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Precision measurements by AMS of the fluxes of cosmic ray positrons, electrons, antiprotons, protons as well as their rations reveal several unexpected and intriguing features. The presented measurements extend the energy range of the previous observations with much increased precision. The new results show that the behavior of positron flux at around 300 GeV is consistent with a new source that produce equal amount of high energy electrons and positrons. In addition, in the absolute rigidity range 60–500 GV, the antiproton, proton, and positron fluxes are found to have nearly identical rigidity dependence and the electron flux exhibits different rigidity dependence. [ABSTRACT FROM AUTHOR]

The PADME experiment, starting data taking this year at Laboratori Nazionali di Frascati, INFN, Italy will search for the e+e → γA′ process in a positron-on-target experiment, assuming a decay of the A′ into invisible particles of the hidden sector. 550 MeV positron beam from the DAΦNE Beam-Test Facility will impinge on a thin diamond target and the recoil photon will be registered by a segmented crystal calorimeter, allowing to reconstruct the missing mass of the event. The suppression of the background due to bremsstrahlung emission from the beam positrons requires high efficient charged particle detectors with optimized geometry and sub ns time resolution. A fine-grained plastic scintillator veto composed of three stations in vacuum is being assembled and will be operational in PADME. Two stations are placed inside a dipole magnet with 0.6 T magnetic field and will also provide momentum measurement at the 5 percent level. The light is taken by WLS fibers to a custom developed SiPM readout system which allows to achieve time resolution of the order of 500 ps. The design of the charged particle vetoes and their initial performance is presented. [ABSTRACT FROM AUTHOR]

High energy positron beams are an important tool for fixed-target experiments searching for new particles produced in the annihilation on atomic electrons of a target. The status of existing or planned infrastructures is reviewed. [ABSTRACT FROM AUTHOR]

The proposed Particle Factory detector at Turkish Accelerator Center (TAC-PF) aims to search for charm physics, CP violation and mixing of D0 mesons as well as new physics effects by investigating head-on collisions of 1 GeV electron from Energy Recovery Linac (ERL) with 3.56 GeV positrons from synchrotron storage ring. In this work, we constructed the TAC-PF detector design by using a recently developed framework namely Detector Description for High Energy Physics (DD4hep). The baseline TAC-PF detector design and its qualifications were summarized, followed by a general description. [ABSTRACT FROM AUTHOR]

The fast ignition is a new scheme in laser fusion, in which higher energy gain is expected with smaller laser pulse energy. The cone target has been introduced for realizing higher coupling efficiency. At ILE, Osaka University, the laser with 4 beams and the total output of 10kJ/ps: LFEX has been built and we have started the integrated experiments. The experiments showed that the coupling efficiency is degraded because of the laser pre-pulse. Namely, the main pulse is absorbed in a long scale pre-plasma produced by the pre-pulse and hot electron energy is higher than that for a clean pulse. Furthermore, the distance between the hot electron source and the core plasma is long. So, we are exploring how to overcome the pre-pulse effects on the cone target. The next series of experiments is planned for this fall. In these experiments, the LFEX pre-pulse level will be reduced and advanced targets for mitigating the pre-pulse effects will be introduced. In this paper, it is proposed that a thin foil cover the laser entrance of a cone to mitigate the pre-plasma and a double cone reduce loss of high energy electrons from the side wall of the cone. The simulations indicate that higher coupling efficiency is expected for the double cone target with a thin foil on the laser entrance. Namely, the pre-pulse will be absorbed by the foil and the electro-magnetic fields generated on the surface of the inner cone will confine high energy electrons. The goal of the next series of experiments will be high coupling efficiency to heat a compressed plasma to temperatures higher than 2 keV. [ABSTRACT FROM AUTHOR]

Gravitino dark matter, together with thermal leptogenesis, implies an upper bound on the masses of superparticles. In the case of broken R-parity the constraints from primordial nucleosynthesis are naturally satisfied and decaying gravitinos lead to characteristic signatures in high energy cosmic rays. Electron and positron fluxes from gravitino decays cannot explain both, the PAMELA positron fraction and the electron+positron flux recently measured by Fermi LAT. The observed fluxes require astrophysical sources. The measured antiproton flux allows for a sizable contribution of decaying gravitinos to the gamma-ray spectrum, in particular a line at an energy below 300 GeV. [ABSTRACT FROM AUTHOR]

