Photon-photon Collisions Research Articles

Calorimetry of Photon Gases in Nonlinear Multimode Optical Fibers

Recent studies have shown that light propagating in a nonlinear, highly multimode system can thermalize in a manner totally analogous to that encountered in traditional statistical mechanics. At thermal equilibrium, the system’s entropy is at a maximum, in full accord with the second law of thermodynamics. In such arrangements, the entropy is extremized once the statistical power allocation among modes associated with this photon gas attains a Rayleigh-Jeans distribution that is fully characterized by an optical temperature T and a chemical potential μ. However, it has been theoretically argued that the variables T and μ represent actual thermodynamic forces that control the exchange of the respective conjugate quantities between two subsystems. In this work, we report, for the first time, optical calorimetric measurements in nonlinear multimode fibers, which unambiguously demonstrate that both the temperature T and the chemical potential μ dictate the flow of their associated extensive quantities, i.e., the energy and the optical power. Specifically, we study the process of light thermalization associated with two orthogonally polarized laser beams. Our observations are enabled by recently developed techniques that allow one to judiciously multiplex/demultiplex the optical power within various mode groups. Our results indicate that because of photon-photon collisions, “heat” only flows from a hot to a cold photon gas subsystem—thus providing an unequivocal demonstration of the second law in such all-optical thermodynamic arrangements. In addition to being fundamental, our findings provide a new approach to manipulate laser beams using thermodynamic principles. Published by the American Physical Society 2024

Next-to-leading-order relativistic and QCD corrections to prompt pair photoproduction at future colliders* *Supported in part by the German Research Foundation DFG through Research Unit FOR 2926 "Next Generation Perturbative QCD for Hadron Structure: Preparing for the Electron-Ion Collider" (409651613). The work of X.B.J. was supported in part by National Natural Science Foundation of China (12061131006). The work of R.L. was

Within the framework of nonrelativistic-QCD factorization, we calculate both the next-to-leading-order relativistic and QCD corrections to prompt pair production, with feed-down from mesons, via photon-photon collisions at future colliders, including the Future Circular Lepton Collider (FCC-ee), the Circular Electron Positron Collider (CEPC), and the Compact Linear Collider (CLIC). We present total cross sections and distributions in single transverse momentum and rapidity, as well as in pair invariant mass. The relativistic and QCD corrections both turn out to be large and negative. However, the production rates are large enough for useful experimental studies.

Investigation of γ-photon sources using near-critical density targets towards the optimization of the linear Breit–Wheeler process

In this paper we analyze the production of high energy synchrotron gamma photons in laser-plasma interaction for a laser intensity in 1022– 5⋅1023Wcm−2 and a near-critical density target using two dimensional particle-in-cell simulations. In the optimum configuration to maximize the conversion efficiency of the laser energy to γ-photons, we studied the production of electron–positron pairs by the linear Breit–Wheeler process in the collision of two identical γ-photon beams using a dedicated photon-photon collision simulation code. A maximum laser energy conversion coefficient of 33% in high energy photons was obtained and a photon beam intensity, with energies above 1MeV , of 2⋅1020Wcm−2 at 150μm distance from the initial position of the target (for the highest laser intensity considered). We show that the optimum case to detect the linear Breit–Wheeler pairs corresponds to a laser intensity of 1023Wcm−2 . Our results can be used for the preparation of experimental campaigns for the detection of linear Breit–Wheeler pairs at the Apollon and ELI laser facilities.

Thermal pair production from photon-photon collision: Breit–Wheeler process at finite temperature

In this paper we examine the pair production through the Breit–Wheeler process γγ→e+e-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma ~\\gamma \\rightarrow e^+ e^-$$\\end{document} in a thermal background. We compute the thermal contribution to the Breit–Wheeler differential cross section within the thermofield dynamics formalism. We evaluate in details the cross section for this process, which possess a surprisingly simple expression valid for any temperature β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta $$\\end{document}, from which we discuss some physically relevant aspects. We also consider the high temperature regime of the cross section in order to have a better understanding about its thermal behavior.

