Introduction

Overview

Teaching: 0 min
Exercises: 0 min

Questions

• What is pileup? Why should we care about it?

Objectives

• Understand the concepts of bunch crossing, pileup, and pileup modeling.

What is pileup?

• bunch crossing
• bx rate during run 1 and run 2
• number of simultaneous interactions - example calculation
• number of pileup
• difference w.r.t. underlying event
• comparison of pileup in run1 vs. run2, larger effect during run 2

Why should we care about pileup?

• how pileup shows up in detector: extra junk, tracks, jets, you name it
• affects everything from trigger rates to reconstruction, e.g. tracking and jet clustering
• we try to make pileup resistant algorithms but usually there is some residual pileup dependence
• in-time-pileup vs. out-of-time pileup

Measuring pileup in data

• basic idea: measure luminosity, calculate cross section, infere pileup

Modeling pileup in simulation

• we need to simulate pileup if we want simulations to match data
• basic idea idea: how do we simulate it? by mixing pileup events with the hard processes with some randomness
• exact pileup distribution can depend on what data samples you select; so we need to reweight the simulation (or maybe we simulated already before the data was collected!); these are called pileup corrections

Outline of the exercise

• learning goal: how to check pileup distributions of data and simulated samples, and correct them
• practical example: HTT analysis

Key Points

• First key point. Brief Answer to questions. (FIXME)