Weak Mixing Angle Measurement

Analysis of W and Z boson production in LHC collisions to measure the weak mixing angle (sin²θw)

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Project Overview

This project investigates W bosons produced in the LHC's 8 TeV proton-proton collisions to measure the weak mixing angle, a fundamental parameter of the Standard Model of particle physics. The analysis focuses on jet physics and particle identification techniques.

Key Physics Concepts

W Boson Production

The W boson is produced through quark-antiquark annihilation in proton-proton collisions. The process involves the weak interaction, and the W boson can decay into various final states, including quark pairs that form jets.

Lorentz Boost

When W bosons have high energy, their decay products are confined within a narrow cone due to relativistic effects. This allows both decay products to be reconstructed as a single "fat jet" rather than separate jets.

Weak Mixing Angle

The weak mixing angle (sin²θw) is a fundamental parameter that describes the mixing between the W³ and B fields in the electroweak theory. It can be measured through the ratio of W and Z boson masses.

Background Suppression

The main background comes from QCD multijet production. Sophisticated algorithms are used to distinguish between signal events (W→qq) and background events (quark/gluon jets).

Analysis Features

Jet Analysis

Comprehensive analysis of fat jets using various algorithms including soft drop, pruning, and trimming techniques.

Particle Identification

Advanced algorithms for distinguishing between quark and gluon jets, and identification of b-quarks within jets.

Statistical Analysis

Robust statistical methods for background estimation and signal extraction with proper uncertainty quantification.

Analysis Methodology

1
Data Selection

Apply trigger requirements and basic kinematic cuts to select events with high-pT jets. Use both 8 TeV and 13 TeV collision data for comprehensive analysis.

2
Jet Reconstruction

Reconstruct fat jets using large-radius algorithms to capture both W decay products. Apply PUPPI algorithm for pileup mitigation.

3
Background Modeling

Model QCD multijet background using simulation and data-driven methods. Include contributions from top quark pairs and diboson production.

4
Signal Extraction

Extract W boson signal using mass window analysis and fit procedures. Measure the W peak position and width for mass calibration.

5
Parameter Measurement

Measure the weak mixing angle through the ratio of W and Z boson masses, accounting for systematic uncertainties and detector effects.

Key Results

W Boson Peak Detection

Successfully identified and characterized the W boson mass peak in the fat jet mass distribution, demonstrating effective signal extraction from background.

Mass Calibration

Performed precise mass calibration using known W and Z boson masses, enabling accurate measurement of the weak mixing angle.

Background Suppression

Implemented effective background suppression techniques, achieving high signal-to-background ratios for reliable measurements.

Statistical Precision

Achieved competitive statistical precision in the weak mixing angle measurement, contributing to tests of the Standard Model.

Visual Results

W Boson Mass Peak
W Boson Mass Peak

Invariant mass distribution showing clear W boson peak at ~80.4 GeV

Z Boson Mass Peak
Z Boson Mass Peak

Invariant mass distribution showing Z boson peak at ~91.2 GeV

Jet Substructure Analysis
Jet Substructure Analysis

Tau21 distribution showing quark/gluon jet separation and background modeling

W Boson Fitting Analysis
W Boson Fitting Analysis

Statistical fit showing signal extraction and background modeling with uncertainties

Z Boson Fit Components
Z Boson Fit Components

Detailed analysis of Z boson fit components and background contributions

Technologies & Data Sources

Python

Data analysis and statistical computing

ROOT

High energy physics data analysis framework

LHC Data

8 TeV and 13 TeV collision data

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