arXiv subjects

B. Hong

Publications and source records attributed to B. Hong.

At least 55 records · Page 3Linked to original sources

arXiv2021

Transverse momentum dependent forward neutron single spin asymmetries in transversely polarized $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV

In 2015, the PHENIX collaboration has measured very forward ($η>6.8$) single-spin asymmetries of inclusive neutrons in transversely polarized proton-proton and proton-nucleus collisions at a center of mass energy of 200 GeV. A previous publication from this data set concentrated on the nuclear dependence of such asymmetries. In this measurement the explicit transverse-momentum dependence of inclusive neutron single spin asymmetries for proton-proton collisions is extracted using a bootstrapping-unfolding technique on the transverse momenta. This explicit transverse-momentum dependence will help improve the understanding of the mechanisms that create these asymmetries.

hep-ex↗

arXiv2021

Isospin diffusion measurement from the direct detection of a Quasi-Projectile remnant

The neutron-proton equilibration process in 48 Ca+ 40 Ca at 35 MeV/nucleon bombarding energy has been experimentally estimated by means of the isospin transport ratio. Experimental data have been collected with a subset of the FAZIA telescope array, which permitted to determine Z and N of detected fragments. For the first time, the QP evaporative channel has been compared with the QP break-up one in a homogeneous and consistent way, pointing out to a comparable n-p equilibration which suggests close interaction time between projectile and target independently of the exit channel. Moreover, in the QP evaporative channel n-p equilibration has been compared with the prediction of the Antisymmetrized Molecular Dynamics (AMD) model coupled to the GEMINI statistical model as an afterburner, showing a larger probability of proton and neutron transfers in the simulation with respect to the experimental data.

nucl-ex↗

arXiv2020

CMS RPC Background -- Studies and Measurements

The expected radiation background in the CMS RPC system has been studied using the MC prediction with the CMS FLUKA simulation of the detector and the cavern. The MC geometry used in the analysis describes very accurately the present RPC system but still does not include the complete description of the RPC upgrade region with pseudorapidity $1.9 < \lvert η\rvert < 2.4$. Present results will be updated with the final geometry description, once it is available. The radiation background has been studied in terms of expected particle rates, absorbed dose and fluence. Two High Luminosity LHC (HL-LHC) scenarios have been investigated - after collecting $3000$ and $4000$ fb$^{-1}$. Estimations with safety factor of 3 have been considered, as well.

physics.ins-det↗

arXiv2020

Symmetry energy investigation with pion production from Sn+Sn systems

In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of state, a property that is key to our understanding of neutron stars. In a new experiment designed to study the symmetry energy, the multiplicities of negatively and positively charged pions have been measured with high accuracy for central $^{132}$Sn+$^{124}$Sn, $^{112}$Sn+$^{124}$Sn, and $^{108}$Sn+$^{112}$Sn collisions at $E/A=270~\mathrm{MeV}$ with the S$π$RIT Time Projection Chamber. While the uncertainties of individual pion multiplicities are measured to 4\%, those of the charged pion multiplicity ratios are measured to 2\%. We compare these data to predictions from seven major transport models. The calculations reproduce qualitatively the dependence of the multiplicities and their ratios on the total neutron to proton number in the colliding systems. However, the predictions of the transport models from different codes differ too much to allow extraction of reliable constraints on the symmetry energy from the data. This finding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au+Au system. These new results call for better understanding of the differences among transport codes, and new observables that are more sensitive to the density dependence of the symmetry energy.

nucl-ex↗

arXiv2020

The S$π$RIT Time Projection Chamber

The SAMURAI Pion Reconstruction and Ion-Tracker Time Projection Chamber (S$π$RIT TPC) was designed to enable measurements of heavy ion collisions with the SAMURAI spectrometer at the RIKEN Radioactive Isotope Beam Factory and provide constraints on the Equation of State of neutron-rich nuclear matter. The S$π$RIT TPC has a 50.5 cm drift length and an 86.4 cm $\times$ 134.4 cm pad plane with 12,096 pads that are equipped with the Generic Electronics for TPCs readout electronics. The S$π$RIT TPC allows excellent reconstruction of particles and provides isotopic resolution for pions and other light charged particles across a wide range of energy losses and momenta. Details of the S$π$RIT TPC are presented, along with discussion of the TPC performance based on cosmic ray and experimental data.

physics.ins-det↗

arXiv2020

Transverse single-spin asymmetry for very forward neutral pion production in polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV

Transverse single-spin asymmetries of very forward neutral pions generated in polarized $p + p$ collisions allow us to understand the production mechanism in terms of perturbative and non-perturbative strong interactions. During 2017 the RHICf Collaboration installed an electromagnetic calorimeter in the zero-degree region of the STAR detector at the Relativistic Heavy Ion Collider (RHIC) and measured neutral pions produced at pseudorapidity larger than 6 in polarized $p$+$p$ collisions at $\sqrt{s}$ = 510 GeV. The large non-zero asymmetries increasing both in longitudinal momentum fraction $x_{F}$ and transverse momentum $p_{T}$ have been observed at low transverse momentum $p_{T} < 1$ GeV/$c$ for the first time at this collision energy. The asymmetries show an approximate $x_{F}$ scaling in the $p_{T}$ region where non-perturbative processes are expected to dominate. A non-negligible contribution from soft processes may be necessary to explain the nonzero neutral pion asymmetries.

hep-ex↗

arXiv2020

Nuclear-modification factor of charged hadrons at forward and backward rapidity in $p$$+$Al and $p$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

The PHENIX experiment has studied nuclear effects in $p$$+$Al and $p$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV on charged hadron production at forward rapidity ($1.4<η<2.4$, $p$-going direction) and backward rapidity ($-2.2<η<-1.2$, $A$-going direction). Such effects are quantified by measuring nuclear modification factors as a function of transverse momentum and pseudorapidity in various collision multiplicity selections. In central $p$$+$Al and $p$$+$Au collisions, a suppression (enhancement) is observed at forward (backward) rapidity compared to the binary scaled yields in $p$+$p$ collisions. The magnitude of enhancement at backward rapidity is larger in $p$$+$Au collisions than in $p$$+$Al collisions, which have a smaller number of participating nucleons. However, the results at forward rapidity show a similar suppression within uncertainties. The results in the integrated centrality are compared with calculations using nuclear parton distribution functions, which show a reasonable agreement at the forward rapidity but fail to describe the backward rapidity enhancement.

hep-ex↗

arXiv2020

Charged particle track reconstruction with S$π$RIT Time Projection Chamber

In this paper, we present a software framework, S$π$RITROOT, which is capable of track reconstruction and analysis of heavy-ion collision events recorded with the S$π$RIT time projection chamber. The track-fitting toolkit GENFIT and the vertex reconstruction toolkit RAVE are applied to a box-type detector system. A pattern recognition algorithm which performs helix track finding and handles overlapping pulses is described. The performance of the software is investigated using experimental data obtained at the Radioactive Isotope Beam Facility (RIBF) at RIKEN. This work focuses on data from $^{132}$Sn + $^{124}$Sn collision events with beam energy of 270 AMeV. Particle identification is established using $\left $ and magnetic rigidity, with pions, hydrogen isotopes, and helium isotopes.

physics.ins-det↗

arXiv2019

SLAC UED LLRF System Upgrade

The SLAC mega-electron-volt (MeV) ultrafast electron diffraction (UED) instrument is a powerful "electron camera" for the study of time-resolved, ultrafast atomic & molecular dynamics in chemical and solid-state systems. The UED laser timing synchronization is upgraded to SLAC (Advanced Telecommunications Computing Architecture) ATCA based femtosecond laser timing synchronization system. UED radio frequency (RF) gun cavity low level RF (LLRF) control is also being upgraded to SLAC ATCA based LLRF system to provide improved performance and maintainability. The new laser timing synchronization and LLRF control are implemented in one ATCA crate located in the laser room. A 2nd ATCA crate is set up to monitor the Klystron and sub-booster performance. With the ATCA based RF control system, the laser timing jitter has achieved 10 fs. The UED operation beam rate is being upgraded from 180 Hz to 360 Hz, which paves the way for a further upgrade of operation beam rate to 1 kHz in the future. In this paper, we present design details and characterization results of the implementation.

physics.acc-ph↗

arXiv2019

ATCA LLRF System for ASU Compact FEL

SLAC National Accelerator Laboratory is collaborating with Arizona State University to design a LLRF system towards the advancement of the ASU Compact X-ray Light Source (CXLS). The CXLS is a phased project to develop small brilliant x-ray sources that may produce coherent x-rays appropriate as a seed source for LCLS and LCLS II. The CXLS electron beam is produced by an x-band photoinjector and linac operating at 9.3 GHz RF frequency and 1 kHz repetition rate with up to 300 pC per bunch. The linac consists of 3 short 20-cell sections of standing wave linac. The RF gun and linac sections are powered by two 6 MW transmitters using L3 klystrons and Scandi-nova K1 modulators. The accelerator will initially operate in single-bunch mode and may be upgraded to multi-bunch operation at a later date. SLAC National Laboratory has developed a LLRF system in Advanced Telecommunication Computing Architecture (ATCA) for the ASU project. This talk will discuss the design of the LLRF for this project and discuss the ATCA implementation.