Kaluza-Klein dark matter is an attractive weakly interacting massive particle in universal extra dimension model. In the recent extension “split-UED”, annihilation of Kaluza-Klein dark matter with a mass range 600–1000 GeV provides excellent fits to the recently observed excesses in cosmic electron and positron fluxes of Pamela, ATIC and Fermi-LAT experiments. The cosmic gamma-ray flux in the same process can be significant around 300 GeV, thus can be observed or constrained by the forthcoming Fermi-LAT diffuse gamma-ray data. The collider signal at the LHC is the resonance in the dijets channels and the large missing energy in the missing energy plus jets. [ABSTRACT FROM AUTHOR]

The future Electron-Ion Collider (EIC) is a proposed new facility to collide high-energy electrons with beams of polarized protons/light nuclei and unpolarized nuclei. We overview the goals of the project and key measurements at the EIC. We also briefly comment on recent developments of the project. [ABSTRACT FROM AUTHOR]

The beam charge asymmetry helps to isolate the real part of the deeply virtual Compton scattering (DVCS) amplitude. It is discussed what information can be gained both from the real and imaginary part of the DVCS amplitude. [ABSTRACT FROM AUTHOR]

We review the compelling case for establishing a capability to accelerate positrons at Jefferson Lab. The potential applications range from the study of two-photon exchange and deeply-virtual Compton scattering to exploiting the charged current weak interaction to probe the flavor structure of hadrons and nuclei. There are also fascinating ideas for using such a capability to discover new physics beyond the Standard Model of nuclear and particle physics. [ABSTRACT FROM AUTHOR]

A Free-Electron Laser (FEL) places many exacting demands on a Negative Electron Affinity (NEA) photocathode, such as the need for an ultra-fast response time, low energy spread for emitted electrons, high quantum efficiency (Q.E.) and a high average photocurrent. However, these key requirements are conflicting, and cannot be fulfilled by conventional photocathode design. For example, to achieve ∼10 ps response time, the photocathode active layer should be thinned to ∼100–150 nm, but this thickness is insufficient to provide near-complete absorption of light with hv≈[variant_greek_epsilon]g so high Q.E. cannot be achieved. Complete optical absorption and high Q.E. can be obtained using a thin active layer at higher photon energies, but this generates photoelectrons with excess kinetic energy within the semiconductor. These photoelectrons do not thermalise in a thin active layer, so yield a broad energy distribution in the emitted electrons. Moreover, cooling of the conventional semiconductor photocathode structure is ineffective due to its fragility, so it cannot be pressed firmly to a heat sink to attain good thermal contact. Consequently, the maximum CW photocurrent is limited to a few miiliamps. The goal of our work is to develop a new design of NEA-photocathode which is optimised for FEL applications. [ABSTRACT FROM AUTHOR]

An experiment is under way to prove the feasibility of a super-conducting RF gun for the production of polarized electrons. We report on the progress of the experiment and on simulations predicting the possibility of success. [ABSTRACT FROM AUTHOR]

A novel concept for producing polarized positrons at Jefferson Lab using the CEBAF polarized electron photo-injector is presented. This approach relies on the polarization transfer from low energy highly polarized electrons to positrons via bremsstrahlung followed by pair production in a conversion target. An experiment to test this concept is discussed on the basis of GEANT4 simulations. It is shown that this low energy approach, which benefits from recent advances in high current high polarization electron sources, can yield positron longitudinal polarization up to 40%. [ABSTRACT FROM AUTHOR]

The capabilities of the personal computers allow the application of Monte Carlo methods to simulate very complex problems that involve the transport of particles through matter. Among the several codes commonly employed in nuclear physics problems, the GEANT4 has received great attention in the last years, mainly due to its flexibility and possibility to be improved by the users. Differently from other Monte Carlo codes, GEANT4 is a toolkit written in object oriented language (C++) that includes the mathematical engine of several physical processes, which are suitable to be employed in the transport of practically all types of particles and heavy ions. GEANT4 has also several tools to define materials, geometry, sources of radiation, beams of particles, electromagnetic fields, and graphical visualization of the experimental setup. After a brief description of the GEANT4 toolkit, this presentation reports investigations carried out by our group that involve simulations in the areas of dosimetry, nuclear instrumentation and medical physics. The physical processes available for photons, electrons, positrons and heavy ions were used in these simulations. [ABSTRACT FROM AUTHOR]

We have recently proposed a new concept for generating, injecting and accelerating positrons in a plasma using a double-pulse electron bunch. Monte Carlo simulations show that the number of the positrons produced in a foil target has an exponentially decay energy spectrum. The energy threshold for the trapping of these positrons in a ultra-relativistic electron wake is investigated numerically. For a typical 28.5 GeV electron drive bunch, the trapping threshold for the positrons is a few MeV, and therefore a majority of positrons generated in the foil target are focused and accelerated by the plasma wake. [ABSTRACT FROM AUTHOR]

