Efficiency of the CMS Level-1 Trigger to Selected Physics

Channels

by: Corey Sulkko

Faculty Mentor: prof. Darin AcostaFunded by: National Science Foundation

Presentation overview

Overview of CMS experiment The importance of the Level-1

Trigger to CMSMethods of calculating the efficiency

of the Level-1 TriggerResultsFuture 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 ,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

2mcE

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 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

endcap detectors

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

SignalZebra fileswith HITS

ORCADigitization

(merge signal and MB)

ObjectivityDatabase

HEPEVTntuples

CMSIM

HLT AlgorithmsNew

ReconstructedObjects

MC

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RC

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HLT G

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Data

bases

ORCAooHit

FormatterObjectivityDatabase

MB

ObjectivityDatabase

Catalog import

Catalog import

ObjectivityDatabaseObjectivityDatabaseytivitcejbOytivitcejbOesabataDesabataD

Mirro

red

Db

’s(C

ER

N, U

S, Ita

ly,

…)

Detection

Co

llis

ion

sSimulating the Experiment

Tri

gg

erin

g

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/ -> 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: inalmost all cases within at least .05 of the values for HZo Zou+ u- u+ u-

Efficiency of the L1T to select 1 or 2 muon events for minbias B -> J/ -> µµ decays

The efficiency of the L1T to select muons from B -> J/ -> 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’sEfficiency 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 inendcap

.844 +/- .011 .232 +/- .013 .035 +/- .006

2 mu inendcap

.689 +/- .015 .067 +/- .008 0.00

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/ -> 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’sin endcap

.27 +/- .014 .015 +/- .004 0.00

2 or more mu’sin endcap

.05 +/- .007 0.00 0.00

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