Direct Photon Research Articles

Performance and upgrade plans of the ALICE Photon Spectrometer

PHOS is a highly granulated precision spectrometer, one of the two electromagnetic calorimeters of ALICE (A Large Ion Collider Experiment) at the LHC. It is based on scintillating PbWO4 crystals and is dedicated to the precise measurements of spectra, correlations and collective flow of neutral mesons, thermal and prompt direct photons in ultra-relativistic nuclear collisions at LHC energies. PHOS participated in LHC Run 1 (2009–2013) and Run 2 (2015–2018), during which a large amount of physical data were collected in pp, p-Pb and Pb-Pb collisions.We present an overview of the PHOS performance during Runs 1 and 2 and plans for an upgrade for future LHC runs.

Measurement of jet-medium interactions via direct photon-hadron correlations in Au+Au and d+Au collisions at sNN=200 GeV

We present direct photon-hadron correlations in 200 GeV/A Au$+$Au, $d$$+$Au and $p$$+$$p$ collisions, for direct photon $p_T$ from 5--12 GeV/$c$, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in $d$$+$Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au$+$Au compared to $p$$+$$p$ and $d$$+$Au. As the momentum fraction decreases, the yield of hadrons in Au$+$Au increases to an excess over the yield in $p$$+$$p$ collisions. The excess is at large angles and at low hadron $p_T$ and is most pronounced for hadrons associated with lower momentum direct photons. Comparison to theoretical calculations suggests that the hadron excess arises from medium response to energy deposited by jets.

Influence of quintessence dark energy on the shadow of black hole

We investigate the effects of quintessence dark energy on the shadows of black hole, surrounded by various profiles of accretions. For the thin-disk accretion, the images of the black hole comprises the dark region and bright region, including direct emission, lensing rings and photon rings. Although their details depend on the form of the emission, generically, direct emission plays a major role for the observed brightness of the black hole, while the lensing ring makes a small contribution and the photon ring makes a negligible contribution. The existence of a cosmological horizon also plays an important role in the shadows, since the observer in the domain of outer communications is near the cosmological horizon. For spherically symmetric accretion, static and infalling matters are considered. We find that the positions of photon spheres are the same for both static and infalling accretions. However, the observed specific intensity of the image for infalling accretion is darker than for static accretion, due to the Doppler effect of the infalling motion.

Clinical Outcomes, Cosmesis and Quality of Life in Hypofractionation Versus Conventional Fractionation Radiotherapy to Whole Breast and Regional Nodes: A Phase II Randomized Study

Whole Breast Radiotherapy (WBRT) is indicated as adjuvant treatment in the multimodality management of Breast Cancer after Breast Cancer Surgery (BCS). Regional Nodal Irradiation (RNI) improves outcomes in patients with positive nodes after axillary dissection. Hypofractionation in WBRT is equivalent to standard fractionation in terms of long-term outcomes, but the role of hypofractionation in the settings of RNI has not been explored. We prospectively conducted a phase II randomized study comparing Hypofractionation and Standard fractionation in WBRT with RNI to evaluate clinical outcomes, cosmesis and quality of life (QOL) between the two modalities. Women aged ≥ 18 years with breast cancer undergoing BCS and axillary dissection were recruited in the study after Institutional Ethics Committee approval. 52 patients were randomized into two groups, with 26 patients in arm 1 (standard fractionation) WBRT 50Gy/25fraction/5weeks followed by boost 16Gy/8fraction and other 26 patients in arm II (hypofractionation) WBRT 40Gy/15fraction/3 weeks followed by boost 10Gy/4fraction. Contouring was done as per the standard RTOG guidelines. WBRT was planned using forward planning IMRT. Direct or oblique photon fields were used for RNI of SCF/ Axillary region as clinically indicated. Contouring and planning was done on MONACO treatment planning system. Clinical acute toxicity, late toxicity was noted with RTOG acute toxicity criteria. Quality of life (QOL) was assessed with EORTC BR 23 questionnaire. Statistical analysis was done with SPSS v 21 and p-value < 0.05 was considered as significant. All patients received planned allocated treatment and were eligible for analysis. At treatment completion, the Grade II skin toxicity was higher in arm I compared to arm II, with 84% vs 11% (p <0.01), Grade III skin toxicity was not noted in arm II, but present in 3(11%) patients of arm I (p <0.01). The skin toxicity at 6 months was similar at 6 months with only Grade I skin toxicity. At completion of radiation, good cosmesis was noted in 8(32%) patients of arm I and 20(77%) patients of arm II, whereas fair cosmesis was observed in 17 (65%) patients of arm I and 6(23%) patients of arm II. The cosmesis at 6 months post radiation was excellent in 21(80%) patients of arm I and 23(88%) patients of arm II, and good cosmesis was seen in 5(20%) patients of arm I and 3(12%) patients of arm II. The cosmesis improved in both the arms at 6 months, and the results were comparable between the groups. There was no significant difference in subcutaneous toxicity, arm toxicity or lymphedema between the two arms at 3 and 6 months. There was no difference in QOL between two arms at 3 and 6 months. WBRT with RNI is feasible with hypofractionation and it is not associated with decreased clinical outcomes as compared to standard fractionation. Lymphedema was similar with hypofractionation. The clinical acute toxicity, cosmesis and QOL was similar with hypofractionation and standard fractionation.

