LHCb Masterclass measurement of the Dº lifetime 37th International Conference on High Energy Physics LHCb Masterclass measurement of the Dº lifetime Ana Trisovic on behalf of the LHCb collaboration

International Masterclasses Discovery of Particle Physics for high-school students Lectures, exercises and computer applications for the visualization and calculation of physical phenomena For the first time with the LHCb Measurement International Masterclasses are a physics organization that provides an opportunity for thousands of students to get an insight into the topics and methods of fundamental particle physics research. It enables students to perform measurements on real data from the particle physics experiments themselves. LHCb statistics: 7 days of LHCb MC 20 institutes ~600 students th Edition in 2014

10 ps (and even longer) inside the experiment The Dº Meson 10% of LHC interactions produce a charm hadron - collected more than 1 billion signal charm decays Measuring the Dº Lifetime K- v ≈ 0.99919 · c s = ~ 0.12 + ~ 3 mm ~3.9% Lifetime at rest: 0.41 ps pi+ Dº meson 10 ps (and even longer) inside the experiment Charm quark Up anti-quark

Signal finding Appearance of the Event Display Students get a file with 30 selected candidates They look for displaced vertices, compute invariant mass and add it to the histogram Teacher gathers histograms between students

Functionality Projections Close-up view

Signal finding Step 1: The goal is to find a D° particle in the event, which decays K- and pi+

Step 2: Calculating invariant masses Step 3: Building up the histogram Combining all the histograms + discussion

Demonstration

Lifetime fit Requires a large number of events for reasonable accuracy ~15% off We have a systematic bias Fitting the lifetime and improving S/N ratio by cutting on the Dº Impact parameter (IP) Student get files with ~54000 candidate events Perform mass and lifetime fit and study the effect of various cuts (especially the Dº IP)

Lifetime fit Two types of data: Effect of IP cut: The final result K- pi+ K- pi+ D° D° B IP p p p p The final result PDG lifetime

Users’ feedback High interest from the students Great success! Many questions about CERN Great success! Very positive feedback!

Technical details Data: 2011 - 2012 data-taking Developed in MS Visual Studio 2012 Programming languages: ROOT C++ General requirements: ROOT and Cmake Need to make the software as easy and portable as possible Collaboration with CERN Media Lab

Total Event Visualizer Scientific discovery tool for general public Based on computer gaming technology Suitable for multiple platforms including Windows, Mac OS, Android, web browser…

LHCb in TEV

Thank you for your attention! For more info: http://lhcb-public.web.cern.ch/lhcb-public/en/LHCb-outreach/masterclasses/en/