Gamma- (γ-) ray beams of high average power and peak brightness are of demand for a number of applications in high-energy physics, material processing, medicine, etc. One of such examples is gamma conversion into polarized positrons and muons that is under consideration for projected lepton colliders. A γ-source based on the Compton backscattering from the relativistic electron beam is a promising candidate for this application. Our approach to the high-repetition γ-source assumes placing the Compton interaction point inside a CO2 laser cavity. A laser pulse interacts with periodical electron bunches on each round-trip inside the laser cavity producing the corresponding train of γ-pulses. The round-trip optical losses can be compensated by amplification in the active laser medium. The major challenge for this approach is in maintaining stable amplification rate for a picosecond CO2-laser pulse during multiple resonator round-trips without significant deterioration of its temporal and transverse profiles. Addressing this task, we elaborated on a computer code that allows identifying the directions and priorities in the development of such a multi-pass picosecond CO2 laser. Proof-of-principle experiments help to verify the model and show the viability of the concept. In these tests we demonstrated extended trains of picosecond CO2 laser pulses circulating inside the cavity that incorporates the Compton interaction point. [ABSTRACT FROM AUTHOR]

We have developed a hybrid method to treat charged-particle impact ionization of complex atoms and ions. The essential idea is to describe the interaction between a fast projectile and the target perturbatively, up to second order, while the initial bound state and the ejected-electron—residual-ion interaction can be handled via a convergent R-matrix with pseudo-states (close-coupling) expansion. Example results for ionization of the heavy noble gases (Ne—Xe) by positron and electron impact are presented. The general scheme for a distorted-wave treatment of ionization by heavy-particle impact is described. [ABSTRACT FROM AUTHOR]

ATRAP has made many important improvements since CERN's Antiproton Decelerator (AD) was restarted in 2006. These include substantial increases in the number of positrons (e+) and antiprotons (Pbars) used to make antihydrogen (Hbar) atoms, a new technique for loading electrons (e-) that are used to cool Pbars and e+, implementation of a completely new, larger and more robust apparatus in our second experimental zone and the inclusion of a quadrupole Ioffe trap intended to trap the coldest Hbar atoms produced. Using this new apparatus we have produced large numbers of Hbar atoms within a Penning trap that is located within this quadrupole Ioffe trap using a new technique which shows promise for producing even colder atoms. These observed Hbar atoms resolve a debate about whether positrons and antiprotons can be brought together to form atoms within the divergent magnetic fields of a quadrupole Ioffe trap. [ABSTRACT FROM AUTHOR]

Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as ten, achieved by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile, and its relation to that of the electron plasma. We also measure the outer radial profile by ejecting antiprotons to the trap wall using an octupole magnet. [ABSTRACT FROM AUTHOR]

Polarised positrons have a range of applications in modern physics: from surface science measurements requiring energies as low as a few eV, to studies of the proton structure function and of the fundamental interactions of elementary particles at energies approaching the TeV scale. The common challenge for all of these studies is to generate sufficient numbers of positrons. A discussion of this topic is pertinent to these proceedings as it has been suggested that anti-protons can be efficiently polarised through a hyperfine spin-flip interaction with polarised positrons. In this paper I review the current state of high-intensity sources of polarised positrons. Emphasis is placed on those sources being developed to meet the requirements of future e+ e- colliders. [ABSTRACT FROM AUTHOR]

A proof-of-principle experiment has been carried out in the Final Focus Test Beam (FFTB) at SLAC to demonstrate production of polarized positrons in a manner suitable for implementation at the ILC. A helical undulator of 2.54 mm period and 1-m length produced circularly polarized photons of first harmonic endpoint energy of 8 MeV when traversed by a 46.6 GeV electron beam. The polarized photons were converted to polarized positrons in a 0.2-radiation-length tungsten target. The polarization of these positrons was measured at several energies, with a peak value in excess of 80%, by transmission polarimetry of photons obtained on reconversion of the positrons in a second tungsten target. [ABSTRACT FROM AUTHOR]

Hard exclusive production of mesons provides access to the unknown generalized parton distributions (GPDs), which give a unified description of the structure of the nucleon. Exclusive electroproduction of π+ and ρ0 mesons has been measured on an internal hydrogen gas target at HERMES by using the 27.6 GeV polarized electron or positron beam of HERA. The cross section for exclusive π+ production is presented and compared with calculations based on GPD models. For ρ0 production, the azimuthal single spin asymmetry for a transversely polarized target is sensitive to Jq, the quark total angular momentum contribution to the proton spin. Preliminary results are compared to GPD based calculations. In addition, new measurements are reported for the Spin-Density Matrix Elements (SDMEs) for ρ0 production on an unpolarized target. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

At the extreme densities and temperatures typical of the central engine of GRBs, the accreting torus is cooled mainly by advection and by neutrino emission. The latter process is dominated by electron and positron capture onto nucleons (β reactions). We calculate the reaction rates and the nuclear composition of matter, assuming that the torus consists of helium, eletron-positron pairs, free neutrons and protons. After determining the equation of state and solving for the disk structure for a given initial accretion rate, we subsequently follow its time evolution. We find that, for accretion rates of the order of 10M⊙s-1, likely typical for the early stages of the accretion event, the disk becomes unstable, giving rise to variable energy output. This instability may play an important role for producing internal shocks. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Low Particle Toroidal Accumulator (LEPTA) project is under development at JINR. The ring assembling is completed. The test experiments with circulating electron beam are in progress and the results are presented. Assembling and test of the positron injector is started. The program of experiment on directed o-Ps flux generated at LEPTA is listed in the report. The first experiment that is under preparation presently has the goal to measure p-Ps life time by interference of ortho- and para- states of Ps in magnetic field. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Detailed analysis of an extended exponential tail observed in the decay curve of the 2P3/2-2P1/2 magnetic dipole (M1) transition in boron-like Ar13+ provides evidence that electrons and ions might coexist in the same spatial region in the Heidelberg Electron Beam Ion Trap (HD-EBIT). On this basis, new trapping-cooling-recombination schemes for positron-antiproton plasmas are envisioned, integrated in a magnetic bottle configuration that should be able to trap the subsequently formed recombined cold antihydrogen. Moreover, the EBIT configuration, providing excellent spectroscopic access to the trapping region via seven view ports is shown to be well suited for performing precision spectroscopy of antiprotonic ions. Those might be generated either by recombination of antiprotons with neutral gas atoms or through radiative recombination and state-selective dielectronic-recombination-like processes with highly charged ions produced and stored in the EBIT simultaneously in a nested trap configuration. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Data taken with the H1 detector, with longitudinally polarised electrons and positrons in collision with unpolarised protons at HERA, are used to measure the charged current cross section σCCtot for Q2 > 400 GeV2 and inelasticity y < 0.9. The polarisation dependence of the measured cross section is in agreement with the Standard Model predictions. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

A proposed luminosity upgrade to RHIC includes a novel electron cooling section, which would use ∼55 MeV electrons to cool fully-ionized 100 GeV/nucleon gold ions. High-current bunched electron beams are required for the RHIC cooler, resulting in very high transverse temperatures and relatively low values for the magnetized cooling logarithm. The accuracy of analytical formulae in this regime requires careful examination. Simulations of the friction coefficient, using the VORPAL code, for single gold ions passing once through the interaction region, are compared with theoretical calculations. Charged particles are advanced using a fourth-order Hermite predictor-corrector algorithm. The fields in the beam frame are obtained from direct calculation of Coulomb’s law, which is more efficient than multipole-type algorithms for less than ∼106 particles. Because the interaction time is so short, it is necessary to suppress the diffusive aspect of the ion dynamics through the careful use of positrons in the simulations. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Inclusive neutral and charged current cross sections and structure functions measured at HERA-I are briefly reviewed. The impact of these measurements on parton density functions is discussed. The emphasis is put on the high x region. A first result obtained using the HERA-II data is also shown followed by future prospects for HERA. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The transverse polarization components of the positrons from the decay of polarized muons have been measured at the Paul Scherrer Institute by annihilating in flight the decay positrons with polarized electrons. The use of a stroboscopic method greatly reduces systematic errors. The energy dependence of the transverse polarization component PT1, which lies in the plane spanned by muon spin and positron momentum, yields the low energy parameter η and thus an improved model-independent value of the Fermi coupling constant. A non-zero value of the transverse component PT2, which is perpendicular to the plane mentioned above, would be the first observation of time reversal violation in a purely leptonic decay. Part of the data (40 × 108 annihilation events) have been evaluated. Both PT1 and PT2, averaged over the positrons’ energy, are consistent with zero with a precision improved by a factor of three as compared with the previous measurement. The preliminary results are = (7 ± 8) × 10-3, = (-1 ± 8) × 10-3 in full agreement with the standard model. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The HERMES experiment studies the spin structure of the nucleon using the 27.6 GeV longitudinally polarized positron beam of HERA and internal targets of pure gases. Recently, HERMES has published measurements of azimuthal single-spin asymmetries in the hard electroproduction of photons on an unpolarized hydrogen target arising from the interference of the amplitudes of the Bethe-Heitler (BH) and the Deeply Virtual Compton Scattering (DVCS) processes. The measurements constitute an effort towards accessing generalized parton distributions, and open a new approach to study the spin structure of the nucleon. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]