Direct Photons from Hot Quark Matter in Renormalized Finite-Time-Path QED

Within the finite-time-path out-of-equilibrium quantum field theory (QFT), we calculate direct photon emission from early stages of heavy ion collisions, from a narrow window, in which uncertainty relations are still important and they provide a new mechanism for production of photons. The basic difference with respect to earlier calculations, leading to diverging results, is that we use renormalized QED of quarks and photons. Our result is a finite contribution that is consistent with uncertainty relations.

Ellipticity of photon emission from strongly magnetized hot QCD plasma

By making use of an explicit representation for the imaginary part of the photon polarization tensor in terms of transitions between the Landau levels of light quarks, we study the angular dependence of direct photon emission from a strongly magnetized quark-gluon plasma. Because of the magnetic field, the leading order photon rate comes from the three processes of the zeroth order in the coupling constant $\alpha_s$: (i) the quark splitting ($q\rightarrow q+\gamma $), (ii) the antiquark splitting ($\bar{q} \rightarrow \bar{q}+\gamma $), and (iii) the quark-antiquark annihilation ($q + \bar{q}\rightarrow \gamma$). In a wide range of moderately high temperatures, $T\gtrsim m_\pi$, and strong magnetic fields, $|eB|\gtrsim m_\pi^2$, the direct photon production is dominated by the two splitting processes. We show that the Landau-level quantization of quark states plays an important role in the energy and angular dependence of the photon emission. Among other things, it leads to a nontrivial momentum dependence of the photon ellipticity coefficient $v_2$, which takes negative values at small transverse momenta and positive values at large transverse momenta. The crossover between the two regimes occurs around $k_T\simeq \sqrt{|eB|}$. In application to heavy-ion collisions, this suggests that a large value of $v_2$ for the direct photons could be explained in part by the magnetic field in the quark-gluon plasma.

Azimuthal anisotropy and multiplicities of hard photons and free nucleons in intermediate-energy heavy-ion collisions

Anisotropic flow can offer significant information of evolution dynamics in heavy-ion collisions. A systematic study of the directed flow $v_1$ and elliptic flow $v_2$ of hard photons and free nucleons is performed for $^{40}$Ca+$^{40}$Ca collisions in a framework of isospin dependent quantum molecular dynamics (IQMD) model. The study firstly reveals that thermal photons emitted in intermediate-energy heavy-ion collisions have the behaviors of directed and elliptic flows. The interesting phenomena of incident energy dependence of $v_1$ and $v_2$ for thermal photons in central collisions also confirmed that it can be regarded as a good probe of evolution dynamics. Moreover, the multiplicities of hard photons and free nucleons and their correlation are also investigated. We find that direct photon emission is positively related to free nucleons emission, however, there exists an anti-correlation for thermal photons with free nucleons.