Collider constraints on massive gravitons coupling to photons

We study the discovery potential of massive graviton-like spin-2 particles coupled to standard model fields, produced in photon-photon collisions at the Large Hadron Collider (LHC) as well as in electron-positron (e+e−) collisions, within an effective theory with and without universal couplings. Our focus is on a massive graviton G coupled to the electromagnetic field, which decays via G→γγ and leads to a resonant excess of diphotons over the light-by-light scattering continuum at the LHC, and of triphoton final states at e+e− colliders. Based on similar searches performed for pseudoscalar axion-like particles (ALPs), and taking into account the different cross sections, γγ partial widths, and decay kinematics of the pseudoscalar and tensor particles, we reinterpret existing experimental bounds on the ALP-γ coupling into G-γ ones. Using the available data, exclusion limits on the graviton-photon coupling are set down to gGγ≈1–0.05 TeV−1 for masses mG≈100 MeV–2 TeV. Such bounds can be improved by factors of 100 at Belle II in the low-mass region, and of 4 at the HL-LHC at high masses, with their expected full integrated luminosities.

Positron Generation and Acceleration in a Self-Organized Photon Collider Enabled by an Ultraintense Laser Pulse.

We discovered a simple regime where a near-critical plasma irradiated by a laser of experimentally available intensity can self-organize to produce positrons and accelerate them to ultrarelativistic energies. The laser pulse piles up electrons at its leading edge, producing a strong longitudinal plasma electric field. The field creates a moving gamma-ray collider that generates positrons via the linear Breit-Wheeler process-annihilation of two gamma rays into an electron-positron pair. At the same time, the plasma field, rather than the laser, serves as an accelerator for the positrons. The discovery of positron acceleration was enabled by a first-of-its-kind kinetic simulation that generates pairs via photon-photon collisions. Using available laser intensities of 10^{22} W/cm^{2}, the discovered regime can generate a GeV positron beam with a divergence angle of around 10° and a total charge of 0.1pC. The result paves the way to experimental observation of the linear Breit-Wheeler process and to applications requiring positron beams.

Angle-dependent pair production in the polarized two-photon Breit-Wheeler process

The advent of laser-driven high-intensity $\gamma$-photon beams has opened up new opportunities for designing advanced photon-photon colliders. Such colliders have the potential to produce a large yield of linear Breit-Wheeler (LBW) pairs in a single shot, which offers a unique platform for studying the polarized LBW process. In our recent work [Phys. Rev. D 105, L071902(2022)], we investigated the polarization characteristics of LBW pair production in CP $\gamma$-photon collisions. To fully clarify the polarization effects involving both CP and LP $\gamma$-photons, here we further investigate the LBW process using the polarized cross section with explicit azimuthal-angle dependence due to the base rotation of photon polarization vectors. We accomplished this by defining a new spin basis for positrons and electrons, which enables us to decouple the transverse and longitudinal spin components of $e^\pm$. By means of analytical calculations and Monte Carlo simulations, we find that the linear polarization of photon can induce the highly angle-dependent pair yield and polarization distributions. The comprehensive knowledge of the polarized LBW process will also open up avenues for investigating the higher-order photon-photon scattering, the laser-driven quantum electrodynamic plasmas and the high-energy astrophysics.

Prospects for ditauonium discovery at colliders

The feasibility of observing ditauonium, the bound state of two tau leptons, at e+e− colliders (BES III at s=3.78 GeV, Belle II at s=10.6 GeV, a future super tau-charm factory (STCF) at s≈2mτ, and the FCC-ee at s=91.2 GeV) as well as in hadronic and photon-photon collisions at the LHC, is studied. Cross sections and expected yields for spin-0 para- (T0) and spin-1 ortho- (T1) ditauonium are presented for nine different production and decay processes. Para-ditauonium can be observed at the FCC-ee via photon fusion in its diphoton decay (γγ→T0→γγ). Ortho-ditauonium can be observed at STCF via e+e−→T1→μ+μ−, where a threshold scan with monochromatized beams can also provide a very precise extraction of the tau lepton mass with O(25 keV) uncertainty. Observing pp →T1(μ+μ−)+X at the LHC is possible by identifying its displaced vertex with a good control of the combinatorial dimuon background. In addition, we compute the rare decay branching fractions of ditauonium into quarkonium plus a photon.

