Welcome to the E831-FOCUS beam spot page

The beam spot snapshot taken using the FOCUS microvertex detector, and

the beam profiles (still experimental, updates will be infrequent for the time being, stay tuned...)

The above histograms are divided in two pages:

• the first one (with colors), shows five plots. Starting from the top-left (clockwise):
  1. This plot is the X versus Y intercept of each microvertex reconstructed track at the z=granite block (which is our z=0). This is a rather accurate intensity indicator, but it is affected by a relatively high contamination of spurious tracks and out-of-time tracks.
     The beam exits the page: the horizontal axis is parallel to the Wide Band floor while the vertical axis goes up from floor to ceiling (this is called the spectrometer reference-frame.
  2. This second plot is the X versus Y of each microvertex reconstructed vertex (in this case, each XY pair corrsponds to a different reconstructed Z, obviously). This is a more accurate representation of the beam intensity, because the background contribution from spurious tracks is greatly reduced, as well as that from out-of-time tracks (these categories of tracks seldom make a vertex in space).
     For historical reasons (essentially due to precision requirements in the computation), the X-Y of a reconstructed vertex are expressed in the microvertex reference-frame, which is rotated with respect to the spectrometer reference-frame by 225 degrees counterclockwise: I know this is cumbersome to remember and promise I will appropriately modify the code as soon as I can.
  3. This third plot is exactly the same as the preceding one, with a superimposed smoothing that facilitates the identification of the maximum intensity location of the beam slice.
  4. Finally, the two black-and-white plots, show the number of reconstructed vertices per unit of lenght along the Z direction (beam direction is left to right).
     • The top plot uses reconstructed vertices of any multiplicity, so two-track vertices (mostly due to e⁺e^- pairs, which make almost parallel tracks in the microvertex) contribute with badly determined Z positions (which shows up in this plot as a sort of "background" to the target shape).
     • The bottom plot, instead, uses only at-least-three-track-multiplicity vertices, which are usually produced by hadronic interactions and very well determined along Z.
     In both plots (more details about the microvertex region geometry here), the four large towers correspond the the four elements of the segmented Beryllium target, the following smaller peak to the scintillator trigger counter (called Tr1), and the remaining ones to the first two stacks of microvertex detector planes.

• The remaining twelve histograms correspond to hit count profiles for each of the twelve microvertex detector planes. Each plane consists of 688 strips divided in two regions of high resolution (central region) and low resolution (lateral regions): in particular the first three planes have pitches of 25 and 50 microns while the remaining ones 50 and 100 microns. This is the reason for the sharp peaks featured by each of the histograms: lower resolution strips count twice as much as the higher resolutions one (assuming same particles intensisty per unit-area)

Anyway, even without running spot, people on shift can check the beam postion.

First of all, one can check the mean values for PB4WC2 and PB4WC3.
According to the last (4-JAN-1997) beam tuning, those values should be:

			PB4WC2V ~ 3.0

			PB4WC2H ~ 1.2

		~boss/ghost/SSDview.conf

from the main HISTOSCOPE window on the GHOST console.

(remember that the microvertex reference frame is rotated with respect to the spectrometer frame...)

Should GHOST not be running, log on dd831 as 
boss on the GHOST Console, do 

		setup ghost 

		ghost 

Then in the File/process menu choose Load Configuration...

NOTICE: make sure that no other GHOST process is running by doing a 

		ps -uboss on dd831