A proposal for an electrical connection between the gravitational field and light

Based on well-established equations, we provide evidence of an electrical connection between the gravitational field and light. Each is modeled using the inductance‐capacitance ( &lt;mml:math display="inline"&gt; &lt;mml:mrow&gt; &lt;mml:mi&gt;L&lt;/mml:mi&gt; &lt;mml:mi&gt;C&lt;/mml:mi&gt; &lt;/mml:mrow&gt; &lt;/mml:math&gt; ) circuit as the building block. A proposed direct photon force (not a pressure and not by means of a force carrier), the relationship between the speed of light and gravity, the frequency and wavelength of gravitational waves, gravitational redshift, the trajectory of planets around the sun, and equations of plane electromagnetic waves may all be expressed with the assistance of an ideal (no resistance) &lt;mml:math display="inline"&gt; &lt;mml:mrow&gt; &lt;mml:mi&gt;L&lt;/mml:mi&gt; &lt;mml:mi&gt;C&lt;/mml:mi&gt; &lt;/mml:mrow&gt; &lt;/mml:math&gt; circuit model of light. Each begins with the Planck‐Einstein relationship. Each suggests that gravity and electromagnetism interact directly through fluctuating electrical and magnetic fields from both sources. With this perspective Einstein's concept of the warping of spacetime may not be needed to explain gravitation.

Remodelling of fibrillin-rich microfibrils by solar-simulated radiation: impact of skin ethnicity

Fibrillin-rich microfibrils (FRMs) constitute integral components of the dermal elastic fibre network with a distinctive ultrastructural ‘beads-on-a-string’ appearance that can be visualised using atomic force microscopy and characterised by measurement of their length and inter-bead periodicity. Their deposition within the dermis in photoprotected skin appears to be contingent on skin ethnicity, and influences the ultrastructure of papillary – but not reticular – dermal FRMs. Truncation and depletion of FRMs at the dermal-epidermal junction of skin occurs early in photoageing in people with lightly pigmented skin; a process of accelerated skin ageing that arises due to chronic sun exposure. Accumulation of ultraviolet radiation (UVR)-induced damage, either by the action of enzymes, oxidation or direct photon absorption, results in FRM remodelling and changes to ultrastructure. In the current study, the direct effect of UVR exposure on FRM ultrastructure was assayed by isolating FRMs from the papillary and reticular dermis of photoprotected buttock skin of individuals of either black African or white Northern European ancestry and exposing them to solar-simulated radiation (SSR). Exposure to SSR resulted in significant reduction in nter-bead periodicity for reticular dermis-derived FRMs across both cohorts. In contrast, papillary dermal FRMs exhibited significantly increased inter-bead periodicity, with the magnitude of damage greater for African FRMs, as compared to Northern European FRMs. Our data suggest that FRMs of the dermis should be considered as two distinct populations that differentially accrue damage in response to SSR. Furthermore, papillary dermal FRMs derived from black African subjects show greater change following UVR challenge, when extracted from skin. Future studies should focus on understanding the consequences of UVR exposure in vivo, regardless of skin ethnicity, on the molecular composition of FRMs and how this UVR-induced remodelling may affect the role FRMs play in skin homeostasis.

Probing the evolution of heavy-ion collisions using direct photon interferometry

We investigate the measurement of Hanbury Brown-Twiss (HBT) photon correlations as an experimental tool to discriminate different sources of photon enhancement, which are proposed to simultaneously reproduce the direct photon yield and the azimuthal anisotropy measured in nuclear collisions at RHIC and the LHC. To showcase this, we consider two different scenarios in which we enhance the yields from standard hydrodynamical simulations. In the first, additional photons are produced from the early pre-equilibrium stage computed from the \textit{bottom-up} thermalization scenario. In the second, the thermal rates are enhanced close to the pseudo-critical temperature $T_c\approx 155\,\text{MeV}$ using a phenomenological ansatz. We compute the correlators for relative momenta $q_o, \,q_s$ and $q_l$ for different transverse pair momenta, $K_\perp$, and find that the longitudinal correlation is the most sensitive to different photon sources. Our results also demonstrate that including anisotropic pre-equilibrium rates enhances non-Gaussianities in the correlators, which can be quantified using the kurtosis of the correlators. Finally, we study the feasibility of measuring a direct photon HBT signal in the upcoming high-luminosity LHC runs. Considering only statistical uncertainties, we find that with the projected $\sim 10^{10}$ heavy ion events a measurement of the HBT correlations for $K_\perp<1\, \text{GeV}$ is statistically significant.

