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43 PARTICLE ACCELERATORS↗
Engineering topics
Sakai, Y.
Publications and source records attributed to Sakai, Y..
An ultra-compact x-ray free-electron laser
In the field of beam physics, two frontier topics have taken center stage due to their potential to enable new approaches to discovery in a wide swath of science. These areas are: advanced, high gradient acceleration techniques, and x-ray free electron lasers (XFELs). Further, there is intense interest in the marriage of these two fields, with the goal of producing a very compact XFEL. In this context, recent advances in high gradient radio-frequency cryogenic copper structure research have opened the door to the use of surface electric fields between 250 and 500 MV m -1 . Such an approach is foreseen to enable a new generation of photoinjectors with six-dimensional beam brightness beyond the current state-of-the-art by well over an order of magnitude. This advance is an essential ingredient enabling an ultra-compact XFEL (UC-XFEL). In addition, one may accelerate these bright beams to GeV scale in less than 10 m. Such an injector, when combined with inverse free electron laser-based bunching techniques can produce multi-kA beams with unprecedented beam quality, quantified by 50 nm-rad normalized emittances. The emittance, we note, is the effective area in transverse phase space (x, p x /m e c) or (y, p y /m e c) occupied by the beam distribution, and it is relevant to achievable beam sizes as well as setting a limit on FEL wavelength. These beams, when injected into innovative, short-period (1–10 mm) undulators uniquely enable UC-XFELs having footprints consistent with university-scale laboratories. We describe the architecture and predicted performance of this novel light source, which promises photon production per pulse of a few percent of existing XFEL sources. We review implementation issues including collective beam effects, compact x-ray optics systems, and other relevant technical challenges. To illustrate the potential of such a light source to fundamentally change the current paradigm of XFELs with their limited access, we examine possible applications in biology, chemistry, materials, atomic physics, industry, and medicine—including the imaging of virus particles—which may profit from this new model of performing XFEL science.
47 OTHER INSTRUMENTATION↗
Update of inclusive cross sections of single and pairs of identified light charged hadrons
Not Available
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Azimuthal asymmetries of back-to-back π ± - ( π 0 , η , π ± ) pairs in e + e - annihilation
This work reports the first observation of azimuthal asymmetries around the thrust axis in e + e – annihilation of pairs of back-to-back charged pions in one hemisphere, and π 0 and η mesons in the opposite hemisphere. These results are complemented by a new analysis of pairs of back-to-back charged pions. The π 0 and η asymmetries rise with the relative momentum z of the detected hadrons as well as with the transverse momentum with respect to the thrust axis. These asymmetries are sensitive to the Collins fragmentation function $H$ $^{1}_{⊥}$ and provide complementary information to previous measurements with charged pions and kaons in the final state. In particular, the η final states will provide additional information on the flavor structure of $H$ $^{1}_{⊥}$. This is the first measurement of the explicit transverse-momentum dependence of the Collins fragmentation function from Belle data. It uses a dataset of 980.4 fb –1 collected by the Belle experiment at or near a center- of-mass energy of 10.58 GeV.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
An inverse free electron laser acceleration-driven Compton scattering X-ray source
Abstract The generation of X-rays and γ-rays based on synchrotron radiation from free electrons, emitted in magnet arrays such as undulators, forms the basis of much of modern X-ray science. This approach has the drawback of requiring very high energy, up to the multi-GeV-scale, electron beams, to obtain the required photon energy. Due to the limit in accelerating gradients in conventional particle accelerators, reaching high energy typically demands use of instruments exceeding 100’s of meters in length. Compact, less costly, monochromatic X-ray sources based on very high field acceleration and very short period undulators, however, may enable diverse, paradigm-changing X-ray applications ranging from novel X-ray therapy techniques to active interrogation of sensitive materials, by making them accessible in energy reach, cost and size. Such compactness and enhanced energy reach may be obtained by an all-optical approach, which employs a laser-driven high gradient accelerator based on inverse free electron laser (IFEL), followed by a collision point for inverse Compton scattering (ICS), a scheme where a laser is used to provide undulator fields. We present an experimental proof-of-principle of this approach, where a TW-class CO 2 laser pulse is split in two, with half used to accelerate a high quality electron beam up to 84 MeV through the IFEL interaction, and the other half acts as an electromagnetic undulator to generate up to 13 keV X-rays via ICS. These results demonstrate the feasibility of this scheme, which can be joined with other techniques such as laser recirculation to yield very compact photon sources, with both high peak and average brilliance, and with energies extending from the keV to MeV scale. Further, use of the IFEL acceleration with the ICS interaction produces a train of high intensity X-ray pulses, thus enabling a unique tool synchronized with a laser pulse for ultra-fast strobe, pump-probe experimental scenarios.
