This lesson is in the early stages of development (Alpha version)

CMSDAS: Measurement of B0s→μ+μ− Long Exercise

$B_s^0 \to \mu^+\mu^-$

Prerequisites

Goal of this exercise

To find new Physics.

The exercise is performed on data collected during Run 2.

Facilitators CMSDAS LPC 2026

These instructions were created by Kai-Feng Chen and Federica Riti for CERN CMSDAS 2024, and are minorly augmented here to run on cmslpc for LPC CMSDAS 2026. Big thanks and all credit to them for their hard work in creating and maintaining this exercise!

This is an introduction to the exercise based on the recent publication on the measurement of $B_s^0 \to \mu^+\mu^-$ decay branching fraction and effective lifetime using the CMS Run-2 data sets (a.k.a. BMM5 analysis), see BPH-21-006 for details. In this exercise we will start with an introductory presentation, quickly touch the reconstruction of B meson using the standard tool from BPH group, and practice how to construct an unbinned maximum likelihood fitter to extract the decay branching fractions based on RooFit (the real main task!).

Introductory slides

We will start with this introductory slides: CMSDAS_BsMuMu.pdf.

Support

Join the LongEX BsMuMU Mattermost channel and don’t hesitate to ask for help from the facilitators in the room.

Schedule

Setup Download files required for the lesson
00:00 1. Introduction What is the physics motivation for measuring $B_s^0 \to \mu^+\mu^-$?
What is the overall analysis strategy?
00:15 2. Signal MC Fit How do we model the $B^+ \to J/\psi K^+$ signal peak?
How do we apply MC-derived shape parameters to data?
01:05 3. Normalization Channel How do we fit the normalization channel $B^+ \to J/\psi K^+$?
How do we extract the $B^+ \to J/\psi K^+$ yield and efficiency?
How do we compute the fs/fu production fraction ratio?
01:45 Finish

The actual schedule may vary slightly depending on the topics and exercises chosen by the instructor.