Exotic Meeting Topics: Comments at the Talk

Our previous studies on MC VH signal and background had shown that the combined requirement of at

Level 1
one single calorimetric tower over 10 GeV

Level 2 almost 3 cluster with Et>10 GeV, and SumET > 90 GeV,
2 SVT good tracks (that means chi2<12.6, Pt>2 GeV,
start and end in the same half barrel) wiht IP>100 microns

led to a rate into L3 of about 1.5 Hz (this is equal to a cross section, extrapolated to the Project Luminosity of 15 nbarn).

With the data collecting this summer we have perform a sort of validation of the expected rate of such an ensemble of requirements. The results have to be considered only demonstrative yet, due to the fact that the correction we made on the impact parameter measured by SVT was not very accurated, and lots of the sector of the silicon detector were not fully operational. In any way the conclusion is that data seems to validate our prediction in term of expected rate.

Few days ago we have found some disagreement in the result given by the two existent simulation of the SVT detector, svtqwksim (written by G.Punzi) and svtsim (by Bill Ashmanskas), as respect to the efficency of the impact parameter's cuts on tracks coming from simulated signal events. We did not understand, at the fist time, the reason of the differences we were going to see as output of the two simulator. After we realized that the problems could be related to the fact that the real SVT could have something working not so well. The svtsim code simulated bit by bit the working of the real SVT (the agreement with the real device is about 95-98% as known by the SVT group).

Related to this, there is the iussie that the real SVT seems to be less efficient than expected as respect to the offline reconstructed tracks, as shown in the lines, reporting a mail to svt group, reported below.

These fact led us to consider a sort of backup solution for our trigger. Yesterday we did not have more information about that, we didn't know very well were the problems for the SVT inefficiences would be searched, and for how many time this problem vill be persistent. Now it seems that the problems is clear to the SVT working group, as is shown by the following information taken from a mail to svt group.


Studies on svt efficiency


Studies performed on real data on the J/Psi decay into muons show that:

if the hit matching requirement is looser: the closest svt match to the offline clusters is declared valid if it is within +/- 2 strips (instead of half a strip like in the previous mail). This is to consider as matching clusters that fall in the same superstip.
total tracks  420  -  - 
at least one hit didn't match  48  (48/420)= 11%  48/420)= 11% 
pattern didn't fire = 52  52  (52/420)= 12%  (52/(420-48))= 14%
different parameters  (chi[svt-offl] < 20) 44  (44/420)= 8% (44/(420-48-52))= 14%
Total Tracks lost 144  34%  - 
Tracks with parameters matching but missing hit and/or pattern   26  6%  - 
tracks matched (hit, pattern and parameters)  276  66%  - 

 
  This shows that in many cases the hits are not lost but rather "mismeasured" and this is anyway recovered by the pattern recognition. Note that tracks "migrated" from the next-to last to the last line...

As expected the tracks matching "by chance" mostly come from hit combinations which in fact are physically connected to those of the offline tracks.



Such an inefficiency would clearly affect our studies and could led to the neccessity of a change in our requirements on the SVT tracks, if the problems would be persistent. But it is also clear that the problems had to be solved as soon as possible: SVT was designed to be efficient for 95% as respect to the offline tracks. At the moment such efficiency is lower (66%).

Considering all these facts,
  • the solution that we had proposed yesterday at the meeting, consistent of requiring only 1 SVT tracks instead of 2, is only to be considered as backup solution
    • .

    We are not thinking about this in any different ways,
  • we are only looking with prudence at what is going to happen around the SVT detector
    • .

    The frozen settings of requirements for the multijet+SVT trigger still remain those with the two SVT tracks.





    Giorgio_Cortiana
    Last modified: Sat Nov 24 10:44:06 CST 2001