Pair Production Mechanism Research Articles

QED peripheral mechanism of pair production at colliders

Cross sections of the processes of production of neutral pions and pairs of charged fermions and bosons in peripheral interaction of leptons and photons are calculated in the main logarithmic approximation. We investigate the phase volumes and differential cross sections. The differential cross sections of production of a few neutral pions and a few pairs are written down explicitly. Considering the academic problem of summation over a number of pairs for massless particles we reproduce the known results obtained in the 1970s. The possibility of constructing the generator for Monte Carlo modeling of these processes based on these results is discussed.

Schwinger Mechanism and Hawking Radiation as Quantum Tunneling

The common interpretation of the Hawking radiation as quantum tunneling has some ambiguity such as coordinate-dependence of tunneling rate and non-invariance of the action under canonical transformations. It is shown that the tunneling process of black holes can be successfully described by Rindler coordinates in analogy with the Schwinger mechanism for pair production. We study the tunneling process of a charged black hole and a BTZ black hole.

Direct Search for Dirac Magnetic Monopoles inpp¯Collisions ats=1.96 TeV

We search for pair-produced Dirac magnetic monopoles in 35.7 pb^-1 of proton-antiproton collisions at sqrt(s) = 1.96 TeV with the Collider Detector at Fermilab (CDF). We find no monopole candidates corresponding to a 95% confidence-level cross-section limit sigma < 0.2 pb for a monopole with mass between 200 and 700 GeV/c^2. Assuming a Drell-Yan pair production mechanism, we set a mass limit m>360 GeV/c^2.

Single and pair production of doubly charged Higgs bosons at hadron colliders

Current searches for doubly charged Higgs bosons (H^{\pm\pm}) at the Fermilab Tevatron are sensitive to single production of H^{\pm\pm}, although the pair production mechanism q\bar q\to H^{++}H^{--} is assumed to be dominant. In the context of a Higgs Triplet Model we study the mechanism q'\bar q\to H^{\pm\pm}H^{\mp} at the Tevatron and CERN Large Hadron Collider, and show that its inclusion can significantly improve the search potential for H^{\pm\pm}. Moreover, assuming that the neutrino mass is generated solely by the triplet field Yukawa coupling to leptons, we compare the branching ratios of H^{\pm\pm}\to l^\pm l^\pm and H^{\pm\pm}\to H^\pm W^* for the cases of a normal hierarchical, inverted hierarchical and degenerate neutrino mass spectrum.

TACHYONIC FLUCTUATIONS ABOUT THE ELECTROWEAK VACUUM

Fifty years ago Schwinger [1] calculated the non-perturbative persis­ tence probability for e+e- pair production by very strong, constant electric fields; since then, many generalizations have been found [2], of which the more recent [3] treat fields which contain both spatial and temporal variations. When the new SLAC/DESY free-electron, high-intensity, X-ray lasers [4] become operational, one expects copious charged-particle production when such laser beams strike matter, and/or in the regions where two or more such beams intersect.[5] The Physics of the Schwinger mechanism for such pair production by an electromagnetic field is well-understood: Many of the virtual photons that comprise the field are absorbed by the fluctuating electron-positron pair, and when enough momentum and energy have been absorbed for the pair to become real (that is, to leave their virtual state), they do so, and with energy E(p) > p. If one assumes that the vacuum contains virtual, charged-tachyon modes - and there are two distinct reasons for such an assumption - then the natural question arises as to whether real, charged tachyons could be produced in the Schwinger manner by a sufficiently intense AeJct(x). If so, the analysis would be quite similar, except that p > E(p), with far-reaching astrophysical consequences leading to at least a partial explanation of dark matter, and of gamma-ray bursts and ultra-high-energy cosmic rays coming from galactic distances. Even though we never experience charged tachyons in our v < c world, there are two reasons for raising the question. The first is associated with the well-known Weinberg/Salam electroweak vacuum, in which a tachyonic Lagrangian - one with a negative mass-squared and a self-interacti on term - is used to define the brokensymmetry, true ground of that system. The relevant observation to be made here is that, if those tachyons are electrically charged, and if there exists in some local region an extremely strong electric field, then fluctuations about that ground state could in principle occur, and could in principle produce T and T pairs. The second reason is the prediction of possible electromagnetic external fields produced at extremely short distances by a form of QED bootstrap fluctuations,[6] with the ability to reproduce our observationally-accelerating Universe, [7] while