Joint ATLAS/CMS ZDC upgrade project for the High Luminosity LHC

The High Luminosity LHC (HL-LHC) provides the opportunity to study heavy ion, proton-nucleus, photon-nucleus and photon-photon collisions with unprecedented luminosities at the TeV scale. The LHC heavy ion community has mapped out an extensive range of physics measurements at the HLLHC that will push forward our understanding of both QCD, QED and even electroweak physics. The measurement of forward neutrons and photons in Zero Degree Calorimeters (ZDCs) is essential for event classification and triggering. In order to reach the required luminosities, the LHC interaction regions will be redesigned, necessitating the need to build new ZDCs that will be both narrower and much more radiation tolerant. This challenge motivated the formation of a joint project between ATLAS and CMS to build new ZDCs for Run 4, JZCaP. The ZDCs are based on radiation-hard fused silica rods that produce Cherenkov light. These rods have been developed by Heraeus Quartzglas in collaboration with JZCaP and the LHC BRAN and FLUKA groups. The Run 4 ZDCs (HL-ZDCs) are the first joint detector project between CMS and ATLAS. This talk will present the capabilities of the new ZDCs and recent R&D highlights.

White Paper on Forward Physics, BFKL, Saturation Physics and Diffraction

The goal of this whitepaper is to give a comprehensive overview of the rich field of forward physics. We discuss the occurrences of BFKL resummation effects in special final states, such as Mueller-Navelet jets, jet gap jets, and heavy quarkonium production. It further addresses TMD factorization at low x and the manifestation of a semi-hard saturation scale in (generalized) TMD PDFs. More theoretical aspects of low x physics, probes of the quark gluon plasma, as well as the possibility to use photon-hadron collisions at the LHC to constrain hadronic structure at low x, and the resulting complementarity between LHC and the EIC are also presented. We also briefly discuss diffraction at colliders as well as the possibility to explore further the electroweak theory in central exclusive events using the LHC as a photon-photon collider.

Search for sub-eV axion-like particles in a stimulated resonant photon-photon collider with two laser beams based on a novel method to discriminate pressure-independent components

Sub-eV axion-like particles (ALPs) have been searched for by focusing two-color near-infrared pulse lasers into a vacuum along a common optical axis. Within the focused quasi-parallel collision system created by combining a creation field (2.5 mJ/47 fs Ti:Sapphire laser) and a background inducing field (1.5 mJ/9 ns Nd:YAG laser), the detection of signal photons via stimulated resonant photon-photon scattering by exchanging ALPs was attempted in a vacuum chamber. The signal wavelength can be determined via energy-momentum conservation in the vacuum, and it coincides with that determined from the atomic four-wave-mixing (aFWM) process. In this work, the pulse energies were one order of magnitude higher than those in the previous search, allowing aFWM from optical elements to be observed as a pressure-independent background for the first time, in addition to the residual-gas-originating aFWM following a quadratic pressure dependence. In principle the four-wave-mixing process in vacuum via ALP exchanges (vFWM) must also be pressure-independent, so the development of a new method for discriminating the optical-element aFWM is indispensable for increasing the pulse energies to the values needed for future upgraded searches. In this paper, we will present the established method for quantifying the yield from the optical-element aFWM process based on the beam cross- section dependence. With the new method, the number of signal photons was found to be consistent with zero. We then successfully obtained a new exclusion region in the relation between ALP-photon coupling, g/M, and the ALP mass m, reaching the most sensitive point g/M = 1.14 × 10−5 GeV−1 at m = 0.18 eV.

STUDY FOR FERMION DARK MATTER PRODUCTION IN PHOTON-PHOTON COLLISION

Fermion dark matter (FDM) production is investigated via photonphoton collision and the cross section of the FDM production is calculated in detail. Our results are evaluated at different values of the dark matter scale  and the light FDM mass.

