We present measurements of the cross section and double-helicity asymmetry
$A_{LL}$ of direct-photon production in $\vec{p}+\vec{p}$ collisions at
$\sqrt{s}=510$ GeV. The measurements have been ...performed at midrapidity
($|\eta|<0.25$) with the PHENIX detector at the Relativistic Heavy Ion
Collider. At relativistic energies, direct photons are dominantly produced from
the initial quark-gluon hard scattering and do not interact via the strong
force at leading order. Therefore, at $\sqrt{s}=510$ GeV, where
leading-order-effects dominate, these measurements provide clean and direct
access to the gluon helicity in the polarized proton in the
gluon-momentum-fraction range $0.02<x<0.08$, with direct sensitivity to the
sign of the gluon contribution.
Phys. Rev. C 109, 044912 (2024) The measurement of the direct-photon spectrum from Au$+$Au collisions at
$\sqrt{s_{_{NN}}}=200$ GeV is presented by the PHENIX collaboration using the
...external-photon-conversion technique for 0\%--93\% central collisions in a
transverse-momentum ($p_T$) range of 0.8--10 GeV/$c$. An excess of direct
photons, above prompt-photon production from hard-scattering processes, is
observed for $p_T<6$ GeV/$c$. Nonprompt direct photons are measured by
subtracting the prompt component, which is estimated as $N_{\rm coll}$-scaled
direct photons from $p$$+$$p$ collisions at 200 GeV, from the direct-photon
spectrum. Results are obtained for $0.8<p_T<6.0$ GeV/$c$ and suggest that the
spectrum has an increasing inverse slope from ${\approx}0.2$ to 0.4 GeV/$c$
with increasing $p_T$, which indicates a possible sensitivity of the
measurement to photons from earlier stages of the evolution of the collision.
In addition, like the direct-photon production, the $p_T$-integrated nonprompt
direct-photon yields also follow a power-law scaling behavior as a function of
collision-system size. The exponent, $\alpha$, for the nonprompt component is
found to be consistent with 1.1 with no apparent $p_T$ dependence.
The ECCE detector has been recommended as the selected reference detector for the future Electron-Ion Collider (EIC). A series of simulation studies have been carried out to validate the physics ...feasibility of the ECCE detector. In this paper, detailed studies of heavy flavor hadron and jet reconstruction and physics projections with the ECCE detector performance and different magnet options will be presented. The ECCE detector has enabled precise EIC heavy flavor hadron and jet measurements with a broad kinematic coverage. These proposed heavy flavor measurements will help systematically study the hadronization process in vacuum and nuclear medium especially in the underexplored kinematic region.
We performed feasibility studies for various measurements that are related to unpolarized TMD distribution and fragmentation functions. The processes studied include semi-inclusive Deep inelastic ...scattering (SIDIS) where single hadrons (pions and kaons) were detected in addition to the scattered DIS lepton. The single hadron cross sections and multiplicities were extracted as a function of the DIS variables \(x\) and \(Q^2\), as well as the semi-inclusive variables \(z\), which corresponds to the momentum fraction the detected hadron carries relative to the struck parton and \(P_T\), which corresponds to the transverse momentum of the detected hadron relative to the virtual photon. The expected statistical precision of such measurements is extrapolated to accumulated luminosities of 10 fb\(^{-1}\) and potential systematic uncertainties are approximated given the deviations between true and reconstructed yields.
We performed feasibility studies for various single transverse spin measurements that are related to the Sivers effect, transversity and the tensor charge, and the Collins fragmentation function. The ...processes studied include semi-inclusive deep inelastic scattering (SIDIS) where single hadrons (pions and kaons) were detected in addition to the scattered DIS lepton. The data were obtained in {\sc pythia}6 and {\sc geant}4 simulated e+p collisions at 18 GeV on 275 GeV, 18 on 100, 10 on 100, and 5 on 41 that use the ECCE detector configuration. Typical DIS kinematics were selected, most notably \(Q^2 > 1 \) GeV\(^2\), and cover the \(x\) range from \(10^{-4}\) to \(1\). The single spin asymmetries were extracted as a function of \(x\) and \(Q^2\), as well as the semi-inclusive variables \(z\), and \(P_T\). They are obtained in azimuthal moments in combinations of the azimuthal angles of the hadron transverse momentum and transverse spin of the nucleon relative to the lepton scattering plane. The initially unpolarized MonteCarlo was re-weighted in the true kinematic variables, hadron types and parton flavors based on global fits of fixed target SIDIS experiments and \(e^+e^-\) annihilation data. The expected statistical precision of such measurements is extrapolated to 10 fb\(^{-1}\) and potential systematic uncertainties are approximated given the deviations between true and reconstructed yields. The impact on the knowledge of the Sivers functions, transversity and tensor charges, and the Collins function has then been evaluated in the same phenomenological extractions as in the Yellow Report. The impact is found to be comparable to that obtained with the parameterized Yellow Report detector and shows that the ECCE detector configuration can fulfill the physics goals on these quantities.