Prompt J/psi photoproduction within the non-relativistic QCD framework at the CEPC

The prompt J/psi photoproduction within the non-relativistic QCD (NRQCD) framework at the future Circular Electron Positron Collider (CEPC) is studied, including the contributions from both direct and resolved photons. Employing different sets of long distance matrix elements, the total cross section is dominated by the color-octet channel. We present different kinematic distributions of J/psi production and the results show there will be about 50 J/psi events when the transverse momentum of J/psi is up to 20 GeV. It renders that the J/psi photoprodution at the CEPC is a well laboratory to test the NRQCD and further clarify the universality problem in NRQCD between electron positron collider and hadron collider.

High-Performance Nonfullerene Organic Photovoltaics Applicable for Both Outdoor and Indoor Environments through Directional Photon Energy Transfer.

With the advent of the smart factory and the Internet of Things (IoT) sensors, organic photovoltaics (OPVs) gained attention because of their ability to provide indoor power generation as an off-grid power supply. To satisfy these applications, OPVs must be capable of power generation in both outdoor and indoor at the same time for developing environmentally independent devices. For high performances in indoor irradiation, a strategy that maximizes photon utilization is essential. In this study, graphene quantum dots (GQDs), which have unique emitting properties, are introduced into a ZnO layer for efficient photon utilization of nonfullerene-based OPVs under indoor irradiation. GQDs exhibit high absorption properties in the 350-550 nm region and strong emission properties in the visible region due to down-conversion from lattice vibration. Using these properties, GQDs provide directional photon energy transfer to the bulk-heterojunction (BHJ) layer because the optical properties overlap. Additionally, the GQD-doped ZnO layer enhances shunt resistance (RSh) and forms good interfacial contact with the BHJ layer that results in increased carrier dissociation and transportation. Consequently, the fabricated device based on P(Cl-Cl)(BDD = 0.2) and IT-4F introduces GQDs exhibiting a maximum power conversion efficiency (PCE) of 14.0% with a superior enhanced short circuit current density (JSC) and fill factor (FF). Furthermore, the fabricated device exhibited high PCEs of 19.6 and 17.2% under 1000 and 200 lux indoor irradiation of light emitting diode (LED) lamps, respectively.

Direct photon emission and influence of dynamical wave packets in an extended quantum molecular dynamics model

Direct photon produced from first proton-neutron ($p$-$n$) collision during the early stage of heavy ion reaction is a sensitive probe to reflect energy and momentum distribution of nucleons. In this work, we embedded the hard photon production channel in an extended quantum molecular dynamics (EQMD) model, and took the direct photon as a possible probe to improve namely the Fermi motion in the EQMD model. A possible scheme is offered to handle the dynamical wave packet width within incoherent bremsstrahlung process. Direct photons calculated by our modified EQMD were compared with data of $^{14}$N + $^{12}$C at beam energies $E/A$ = 20, 30 and 40 MeV, and it is found that the yield, inverse slope and angular distribution of direct photons could be reasonably reproduced. In addition, asymmetric reaction systems of $^{4}$He + C and $^{4}$He + Zn at $E/A$ = 53 MeV are also simulated in this work. It is found that the symmetric angular distribution in the nucleon-nucleon ($N$-$N$) center-of-mass (c.m.) frame and the velocity of $ the \gamma$-emission source can be reasonably obtained from our method although there is some quantitative differences.

