High-energy Electron-positron Research Articles

Resonant annihilation and production of high-energy electron-positron pairs in an external electromagnetic field

A resonant process of annihilation and production of high-energy electron-positron pairs in an external electromagnetic field is studied theoretically. This process is the annihilation channel of an electron-positron scattering. It is shown that the resonance in an external electromagnetic field is possible only when the certain combination of electron and positron initial energies is more than threshold energy. Also, the angle between initial electron and initial positron momenta directions must be small and satisfy the resonant conditions. This angle is determined by the high-energy of the initial pair and the threshold energy. An emerging electron-positron pair also flies out in a narrow cone along the direction of the initial pair and must be ultrarelativistic. For each fixed angle, energies of the final electron and positron can take from one to two values. It is shown that the resonant differential cross section can significantly exceed the corresponding Bhabha cross section without an external field.

Resonant photoproduction of high-energy electron-positron pairs in the field of a nucleus and a weak electromagnetic wave

The resonant photoproduction of ultrarelativistic electron-positron pairs (PPP) in a nuclear field and a weak laser field is theoretically studied. Under resonance conditions, the intermediate virtual electron (positron) in the laser field becomes a real particle. As a result, the initial process of the second order in the fine structure constant in the laser field effectively reduces into two successive processes of the first order: single-photon production of electron-positron pair in a laser field (laser-stimulated Breit-Wheeler process) and laser-assisted process of electron (positron) scattering on a nucleus. Resonant kinematics of PPP is studied in details. It is shown that for the considered laser intensities resonance is possible only for the initial photon energies greater than the characteristic threshold energy. At the same time, the ultrarelativistic electron and positron propagate in a narrow cone along the direction of the initial photon momentum. The resonant energy of the positron (electron) can has two values for each radiation angle which varies from zero to some maximum value determined by the energy of the initial photon and the threshold energy. Resonant differential cross section of the studied process was obtained. It is shown that the resonant differential cross section of the PPP can significantly exceed the corresponding cross section of the PPP without an external field. The project calculations may be experimentally verified by the scientific facilities of pulsed laser radiation (SLAC, FAIR, XFEL, ELI, XCELS)

Future Prospects of Gamma–Gamma Collider

Gamma–gamma colliders based on backward Compton scattering have been discussed mainly as an option for high energy electron–positron linear colliders, aiming to play a complementary role in energy frontier physics. The flexibility of gamma-ray beam by the Compton scheme, however, allows us to apply them to physics in a wide energy range, from MeV to TeV. In this paper, we review the future prospects of gamma–gamma colliders including recent discussions about Higgs boson factories and mid- and low-energy colliders as well as the option for electron–positron linear colliders.

Model-independent sensibility studies for the anomalous dipole moments of theντat the CLIC basede+e−andγe−colliders

To improve the theoretical prediction of the anomalous dipole moments of the $\tau$-neutrino, we have carried out a study through the process $\gamma e^- \to \tau \bar\nu_\tau \nu_e$, which represents an excellent and useful option in determination of these anomalous parameters. To study the potential of the process $\gamma e^- \to \tau \bar\nu_\tau \nu_e$, we apply a future high-energy and high-luminosity linear electron-positron collider, such as the CLIC, with $\sqrt{s}=380, 1500, 3000\hspace{0.8mm}GeV$ and ${\cal L}=10, 50, 100, 200, 500, 1000, 1500, 2000, 3000\hspace{0.8mm}fb^{-1}$, and we consider systematic uncertainties of $\delta_{sys}=0, 5, 10\%$. With these elements, we present a comprehensive and detailed sensitivity study on the total cross-section of the process $\gamma e^- \to \tau \bar\nu_\tau \nu_e$, as well as on the dipole moments $\mu_{\nu_\tau}$ and $d_{\nu_\tau}$ at the $95\%$ C.L., showing the feasibility of such process at the CLIC at the $\gamma e^-$ mode with unpolarized and polarized electron beams.

Hadronic vs. electromagnetic pulse shape discrimination in CsI(Tl) for high energy physics experiments

Pulse shape discrimination using CsI(Tl) scintillators to perform neutral hadron particle identification is explored with emphasis towards application at high energy electron-positron collider experiments. Through the analysis of the pulse shape differences between scintillation pulses from photon and hadronic energy deposits using neutron and proton data collected at TRIUMF, it is shown that the pulse shape variations observed for hadrons can be modelled using a third scintillation component for CsI(Tl), in addition to the standard fast and slow components. Techniques for computing the hadronic pulse amplitudes and shape variations are developed and it is shown that the intensity of the additional scintillation component can be computed from the ionization energy loss of the interacting particles. These pulse modelling and simulation methods are integrated with GEANT4 simulation libraries and the predicted pulse shape for CsI(Tl) crystals in a 5 × 5 array of 5 × 5 × 30 cm3 crystals is studied for hadronic showers from 0.5 and 1 GeV/c KL0 and neutron particles. Using a crystal level and cluster level approach for photon vs. hadron cluster separation we demonstrate proof-of-concept for neutral hadron detection using CsI(Tl) pulse shape discrimination in high energy electron-positron collider experiments.

Direct searches of Type-III seesaw triplet fermions at high energy e^+e^- collider

The signatures of heavy fermionic isotriplets (Sigma ) are probed through their direct production and subsequent decay at high energy electron–positron colliders. Unlike the case of LHC, the production process has strong dependence on the mixing of Sigma with electron (V_{e}), making the leptonic collider unique to fingerprint the presence of such mixing. We establish that pair production considered at sqrt{s}=2 TeV can be employed to study both the cases of V_e=0 and of V_ene 0 with sim 100 fb^{-1} luminosity, while the single production can probe the latter case with a few inverse femto barn luminosity at sqrt{s}=1 TeV. Exploring the mass reach, both the single and pair productions are capable of probing Sigma of mass close to the kinematic limits through selected channels. Investigating simultaneous limits on the M_Sigma -V_e parameter space, we identify suitable final states and their 3sigma reach on V_e and M_Sigma at 300 (100) fb^{-1} luminosity in the case of pair (single) Sigma production.

Design and standalone characterisation of a capacitively coupled HV-CMOS sensor chip for the CLIC vertex detector

The concept of capacitive coupling between sensors and readout chips is under study for the vertex detector at the proposed high-energy CLIC electron positron collider. The CLICpix Capacitively Coupled Pixel Detector (C3PD) is an active High-Voltage CMOS sensor, designed to be capacitively coupled to the CLICpix2 readout chip. The chip is implemented in a commercial 180 nm HV-CMOS process and contains a matrix of 128×128 square pixels with 25μm pitch. First prototypes have been produced with a standard resistivity of ∼20 Ωcm for the substrate and tested in standalone mode. The results show a rise time of ∼20 ns, charge gain of 190 mV/ke− and ∼40 e− RMS noise for a power consumption of 4.8μW/pixel. The main design aspects, as well as standalone measurement results, are presented.

Bounds on the Electromagnetic Dipole Moments through the Single Top Production at the CLIC

We obtain bounds on the anomalous magnetic and electric dipole moments of thet-quark from a future high-energy and high-luminosity linear electron positron collider, as the CLIC, with polarized and unpolarized electron beams which are powerful tools for determining new physics. We consider the processesγe-→t¯bνe(γis the Compton backscattering photon) ande+e-→e-γ⁎e+→t¯bνee+(γ⁎is the Weizsacker-Williams photon) as they are one of the most important sources of single top quark production. For systematic uncertainties ofδsys=0% (5%),b-tagging efficiency=0.8, center-of-mass energy ofs=3 TeV, and integrated luminosity ofL=2ab-1the futuree+e-collider may put bounds on the electromagnetic dipole momentsa^Vanda^Aof the top quark of the order ofO(10-2–10-1)at the2σ (3σ)level, which are competitive with those recently reported in previous studies at hadron colliders and the ILC.

Sneutrino identification in tau pair production at ILC with polarized beams

Many scenarios of new physics can lead to deviations of the observables (cross sections, asymmetries) from the Standard Model predictions in e+e- collision. The possibility of uniquely identifying the indirect effects of s-channel sneutrino exchange, as predicted by supersymmetric theories with R-parity violation, against other new physics scenarios in high-energy electron-positron annihilation into tau pairs at the International Linear Collider has been studied.

Study of single top production at high energy electron positron colliders

The effect of single top production on the study of top quark pair production in future high energy electron–positron colliders is evaluated. The rate of the single top quark production process is sizeable throughout a large range of center-of-mass energies and the final state cannot easily be distinguished from the dominant pair production process. We discuss the impact on the top quark mass extraction from a scan through the pair production threshold and the determination of top quark form factors in the continuum. These results advocate for the exploration of the inclusive $$e^+e^-\rightarrow W^+bW^-\bar{b}$$ process, that includes both top quark pair and single top quark production.

能量前沿正负电子对撞机的研究进展

In 2012, the discovery of a particle matching the Higgs boson at CERNs Large Hadron Collider became a very important milestone in high energy physics history. Research and development towards future high-energy electron-positron colliders is actively explored around the world with the purpose of measuring precisely the properties of this unconfirmed Higgs boson and to discover new physics beyond the Standard Model of particle physics. In this paper, we briefly review the history from the past half century of electron-positron colliders at the high-energy frontier, including the first electron-positron collider AdA, as well as the colliders based AdA, such as ACO, VEPP-II, ADONE, and the later colliders SPEAR, DORIS, CESR, TRISTAN etc., and the last and largest electron-positron collider in the world up to now, LEP. Then, the paper reports several proposals for future electron-positron colliders from around the world such as ILC, CLIC TLEP and so on, in particular Chinas entry, the Circular Electron-Positron Collider.

The influence of non-parallelism of electron and positron velocities upon high-energy e+e− pair ionization loss in thin plate

The problem of high-energy electron–positron pair ionization loss in thin plate is considered. It is shown that in this case the approximation of parallel electron and positron velocities which is usually used for calculation of pair ionization loss may not be strictly valid and the existence of non-zero angle of pair divergence can lead to slight suppression of the Chudakov effect of pair ionization loss reduction. The conditions under which such suppression has noticeable value are discussed.

Z′Resonance and AssociatedZhProduction at Future Higgs Boson Factory: ILC and CLIC

We study the prospects of theB-Lmodel with an additionalZ′boson to be a Higgs boson factory at high-energy and high-luminosity linear electron positron colliders, such as the ILC and CLIC, through the Higgs-strahlung processe+e-→(Z,Z′)→Zh, including both the resonant and the nonresonant effects. We evaluate the total cross section ofZhand we calculate the total number of events for integrated luminosities of 500–2000 fb−1and center of mass energies between 500 and 3000 GeV. We find that the total number of expectedZhevents can reach 106, which is a very optimistic scenario and it would be possible to perform precision measurements for bothZ′and Higgs boson in future high-energye+e-colliders experiments.

CLICdp Overview. Overview of physics potential at CLIC

CLICdp, the CLIC detector and physics study, is an international collaboration presently composed of 23 institutions. The collaboration is addressing detector and physics issues for the future Compact Linear Collider (CLIC), a high-energy electron-positron accelerator which is one of the options for the next collider to be built at CERN. Precision physics under challenging beam and background conditions is the key theme for the CLIC detector studies. This leads to a number of cutting-edge R&D activities within CLICdp. The talk includes a brief introduction to CLIC, accelerator and detectors, hardware R&D as well as physics studies at CLIC.

