1. 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

2. 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

3. 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 ≈ · c
s = ~ ~ 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

4. 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

5. Functionality
Projections
Close-up view

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

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

8. Demonstration

9. 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)

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

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

12. 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

13. 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…

14. LHCb in TEV

15. Thank you for your attention!
For more info: