New Run IIb L1Cal EM Algorithm
Greg Pawloski
Rice University
Run IIb L1Cal Meeting
May 31, 2005
The Situation
The original RunIIb Atlas EM algorithm found trigger
objects by looking for a cluster of 2 trigger towers (TTs)
that was a local maximum (LM)
For an object to be a LM it must:
TTs
TTs
Have a higher Et than all
the possible vertical
objects in the blue region
Phi
Eta
LM
Have a higher Et than all
the possible horizontal
objects in the blue region
Phi
Eta
same LM
Problem: If two electrons are in the blue region then
only the highest Et one will be found
Greg Pawloski
Run IIb L1Cal Meeting
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Proposed Solutions
To overcome this limitation a new style of algorithm was
designed that uses an Object Inhibiting Mask instead of LM cuts
3 test algorithms were created:
1.
2.
3.
Searches for a seed TT by requiring the TT to have the highest Et in a 3x3
TT area and then finds the highest Et nearest neighbor to form a cluster.
Searches for a seed TT by requiring the TT to have a higher Et than its
four nearest neighbors (a cross pattern) and then finds the highest Et
nearest neighbor to form a cluster.
Searches for entire 2TT clusters by looking for vertical and horizontal
objects separately.
Each test algorithm has a potential weakness (see next slides)
Greg Pawloski
Run IIb L1Cal Meeting
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Potential Flaw in Algo 1
The test algo that use a 3x3 search window to find seed
TTs still has some cases where it will not find two
neighboring electrons
> > >
> = >
> > >
For the following
configuration of TT Ets
5
10
10
Only this trigger object is
found
Phi
Eta
Greg Pawloski
1
Seed TTs
must pass
this condition
Run IIb L1Cal Meeting
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Potential Flaw in Algo 2
The test algo that use a cross pattern search window to
find seed TTs can form an object out of neighboring
noise instead of the true signal
For the following
configuration of TT Ets
Only the yellow trigger
objects are found
Phi
-.5 -.25
-.25
.25
-.25
.25 9 10.25
.75 .75
.25 .25
-.25 -.25
Seed TTs are
found here
The inhibiting mask
prevents 2 neighboring
horizontal objects from
forming
Eta
Greg Pawloski
Run IIb L1Cal Meeting
5
Potential Flaw in Algo 3
The test algo that searches for entire trigger objects will
occasionally form a trigger objects that contains the true
hot TT, but not the correct nearest neighbor
Lots of Et now in
isolation region
For the following
configuration of TT Ets
28 15
1 1
Only this trigger object is
found
Phi
Eta
Greg Pawloski
Isolation cut will
now fail for this
electron
Algo finds a horizontal 28+15 object
and a vertical 28+1 object.
The mask removes overlapping objects by
choosing the vertical object
Run IIb L1Cal Meeting
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Choosing a New EM algo
Conditions for choosing a new EM algo:
1. The new algo must reproduce the old Atlas algorithm’s
results when there are no neighboring electrons
This will be tested with the CSG Z→ee Data Sample
2. The new algo must out perform the Atlas algorithm when
there are neighboring electrons
This will be tested with the CSG J/Psi→ee Data Sample
Greg Pawloski
Run IIb L1Cal Meeting
7
Z→ee Data Sample
Et only cuts
The new algo w/ the 3x3 search
window reproduces the Atlas
algorithm exactly
The others are less efficient
Greg Pawloski
Run IIb L1Cal Meeting
8
Z→ee Data Sample
w/ isolation and em
fraction cuts
Again, the new algo
w/ the 3x3 search
window reproduces
the Atlas algorithm
exactly
Trigger object w/
wrong NN kills
isolation efficiency
Greg Pawloski
Run IIb L1Cal Meeting
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J/Psi→ee Data Sample
Et only cuts
For the same rate the new algos
are more efficient than the Atlas
For the trigger term CEM(2,3):
Atlas is ~74% efficient
The new algos are ~94% efficient
Greg Pawloski
Run IIb L1Cal Meeting
10
J/Psi→ee Data Sample
w/ isolation and em
fraction cuts
For the same rate the new algos
are more efficient than the Atlas
Greg Pawloski
Run IIb L1Cal Meeting
11
Conclusion
The test EM algo that uses a 3x3 search window would
be the best choice for a new EM algorithm
It reproduces the old Atlas when there are no neighboring
electrons
It out performs the old Atlas algorithm when there are
neighboring electrons
This algorithm is also known as “Algo 4” on the DØ
Run IIb Level 1 Calorimeter Trigger website:
http://www.nevis.columbia.edu/~evans/l1cal/algos/em_algo/working/em_comp.html
Greg Pawloski
Run IIb L1Cal Meeting
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