Measurement of

We report a measurement of the process γγ* → π0 with a 759 fb-1 data sample recorded with the Belle detector at the KEKB asymmetric-energy e+e- collider. The pion transition form factor, F(Q2), is measured for the kinematical region GeV2 ≲ Q2 ≲ 40 GeV2, where −Q2 is the invariant mass squared of a virtual photon. The measured values of Q2|F(Q2)| agree well with the previous measurements below Q2 ≃ 9 GeV2 but do not exhibit the rapid growth in the higher Q2 region seen in another recent measurement, which exceeds the asymptotic QCD expectation by as much as 50%

Simulation Study on Luminosity Feedback for Horizontal Beam Stabilization at Superkekb

International audienceThe SuperKEKB e⁺ e⁻ collider uses highly focused ultra-low emittance bunches colliding every 4 ns to reach a very high luminosity of 8× 10³⁵ cm⁻²s⁻¹. It is quite essential to have an orbit feedback system at the Interaction Point (IP) to maintain the optimum overlap between the colliding beams in the presence of ground motion disturbances. For the horizontal motion, a luminosity monitoring system, based on measuring the rate of the Bhabha process at vanishing scattering angle, is developed as input signal to the feedback system. The relative precision needed for this monitor is studied in detail, for the different successive stages of luminosity operation, based on a full simulation of this system, including the detector, DAQ, lock-in amplifier, and feedback control

Fast Luminosity Monitoring for the SuperKEKB Collider (LumiBelle2 Project)

International audienceLumiBelle2 is a fast luminosity monitoring system prepared for SuperKEKB*. It uses sCVD diamond detectors placed in both the electron and positron rings to measure the Bhabha scattering process at vanishing scattering angle. Two types of online luminosity signals are provided, a Train-Integrated-Luminosity at 1 kHz as input to the dithering feedback system used to maintain optimum overlap between the colliding beams in horizontal plane, and Bunch-Integrated-Luminosities at about 1 Hz to check for variations along the bunch trains. Individual beam sizes and offsets can also be determined from collision scanning. The design of LumiBelle2 will be described and its performance during the Phase-2 commissioning of SuperKEKB will be reported

First Tests of Superkekb Fast Luminosity Monitors During 2018 Phase-2 Commissioning

International audienceThe SuperKEKB e⁺e⁻ collider aims to reach a very high luminosity of 8× 10³⁵ cm⁻²s⁻¹, by using highly focused ultra-low emittance bunches colliding every 4 ns, it is essential to have an orbit feedback system at the Interaction Point (IP) to maintain the optimum overlap between two colliding beams. Luminosity monitoring systems including LumiBelle2 and ZDLM as input to dithering feedback system used to stabilize the horizontal orbit at the IP were developed and will be described, including the detectors, mechanical set-up, DAQ. Preliminary measurements and analysis of background and first stage luminosity monitoring data collected will be reported and compared with simulation

Vibration and luminosity frequency analysis of the SuperKEKB collider

International audienceThe SuperKEKB collider has entered the physics production phase with the aim to reach its target luminosity of 6×1035 cm−2s−1. Vibrations of the accelerator elements, especially around the Interaction Point (IP), could limit the performance of the collider. Since 2018, a 24-hour monitoring system of vibrations has been put in place on both sides of the Belle II detector. Measurements and analyses of the spectral components of these vibrations and of the transfer function of the mechanical supports are presented, along with measurements of luminosity spectra from the LumiBelle2 detectors, showing good agreement in spectral peak frequencies for several of the vibration sources

First Tests of SuperKEKB Luminosity Monitors during 2016 Single Beam Commissioning

International audienceThe SuperKEKB e⁺e⁻ collider aims to reach a very high luminosity of 8 10³⁵ cm⁻²s^{−1}, using highly focused ultra-low emittance bunches colliding every 4ns. Fast luminosity monitoring is required for luminosity feedback and optimisation in presence of dynamic imperfections. The aimed relative precision is about 10⁻³ in 1ms, which can be in principle achieved thanks to the very large cross-section of the radiative Bhabha process at zero degree scattering angle. Diamond, Cherenkov and scintillator sensors are to be placed just outside the beam pipe, downstream of the interaction point in both rings, at locations with event rates consistent with the aimed precision and small enough backgrounds from single-beam particle losses. The initial configuration installed for the 2016 "phase 1" single beam commissioning will be described, including the sensors, mechanical setup, readout electronics and first stage DAQ. Preliminary measurements and analysis of beam gas Bremsstrahlung loss data collected with the luminosity monitors will be reported and compared with a detailed simulation, for several experimental conditions during the SuperKEKB commissioning