nuclear matter effects on $J/ψ$ production in asymmetric Cu+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV

We report on $J/ψ$ production from asymmetric Cu+Au heavy-ion collisions at $\sqrt{s_{_{NN}}}$=200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of $J/ψ$ yields in Cu$+$Au collisions in the Au-going direction is found to be comparable to that in Au$+$Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, $J/ψ$ production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-$x$ gluon suppression in the larger Au nucleus. The relative suppression is opposite to that expected from hot nuclear matter dissociation, since a higher energy density is expected in the Au-going direction.

nucl-ex↗

arXiv2014

The PHENIX Forward Silicon Vertex Detector

A new silicon detector has been developed to provide the PHENIX experiment with precise charged particle tracking at forward and backward rapidity. The Forward Silicon Vertex Tracker (FVTX) was installed in PHENIX prior to the 2012 run period of the Relativistic Heavy Ion Collider (RHIC). The FVTX is composed of two annular endcaps, each with four stations of silicon mini-strip sensors, covering a rapidity range of $1.2<|η|<2.2$ that closely matches the two existing PHENIX muon arms. Each station consists of 48 individual silicon sensors, each of which contains two columns of mini-strips with 75 $μ$m pitch in the radial direction and lengths in the $ϕ$ direction varying from 3.4 mm at the inner radius to 11.5 mm at the outer radius. The FVTX has approximately 0.54 million strips in each endcap. These are read out with FPHX chips, developed in collaboration with Fermilab, which are wire bonded directly to the mini-strips. The maximum strip occupancy reached in central Au-Au collisions is approximately 2.8%. The precision tracking provided by this device makes the identification of muons from secondary vertices away from the primary event vertex possible. The expected distance of closest approach (DCA) resolution of 200 $μ$m or better for particles with a transverse momentum of 5 GeV/$c$ will allow identification of muons from relatively long-lived particles, such as $D$ and $B$ mesons, through their broader DCA distributions.

physics.ins-det↗

arXiv2014

Concept for an Electron Ion Collider (EIC) detector built around the BaBar solenoid

The PHENIX collaboration presents here a concept for a detector at a future Electron Ion Collider (EIC). The EIC detector proposed here, referred to as ePHENIX, will have excellent performance for a broad range of exciting EIC physics measurements, providing powerful investigations not currently available that will dramatically advance our understanding of how quantum chromodynamics binds the proton and forms nuclear matter.

nucl-ex↗

arXiv2012

sPHENIX: An Upgrade Concept from the PHENIX Collaboration

The PHENIX collaboration presents a concept for a major upgrade to the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). This upgrade, referred to as sPHENIX, brings exciting new capability to the RHIC program by opening new and important channels for experimental investigation and utilizing fully the luminosity of the recently upgraded RHIC facility. sPHENIX enables a compelling jet physics program that will address fundamental questions about the nature of the strongly coupled quark-gluon plasma discovered experimentally at RHIC to be a perfect fluid. The upgrade concept addresses specific questions whose answers are necessary to advance our understanding of the quark-gluon plasma: (1) How to reconcile the observed strongly coupled quark-gluon plasma with the asymptotically free theory of quarks and gluons? (2) What are the dynamical changes to the quark-gluon plasma in terms of quasiparticles and excitations as a function of temperature? (3) How sharp is the transition of the quark-gluon plasma from the most strongly coupled regime near Tc to a weakly coupled system of partons known to emerge at asymptotically high temperatures? In three Appendices, we detail the additional physics capabilities gained through further upgrades: (A) two midrapidity detector additions, (B) a forward rapidity upgrade, and (C) an evolution to an ePHENIX detector suitable for a future Electron Ion Collider at RHIC.

nucl-ex↗

arXiv2003

Hall effect in the normal state of high Tc cuprates

We propose a model for explaining the dependence in temperature of the Hall effect of high Tc cuprates in the normal state in various materials. They all show common features: a decrease of the Hall coefficient RH with temperature and a universal law, when plotting RH(T)/RH(T0) versus T/T0, where T0 is defined from experimental results. This behaviour is explained by using the well known electronic band structure of the CuO2 plane, showing saddle points at the energies ES in the directions (0,+/-pi) and (+/-pi,0). We remark that in a magnetic field, for energies E>ES the carrier orbits are hole-like and for E<ES they are electron-like, giving opposite contributions to RH. We are abble to fit the experimental results for a wide range of hole doping, and to fit the universal curve. For us kb*T0 is simply EF-ES, where EF is the Fermi level varying with the doping.

cond-mat.supr-con↗

arXiv2003

The effect of Cu substitution on the A1g mode of La(0.7)Sr(0.3)MnO3 manganites

We report on the first Raman data of Cu substituted La(1-y)Sr(y)Mn(1-x)Cu(x)O3 (0 < x < 0.10 and 0.17 < y < 0.3, accordingly in order to have the same Mn(4+)/[Mn(4+)+Mn(3+)] ratio), collected in the frequency range 100-900 cm-1 and at room temperature, with parallel and crossed polarizations of the incident and scattered light. Spectra were fitted with a Drude-Lorentz model, and peaks at 190-220 and 430 cm-1, together with two broad structures centered at near 500 and 670 cm-1, have been found. We also have observed that the A1g mode is substantially shifted with increasing Cu substitution. The A1g phonon shift is a linear function of the tolerance factor t and the rhombohedral angle, thus following the structural changes of the MnO6 octahedra in the system.

cond-mat.mtrl-sci↗

arXiv2002

Langevin approach to the Porto system

M. Porto (Phys. Rev. E 63 (2001) 030102) suggested a system consisting of Coulomb interacting particles, forming a linear track and a rotor, and working as a molecular motor. Newton equations with damping for the rotor coordinate on the track x, with a prescribed time-dependence of the rotor angle theta, indicated unidirectional motion of the rotor. Here, for the same system, the treatment was generalized to nonzero temperatures by including stochastic forces and treating both x and theta via two coupled Langevin equations. Numerical results are reported for stochastic homogeneous distributions of impact events and Gaussian distributions of stochastic forces acting on both the variables. For specific values of parameters involved, the unidirectional motion of the rotor along the track is confirmed, but with a mechanism that is not necessarily the same as that one by Porto. In an additional weak homogeneous potential field U(x)=const.x acting against the motion, the unidirectional motion persists. Then the rotor accumulates potential energy at the cost of thermal stochastic forces from the bath.

cond-mat.stat-mech↗

arXiv2002

Stationary flows in quantum dissipative closed circuits as a challenge to thermodynamics

An experimentally inspired model is constructed and rigorously solved from the Hamiltonian level where a dc circular spontaneous flow exists in absence of a magnetic field, irrespective of presence of dissipation causing otherwise proper relaxation. The flow causes a spontaneous unidirectional transfer of heat from one bath to another one, even against temperature step. This is what is explicitly forbidden by the Clausius form of the Second law of thermodynamics. The unidirectionality of the flow is caused by that of spontaneous processes known to bear this property since their introduction by Einstein. The model slightly improves the previous one (Čápek & Sheehan 2002), describes a realistic plasma system for which experimental results violating the second law were announced, and the result obtained fully supports the experimental conclusions (Sheehan 1995). Analytical proof of the violation is supported by numerical results. All mathematical details are exposed, two fully independent types of mathematical arguments behind starting equations are invoked, and no approximations that could be made responsible for the striking conclusions are used. It shows how the physics beyond the Second law is still little understood.

physics.plasm-ph↗