Caroline Steiblin Prof Al Goshaw Dr Andrea Bocci Duke University 1 Purpose C omparing MonteCarlo MC simulations of Z boson mass reconstruction from muons photons and electrons ID: 382545
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Slide1
Z boson mass reconstruction
Caroline SteiblinProf. Al GoshawDr. Andrea BocciDuke University
1Slide2
Purpose
Comparing Monte-Carlo (MC) simulations of Z boson mass reconstruction from muons, photons, and electrons to LHC data, to find agreement and qualitative proof of electron-photon fake rates
Identify the Z boson as a true photon source for identification tests
2Slide3
ATLAS Detector
A Toroidal LHC ApparatuSThe ATLAS detector consists of four major components:The inner detector to measure the momentum of charged particles
A calorimeter to measure particle
energy (main part used)
A muon spectrometer to identify
muons
and measure their momenta
A magnet system to bend charged particles for measurementReconstruction algorithms are used to identify different particle trajectories for identification and analysis
3Slide4
Standard Model
The Standard Model allows the Z boson to decay into a lepton and anti-lepton (eg.+/- muon) and a photon, but not three leptons (eg. +/- muon
and an electron)
.
Data can show a violation of the Standard Model with three leptons, which
may demonstrate the possibility of an electron faking a
photon.
4Slide5
Z boson
Charge-less, spin 1, 91 GeV particleDecays to a an fermion/anti-fermion pair
Experimentally well understood and easy to reconstruct with low background
Focused on Z
μ
+
μ-γ and Z μ+
μ
-
e
-
decay, as muons are efficiently reconstructed, and offer a sample of pure photonsData used from full 2012 8 TeV data and simulated Monte Carlo program
5Slide6
Photon reconstruction
Reconstruction of photons, which do not leave tracks in the calorimeterElectrons leave tracks though, and are placed with similar electromagnetic clusters, so interchanging one for the other is not uncommonWhile traversing a material, a photon can decay into an electron and positron, which leads to misidentification
6Slide7
Fake rate of electrons and photons
Misidentification of photons during Z boson reconstruction can lead to anomalies in data, which can lead to inaccurate results, and mass predictionsNumber of electrons present in both full data sample and Monte Carlo is much lower than that of photons produced in the muon channel
7Slide8
ISR and FSR
I
nitial
S
tate Radiation
(ISR
)- not used in this project, but creates a Z boson with a radiated photon before decay
Final State Radiations (FSR)- used for research to identify pure photons and measure photon energies after Z boson decay
8Slide9
Monte Carlo (MC) Simulation
MC used to simulate events from pp collision and particles produced“Data” reconstructed similarly to that of LHC dataCan find agreement with LHC to test the performance of the ATLAS detector
9Slide10
Cut Flow
Monte Carlo
LHC Data
10Slide11
Analysis Cuts
SpecificVertex where two particle tracks are present within 200 mm of each-other (MC: 99.99% Data: 99.95%)Muon where both a positive and negative muon exist in an event, with a transverse momentum over 25
GeV
, eta under 2.4 radians, and energy ratio is under 0.2 (MC: 22.06% Data: 11.7%)
Photon where a photon exists with a transverse energy over 10
GeV
, eta in the range of
0<|eta|<1.37, 1.52<|eta|<2.37
radians, isolation under 4
GeV
(MC: 13.85% Data: 3.56%
) Symbol: P1
Photon Invariant Mass where the reconstructed events yield results in the range of the Z boson 80 GeV < Mass < 96 GeV (MC: 9.36% Data: 1.38%
) Symbol: P2
Electron
when an electron exists
with a transverse energy over 10
GeV
, eta in the range of
0<|eta|<1.37, 1.52<|eta|<2.37
radians, isolation under 4
GeV
(MC:
5.50%
Data
: 0.86%
) Symbol: E1
Electron Invariant
Mass where the reconstructed events yield results in the range of the Z boson 80
GeV
< Mass < 96
GeV
(MC:
4.27% Data: 0.69%
) Symbol: E2
11Slide12
Cut Flow
Monte Carlo
LHC Data
12Slide13
Invariant Mass from Z(
mumug) Before Photon Selection (After P1)
Monte Carlo
LHC Data
13Slide14
Invariant
Mass from Z(mumug) After Photon Selection (After P2)
Monte Carlo
LHC Data
14Slide15
Invariant Mass from Z(
mumue) Before Electron Selection (After E1)
Monte Carlo
LHC Data
15Slide16
Invariant
Mass from Z(mumue) After Electron Selection (After E2)
Monte Carlo
LHC Data
16Slide17
deltaR (muon-photon)
After Photon Selection (After P2)
Monte Carlo
LHC Data
17Slide18
deltaR (muon-electron)
After Electron Selection (After E2)
Monte Carlo
LHC Data
18Slide19
Photon Eta
After Photon Selection (After P2)
Monte Carlo
LHC Data
19Slide20
Electron Eta
After Electron Selection (After E2)
Monte Carlo
LHC Data
20Slide21
Photon transverse energy
After Photon Selection (After P2)
Monte Carlo
LHC Data
21Slide22
Electron transverse energy
After Electron Selection (After E2)
Monte Carlo
LHC Data
22Slide23
Photon & Electron transverse energy
After Photon & Electron Cuts (After P2 & E2)23
Monte Carlo
LHC DataSlide24
Photon isolation
After Photon Selection (After P2)
Monte Carlo
LHC Data
24Slide25
Electron isolation
After Electron Selection (After E2)
Monte Carlo
LHC Data
25Slide26
Summary
No way to accurately measure the fake-rate quantitativelyMonte Carlo and LHC Data results demonstrate similar trendsStandard Model predictions reaffirmed
26