Efficiency of the CMS Level-1 Trigger to Selected Physics Channels

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Efficiency of the CMS Level-1 Trigger to Selected
Physics Channels

• by Corey Sulkko
• Faculty Mentor prof. Darin Acosta
• Funded by National Science Foundation

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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

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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 ,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

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the Large Hadron Collider
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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...

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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

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endcap detectors

• Endcap detectors use Cathode Strip Chamber(CSC)
  detectors
• The CSCs 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

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Using reconstructed paths to calculate transverse
momentum of muon

• By knowing where the muon hit on each of the four
  CSCs, 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

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the Level-1 Muon Trigger

• Since the LHC will be colliding ps at 40,000,000
  per second, something is needed to filter out
  muons with low Pts, because they couldnt 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

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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

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Calculating the Efficiency of the Trigger

• run simulations of the collisions, the detectors,
  and the Trigger
• calculate the efficiency

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Simulating the Experiment
Signal
Detection
Zebra files with HITS
Collisions
HEPEVT ntuples
CMSIM
MC Prod.
MB
Catalog import
ORCA Digitization (merge signal and MB)
Objectivity Database
ORCA ooHit Formatter
Objectivity Database
ORCA Prod.
Triggering
Catalog import
HLT Algorithms New Reconstructed Objects
Objectivity Database
HLT Grp Databases
Mirrored Dbs (CERN, US, Italy,)
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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 -gt H -gt ZZ -gt µµµµ, pp -gt H -gt WW -gt µµ
• B -gt J/y -gt µµ
• Generate many events

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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

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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 gt 0, Pt gt 10, and Pt
  gt 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

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Efficiency of the L1T to select 1 and 2 muon
events as a function of Higgs mass for select
Higgs decays
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Efficiency of the L1T to select 1 or 2 muon
events for minbias B -gt J/y -gt µµ decays

• The efficiency of the L1T to select muons from B
  -gt J/y -gt 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 Pts

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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

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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

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Probability of B -gt J/y -gt µµ generating one or
two muons in the endcap

• The probability if B -gt J/y -gt µµ producing 1 or
  more muons in the endcaps was found to be about
  27

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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

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Acknowledgements

• Thanks to NSF, Kevin Ingersent, and Alan Dorsey
  for the REU program
• Thanks to Prof. Darin Acosta for guiding my
  research