Prompt quark production by exploding sphalerons

Following recent works on the production and subsequent explosive decay of QCD sphaleronlike clusters, we discuss the mechanism of quark pair production in this process. We first show how the gauge field explosive solution of Luscher and Schechter can be achieved by noncentral conformal mapping from the O(4)-symmetric solution. Our main result is a new solution to the Dirac equation in real time in this configuration, obtained by the same inversion of the fermion O(4) zero mode. It explicitly shows how the quark acceleration occurs, starting from the spherically O(3)-symmetric zero energy chiral quark state to the final spectrum of nonzero energies. The sphaleronlike clusters with any Chern-Simons number always produce ${N}_{F}\mathbf{L}\ifmmode\bar\else\textasciimacron\fi{}\mathbf{R}$ quarks, and the antisphaleron-like clusters the opposite chirality. The result are relevant for hadron-hadron and nucleus-nucleus collisions at large $\sqrt{s},$ wherein such clusters can be produced.

On the Formation of Inner Vacuum Gaps in Radio Pulsars

The problem of formation of the Ruderman-Sutherland type inner vacuum gap in neutron stars with ${\bf\Omega}\cdot{\bf B} 1$ (where $T_i$ is the critical temperature above which $^{56}_{26}$Fe ions will not be bound at the surface and $T_s$ is the actual temperature of the polar cap surface heated by the back-flow of relativistic electrons) that the inner vacuum gap can form, provided that the actual surface magnetic field is extremaly strong ($B_s\gtrsim 10^{13}$ G) and curved (${\cal R}<10^6$ cm), irrespective of the value of dipolar component measured from the pulsar spin down rate. Calculations are carried out for pulsars with drifting subpulses and/or periodic intensity modulations, in which the existence of the quasi steady vacuum gap discharging via ${\bf E}\times{\bf B}$ drifting sparks is almost unavoidable. Using different pair-production mechanisms and different estimates of the cohesive energies of surface iron ions, we show that it is easier to form the vacuum gap controlled by the resonant inverse Compton scaterring seed photons than by the curvature radiation seed photons.

Schwinger mechanism of electron-positron pair production by the field of optical and X-ray lasers in vacuum

The probability W of e + e −-pair production in vacuum by an intense time-varying electric field created by optical or X-ray laser is calculated. Two characteristic regions γ≪1 and γ≫1 of adiabaticity parameter γ are considered. With an increase in γ and on passing from monochromatic radiation to a finite laser pulse, the probability W increases sharply (for the same field intensity). The dependence of the probability W and the electron and positron momentum spectrum on the pulse shape is discussed (the dynamic Schwinger effect).

Pair production from vacuum at the focus of an X-ray free electron laser

There are definite plans for the construction of X-ray free electron lasers (FEL), both at DESY, where the so-called XFEL is part of the design of the electron-positron linear collider TESLA, as well as at SLAC, where the so-called Linac Coherent Light Source (LCLS) has been proposed. Such an X-ray laser would allow for high-field science applications: One could make use of not only the high energy and transverse coherence of the X-ray beam, but also of the possibility of focusing it to a spot with a small radius, hopefully in the range of the laser wavelength. Along this route one obtains very large electric fields, much larger than those obtainable with any optical laser of the same power. In this letter we discuss the possibility of obtaining an electric field so high that electron-positron pairs are spontaneously produced in vacuum (Schwinger pair production). We find that if X-ray optics can be improved to approach the diffraction limit of focusing, and if the power of the planned X-ray FELs can be increased to the terawatt region, then there is ample room for an investigation of the Schwinger pair production mechanism.

QED radiative corrections to impact factors

We consider radiative corrections to the electron and photon impact factors. The generalized eikonal representation for the e + e − scattering amplitude at high energies and fixed momentum transfers is violated by nonplanar diagrams. An additional contribution to the two-loop approximation appears from the Bethe-Heitler mechanism of fermion pair production with the identity of the fermions in the final state taken into account. The violation of the generalized eikonal representation is also related to the charge parity conservation in QED. A one-loop correction to the photon impact factor for small virtualities of the exchanged photon is obtained using the known results for the cross section of the e + e − production during photon-nuclei interactions.