Direct photon production and scaling properties in large and small system collisions

We present recent measurement results of low momentum direct photons obtained by the PHENIX collaboration from Cu+Cu at 200 GeV and Au+Au at 200 GeV, 62.4 GeV, 39 GeV, as well as from p+p and p+Au at 200 GeV. In these measurements a large excess over the scaled reference p+p yield of direct photons is observed in A+A collisions, and a non-zero excess over the scaled p+p yield is found within systematic uncertainties in central p+Au collisions. Based upon the comparison between this recent data and the PHENIX published Au+Au data at 200 GeV, along with including the ALICE Pb+Pb data at 2760 GeV, PHENIX has found that the direct photon pT-spectra and their integrated yield, dNγ /dy, above 1 GeV/c in pT follow a universal scaling as a function of the charged-hadron multiplicity, (dNch /dρ]) α , with α = 1.25. Within experimental uncertainties, the direct photon scaling properties observed in large collision systems is independent of the colliding species, collision centrality selection and center-of-mass energy. One possible explanation is that the photon radiation sources may have similar properties for all colliding large systems across different energies. There is also another trend coming from integrated direct photon pT-spectra of small systems, which suggests that the QGP turn off/on transition region may exist between large and small system collisions.

Scaling properties of direct photon yields in heavy ion collisions

A recent analysis from the PHENIX collaboration of available direct photon measurement results in collisions of various systems such as Au+Au, Cu+Cu, and Pb+Pb, at different beam energies ranging from 39 to 2760 GeV, has shown a universal, within experimental uncertainties, multiplicity scaling, in which direct photon p_{T}-spectra for transverse momenta up to 2 GeV/c are scaled with charged hadron pseudorapidity density at midrapidity raised to power alpha =1.25. On the other hand, those direct photon p_{T}-spectra also exhibit geometrical scaling in the similar p_{T} range. Assuming power-law dependence of the scaled photon spectra for both scaling laws, we formulate two independent conditions for the power alpha , which overshoot experimental data by sim 10% on average. We discuss possible sources that might improve this estimate.

Quantum thermometry based on a cavity-QED setup

We present a quantum thermometry scheme based on a cavity-QED setup, which attains a sensitivity with Heisenberg scaling. A stream of identical two-level systems passes through a thermal bath to be tested. Each system partially thermalizes, carrying information on the temperature of the thermal bath, and it then interacts with a dissipative single-mode cavity. The Heisenberg scaling is attained from the initial coherence of each system. The systems cannot be fully thermalized by the thermal bath. The optimal interaction time between the system and the thermal bath is derived. Direct photon detection is proved to be an optimal measurement when there is no extra thermal bath in the cavity. In the case where there is an extra thermal bath in the cavity independent of the thermal bath to be tested, homodyne detection is the optimal measurement. Moreover, we show that direct photon detection obtains less information in the case where the extra thermal bath in the cavity is in thermal equilibrium with the thermal bath. However, the optimal measurement can utilize the information from the extra thermal bath to improve the estimation precision of the temperature.

Prompt, pre-equilibrium, and thermal photons in relativistic nuclear collisions

The direct photon emission model in relativistic nuclear colliders has been improved in recent years for reducing the discrepancy between theoretical estimations and experimental data and for understanding the properties of the QCD matter. In this study, the contribution of pre-equilibrium photons are investigated in addition to those of prompt and thermal photons in the framework of a relativistic hydrodynamic model. The numerical simulations at an LHC energy suggest that the pre-equilibrium photons may be relevant at intermediate transverse momentum near the saturation momentum scale, increasing particle spectra and reducing elliptic flow of direct photons.

Iron line reverberation mapping in Ghasemi-Nodehi\u2013Bambi background

The reverberation associated with the iron line is the time lag between direct photons from the corona and the photons reflected from the disk. The resulting line spectrum is called the 2D transfer function. The shape of the 2D transfer function is determined by the geometry of spacetime and the properties of BH. In a paper (Ghasemi-Nodehi and Bambi in EPJC 76:290, 2016), the authors have proposed a parametrization. This parametrization is aimed to test the Kerr nature of astrophysical black hole candidates. In this paper, I provide a reverberation mapping of the Ghasemi-Nodehi–Bambi metric in order to constrain the parameter of spacetime. All parameters can be constrained with the exception of b_{11}. The parameter b_4 is harder to constrain too.