Exclusive heavy quarkonium photoproduction is one of the most popular
processes in EIC, which has a large cross section and a simple final state. Due
to the gluonic nature of the exchange Pomeron, ...this process can be related to
the gluon distributions in the nucleus. The momentum transfer dependence of
this process is sensitive to the interaction sites, which provides a powerful
tool to probe the spatial distribution of gluons in the nucleus. Recently the
problem of the origin of hadron mass has received lots of attention in
determining the anomaly contribution $M_{a}$. The trace anomaly is sensitive to
the gluon condensate, and exclusive production of quarkonia such as J/$\psi$
and $\Upsilon$ can serve as a sensitive probe to constrain it. In this paper,
we present the performance of the ECCE detector for exclusive J/$\psi$
detection and the capability of this process to investigate the above physics
opportunities with ECCE.
The recently approved Electron-Ion Collider (EIC) will provide a unique new
opportunity for searches of charged lepton flavor violation (CLFV) and other
new physics scenarios. In contrast to the $e ...\leftrightarrow \mu$ CLFV
transition for which very stringent limits exist, there is still a relatively
large discovery space for the $e \to \tau$ CLFV transition, potentially to be
explored by the EIC. With the latest detector design of ECCE (EIC Comprehensive
Chromodynamics Experiment) and projected integral luminosity of the EIC, we
find the $\tau$-leptons created in the DIS process $ep\to \tau X$ are expected
to be identified with high efficiency. A first ECCE simulation study,
restricted to the 3-prong $\tau$-decay mode and with limited statistics for the
Standard Model backgrounds, estimates that the EIC will be able to improve the
current exclusion limit on $e\to \tau$ CLFV by an order of magnitude.
We describe the design and performance the calorimeter systems used in the ECCE detector design to achieve the overall performance specifications cost-effectively with careful consideration of ...appropriate technical and schedule risks. The calorimeter systems consist of three electromagnetic calorimeters, covering the combined pseudorapdity range from -3.7 to 3.8 and two hadronic calorimeters. Key calorimeter performances which include energy and position resolutions, reconstruction efficiency, and particle identification will be presented.
Phys. Rev. C 105, 064912 (2022) Suppression of the $J/\psi$ nuclear-modification factor has been seen as a
trademark signature of final-state effects in large collision systems for
decades. In small ...systems, the nuclear modification was attributed to
cold-nuclear-matter effects until the observation of strong differential
suppression of the $\psi(2S)$ state in $p/d$$+$$A$ collisions suggested the
presence of final-state effects. Results of $J/\psi$ and $\psi(2S)$
measurements in the dimuon decay channel are presented here for $p$$+$$p$,
$p$$+$Al, and $p$$+$Au collision systems at $\sqrt{s_{_{NN}}}=200$ GeV. The
results are predominantly shown in the form of the nuclear-modification factor,
$R_{pA}$, the ratio of the $\psi(2S)$ invariant yield per nucleon-nucleon
collision in collisions of proton on target nucleus to that in $p$$+$$p$
collisions. Measurements of the $J/\psi$ and $\psi(2S)$ nuclear-modification
factor are compared with shadowing and transport-model predictions, as well as
to complementary measurements at Large-Hadron-Collider energies.
The Electron-Ion Collider (EIC) is a cutting-edge accelerator facility that will study the nature of the "glue" that binds the building blocks of the visible matter in the universe. The proposed ...experiment will be realized at Brookhaven National Laboratory in approximately 10 years from now, with detector design and R&D currently ongoing. Notably, EIC is one of the first large-scale facilities to leverage Artificial Intelligence (AI) already starting from the design and R&D phases. The EIC Comprehensive Chromodynamics Experiment (ECCE) is a consortium that proposed a detector design based on a 1.5T solenoid. The EIC detector proposal review concluded that the ECCE design will serve as the reference design for an EIC detector. Herein we describe a comprehensive optimization of the ECCE tracker using AI. The work required a complex parametrization of the simulated detector system. Our approach dealt with an optimization problem in a multidimensional design space driven by multiple objectives that encode the detector performance, while satisfying several mechanical constraints. We describe our strategy and show results obtained for the ECCE tracking system. The AI-assisted design is agnostic to the simulation framework and can be extended to other sub-detectors or to a system of sub-detectors to further optimize the performance of the EIC detector.