Observing true tauonium via two-photon fusion at e+e− and hadron colliders

The feasibility of observing true tauonium, the bound state of two tau leptons, $\mathcal{T}_0\equiv(\tau^+\tau^-)_0$, via photon-photon collisions at $e^+e^-$ colliders and at the LHC, is studied. The production cross sections of the process $\gamma\gamma\to\mathcal{T}_0\to\gamma\gamma$ -- as well as those of all relevant backgrounds: spin-0 and 2 charmonium resonances decaying to diphotons, and light-by-light scattering -- are computed in the equivalent photon approximation for $e^+e^-$ collisions at BES III ($\sqrt{s} = 3.8$ GeV), Belle II ($\sqrt{s} = 10.6$ GeV), and FCC-ee ($\sqrt{s} = 91.2$ GeV), as well as for ultraperipheral p-p, p-Pb, and Pb-Pb collisions at the LHC. Despite small $\mathcal{T}_0$ production cross sections and a final state swamped by decays from overlapping pseudoscalar and tensor charmonium states -- the $\mathrm{\chi_{c2}}$, $\mathrm{\eta_{c}(2S)}$, and $\mathrm{\chi_{c0}}$ states have masses only 2.5, 84, and 139 MeV away, respectively, from the $\mathcal{T}_0$ peak -- evidence and observation of the ground state of the heaviest leptonium appears feasible at Belle II and FCC-ee, respectively, with in-situ high-precision measurements of the irreducible backgrounds.

NLO QCD corrections to pseudoscalar quarkonium production with two heavy flavors in photon-photon collision

We calculate the next-to-leading order (NLO) QCD corrections to $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c}+c+\overline{c}$, $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{b}+b+\overline{b,}$ and $\ensuremath{\gamma}+\ensuremath{\gamma}\ensuremath{\rightarrow}{B}_{c}+b+\overline{c}$ processes in the framework of nonrelativistic QCD factorization formalism. The cross sections at the SuperKEKB electron-positron collider, as well as the future collider like the Circular Electron Positron Collider, are evaluated. Numerical results indicate that the NLO corrections are significant, and the uncertainties in theoretical predictions with NLO corrections are reduced as expected. Due to the high luminosity of the SuperKEKB collider, the ${\ensuremath{\eta}}_{c}+c+\overline{c}$ production is hopefully observable in the near future.

E + e − γ production at photon-photon colliders at complete electroweak NLO accuracy * *Supported in part by the National Natural Science Foundation of China (11775211, 12061141005) and the CAS Center for Excellence in Particle Physics (CCEPP)

We present the NLO electroweak radiative corrections to the production in γγ collision, which is an ideal channel for calibrating the beam luminosity of a Photon Linear Collider. We analyze the dependence of the total cross section on the beam colliding energy, and then investigate the kinematic distributions of final particles at various initial photon beam polarizations at EW NLO accuracy. The numerical results indicate that the EW relative corrections to the total cross section are non-negligible and become increasingly significant as the increase of the beam colliding energy, even can exceed –10% in the γγ collision at . Such EW corrections are very important and should be taken into consideration in precision theoretical and experimental studies at high-energy γγ colliders.

Planck Speed: the Missing Speed of Physics? Absolute Still Without Breaking Lorentz Symmetry!


 
 
 Today, the speed of light is one of the cornerstones of modern physics. It is the maximum speed limit for transferring information, and plays a very central role in relativity theory. It also seems to be the same as the assumed and measured speed of gravity (gravitons and/or gravitational waves). We are not questioning the speed of light, as we indeed think it is the maximum speed limit and that it is identical to the speed ofgravity, but we also think photons lead us to a second speed limit, which we will term the Planck speed. Photon-photon collisions are part of modern physics, but what is not discussed is the speed of two photons during the very moment of a photon-photon collision. How can photons move during a collision? Or, assumea photon is reflected by a mirror; to do so it must collide with the building blocks of the mirror, yet how can it be moving during the very collision point? Also, modern physics assumes mass can be created in a photon-photon collision. We suggest this mass is the Planck mass particle and that it only lasts one Planck time, so when two photons collide, we will claim they must stand still for the direct observer. That is, we suggest thatthe speed of the Planck mass particle is always zero, but that this zero-velocity can only last for one Planck time. That it only lasts one Planck time means it will not break with the relativity principle or Lorenz symmetry, or at least what we can call weak Lorentz symmetry. We will show that the missing Plank mass particle is the very collision point between two photons, and that this is fully in line with predictions in other researchers’ findings in relation to the possible photon mass. This new view seems to solve the missing mass-gap, and seems able to unify gravity with quantum mechanics. This again seems to unify photons with mass, because one of the long-outstanding questions in physics is whether photons have mass or not. In addition, we showhow to find, in a very simple way directly from gravitational observations, lp/tp= cg = c, which is the upper speed limit (the speed of light and gravity) independent of any knowledge of G or ~ or c.
 