P551Permanent cardiac implantable device damage during direct photon exposure for oncologic radiotherapy: a multicentre, in-vitro observation

Abstract Funding Acknowledgements None Backgroung. Direct photon exposure of cardiac implantable devices (CIEDs), both pacemakers (PMs) or implantable cardioverter defibrillators (ICDs), during oncologic radiotherapy (RT) courses may transiently or permanently affect normal device function. Purpose To evaluate CIED damage by direct exposure to doses up to 10 Gy in oncologic RT, commonly considered unsafe or even potentially harmful, 206 CIEDs (143 PMs and 63 ICDs) from three different centres, with at least 4 months to Elective Replacement Indicator (E.R.I.) were observed. Methods. All CIEDs had a baseline telemetry interrogation. Single chamber devices were programmed in the VVI/40 mode and dual or triple chamber ones were programmed in the DDD/40 mode. Rate adaptive function was disabled. In ICDs, antitachycardia therapies were disabled with the ventricular tachycardia/fibrillation window left enabled. A centering Computed Tomography was performed to build the corresponding treatment plan and CIEDs were blinded randomized to receive either 2, 5 or 10 Gy (direct exposure) by a 6 MV linear accelerator in a home-made water phantom. An in-vivo dosimetry randomly assessed the effective dose received by the CIEDs. All CIEDs were interrogated immediately after exposure and monthly during a three-month follow-up. Results. Immediately after photon exposure, no changes in device setting or software errors were observed in 205 CIEDs (99·5%). Reset to emergency back-up mode was observed in a PM (0·49% overall; 0·7% among PMs). Seven PMs reached the E.R.I immediately after exposure (3·4% overall; 4·9% among PMs). Sixteen ICDs (7·8% overall; 25·4% among ICDs) reported multiple ventricular tachycardia/fibrillation detections stored in the device memory. During follow-up, a non-reprogrammable software reset (emergency backup VVI/65 mode) was observed in one PM after a single dose of 2 Gy (0·49% overall; 0.7% among PMs), whereas an abnormal battery drain was observed in 6 PMs (2.9% overall; 4.2% among PMs). No battery issues were observed in ICDs. All reported events occurred regardless of either 2, 5, or 10 Gy direct exposure. Malfunctions were observed in only older CIEDs. Conclusions. Recent CIEDs have shown to be safe during oncologic RT, withstanding direct exposure up to 10 Gy, commonly considered not recommended or even unsafe by manufacturers statements and clinical guidelines. Malfunctions occurred solely in older devices.

Pathways to excitation of atoms with bicircular laser pulses

We study the excitation of the hydrogen atom by bichromatic circularly polarized laser pulses using numerical solutions of the time-dependent Schr\"odinger equation. The results are in agreement with the selection rules for multiphoton processes in such fields, namely, excited states are populated in which orbital angular momentum and magnetic quantum numbers are either both odd or both even, independent of the relative helicity, peak intensity, and pulse duration of the pulses. For co-rotating pulses the results show that excitation predominantly proceeds to states with magnetic quantum number of the same helicity as the laser pulses. Besides pathways via direct photon absorption from the ground state our results indicate that a transfer of population among the Rydberg states occurs via $\mathrm{\ensuremath{\Lambda}}$-type transitions. In the case of counter-rotating pulses the largest excitation probability is found for Rydberg states that differ in magnetic quantum number by $\mathrm{\ensuremath{\Delta}}m=\ifmmode\pm\else\textpm\fi{}3$. This pattern allows us to estimate how many photons from each of the two bichromatic fields have been absorbed. Finally, we confirm that a population in Rydberg states beyond a maximum orbital angular quantum number is unlikely.