physics.acc-ph↗

arXiv2019

Nuclear dependence of the transverse single-spin asymmetry in the production of charged hadrons at forward rapidity in polarized $p+p$, $p+$Al, and $p+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

We report on the nuclear dependence of transverse single-spin asymmetries (TSSAs) in the production of positively-charged hadrons in polarized $p^{\uparrow}+p$, $p^{\uparrow}+$Al and $p^{\uparrow}+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The measurements have been performed at forward rapidity ($1.4<η<2.4$) over the range of $1.8<p_{T}<7.0$ GeV$/c$ and $0.1<x_{F}<0.2$. We observed a positive asymmetry $A_{N}$ for positively-charged hadrons in \polpp collisions, and a significantly reduced asymmetry in $p^{\uparrow}$+$A$ collisions. These results reveal a nuclear dependence of charged hadron $A_N$ in a regime where perturbative techniques are relevant. These results provide new opportunities to use \polpA collisions as a tool to investigate the rich phenomena behind TSSAs in hadronic collisions and to use TSSA as a new handle in studying small-system collisions.

hep-ex↗

arXiv2019

Measurement of charm and bottom production from semileptonic hadron decays in $p$$+$$p$ collisions at $\sqrt{s_{NN}}=200$ GeV

Measurements of the differential production of electrons from open-heavy-flavor hadrons with charm- and bottom-quark content in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV are presented. The measurements proceed through displaced-vertex analyses of electron tracks from the semileptonic decay of charm and bottom hadrons using the PHENIX silicon-vertex detector. The relative contribution of electrons from bottom decays to inclusive heavy-flavor-electron production is found to be consistent with fixed-order-plus-next-to-leading-log perturbative-QCD calculations within experimental and theoretical uncertainties. These new measurements in $p$$+$$p$ collisions provide a precision baseline for comparable forthcoming measurements in A$+$A collisions.

hep-ex↗

arXiv2019

Nonperturbative transverse momentum broadening in dihadron angular correlations in $\sqrt{s_{NN}}=200$ GeV proton-nucleus collisions

The PHENIX collaboration has measured high-$p_T$ dihadron correlations in $p$$+$$p$, $p$$+$Al, and $p$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The correlations arise from inter- and intra-jet correlations and thus have sensitivity to nonperturbative effects in both the initial and final states. The distributions of $p_{\rm out}$, the transverse momentum component of the associated hadron perpendicular to the trigger hadron, are sensitive to initial and final state transverse momenta. These distributions are measured multi-differentially as a function of $x_E$, the longitudinal momentum fraction of the associated hadron with respect to the trigger hadron. The near-side $p_{\rm out}$ widths, sensitive to fragmentation transverse momentum, show no significant broadening between $p$$+$Au, $p$$+$Al, and $p$$+$$p$. The away-side nonperturbative $p_{\rm out}$ widths are found to be broadened in $p$$+$Au when compared to $p$$+$$p$; however, there is no significant broadening in $p$$+$Al compared to $p$$+$$p$ collisions. The data also suggest that the away-side $p_{\rm out}$ broadening is a function of $N_{\rm coll}$, the number of binary nucleon-nucleon collisions, in the interaction. The potential implications of these results with regard to initial and final state transverse momentum broadening and energy loss of partons in a nucleus, among other nuclear effects, are discussed.

hep-ex↗

arXiv2019

Measurements of $μμ$ pairs from open heavy flavor and Drell-Yan in $p+p$ collisions at $\sqrt{s}=200$ GeV

PHENIX reports differential cross sections of $μμ$ pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV at forward and backward rapidity ($1.2<|η|<2.2$). The $μμ$ pairs from $c\bar{c}$, $b\bar{b}$, and Drell-Yan are separated using a template fit to unlike- and like-sign muon pair spectra in mass and $p_T$. The azimuthal opening angle correlation between the muons from $c\bar{c}$ and $b\bar{b}$ decays and the pair-$p_T$ distributions are compared to distributions generated using {\sc pythia} and {\sc powheg} models, which both include next-to-leading order processes. The measured distributions for pairs from $c\bar{c}$ are consistent with {\sc pythia} calculations. The $c\bar{c}$ data presents narrower azimuthal correlations and softer $p_T$ distributions compared to distributions generated from {\sc powheg}. The $b\bar{b}$ data are well described by both models. The extrapolated total cross section for bottom production is $3.75{\pm}0.24({\rm stat}){\pm}^{0.35}_{0.50}({\rm syst}){\pm}0.45({\rm global})$[$μ$b], which is consistent with previous measurements at the Relativistic Heavy Ion Collider in the same system at the same collision energy, and is approximately a factor of two higher than the central value calculated with theoretical models. The measured Drell-Yan cross section is in good agreement with next-to-leading-order quantum-chromodynamics calculations.