43 PARTICLE ACCELERATORS↗
Experimental Characterization of Electron-Beam-Driven Wakefield Modes in a Dielectric-Woodpile Cartesian Symmetric Structure
Photonic structures operating in the terahertz (THz) spectral region enable the essential characteristics of confinement, modal control, and electric field shielding for very high gradient accelerators based on wakefields in dielectrics. We report in this paper an experimental investigation of THz wakefield modes in a three-dimensional photonic woodpile structure. Selective control in exciting or suppressing of wakefield modes with a nonzero transverse wave vector is demonstrated by using drive beams of varying transverse ellipticity. Additionally, we show that the wakefield spectrum is insensitive to the offset position of strongly elliptical beams. Finally, these results are consistent with analytic theory and three-dimensional simulations and illustrate a key advantage of wakefield systems with Cartesian symmetry: the suppression of transverse wakes by elliptical beams.
43 PARTICLE ACCELERATORS↗
Demonstration of Cascaded Modulator-Chicane Microbunching of a Relativistic Electron Beam
Here, we present results of an experiment showing the first successful demonstration of a cascaded microbunching scheme. Two modulator-chicane prebunchers arranged in series and a high power mid-IR laser seed are used to modulate a 52 MeV electron beam into a train of sharp microbunches phase locked to the external drive laser. This configuration is shown to greatly improve matching of the beam into the small longitudinal phase space acceptance of short-wavelength accelerators. We demonstrate trapping of nearly all (96%) of the electrons in a strongly tapered inverse free-electron laser accelerator, with an order-of-magnitude reduction in injection losses compared to the classical single-buncher scheme. These results represent a critical advance in laser-based longitudinal phase space manipulations and find application in high gradient advanced acceleration as well as in high peak and average power coherent radiation sources.
43 PARTICLE ACCELERATORS↗
Measurement of the decays B → η ℓ ν ℓ and B → η ' ℓ ν ℓ in fully reconstructed events at Belle
We report branching fraction measurements of the decays B + → ηℓ + νℓ and B + → η'ℓ + νℓ based on 711 fb –1 of data collected near the Υ(4S) resonance with the Belle experiment at the KEKB asymmetric-energy e + e – collider. This data sample contains 772 million BB¯ events. One of the two B mesons is fully reconstructed in a hadronic decay mode. Among the remaining (“signal-B”) daughters, we search for the η meson in two decay channels, η → γγ and η → π + π – π 0 , and reconstruct the η' meson in η' → ηπ + π – with subsequent decay of the η into γγ. Combining the two η modes and using an extended maximum likelihood, the B + → ηℓ + νℓ branching fraction is measured to be (4.2 ± 1.1(stat.) ± 0.3(syst.)) × 10 –5 . For B + → η'ℓ + νℓ, we observe no significant signal and set an upper limit of 0.72 × 10 –4 at 90% confidence level.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Single shot, double differential spectral measurements of inverse Compton scattering in the nonlinear regime
Not Available
43 PARTICLE ACCELERATORS↗
High duty cycle inverse Compton scattering X-ray source
Inverse Compton Scattering (ICS) is an emerging compact X-ray source technology, where the small source size and high spectral brightness are of interest for multitude of applications. However, to satisfy the practical flux requirements, a high-repetition-rate ICS system needs to be developed. To this end, this article reports the experimental demonstration of a high peak brightness ICS source operating in a burst mode at 40 MHz. A pulse train interaction has been achieved by recirculating a picosecond CO 2 laser pulse inside an active optical cavity synchronized to the electron beam. The pulse train ICS performance has been characterized at 5- and 15- pulses per train and compared to a single pulse operation under the same operating conditions. Lastly, with the observed near-linear X-ray photon yield gain due to recirculation, as well as noticeably higher operational reliability, the burst-mode ICS offers a great potential for practical scalability towards high duty cycles.