 

Observing light-by-light scattering in vacuum with an asymmetric photon collider

The elastic scattering of two real photons in vacuum is one of the most elusive of the fundamentally new processes predicted by quantum electrodynamics. This explains why, although it was first predicted more than eighty years ago, it has so far remained undetected. Here we show that in present-day facilities, the elastic scattering of two real photons can become detectable far off axis in an asymmetric photon-photon collider setup. This may be obtained within one day of operation time by colliding 1 mJ extreme ultraviolet pulses with the broadband gamma-ray radiation generated in nonlinear Compton scattering of ultrarelativistic electron beams with terawatt-class optical laser pulses operating at a 10 Hz repetition rate. In addition to the investigation of elastic photon-photon scattering, this technique allows us to unveil or constrain new physics that could arise from the coupling of photons to yet undetected particles, therefore opening new avenues for searches of physics beyond the standard model.

Perspective of Direct Search for Dark Components in the Universe with Multi-Wavelengths Stimulated Resonant Photon-Photon Colliders

We explore a possibility to detect dark components in the Universe via stimulated photon–photon collisions by focusing two-frequency coherent electromagnetic fields in a vacuum. Those fields are assumed to be pulsed reaching Fourier transform limits in near-infrared, THz, and GHz frequency bands, respectively. The numbers of signal photons as a result of exchange of a pseudoscalar-type pseudo Nambu–Goldstone boson have been evaluated in the individual frequency bands. Within presently available beam intensities, we found that the QCD axion scenarios are thoroughly testable in the mass range 10−6–100 eV based on the common method. Furthermore, we show a possibility to reach the weak coupling domain even beyond the gravitationally weak coupling strength if pulse compression in the GHz band is realized in the near future development.

One-loop electroweak radiative corrections to charged lepton pair production in photon-photon collisions

We provide high-precision predictions for muon-pair and tau-pair productions in a photon-photon collision by considering a complete set of one-loop-level scattering amplitudes, i.e., electroweak (EW) corrections together with soft and hard QED radiation. Accordingly, we present a detailed numerical discussion with particular emphasis on the pure QED corrections as well as genuinely weak corrections. The effects of angular and initial beam polarization distributions on production rates are also discussed. An improvement is observed by a factor of two with oppositely polarized photons. Our results indicate that the one-loop EW radiative corrections enhance the Born cross section and the total relative correction is typically about 10% for both production channels. It appears that the full EW corrections to $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{\ensuremath{-}}{\ensuremath{\ell}}^{+}$ are required to match a percent level accuracy.

Linear Breit-Wheeler pair production by high-energy bremsstrahlung photons colliding with an intense x-ray laser pulse

A possible setup for the experimental verification of linear Breit-Wheeler pair creation of electrons and positrons in photon-photon collisions is studied theoretically. It combines highly energetic bremsstrahlung photons, which are assumed to be generated by an incident beam of GeV electrons penetrating through a high-$Z$ target, with keV photons from an x-ray laser field, which is described as a focused Gaussian pulse. We discuss the dependencies of the pair yields on the incident electron energy, target thickness, laser parameters, and collision geometry. It is shown that, for suitable conditions that are nowadays in reach at x-ray laser facilities, the resulting number of created particles seems to be well accessible for enabling the first experimental observation of the linear Breit-Wheeler process $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$.