hep-ex↗

arXiv2019

Transverse single spin asymmetry for very forward $π^{0}$ production in polarized proton-proton collisions at $\sqrt{s}$ = 510 GeV

Transverse single spin asymmetry, $A_{N}$, of very forward $π^{0}$ production from polarized $p + p$ collisions provides new information toward an understanding of its production mechanism. $A_{N}$ of forward $π^{0}$ in the pseudorapidity region of $3 < η< 4$ has been described by the partonic structure of the proton in the perturbative QCD framework. However, recent data indicates a potential contribution from not only partonic but also diffractive interactions. In order to provide a new insight on the origin of the $A_{N}$, we measured the very forward $π^{0}$ production in the pseudorapidity region of $6 < η$ from $\sqrt{s}$ = 510 GeV polarized $p + p$ collisions at RHIC in 2017. We report our measurement of the very forward $π^{0}$ over the transverse momentum range of $0 < p_{T} < 1$ GeV/$c$ and the preliminary result.

hep-ex↗

arXiv2019

Multi-particle azimuthal correlations for extracting event-by-event elliptic and triangular flow in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

We present measurements of elliptic and triangular azimuthal anisotropy of charged particles detected at forward rapidity $1<|η|<3$ in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, as a function of centrality. The multiparticle cumulant technique is used to obtain the elliptic flow coefficients $v_2\{2\}$, $v_2\{4\}$, $v_2\{6\}$, and $v_2\{8\}$, and triangular flow coefficients $v_3\{2\}$ and $v_3\{4\}$. Using the small-variance limit, we estimate the mean and variance of the event-by-event $v_2$ distribution from $v_2\{2\}$ and $v_2\{4\}$. In a complementary analysis, we also use a folding procedure to study the distributions of $v_2$ and $v_3$ directly, extracting both the mean and variance. Implications for initial geometrical fluctuations and their translation into the final state momentum distributions are discussed.

nucl-ex↗

arXiv2019

Wide acceptance measurement of the K$^-$/K$^+$ ratio from Ni+Ni collisions at 1.91A GeV

The FOPI Collaboration at the GSI SIS-18 synchrotron measured charged kaons from central and semi-central collisions of Ni+Ni at a beam energy of 1.91A GeV. We present the distribution of the K$^-$\K$^+$ ratio on the energy vs polar angle plane in the nucleon-nucleon center-of-mass frame, with and without subtraction of the contribution of $ϕ$(1020) meson decays to the K$^-$ yield. The acceptance of the current experiment is substantially wider compared to the previous measurement of the same colliding system. The ratio of K$^-$ to K$^+$ energy spectra is expected to be sensitive to the in-medium modifications of basic kaon properties like mass. Recent results obtained by the HADES Collaboration at 1.23A and 1.76A GeV indicate that after inclusion of the $ϕ$ meson decay contribution to the K$^-$ production no difference between the slopes of the K$^-$ and K$^+$ energy spectra is observed within uncertainties. For our data a linear fit to this ratio obtained after subtraction of the $ϕ$ meson contribution still shows a decrease with kinetic energy, although a constant value cannot be rejected. The contribution of $Λ(1520) \rightarrow p\text{K}^-$ decays estimated from fitting the thermal model to the experimental yields appears to be another factor of moderate relevance.

nucl-ex↗

arXiv2018

Nonperturbative transverse-momentum-dependent effects in dihadron and direct photon-hadron angular correlations in $p+p$ collisions at $\sqrt{s}=200$ GeV

Dihadron and isolated direct photon-hadron angular correlations are measured in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV. The correlations are sensitive to nonperturbative initial-state and final-state transverse momentum $k_T$ and $j_T$ in the azimuthal nearly back-to-back region $Δϕ\simπ$. In this region, transverse-momentum-dependent evolution can be studied when several different hard scales are measured. To have sensitivity to small transverse momentum scales, nonperturbative momentum widths of $p_{\rm out}$, the out-of-plane transverse momentum component perpendicular to the trigger particle, are measured. These widths are used to investigate possible effects from transverse-momentum-dependent factorization breaking. When accounting for the longitudinal momentum fraction of the away-side hadron with respect to the near-side trigger particle, the widths are found to increase with the hard scale; this is qualitatively similar to the observed behavior in Drell-Yan and semi-inclusive deep-inelastic scattering interactions. The momentum widths are also studied as a function of center-of-mass energy by comparing to previous measurements at $\sqrt{s}=510$ GeV. The nonperturbative jet widths also appear to increase with $\sqrt{s}$ at a similar $x_T$, which is qualitatively consistent to similar measurements in Drell-Yan interactions. To quantify the magnitude of any transverse-momentum-dependent factorization breaking effects, calculations will need to be performed to compare to these measurements.

hep-ex↗