Quantum Charged Fields in (1+1) Rindler Space

We study, using Rindler coordinates, the quantization of a charged scalar field interacting with a constant (Poincaré invariant), external, electric field in (1+1) dimensionnal flatspace: our main motivation is pedagogy. We illustrate in this framework the equivalence between various approaches to field quantization commonly used in the framework of curved backgrounds. First we establish the expression of the Schwinger vacuum decay rate, using the operator formalism. Then we rederive it in the framework of the Feynman path integral method. Our analysis reinforces the conjecture which identifies the zero winding sector of the Minkowski propagator with the Rindler propagator. Moreover, we compute the expression of the Unruh's modes that allow us to make a connection between the Minkowskian and Rindlerian quantization schemes by purely algebraic relations. We use these modes to study the physics of a charged two level detector moving in an electric field whose transitions are due to the exchange of charged quanta. In the limit where the Schwinger pair production mechanism of the exchanged quanta becomes negligible we recover the Boltzman equilibrium ratio for the population of the levels of the detector. Finally we explicitly show how the detector can be taken as the large mass and charge limit of an interacting fields system.

ON THE QUANTIZATION OF CHARGED BLACK HOLES

The Wheeler–DeWitt equation for the wave function Ψ of the Schwarzschild black hole has been derived by Tomimatsu in the form of a Schrödinger equation, valid on the apparent horizon, using the two-dimensional Hamiltonian formalism of Hajicek and the radiating Vaidya metric. Here, the analysis is generalized to the Reissner–Nordström black hole. At constant charge Q, the evaporation rate is calculated from the solution for Ψ to be [Formula: see text], where k is a constant and [Formula: see text] are the radii of the outer event horizon and inner Cauchy horizon. In the extremal limit M → Q, however, the Hawking temperature [Formula: see text] tends to zero, suggesting, when the back reaction is taken into account, that the evaporation cannot occur this way and in agreement with the known discharging process of the hole via the Schwinger electron–positron pair-production mechanism. The more general charged dilaton black holes obtained from the theory L4 = [R4 - 2 (∇ Φ)2 - e-2aΦF2 ]/16π are also discussed, and it is explained why this quantization procedure cannot be applied when a is non-zero.

Defect-antidefect pair production via field oscillations

We show that the mechanism of vortex-antivortex pair production via field oscillations, earlier proposed by two of us for systems with first order transitions in presence of explicit symmetry breaking, is in fact very generally applicable. We further argue that this mechanism applies to all sorts of topological defects (e.g. strings, monopoles, textures) and for second order transitions as well. We also show this explicitly by numerically simulating production of vortex-antivortex pairs by decay of bubble walls for a U(1) global theory in the absence of any explicit symmetry breaking.

Charge transfer from the negative-energy continuum: Alternative mechanism for pair production in relativistic atomic collisions.

As an alternative mechanism for bound-free electron-positron pair production, the transfer of a negative-energy electron in the Coulomb field of one of the collision partners to a bound state of the other is considered, supplementing the usually adopted view that an electron is excited from a negative-energy state to a bound state of the same atom. Under simplifying assumptions, analytic expressions for the differential and total cross sections can be derived, which explicitly exhibit the dependencies on the nuclear charges and show a surprisingly strong increase with the collision energy.

Single leptoquark production at e+e- and gamma gamma colliders.

We consider single production of leptoquarks (LQ's) at ${e}^{+}{e}^{\ensuremath{-}}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ colliders, for two values of the center-of-mass energy: $\sqrt{s}=500$ GeV and 1 TeV. We find that LQ's which couple within the first generation are observable for LQ masses almost up to the kinematic limit, both at ${e}^{+}{e}^{\ensuremath{-}}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ colliders, for an LQ coupling strength equal to ${\ensuremath{\alpha}}_{\mathrm{em}}$. The cross sections for single production of second- and third-generation LQ's at ${e}^{+}{e}^{\ensuremath{-}}$ colliders are too small to be observable. In $\ensuremath{\gamma}\ensuremath{\gamma}$ collisions, on the other hand, second-generation LQ's with masses much larger than $\frac{\sqrt{s}}{2}$ can be detected. However, third-generation LQ's can be seen at $\ensuremath{\gamma}\ensuremath{\gamma}$ colliders only for masses at most $\ensuremath{\sim}\frac{\sqrt{s}}{2}$, making their observation more probable via the pair production mechanism.

