Introduction

The goal of this exercise is to compute the cross-section of $Z \to \tau \tau$ production. As the tau lepton may decay to e, mu, or hadrons there are in fact 6 different final states to be considered. In this exercise, we will focus on those containing at least one hadronically decaying $\tau$ ($\tau_h$): $e+\tau_h, \mu+\tau_h,$ and $\tau_h+\tau_h$. Please choose one.

• We will identify sources of standard model processes other than $Z \to \tau \tau$ which may mimic our signal, and define event selection to minimize their contribution to our analysis.
• The background events will be estimated using both simulation and data-driven approaches.
• We will then prepare a data card as input to the Higgs Combine Tool. This datacard will be used to perform a maximum likelihood fit of the expected signal (taken from simulation) and background yields to extract the best-fit value of the $Z \to \tau \tau$ cross-section. Each student will perform their work in parallel with the other students, and on the final day, we will collectively combine each person’s result into a 15-minute presentation summarizing our results.

Please join the Mattermost chat for discussion and questions: LongExTauTau Mattermost Channel

The plots and performance curves seen here are for example purposes only, they do not serve in any official capacity.

Useful Links

• CMSDAS Indico agenda: https://indico.cern.ch/event/1333922/
• Tau Short exercises: https://github.com/Fengwangdong/CMSDASLPC2024-Tau-Short-Exercise.git
• Github repository: https://github.com/fojensen/nanoAOD-tools/tree/cmsdas2022
• DeepTau documentation: http://cms.cern.ch/iCMS/analysisadmin/cadilines?l - ine=TAU-20-001
• DeepTau DPS notes from 2019: https://cds.cern.ch/record/2694158/
• Tau POG: https://twiki.cern.ch/CMS/Tau
• NANOAOD documentation: https://cms-nanoaod-integration.web.cern.ch/integration/master-102X/mc102X_doc.html
• nanoAOD-tools: https://github.com/cms-nanoAOD/nanoAOD-tools
• Tau hypernews: hn-cms-tauid, hn-cms-tau-hlt
• Tau reconstruction performance in Run 2: https://arxiv.org/abs/1809.02816
• Tau reconstruction performance in Run 1: https://arxiv.org/abs/1510.07488
• Z->tautau at 7 TeV: https://arxiv.org/abs/1104.1617
• Z->tautau at 13 TeV: https://arxiv.org/abs/1801.03535
• NanoAOD autodoc V9: https://cms-nanoaod-integration.web.cern.ch/autoDoc/

Prerequisites

For these exercises, you need to bring your laptop registered to the FNAL network link, have a working LPC account link, and have a valid grid certificate link.