43 PARTICLE ACCELERATORS↗
Observation of redshifting and harmonic radiation in inverse Compton scattering
Not Available
43 PARTICLE ACCELERATORS↗
Search for the Dark Photon and the Dark Higgs Boson at Belle
The dark photon A ' and the dark Higgs boson h ' are hypothetical constituents featured in a number of recently proposed dark sector models. Assuming prompt decays of both dark particles, we search for their production in the so-called Higgstrahlung channel e + e - → A ' h ' , with h ' → A ' A ' . We investigate ten exclusive final states with A ' → e + e - , μ + μ - , or π + π - in the mass ranges 0.1 GeV / c 2 < m A ' < 3.5 GeV / c 2 and 0.2 GeV / c 2 < m h ' < 10.5 GeV / c 2 . We also investigate three inclusive final states 2 ( e + e - ) X , 2 ( μ + μ - ) X , and ( e + e - ) ( μ + μ - ) X , where X denotes a dark photon candidate detected via missing mass, in the mass ranges 1.1 GeV / c 2 < m A ' < 3.5 GeV / c 2 and 2.2 GeV / c 2 < m h ' < 10.5 GeV / c 2 . Using the entire 977 fb - 1 data set collected by Belle, we determine no significant signal. Here, we obtain individual and combined 90% credibility level upper limits on the branching fraction times the Born cross section, B × σ Born , on the Born cross section σ Born , and on the dark photon coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, α D × ε 2 . These limits improve upon and cover wider mass ranges than previous experiments. The limits from the final states 3 ( π + π - ) and 2 ( e + e - ) X are the first placed by any experiment. For α D equal to 1 / 137 , m h ' < 8 GeV / c 2 , and m A ' < 1 GeV / c 2 , we exclude values of the mixing parameter ε above ~ 8×10 -4 .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for the decay B + → K ¯ * 0 K * + at Belle
We report a search for the rare charmless decay B+ → K¯ *0 K *+ using a data sample of 772 × 10 6 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e – collider. Here, no statistically significant signal is found and a 90% confidence-level upper limit is set on the decay branching fraction of B(B + → K¯K *0 K *+ ) < 1.31 × 10 –6 .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
The Physics of the B Factories
This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C. Please note that version 3 on the archive is the auxiliary version of the Physics of the B Factories book. This uses the notation alpha, beta, gamma for the angles of the Unitarity Triangle. The nominal version uses the notation phi_1, phi_2 and phi_3. Please cite this work as Eur. Phys. J. C74 (2014) 3026.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Progress in development of neutron energy spectrometer for deuterium plasma operation in KSTAR
Two types of DD neutron energy spectrometer (NES) are under development for deuterium plasma operation in KSTAR to understand behavior of beam ions in the plasma. One is based on the state-of-the-art nuclear emulsion technique. The other is based on a coincidence detection of a recoiled proton and a scattered neutron caused by an elastic scattering of an incident DD neutron, which is called an associated particle coincidence counting-NES. The prototype NES systems were installed at J-port in KSTAR in 2012. During the 2012 and 2013 experimental campaigns, multiple shots-integrated neutron spectra were preliminarily obtained by the nuclear emulsion-based NES system.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
High-quality electron beams from a helical inverse free-electron laser accelerator
N/A
43 PARTICLE ACCELERATORS↗
Search for the process e + e $-$ → J / ψ X ( 1835 ) at s ≈ 10.6 GeV
We report the results of a search for the X(1835) state in the process e + e - →J/ψX(1835) using a data sample of 672 fb -1 collected with the Belle detector at and near the Υ(4S) resonance at the KEKB asymmetric-energy e + e - collider. No significant evidence is found for this process, and an upper limit is set on its cross section times the branching fraction: σ Born (e + e - →J/ψX(1835))•B(X(1835)→≥3 charged tracks)<1.3 fb at 90% confidence level.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