A fast luminosity monitor for BEPCII

Abstract

The fast luminosity monitor counting the γ photons above a given energy threshold emitted from radiative Bhabha scattering has been operated in the BEPCII to measure the relative luminosity bunch by bunch for the first time and used successfully in beam tuning of BEPCII. In the relative mode the monitor is able to deliver the relative luminosities with an accuracy of 0.8%. By steering the electron beam while observing the counting rate changes of the monitor the horizontal and vertical sizes of the bunch spots can be estimated as: sxe+ = sxe– = 0.356 mm, sye+ = sye– = 0.011 mm.

Influence of the geomagnetic field on the IACT detection technique for possible sites of CTA observatories

“…Neglecting the GF effect, we could expect E th ≈ 9 GeV at this site. However, the GF is strong Taking into account experiments other than CTA, we note that a similar conclusion applies to the location of LHAASO [34], which is planned in Tibet at a similar altitude (4.3 km) and in a similarly strong GF. We caution, however, that both the altitude and the GF strength at these two sites exceed the maximum values for which we made computations and verified our linear relations, so the extrapolations come with an obvious risk.…”

Luminosity monitoring and calibration of BLM

“…One systematic error of n BLM (t) arises from the minor adjustment of the beam orbits which was measured around 1.0%, the other arises from background value caused by beam gas and lost beam which is studied in Ref. [1] and it is less than 4.0%. So the total systematic error of n BLM (t) is 4.1%.…”

“…The BLM determines luminosity by detecting the zero-angle gamma photons from the radiative Bhabha scattering e + e − →e + e − (γ). The luminosity L is proportional to the counting rate of the BLM n BLM [1]:…”

“…A detailed example of the measurement of bunch sizes with relative luminosity by varying the overlap of beams at the IP is reported in Ref. [1]. A complete scan to measure the bunch sizes takes only 20 minutes.…”

“…In practice, Bhabha events e + e − →e + e − (γ) are preferred because of their large cross section and ability to be separated from background events due to their characteristic topology. The BEPC Luminosity Moni-tor [1][2][3] (BLM) and the End-cap Electro-Magnetic Calorimeter (EEMC) both determine luminosity of the BEPC using Bhabha events.…”