Gamma - gamma Attenuation and Relativisitic Beaming in Gamma-Ray Bursts

view Abstract Citations (37) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gamma - gamma Attenuation and Relativisitic Beaming in Gamma-Ray Bursts Baring, Matthew G. Abstract The observation by the BATSE experiment on board the Compton Gamma-Ray Observatory (CGRO) that the gamma-ray burst population is isotropic but inhomogeneous has dramatically bolstered the premise that most bursts are cosmological. At the same time, BATSE has also observed definite spectral breaks (Schaefer et al (1992) between 400 keV and 2 MeV in some bursts, which in three cases have been corroborated by data from EGRET. The presence of these breaks in these sources suggests attenuation by the pair production mechanism γγ → e+e-, which can absorb gamma rays, though it is suppressed when the radiation is highly beamed. In this paper, quantitative constraints that pair production places on radiation collimation in individual sources, due to the presence or absence of breaks in spectra, are presented. Cosmological bursts have extremely relativistic beaming, though the bulk Lorentz factors of their emission regions are reduced markedly for steep source spectra. Such beaming will blueshift the breaks to higher energies, indicating that those CGRO bursts displaying MeV spectral breaks may not be cosmological, or perhaps that their breaks are generated by mechanisms that dominate γ-γ attenuation at MeV energies. Alternative mechanisms for break production are discussed. Publication: The Astrophysical Journal Pub Date: November 1993 DOI: 10.1086/173398 Bibcode: 1993ApJ...418..391B Keywords: GAMMA RAYS: BURSTS; RADIATION MECHANISMS: MISCELLANEOUS; RELATIVITY full text sources ADS | data products SIMBAD (3)

Numerical method for the time evolution of the Dirac equation

We propose an iterative procedure for the numerical evolution of Dirac equation. It is a fast and stable version of the coordinate-space predictor-corrector method and can be extended to (3+1) dimensions for the relativistic mean-field calculation of heavy-ion collisions. A detailed example is worked out for the case of the Bottcher-Strayer pair production mechanism in (1+1) dimensions.

Anomalous electron-pair production in π−p collisions

Anomalous e+e− pairs with invariant mass 0.2 ⩽ M ⩽ 0.7 GeV / c2 have been observed in the collision of pions with protons at a momentum pπ⋍16 GeV/c. Conventional hadronic mechanisms have been unable to reproduce the qualitative features of the observed spectra. The two-photon mechanism for pair production is evaluated in a semi-classical limit. The resulting differential cross sections as a function of the invariant mass, Feynman x, and transverse momentum of the pair are in reasonable quantitative agreement with the data. The dominant contribution to the pair amplitude arises from the magnetic spin-flip term of the proton current. These anomalous lepton pairs are thus consistent with an ab initio calculation of the two-photon mechanism.

Avoided level crossings and pair production in strong Coulomb fields

Generalising previous work on static strong Coulomb fields to the time-dependent case, we propose an alternative e+e--pair production mechanism relying on avoided crossing transitions between positive and negative energy states. The resulting essential independence on the details of the collision process nicely matches experimental findings.

Role of longitudinally polarized W 's in slepton production and decay.

We demonstrate that WW fusion is possibly an important mechanism for slepton pair production if the slepton mass is larger than approx.300 GeV. In addition, we note that for a large range of M/sub l-italic-tilde/ the mass splitting between the l-italic-tilde and its SU(2)-doublet nu-tilde partner can be larger than m/sub W/ without violating limits on ..delta..rho, and that in this case the l-italic-tilde decay can easily be dominated by the two-body mode, l-italic-tilde..-->..Wnu-tilde. In both situations it is the longitudinal W polarizations that dominate. Finally, we remark on the possible importance of similar mechanisms in charged-Higgs-boson production and decay, and in squark production and decay