Check of Multijet Calorimeter Trigger Rates

CDF-5485 describes the study and design of a trigger suitable for the collection of VH decays to four jets, requiring at level 1 a single trigger tower above 10 GeV and using at level 2 the scalar sum of transverse energies of all calorimeter clusters above 10 GeV, which is required to exceed 90 GeV, and their number, which has to be equal or larger than three. The L2 cross section of this multijet trigger has been estimated to be 150 nb, or 15 Hz for the design luminosity of 1032cm-2s-1.


Fig.1: Calorimeter primitives used for rate estimations
Fig.1: calorimeter primitives used for the modeling of the Level 2 multijet trigger.
Using data collected since August 10th it is possible to verify the correctness of the above estimate. We use the Single Tower 10 trigger, from stream G: these events pass Level 1 thanks to a single trigger tower above 10 GeV, and no other requirements. They have thus passed the same Level 1 prerequisite needed by our trigger: we can then study the Level 2 primitives on which the multijet filter would base its selection.
Fig.1 shows the calorimeter primitives used to compute the Level 2 rate of the multijet trigger. From top left clockwise: number of L2 clusters per event, transverse energy of the clusters, number of L2 clusters above the 10 GeV threshold, and scalar sum of their energy.


Fig.2: Dependence of multijet rates on run number
Fig.2: Dependence of multijet rates on run number
Using the information shown above, we can easily compute the accept rate and the cross section of the Level 2 requirements run by run, using the information on L1 rate of each, collected in the run summaries database, and then extrapolating the to the poject instantaneous luminosity (1032 cm-2 s-1.The results are shown in Fig.2).


Fig.3: Dependence of multijet rates on instantaneous luminosity
Fig.3: Dependence of multijet rates on instantaneous luminosity
Another useful check consists in verifying the stability of rates with respect to the instantaneous luminosity of collected data. As Fig.3 shows, the rate (computed for an equivalent luminosity of 1032cm-2s-1) is indeed compatible (less than one sigma away) with being independent of the luminosity. In the future we expect an increase of that rate due to the attainment of the project luminosity, and to the possibility in such an enviroment to have multiple interactions in the same bunch-crossing.


Fig.4: Instantaneous luminosity distribution of the data used
Fig.4: Instantaneous luminosity distribution of the data used
Fig.4 shows the distribution of instantaneous luminosity of the data used to produce Fig. 1, 2 and 3. The data was taken from Stream G, single tower 10 trigger. Run numbers range from 123500 to 128440. (taken between 08/11/2001 and 10/04/2001.



red Back to the multijet trigger page
Giorgio Cortiana
Last modified: Fri Oct 19 03:34:16 CDT 2001