TRACKING CODE FOR COMET PHASE I CYDET DETECTOR BASED ON GENEFIT 2 - PDF document

TRACKING CODE FOR COMET PHASE I CYDET DETECTOR BASED ON GENEFIT 2 Internship report Research internship – Phytem Master 1 Author: Supervisor: SALAMBO DAGO YOSHITAKA KUNO Internship among the KUNO Laboratory, Department of Physics, Osaka University 1-4 Machikaneyama, Toyonaka, Osaka, 560-0043, JAPON From the 17th of April 2017 to the 27th of July 2017 CYDet Detector of COMET Phase -I

Thanks I would like to thank deeply my supervisor Yoshitaka KUNO who supervised and guided my work weekly, and who offered me a great opportunity to take part in the COMET Collaboration work. I would like to express also my deepest thanks to Chen WU who offered me the opportunity to work with him and who advised me and followed my work regularly. Finally, I thank the whole KUNO Laboratory team I had the chance to share my internship with and from whom I learned so much.

Abstract To meet COMET Phase-1 experiment requirements for single event sensitivity of 3.1×10 −15 for µ-e conversions, an accurate tracking of the electrons entering the Cylindrical Drift Chamber (CDC) of the COMET detector is needed. The point of this report is to describe the tracking code which will be used by the KUNO Laboratory during the analysis to reconstruct the initial momentum of the particles entering the CDC. The tracking code is still under development to reach the resolution and the efficiency expected, and is for now only tested with data of pure signal from Monte-Carlo simulation. The performances of the current version of the code, obtained after the definition of a set of quality cuts providing the best balance between the resolution and the efficiency of the code, will then be presented. A theoretical analysis of these results predicts a contamination by the noise from the muon decay in orbit (DIO) of 86.6% to reach a signal acceptance of 90%. That is why some modifications was performed on the tracking code to improve the total momentum resolution which causes such DIO contamination far above the COMET requirements. After a detailed study of the hit selection, we submitted a new version of the code to the analysis: the DIO contamination fell to 12.37% in the 90% signal acceptance window. 3

Overview Abstract .................................................................................................................................................. 3 1.Introduction ........................................................................................................................................ 5 1.1 About the Laboratory ................................................................................................................... 5 1.2 Introduction to COMET Collaboration ......................................................................................... 5 2. Topic and Issue ................................................................................................................................... 5 2.1 Physics Background ...................................................................................................................... 5 2.1.1 Lepton Flavour ...................................................................................................................... 5 2.1.2 Decay of Muon ...................................................................................................................... 5 2.1.3 The µ - e conversion ............................................................................................................... 6 2.2 Experimental device ..................................................................................................................... 7 2.2.1 COMET Phase-1 setup ........................................................................................................... 7 2.2.2 CyDet Detector ...................................................................................................................... 7 2.3 Purpose of the internship ............................................................................................................ 8 3. Understanding and update of the tracking code ............................................................................... 8 3.1 Issues ............................................................................................................................................ 8 3.2 Data and methods ........................................................................................................................ 9 3.3 Main steps of the code .............................................................................................................. 10 4. First results: Tracking code performances ...................................................................................... 11 4.1 Efficiency .................................................................................................................................... 12 4.2 Resolution .................................................................................................................................. 14 4.3 DIO Contamination .................................................................................................................... 14 5. Analysis of the results and improvements on the code .................................................................. 16 5.1 Origin of the bad reconstructions .............................................................................................. 16 5.2 Progress made and prospects .................................................................................................... 16 6. Conclusion ........................................................................................................................................ 18 Bibliography ......................................................................................................................................... 19 ANNEX 1: Tracking code ....................................................................................................................... 20 ANNEX 2: Details on the reconstruction steps .................................................................................... 21 ANNEX 3: Details on the fitting ............................................................................................................ 22 ANNEX 4: Definition of the seeds ........................................................................................................ 23 ANNEX 5: Details on the code version ................................................................................................. 24 4

1.Introduction 1.1 About t the L Laboratory The KUNO Laboratory (1), located on the Osaka University campus, is a research laboratory dedicated to the Particle Physics research. Bringing together 12 researchers and professor, 6 phD students and post-docs, as well as administrative staff, the laboratory is involved in the search for New Physics beyond the Standard Model within the COMET (COherent Muon to Electron Transition) Collaboration. The laboratory teams take part in the design of the detection and acquisition systems of the experience, and in the development of simulation and data analysis programs. I did my internship under the supervision of the Professor Yoshitaka KUNO, in charge of the laboratory and COMET spokesperson, and in close collaboration with the Doctor Chen WU. 1.2 Introductio ion t to COMET C Coll llaboration The COMET Collaboration brings together 32 institutes, including the KUNO Laboratory, in 15 countries where approximately 176 researchers focus on charged lepton flavour violation. In this context, the COMET experiment located at J-PARC 1 , is a new generation experiment using the most intense pulsed muon beam in the world. COMET experiment searches for evidence of charged lepton flavour violation (CLFV) via the neutrino less muon to an electron transition ( µ − 𝑓 conversion) in a nucleus field of aluminium, at a single event sensitivity (SES) of 2.6×10 −17 . This sensitivity 4 order of magnitude smaller than the current upper limit 2 will be reached in 2 steps: the first stage COMET Phase-1 is scheduled to start in 2018 and expects a intermediate sensitivity of 3×10 −15 . 2. Topic and Issue 2.1 Physic ics B Background nd 2.1.1 Lepton Flavour In the Standard Model, flavour in defined as a specie of an elementary particle. There are 6 flavours of quarks and leptons respectively. In lepton sector, there are 3 generations of charged leptons (𝑓 , 𝜈, 𝜐) and neutrinos (𝜉 𝑓 , 𝜉 𝜈 , 𝜉 𝜐 ). The quantum number of lepton flavour is chosen to be (𝑀 𝑓 , 𝑀 𝜈 , 𝑀 𝜐 ) = (1,1,1) for particle and (𝑀 𝑓 , 𝑀 𝜈 , 𝑀 𝜐 ) = (−1, −1, −1) for les anti-particle. 2.1.2 Decay of Muon The muon, of mass 𝑛 𝜈 = 105.66 𝑁𝑓𝑊/𝑑 2 , can be captured by a nucleus and form a muonic atom. To conserve the charge and flavour, the following decay modes are the most common decay mode for captured muons predicted by the Standard Model: 𝜈 − → 𝑓 − 𝜉 𝜈 𝜉 𝑓 ̅ (1) 𝜈 − → 𝑓 − 𝜉 𝜈 𝜉 𝑓 ̅ 𝛿 (2) 𝜈 − → 𝑓 − 𝜉 𝜈 𝜉 𝑓 ̅ 𝑓 + 𝑓 − (3) 1 Japan Proton Accelerator Complex in Tokai, Japan. 2 Limit set by SINDRUM-II experiment at Paul Scherrer Institute (PSI), Switzerland: SES = 2.3 ×10 −13 . 5