Svenska:

Den här webbplatsen kan endast nås som arkivreferens. De officiella webbsidorna för avdelningen för partikelfysik finns på http://particlephysics.physics.lu.se

Sidan nedan slutar uppdateras fr.o.m. 2020-09-22 och uppfyller endast delvis tillgänglighetsdirektivet. Se tillgänglighetsredogörelsen

English:

The webpage you reached is made available for archiving purposes only. The official division of particle physics webpages can be found at http://particlephysics.physics.lu.se

The page below is not updated any longer since September 22, 2020 and does not conform completely to the accessibility regulation. See the accessibility statement

Background in VSAT

At LEP2, VSAT is used mainly to measure the energy and position of the scattered electrons in $\gamma$$\gamma$ collisions. The main background in this type of analysis comes from the enormous off-energy electron background. The probability of having an off-energy electron faking the scattered electron from a $\gamma$$\gamma$  event can be calculated with any sample of events which does not give electrons in VSAT. The largest sample available is the VSAT Bhabha sample and it can be used to calculate the probability with a minute statistical error. To estimate the systematic error, other event samples such as muon events and STIC Bhabha events have also been studied.

In the following discussion, the standard DELPHI coordinate system is used with the x axis pointing towards the centre of LEP, the y axis pointing upwards and the z axis pointing in the direction of the electron beam. $\theta$ is the polar angle in relation to the z axis and $\phi$ is the azimuthal angle around the z axis. In this coordinate system, the numbering of the four VSAT modules is as follows:

Module 1	Module 2	Module 3	Module 4
x < - 5cm, z < - 775cm	x > 5cm, z < - 775cm	x < - 5cm, z > 775cm	x > 5cm, z > 775cm

which means that module 1 and 3 are on the outer circumference of the LEP ring and module 1 and 2 are on the DELPHI A-side while 3 and 4 are on the C-side.