Photon Production Research Articles

High precision real-time insertion device and monochromator synchronization at NSLS-II

Insertion devices have become the dominant photon source at synchrotron and free electron laser light source facilities the world over. Undulators, characterized by their small deflection parameter, exhibit a high degree of constructive interference in photon production from high energy charged particle beams leading to very high photon rates at specific harmonics of the fundamental frequency with relatively narrow spectral widths. Spectroscopic measurements of interest typically span several of these harmonic widths, which requires precision adjustment of an undulator’s magnetic gap to maintain peak flux within the much narrower bandwidth of a beamline monochromator at the desired energy. High precision insertion device controls are developed at NSLS-II including real-time linked control of monochromator hardware allowing for fast, high precision, hardware triggered, spectroscopic measurements. This fast fly scan method is described, compared statistically for self consistency, and shown to be far superior in both efficiency and accuracy as compared to standard step scan measurements.

(Re)Solving reionization with Lyα: how bright Lyα Emitters account for the z ≈ 2–8 cosmic ionizing background

ABSTRACT The cosmic ionizing emissivity from star-forming galaxies has long been anchored to UV luminosity functions. Here, we introduce an emissivity framework based on Lyα emitters (LAEs), which naturally hones in on the subset of galaxies responsible for the ionizing background due to the intimate connection between production and escape of Lyα and LyC photons. Using constraints on the escape fractions of bright LAEs (LLyα > 0.2L*) at z ≈ 2 obtained from resolved Lyα profiles, and arguing for their redshift-invariance, we show that: (i) quasars and LAEs together reproduce the relatively flat emissivity at z ≈ 2–6, which is non-trivial given the strong evolution in both the star formation density and quasar number density at these epochs and (ii) LAEs produce late and rapid reionization between z ≈ 6−9 under plausible assumptions. Within this framework, the >10 × rise in the UV population-averaged fesc between z ≈ 3–7 naturally arises due to the same phenomena that drive the growing LAE fraction with redshift. Generally, a LAE dominated emissivity yields a peak in the distribution of the ionizing budget with UV luminosity as reported in latest simulations. Using our adopted parameters ($f_{\rm {esc}}=50{{\ \rm per\ cent}}$, ξion = 1025.9 Hz erg−1 for half the bright LAEs), a highly ionizing minority of galaxies with MUV < −17 accounts for the entire ionizing budget from star-forming galaxies. Rapid flashes of LyC from such rare galaxies produce a ‘disco’ ionizing background. We conclude proposing tests to further develop our suggested Lyα-anchored formalism.

Time Resolution Studies of Thallium Based Cherenkov Semiconductors

In the context of improving the detector performance of time-of-flight positron emission tomography (TOF-PET), the combination of charge induction readout and prompt Cherenkov photon production in semiconductor materials can lead to an outstanding detector performance in energy, timing, and spatial resolution. Energy resolutions as good as 1.2% at 662 keV and 5% at 122 keV are reported for pixel thallium bromide (TlBr) detectors. The high refractive index of Tl-based materials, between 2.3 and 2.6, leads to a high Cherenkov photon generation yield but can also challenge photon extraction, potentially affecting the time performance. In this work, the timing properties of TlBr and thallium chloride (TlCl) crystals of different geometries are measured using an optimized test setup with high-frequency readout electronics. A coincidence time resolution (CTR) value of 167 ± 6 ps FWHM is achieved using a 3 × 3 × 3 mm3black-painted TlBr crystal. In order to assess potential improvements, a Geant4-based simulation tool kit is developed and validated against experimental measurements. The simulation tool kit is used to predict the contributions limiting the time resolution regarding the crystal and photodetector properties, highlighting the potential of such materials. Finally, paths to further improve the detector performance in TOF-PET are discussed.

Multiple strong topological gaps and hexagonal warping in Bi4Te3

The electronic topology of ${\mathrm{Bi}}_{4}{\mathrm{Te}}_{3}$, composed of alternating ${\mathrm{Bi}}_{2}$ and ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ layers, is investigated by density functional theory and angle-resolved photoemission spectroscopy. We find, remarkably, that there are three adjacent strong topological gaps with associated protected surface states within a 2-eV range of the Fermi level. The existence of three consecutive Dirac cones in $k$ space gives promise for alternative phenomena and applications, e.g., production of single photons with different energies (in the infrared and visible ranges) for multichannel transport of quantum information as well as multiple degrees of freedom in electron pumping for lasers. Additionally, a surface-state Fermi surface with strong hexagonal warping is observed.

The star formation burstiness and ionizing efficiency of low-mass galaxies

ABSTRACT We investigate the burstiness of star formation and the ionizing efficiency of a large sample of galaxies at 0.7 < z < 1.5 using HST grism spectroscopy and deep ultraviolet (UV) imaging in the GOODS-N and GOODS-S fields. The star formation history (SFH) in these strong emission-line low-mass galaxies indicates an elevated star formation rate (SFR) based on the Hα emission line at a given stellar mass when compared to the standard main sequence. Moreover, when comparing the Hα and UV SFR indicators, we find that an excess in SFRHα compared to SFRUV is preferentially observed in lower mass galaxies below 109 M⊙, which are also the highest-EW galaxies. These findings suggest that the burstiness parameters of these strong emission-line galaxies may differ from those inferred from hydrodynamical simulations and previous observations. For instance, a larger burstiness duty cycle would explain the observed SFRHα excess. We also estimate the ionizing photon production efficiency ξion, finding a median value of log(ξion/erg−1 Hz) = 24.80 ± 0.26 when adopting a Galactic dust correction for Hα and an SMC one for the stellar component. We observe an increase of ξion with redshift, further confirming similar results at higher redshifts. We also find that ξion is strongly correlated with EWHα, which provides an approach for deriving ξion in early galaxies. We observe that lower mass, lower luminosity galaxies have a higher ξion. Overall, these results provide further support for faint galaxies playing a major role in the reionization of the Universe.

TeV and keV–MeV Excesses as Probes for Hadronic Process in BL Lacertaes

Abstract A hard TeV γ-ray component excess over the single-zone leptonic model prediction (TeV excess) is observed in the spectral energy distributions (SEDs) of some BL Lacs. Its origin is uncertain. We revisit this issue with four BL Lacs (1ES 0229+200, 1ES 0347–121, 1ES 1101–232, and H2356–309), in which the TeV excess is detected in their intrinsic SEDs. We represent their SEDs with a single-zone leptohadronic model, where radiations of the electrons and protons as well as the cascade electrons produced by the γγ and pγ interactions within their jets are considered. We show that the observed SEDs below the GeV gamma-ray band are attributed to the synchrotron radiations and self-Compton process of the primary electrons, and the TeV excess is explained with the γ-ray emission from the pγ process via the π 0 decay. The cascade emission of the electrons produced via the γγ and pγ interactions results in a keV–MeV excess in the SEDs, illustrated as a bump or plateau. This extra photon field enhances the production of TeV photons from the p γ process, resulting in a reduction of the proton power by about one order of magnitude. However, the derived powers are still 3–4 orders of magnitude larger than the Eddington limit, being challenged by the current black hole accretion physics. Applying our model to Mrk 421, we propose that synergic observations with current and upcoming TeV and keV–MeV telescopes for its tentative TeV and MeV excesses can give insights to the hadronic process in its jet.

The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyα Emission of High-redshift Galaxies*

Abstract We perform joint modeling of the composite rest-frame far-UV and optical spectra of redshift 1.85 ≤ z ≤ 3.49 star-forming galaxies to deduce key properties of the massive stars, ionized interstellar medium (ISM), and neutral ISM, with the aim of investigating the principal factors affecting the production and escape of Lyα photons. Our sample consists of 136 galaxies with deep Keck/LRIS and MOSFIRE spectra covering, respectively, Lyβ through C iii] λλ1907, 1909 and [O ii], [Ne iii], Hβ, [O iii], Hα, [N ii], and [S ii]. Spectral and photoionization modeling indicates that the galaxies are uniformly consistent with stellar population synthesis models that include the effects of stellar binarity. Over the dynamic range of our sample, there is little variation in stellar and nebular abundance with Lyα equivalent width, W λ (Lyα), and only a marginal anticorrelation between age and W λ (Lyα). The inferred range of ionizing spectral shapes is insufficient to solely account for the variation in W λ (Lyα); rather, the covering fraction of optically thick H i appears to be the principal factor modulating the escape of Lyα, with most of the Lyα photons in down-the-barrel observations of galaxies escaping through low column density or ionized channels in the ISM. Our analysis shows that a high star-formation-rate surface density, ΣSFR, particularly when coupled with a low galaxy potential (i.e., low stellar mass), can aid in reducing the covering fraction and ease the escape of Lyα photons. We conclude with a discussion of the implications of our results for the escape of ionizing radiation at high redshift.

Gadolinium loaded Cherenkov detectors for neutron monitoring in high energy air showers

Monitoring of high energy cosmic ray neutrons is of particular interest for cosmic ray water Cherenkov detectors as intense bundles of delayed neutrons have been found to arrive after the initial passage of a high energy air shower. In this paper we explore the possibility of building large-area high-energy neutron monitors using gadolinium-loaded Water Cherenkov Detectors (WCDs). GEANT4 simulations of photon production in WCDs are used to estimate the maximum detection efficiency for a hypothetical system. Requiring a series of neutron induced gamma ray flashes distributed over an extended period of time (up to 20 μs) was shown to be an effective way to discriminate high energy neutron interactions from other backgrounds. Results suggest that neutron detection efficiencies of 4–15% may be possible using a gadolinium-loaded detection system above 200 MeV. The magnitude of gadolinium loading was also shown to significantly modify the timing response of the simulated detector.

Multiband Emission up to PeV Energy from the Crab Nebula in a Spatially Dependent Lepto-hadronic Model

Abstract Multiband emissions from radio to ultra-high-energy gamma-rays in the Crab Nebula have been detected. To explain the observed results, nonthermal photon production in the Crab Nebula is carefully studied in a spatially dependent lepto-hadronic model. In our model, the dynamical evolution of the pulsar wind nebula (PWN) is simulated in a spherically symmetric system. Both electrons and protons are accelerated at the termination shock. The relevant particle propagation equations, as well as the photon evolving equation, are simultaneously solved. For the Crab Nebula, our results reveal that the observed multiband photon spectra can be reproduced with reasonable model parameters. In particular, the photons with energy ≳200 TeV are mainly contributed to by the hadronic component via proton–proton interaction. The contribution of the hadronic component depends on both proton spectral index α p and number density n H of the medium within the PWN. Additionally, high-energy neutrino fluxes are predicted with variable proton spectral indices. The predicted fluxes are not only far below the sensitivities of current neutrino observatories but also beneath the atmospheric neutrino background with energy less than ∼40 TeV. Moreover, the calculated radial profiles of surface brightness and spectral index are presented.

Strong Lyman continuum emitting galaxies show intense C IV λ1550 emission

Using the Space Telescope Imaging Spectrograph, we have obtained ultraviolet spectra from ∼1200 to 2000 Å of known Lyman continuum (LyC) emitting galaxies at low redshift (z ∼ 0.3 − 0.4) with varying absolute LyC escape fractions (fesc ∼ 0.01 − 0.72). Our observations include in particular the galaxy J1243+4646, which has the highest known LyC escape fraction at low redshift. While all galaxies are known Lyman alpha emitters, we consistently detect an inventory of additional emission lines, including C IV λ1550, He II λ1640, O III] λ1666, and C III] λ1909, whose origin is presumably essentially nebular. C IV λ1550 emission is detected above 4σ in six out of eight galaxies, with equivalent widths of EW(C IV) = 12 − 15 Å for two galaxies, which exceeds the previously reported maximum emission in low-z star-forming galaxies. We detect C IV λ1550 emission in all LyC emitters with escape fractions fesc > 0.1 and find a tentative increase in the flux ratio C IV λ1550/C III] λ1909 with fesc. Based on the data, we propose a new criterion to select and classify strong leakers (galaxies with fesc > 0.1): C IV λ1550/C III] λ1909 ≳ 0.75. Finally, we also find He II λ1640 emission in all the strong leakers with equivalent widths from 3 to 8 Å rest frame. These are among the highest values observed in star-forming galaxies and are primarily due to a high rate of ionizing photon production. The nebular He II λ1640 emission of the strong LyC emitters does not require harder ionizing spectra at > 54 eV compared to those of typical star-forming galaxies at similarly low metallicity.

Compton-like dark photon production in electron–nucleus collisions

The Compton-like production of massive dark photons is investigated in ultrarelativistic electron–ion collisions by considering the kinetic mixing between the dark photon and the standard model photon. The quasi-real photons in the heavy ion are described by the equivalent photon approximation, and the model is employed to calculate the integrated cross section and event rates as a function of the dark photon mass, m γ′, and mixing parameter, ɛ. Predictions are shown for electron–ion colliders (EICs) in the mass range 100 ⩽ m γ′ ⩽ 500 MeV. Numerical results are provided within the kinematic coverage of the planned machines: an EIC in China (EicC), a polarized EIC at Jefferson Lab (JLEIC), an EIC/USA (EIC), a large hadron electron collider (LHeC) and a future circular collider (FCC-eA). It complements existing search strategies for dark photons in the considered mass interval.

Exclusive processes in ep collisions at the EIC and LHeC: A closer look on the predictions of saturation models

The exclusive production of vector mesons and photons in $ep$ collisions is investigated considering three phenomenological saturation models based on distinct assumptions for the treatment of the dipole-hadron scattering amplitude. The latest high precision HERA data for the reduced and vector meson cross sections are used to update the saturation model proposed by Marquet Peschanski, and Soyez, which predicts that the saturation scale is dependent of the squared momentum transfer $t$. The Marquet-Peschanski-Soyez predictions for the photon virtuality, energy and $t$ dependencies of the exclusive $\ensuremath{\rho}$, $J/\mathrm{\ensuremath{\Psi}}$, and deeply virtual Compton scattering cross sections are presented and a detailed comparison with the results derived using the impact parameter saturation models is performed. Our results indicate that a future experimental analysis of the $t$ distribution $d\ensuremath{\sigma}/dt$ for exclusive processes in the kinematical range that will covered by the EIC and LHeC, considering the distinct photon polarizations and large values of $t$, will be able to discriminate between the distinct approaches for the QCD dynamics at high energies.

Enhancement of photon creation through the pseudo-Hermitian Dynamical Casimir Effect

We analyse here the pseudo-Hermitian Dynamical Casimir Effect, proposing a non-Hermitian version of the effective Law’s Hamiltonian used to describe the phenomenon. We verify that the average number of created photons can be substantially increased, a result which calls the attention to the possibility of engineering the time-dependent non-Hermitian Hamiltonian we have assumed. Given the well-known difficulty in detecting the Casimir photon production, the present result reinforces the importance of pseudo-Hermitian quantum mechanics as a new chapter of quantum theory and an important tool for the amplification of Hermitian processes such as the degree of squeezing of quantum states.

Multimessenger heavy-ion collision physics

This work studies the production of direct photons in relativistic nuclear collisions, along with the production of hadrons. Radiation from the very first instants to the final moments of the evolution is included. The hybrid model used here describes all stages of relativistic heavy-ion collisions. Chronologically, those are an initial state reflecting the collision of nuclei described within the Color Glass Condensate effective theory; a pre-equilibrium phase based on non-equilibrium linear response; relativistic viscous hydrodynamics, and a hadronic afterburner. The effect of the pre-equilibrium phase on both photonic and hadronic observables is highlighted for the first time. The potential of photon observables -- spectrum, differential elliptic and triangular flow -- to reveal the chemical equilibration time is studied. Finally, we consider "small collision systems", including proton+nucleus collisions and collisions of light nuclei, as probed by hadronic and electromagnetic observables. We demonstrate how photon production can signal the formation of quark-gluon plasma in such small systems.

Effect of Interlayer Coupling and Symmetry on High-Order Harmonic Generation from Monolayer and Bilayer Hexagonal Boron Nitride

High-order harmonic generation (HHG) is a fundamental process which can be simplified as the production of high energetic photons from a material subjected to a strong driving laser field. This highly nonlinear optical process contains rich information concerning the electron structure and dynamics of matter, for instance, gases, solids and liquids. Moreover, the HHG from solids has recently attracted the attention of both attosecond science and condensed matter physicists, since the HHG spectra can carry information of electron-hole dynamics in bands and inter- and intra-band current dynamics. In this paper, we study the effect of interlayer coupling and symmetry in two-dimensional (2D) material by analyzing high-order harmonic generation from monolayer and two differently stacked bilayer hexagonal boron nitrides (hBNs). These simulations reveal that high-order harmonic emission patterns strongly depend on crystal inversion symmetry (IS), rotation symmetry and interlayer coupling.

