Efficiency of the CMS Level-1
Trigger to Selected Physics
Channels
by: Corey Sulkko
Faculty Mentor: prof. Darin Acosta
Funded by: National Science Foundation
Presentation overview
Overview of CMS experiment
The importance of the Level-1 Trigger to
CMS
Methods of calculating the efficiency of
the Level-1 Trigger
Results
Future Research
Overview of the CMS
Experiment
The Standard Model predicts a particle not yet
found, the Higgs Boson
the Higgs is expected to be very
massive, and because E  mc2 ,
it needs high energy
collisions to be created
 Currently the Tevatron collides particles at 2
trillion electron volts, which may not be enough
energy to create the Higgs, which leads us to
the Large Hadron Collider at CERN
the
Large Hadron Collider
the LHC
 the Large Hadron Collider will be used
to collide protons at 14 TeV, which we
think may be enough energy to create
many Higgs particles for study
 To find the Higgs, we will try to
reconsruct the particles that it decays
into, by using the momenta of these
reconstructed particles we can
calculate the mass of the Higgs
 Since a couple of Higgs decays modes
go into muons, we will use a muon
detector...
the Compact Muon Solenoid
 Compact Muon Solenoid
detector
 Solenoid provides
magnetic field to
measure momentum of
particles, which can be
used to calculate their
masses
 UF works with the
endcap detectors and
Trigger system
endcap detectors
 Endcap detectors use Cathode
Strip Chamber(CSC) detectors
 The CSC’s are trapezoidal and
each contain six layers of
detection, they are arranged
overlapping each other to form
a circular disc
 Each endcap consists of four
discs
 CSC contains gas mixture
which ionizes when a muon
passes through, electrons are
collected on high voltage
wires, signals induced on
perpendicular cathode strips
Using reconstructed paths to
calculate transverse momentum of
muon
 By knowing where the muon
hit on each of the four CSC’s,
we can reconstruct the path
that the muon took
 Knowing the change in the
angle , the transverse
momentum(Pt, the momentum
in the direction of the change
in the angle ), the mass can
be calculated
the Level-1 Muon Trigger
 Since the LHC will be colliding p’s at 40,000,000 per
second, something is needed to filter out muons with
low Pt’s, because they couldn’t have possibly come from
the massive Higgs particle, otherwise there would be
too much data to analyze(1 megabyte per collision)
 The CSC detectors create electronic signals, something
is needed to reconstruct the tracks and calculate the Pt
of the muons
 the Level-1 Muon Trigger(L1T), under design at UF, does
these two things
Efficiency of the Level-1 Trigger
 The efficiency of the L1T is the fraction of time that the
trigger reconstructs a particle in the endcap region that
was produced in that region. To select is to allow the
particle to be stored for future analysis
 The L1T is the first of a 3 level trigger system being
designed for the CMS endcaps
 Because the Higgs is expected to be created less than
once every trillion collisions, we want the efficiency for
these particles to be as high as possible.
 Physicists will set the Trigger so that it selects all events
that generate muons above a certain Pt
Calculating the Efficiency of
the Trigger
run simulations of the collisions, the
detectors, and the Trigger
calculate the efficiency
Signal
MB
Detection
CMSIM
HEPEVT
ntuples
Zebra files
with HITS
Objectivity
Database
ORCA
ooHit
Formatter
Objectivity
Database
HLT Grp
Databases
HLT Algorithms
New
Reconstructed
Objects
Objectivity
Objectivity
ytivitcejbO
Database
Database
esabataD
Mirrored Db’s
Catalog import
(CERN, US, Italy,…)
Triggering
Objectivity
Database
ORCA
Digitization
(merge signal
and MB)
ORCA Prod.
Catalog import
MC Prod.
Collisions
Simulating the Experiment
Simulate the Collisions
Use an event generator program to simulate the
particle collisions.
Pythia simulates particle collisions and decays based on the
rules of quantum mechanics
Set the generator to produce only the decays
you are interested in
pp -> H -> ZZ -> µµµµ, pp -> H -> WW -> µµ
B -> J/y -> µµ
Generate many events
Simulate the detection and the
Level-1 Trigger behavior
 Simulated detection using the program CMSIM
simulates the behavior of the particles as they move
through the material of the CMS detector
 Used ORCA to simulate the response of the detectors
and to simulate the behavior of the L1T in response to
the digitized data from the detectors
 ORCA stores the information about the particles
produced by the collision, the generated data, and the
results as interpreted by the L1T all in a binary file
 This file can then be analyzed using the graphical
analysis program ROOT
Results
 ROOT was used to calculate the efficiency of the L1T to
select 1, 2 and 3 muon events for three different Pt
Thresholds: Pt > 0, Pt > 10, and Pt > 25 GeV/c
 This was done for all three decays
 For the Higgs decays this was done for 6 different Higgs
masses between 125 and 250 GeV
 For J/Psi we simulated minbias proton collisions
 The probability of generating 1 or more, 2 or more, and
3 or more muons was also calculated for the three
diffirent Pt thresholds and six diffirent masses
Efficiency of the L1T to select 1 and 2
muon events as a function of Higgs
mass for select Higgs decays
Results from the H WW  u+ u- events were very similar: in
almost all cases within at least .05 of the values for HZo Zo
u+ u- u+ u-
Efficiency of the L1T to select 1 or 2
muon events for minbias B -> J/y -> µµ
decays
 The efficiency of the L1T to select muons from B -> J/y > µµ decays was found to be much lower
 This is because the Higgs boson has a higher mass then
the j/Psi, and is therefore easier to detect at higher Pt’s
Efficiency to select J/Psi decaying to 2 mu for different Pt ranges
and number of particles generated in endcap
Pt >= 0
Pt >= 10
Pt >= 25
1 mu in
.844 +/- .011
.232 +/- .013
.035 +/- .006
endcap
2 mu in
.689 +/- .015
.067 +/- .008
0.00
endcap
Probability of generating 1, 2, or 3 or more
muons in the endcaps as a function of mass
for H  Zo Zo u+ u- u+ u

About 80% of all H  Zo Zo u+ u- u+ u
events had at least 1 muon go into the
endcap
Probability of generating 1, 2, or 3 or more
muons in the endcaps as a function of mass
for H  W+ W- u+ u-

About 50% of all H  W+ W- u+ u- events
had at least 1 muon go into the endcap
Probability of B -> J/y -> µµ generating one
or two muons in the endcap
The probability if B -> J/y -> µµ producing 1 or
more muons in the endcaps was found to be
about 27%
Probability of J/Psi generating one or two muons in the endcap
Pt >= 0
Pt >= 10
Pt >= 25
1 or more mu’s
.27 +/- .014
.015 +/- .004
0.00
in endcap
2 or more mu’s
.05 +/- .007
0.00
0.00
in endcap
Future Research
The L1T is the first in a series of three triggers
for the CMS endcap detectors, efficiency
analysis should be done for the other triggers as
well
Try to calculate the Higgs mass the data
obtained from the L1T
Acknowledgements
 Thanks to NSF, Kevin Ingersent, and Alan Dorsey for the
REU program
 Thanks to Prof. Darin Acosta for guiding my research