Searching for A Dark Photon in the Hps Experiment

The Heavy Photon Search (HPS) experiment at Jefferson Lab is designed to search for a hypothesized elementary particle called a dark (heavy) photon. Such a particle would behave as a mediator between dark matter and the Standard Model through a kinetic mixing with the Standard Model’s photon. The search is performed by scattering GeV-scale electrons off tungsten nuclei in a fixed target and looking for a resonance and/or displaced vertices amidst a background of radiative QED trident events. These background events are kinematically identical to the events in which dark photons are produced and decay into lepton pairs. Several other types of reactions take place in this experiment, such as Bethe-Heitler tridents, Moeller scattering, wide-angle bremsstrahlung and elastic scattering off the nucleus. Each of these types of background reactions are used for calibration of the detector. For one of these calibration studies, we have measured the form factors for electrons scattering elastically and nearly-elastically off a carbon target and compared these to predicted values. A resonance search, performed on 10% of the dataset taken in 2016 with a 2.306 GeV beam, shows no sign of a dark photon in the mass range 45-200 MeV. Preliminary upper limits on the square of the dark-photon’s kinetic coupling to the Standard Model photon have been set in the 10−6 − 10−5 range at 95% confidence for every mass hypothesis in this mass range

Leveraging Staggered Tessellation for Enhanced Spatial Resolution in High-Granularity Calorimeters

We advance the concept of high-granularity calorimeters with staggered tessellations, underscoring the effectiveness of a design incorporating multifold staggering cycles based on hexagonal cells to enhance position resolution. Moreover, we introduce HEXPLIT, a sub-cell re-weighting algorithm tailored to harness staggered designs, resulting in additional performance improvements. By combining our proposed staggered design with HEXPLIT, we achieve an approximately twofold enhancement in position resolution for neutrons across a wide energy range, as compared to unstaggered designs. These findings hold the potential to elevate particle-flow performance across various forthcoming facilities

A Few-Degree Calorimeter for the future Electron-Ion Collider

Measuring the region $0.1 < Q^{2} < 1.0$ GeV$^{2}$ is essential to support searches for gluon saturation at the future Electron-Ion Collider. Recent studies have revealed that covering this region at the highest beam energies is not feasible with current detector designs, resulting in the so-called $Q^{2}$ gap. In this work, we present a design for the Few-Degree Calorimeter (FDC), which addresses this issue. The FDC uses SiPM-on-tile technology with tungsten absorber and covers the range of $-4.6 < \eta < -3.6$. It offers fine transverse and longitudinal granularity, along with excellent time resolution, enabling standalone electron tagging. Our design represents the first concrete solution to bridge the $Q^{2}$ gap at the EIC

Studies of time resolution, light yield, and crosstalk using SiPM-on-tile calorimetry for the future Electron-Ion Collider

We recently proposed a high-granularity calorimeter insert for the Electron-Ion Collider (EIC) that is based on plastic scintillator tiles readout with silicon photomultipliers. In this work, we concretize its design by characterizing its building blocks with measurements of light yield, optical crosstalk, and timing resolutions using cosmic-rays, an LED, and a beta source. We also compared two approaches for the optical isolation of cells: ``megatiles'' with grooved boundaries between cells, and a 3D-printed plastic frame hosting individual cells. We found that the latter suppresses optical crosstalk to negligible levels while providing an easier assembly method. Overall, these performance studies can help inform calorimeter design and realistic simulations of 5D showers (time, energy, position) for the EIC and other experiments.Comment: added journal reference, and updated tex

Neutrino-Tagged Jets at the Electron Ion Collider

We explore the potential of jet observables in charged-current deep inelastic scattering events at the future Electron-Ion Collider. Tagging jets with a recoiling neutrino, which can be identified by the event’s missing transverse momentum, will allow for flavor-sensitive measurements of transverse momentum dependent parton distribution functions. We present the first predictions for transverse-spin asymmetries in azimuthal neutrino-jet correlations and hadron-in-jet measurements. We study the kinematic reach and the precision of these measurements and explore their feasibility using parametrized detector simulations. We conclude that jet production in charged-current deep inelastic scattering, while challenging in terms of luminosity requirements, will complement the Electron-Ion Collider experimental program to study the three-dimensional structure of the nucleon encoded in transverse momentum dependent parton distribution functions

Beam Test of the First Prototype of SiPM-on-Tile Calorimeter Insert for the Electron-Ion Collider Using 4 GeV Positrons at Jefferson Laboratory

We recently proposed a high-granularity calorimeter insert for the Electron-Ion Collider (EIC) that uses plastic scintillator tiles read out by SiPMs. Among its innovative features are an ASIC-away-of-SiPM strategy for reducing cooling requirements and minimizing space use, along with employing 3D-printed frames to reduce optical crosstalk and dead areas. To evaluate these features, we built a 40-channel prototype and tested it using a 4 GeV positron beam at Jefferson Laboratory. The measured energy spectra and 3D shower shapes are well described by simulations, confirming the effectiveness of the design, construction techniques, and calibration strategy. This constitutes the first use of SiPM-on-tile technology in EIC detector designs

Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics

We present measurements of the polarization-transfer components in the $^2$H$(\vec e,e'\vec p)$ reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, $p_{\rm miss}$, up to 220 MeV$/c$, and $Q^2=0.65$ $({\rm GeV}/c)^2$. These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components $P_x$ and $P_z$ and their ratio agree with the theoretical calculations, which use free-proton form factors. Using this, we establish upper limits on possible medium effects that modify the bound proton's form factor ratio $G_E/G_M$ at the level of a few percent. We also compare the measured polarization-transfer components and their ratio for $^2$H to those of a free (moving) proton. We find that the universal behavior of $^2$H, $^4$He and $^{12}$C in the double ratio $\frac{(P_x/P_z)^A}{(P_x/P_z)^{^1\rm H}}$ is maintained in the positive missing-momentum region

Hierarchies of trade in Yiwu and Dushanbe: the case of an Uzbek merchant family from Tajikistan

This article focuses on the trading trajectory of an Uzbek family of merchants from Tajikistan. This family runs businesses in both Tajikistan’s capital, Dushanbe, and China’s famous international trading city: Yiwu. The analysis is centred on the accounts placed by Tajikistan’s Uzbek merchants about their historically sustained experience, often across several generations, in trading activities. These merchants’ claims of belonging to a ‘historical’ trading community rather than being ‘newcomers’ to long-distance commerce are articulated in relation to notions of ‘hierarchies of trade’ as they evolve in a twofold relational model linking Yiwu’s Changchun neighbourhood and Dushanbe. I suggest that the forms of conviviality enacted in Yiwu’s Changchun neighbourhood need to be understood in terms of the historical, multinational and transregional contacts that have occurred within the spaces of the former Soviet Union, as well as along the China-Russia and China-Central Asian borders. Equally, the hierarchies of trade of Uzbek merchants from Tajikistan in Yiwu’s Changchun neighbourhood cut-across markers of identity that juxtapose the roles of Tajik and Uzbek communities in Tajikistan’s contemporary politics and economics

Dark sectors 2016 Workshop: community report

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years