Direct Photon Production in High-Energy Heavy Ion Collisions within the Integrated Hydrokinetic Model

The results on description of direct photon yields, transverse momentum spectra, and flow harmonics, measured in ultrarelativistic heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) for different collision centrality classes, analyzed within the Integrated Hydrokinetic Model (iHKM) are reviewed. The iHKM simulation results, corresponding to the two opposite approaches to the matter evolution treatment at the final stage of the system’s expansion within the model, namely, the chemically equilibrated and the chemically frozen evolution, are compared. The so-called “direct photon puzzle” is addressed, and its possible solution, suggesting the account for additional photon emission at confinement, is considered.

Shedding light on thermal photon and dilepton production

Electromagnetic radiation from the quark-gluon plasma (QGP) is an important observable to be considered in heavy ion collision experiments. I will provide an update on recent advancements from perturbation theory and quenched lattice simulations. The resummed next-to-leading order (NLO) emission rate has recently been decomposed into transverse and longitudinal components, and extended to non-zero baryon chemical potential. The associated spectral function has also been tested against the Euclidean correlator, for continuum-extrapolated lattice data (at μB = 0).

Recent Highlights from the PHENIX Collaboration

These proceedings present a set of PHENIX highlight results using recent high-luminosity data sets for p+p, p (d, 3He)+A, and A+A(B) collisions at RHIC top energies with a focus on: (1) light-flavor particle productions; (2) hard-probes such as jet-like correlations, direct photon, and heavy-quark productions; and (3) azimuthal anisotropy in small collision systems.

Compact Thomson Scattering Source Based on a Mixed Injection Assisted Laser Wakefield Accelerator

In order to establish a compact all-optical Thomson scattering source, experimental studies were conducted on the 45 TW Ti: sapphire laser facility. By including a steel wafer, mixed gas, and plasma mirror into a double-exit jet, several mechanisms, such as shock-assisted ionization injection, ionization injection, and driving laser reflection, were integrated into one source. So, the source of complexity was remarkably reduced. Electron bunches with central energy fluctuating from 90 to 160 MeV can be produced. Plasma mirrors were used to reflect the driving laser. The scattering of the reflected laser on the electron bunches led to the generation of X-ray photons. Through comparing the X-ray spots under different experimental conditions, it is confirmed that the X-ray photons are generated by Thomson scattering. For further application, the energy spectra and source size of the Thomson scattering source were measured. The unfolded spectrum contains a large amount of low-energy photons besides a peak near 67 keV. Through importing the electron energy spectrum into the Monte Carlo simulation code, the different contributions of the photons with small and large emitting angles can be used to explain the origin of the unfolded spectrum. The maximum photon energy extended to about 500 keV. The total photon production was 107/pulse. The FWHM source size was about 12 μm.

Energy spectra of secondaries in proton-proton interactions

We compare the predictions of aafrag for the spectra of secondary photons, neutrinos, electrons, and positrons produced in proton-proton collisions to those of the parametrizations of Kamae et al., Kelner et al. and Kafexhiu et al. We find that the differences in the normalization of the photon energy spectra reach 20%--50% at intermediate values of the transferred energy fraction $x$, growing up to a factor of two for $x\ensuremath{\rightarrow}1$, while the differences in the neutrino spectra are even larger. We argue that LHCf results on the forward production of photons and neutral pions favor the use of the qgsjet-II-04m model on which aafrag is based. The differences in the normalization have important implications in the context of multimessenger astronomy, in particular, for the prediction of neutrino fluxes, based on gamma-ray flux measurements, or regarding the inference of the cosmic ray spectrum, based on gamma-ray data. We note also that the positron-electron ratio from hadronic interactions increases with energy toward the cutoff, an effect which is missed using the average electron-positron spectrum from Kelner et al. Finally, we describe the publicly available python package aafragpy, which provides the secondary spectra of photons, neutrinos, electrons, and positrons. This package complements the aafrag results for protons with energies above 4 GeV with previous analytical parameterizations of particle spectra for lower energy protons.