CLICdp Overview. Overview of physics potential at CLIC

CLICdp, the CLIC detector and physics study, is an international collaboration presently composed of 23 institutions. The collaboration is addressing detector and physics issues for the future Compact Linear Collider (CLIC), a high-energy electron-positron accelerator which is one of the options for the next collider to be built at CERN. Precision physics under challenging beam and background conditions is the key theme for the CLIC detector studies. This leads to a number of cutting-edge R&D activities within CLICdp. The talk includes a brief introduction to CLIC, accelerator and detectors, hardware R&D as well as physics studies at CLIC.

Laser-driven generation of high-quality ultra-relativistic positron beams

An ultra-relativistic electron beam propagating through a high-Z solid triggers an electromagnetic cascade, whereby a large number of high-energy photons and electron–positron pairs are produced mainly via the bremsstrahlung and Bethe–Heitler processes, respectively. These mechanisms are routinely used to generate positron beams in conventional accelerators such as the electron–positron collider (LEP). Here we show that the application of similar physical mechanisms to a laser-driven electron source allows for the generation of high-quality positron beams in a much more compact and cheaper configuration. We anticipate that the application of these results to the next generation of lasers might open the pathway for the realization of an all-optical high-energy electron–positron collider.

The ZFITTER project

The ZFITTER project is aimed at the computation of high-precision theoretical predictions for various observables in high-energy electron-positron annihilation and other processes. The stages of the project development are described. Accent is made on applications to the analysis of LEP data. The present status of the project and perspectives are given as well.

Fundamental physics from the sky: Cosmic rays, gamma rays and the hunt for dark matter

Can we learn about New Physics with astronomical and astro–particle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental nature of dark matter. I will discuss some of the recent puzzling findings in cosmic–ray electron–positron data and in gamma–ray observations that might be related to dark matter. I will argue that recent cosmic–ray data, most notably from the Pamela and Fermi satellites, indicate that previously unaccounted–for powerful sources in the Galaxy inject high–energy electrons and positrons. Interestingly, this new source class might be related to new fundamental particle physics, and specifically to pair–annihilation or decay of galactic dark matter. This exciting scenario is directly constrained by Fermi gamma–ray observations, which also inform us on astrophysical source counterparts that could also be responsible for the high–energy electron–positron excess. Observations of gamma–ray emission from the central regions of the Galaxy as well as claims on a gamma–ray line at around 130 GeV also recently triggered a wide–spread interest: I will address the question of whether we are really observing signals from dark matter annihilation, how to test this hypothesis, and which astrophysical mechanisms constitute the relevant background.

Strong Higgs interactions at a linear collider

We study the impact of Higgs precision measurements at a high-energy and high-luminosity linear electron positron collider, such as CLIC or the ILC, on the parameter space of a strongly interacting Higgs boson. Some combination of anomalous couplings are already tightly constrained by current fits to electroweak observables. However, even small deviations in the cross sections of single and double Higgs production, or the mere detection of a triple Higgs final state, can help establish whether it is a composite state and whether or not it emerges as a pseudo-Nambu-Goldstone boson from an underlying broken symmetry. We obtain an estimate of the ILC and CLIC sensitivities on the anomalous Higgs couplings from a study of WW scattering and hh production which can be translated into a sensitivity on the compositeness scale 4\pi f, or equivalently on the degree of compositeness \xi=v^2/f^2. We summarize the current experimental constraints, from electroweak data and direct resonance searches, and the expected reach of the LHC and CLIC on \xi and on the scale of the new resonances.

Sensitivity on the Dipole Moments of theτ-Neutrino ate+e-Colliders: ILC and CLIC

We study the sensitivity on the anomalous magnetic and electric dipole moments of theτ-neutrino at a high-energy and high-luminosity linear electron positron collider, such as the ILC or CLIC, through the reactione+e-→νν̅γ. We obtain limits on the dipole moments at the future linear colliders energies. For integrated luminosities of 500 fb−1and center of mass energies between 0.5 and 3 TeV, the futuree+e-colliders may improve the existing limits by two or three orders of magnitude.