1. Belarus activity in COMET experiment Dz. Shoukavy, IP NAS of Belarus Gomel, Belarus, July 27 - August 7, 2015

2. Context  Introduction  Muon to electron conversion  COMET experiment  COMET preparation status  Belarus activity

3. Introduction The discovery of a Higgs boson at the LHC in 2012 provided the missing piece in the Standard Model (SM) to explain electroweak symmetry breaking. However there remain many shortcomings in the SM's description of nature, notably: the lack of a dark-matter candidate, no explanation for the observed matter antimatter asymmetry in the universe, no quantum theory of gravity or explanation for neutrino masses. So perhaps Standart Model is only a part of a bigger picture that includes new physics hidden deep in the subatomic world or in the dark recesses of the universe. New information from different experiments will help us to find more of these missing pieces. All these phenomena highlight the need for physics beyond the SM (BSM) and many of these models predict charged lepton flavour violation (CLFV).

4. Muon to electron conversion  One of the most important muon LFV processes is coherent neutrinoless conversion of muons to electrons so called μ - – e - conversion.  When a negative muon is stopped by some material, it is trapped by an atom, and a muonic atom is formed. After it cascades down energy levels in the muonic atom, the muon is bound in its 1s ground state.  Further, in SM the following processes are possible: muon decay in orbit μ − → e− ν μ ν e or  muon capture by a nucleus of mass number A and atomic number Z, i.e. μ − + N (A, Z ) → ν μ + N (A, Z − 1).

5. Muon to electron conversion However, in the context of physics beyond the Standard Model, exotic process of neutrinoless muon capture is expected This process is called μ - – e - conversion in a muonic atom. This process violates the conservation of lepton flavor numbers, L e and L μ, by one unit, but the total lepton number L =L e +L μ +Lτ is conserved. L μ +1 0 0 0 L e 0 0 +1 0

6. Muon to electron conversion μ - + (Z,A)->e - + (Z,A) Backgrounds Radiative π/μ capture Deacay in Flight Cosmic rays Decay in orbit (DIO) B μ - binding energy

7. Muon to electron conversion. Hstory Past experiments on μ - - e - conversion

8. Muon to electron conversion The size of the observable flavour effect for a variety of BSM SUSY and non-SUSY models. large effect visible, but small W. Altmannshofer et.al, Nucl. Phys. B 830 (2010) 17 unobservable AC - Abelian U(1) flavour symmetry model by Agashe and Carone RVV2- non-Abelian model by Ross, Velasco-Sevilla and Vives AKM- Antush, King andMalinsky SU(3) flavour FBMSSM - Flavour-blind MSSM LHT- Littlest Higgs with T-Parity δLL- flavour models RS - Randll-Sundrum model with custodial protection.

9. Muon to electron conversion. Summary μ - + (Z,A) -> e - + (Z,A) Undiscovered process Branching ratio (BR) at Standard Model (SM)~O(-54) BR at beyond SM ~O(-15) Recent upper limit : 7 x 10 -13 (SINDRUM-II at PSI) Observation of muon to electron conversion would indicate a clear signal of physics beyond the SM

10. COMET experiment  COherent Muon to Electron Transition - COMET. Experimental goal search for μ−e conversion in the field of an aluminium nucleus, μ−N → e− N, with a single event sensitivity of 2.6×10 −17

11. COMET experiment  Powerful proton source at J-PARC (Japan)

12. Comet experiment High efficiency π-capture system The pion capture solenoid is of critical importance for capturing pions from the proton target with a large solid angle, and transporting muons from pion decays to the muon stopping target efficiently. In the pion capture solenoid section, a magnetic field of 5 T along the direction of solenoid axis is required at the location of the proton target to capture as many low energy pions as possible. The magnetic field is adiabatically reduced down to 3 T in the matching solenoid section. R - radius of the inner bore of the solenoid magnet

13. Comet experiment Proton target The proton target is required to generate pions which will decay to muons as they are transported to the muon stopping target in the detector solenoid. The target will be installed within the bore of the capture solenoid with a configuration designed to capture low energy negative momentum pions generated proton beam from the J-PARC MR synchrotron. COMET PHASE-I

14. Comet experment The selection of the electric charge and momentum of beam particles can be performed by using curved solenoids. In curved solenoids, the center of the helical trajectory of a charged particle is shifted(D[m]) This drift can be compensated by an auxiliary field parallel to the drift direction given by

15. COMET experiment  The muon-stopping target is placed in the centre of the detector solenoid. The muon-stopping targetis designed to: maximise the muon-stopping efficiency and the acceptance for the μ− N → e− N conversion electrons to arrive at the spectrometer and to minimise the energy loss of the conversion electrons as they exit the muon- stopping target in order to minimise the momentum spread of the electrons. Muon Stopping Target

16. COMET experiment. StrEcal StrEcal high resolution electron detector

17. COMET erxperiment StrEcal detector placed in vacuum and magnetic field of 1T Straw tracker 5 station, diameter 5 mm, gas mixture 50% Ar and 50% - C 2 H 6 thickness 20/12 μm Detection of particle track in magnetic field Momentum resolution : σ p < 200 keV/c for 105 Mev/c electon Spatial resolution < 200 μm Ecal LYSO crystals (Lu 1.8 Y.2 SiO 5 :Ce) Measure the electron energy with resolution < 5% for 105 Mev/c electon Provide particle indentification (E/p) with tracker Ecal will also provide trigger signals Time resolution < 100 ns Cluster position resolution < 1 cm

18. Comet experiment Ecal structure Ecal will consist of crystal modules which have a 2 × 2 cm 2 cross-section and whose length is 12 cm for LYSO crystals. R =55 cm Basic unit: 2x2 crystals -> 1 module

19. COMET experiment. Staged approach COMET Pahse-I COMET Pahse-II

20. Goal of COMET PHASE-I 1. Background study for the full COMET (Phase-II) Direct measurement of potential background for the full COMET experiment using same detector as Phase-II. 2. Search for μ-e conversion a search for μ-e conversion at the intermediate sensitivity which would be 100-times better than the present limit (SINDRUM-II)

21. COMET PHASE-I μ-e conversion search in the Phase I 6x10 9 muon/sec

22. COMET PHASE-I Physics Sensitivity for COMET phase-I 8 GeV, 3,2 KW proton beam is assumed 2,510 12 protons/sec running time is 110 days (9,5 10 6 sec) Expected single event sensitivity Upper limit at 90% C.L.

23. COMET PHASE-I Measure almost all the particles Same detector system for Phase-II Straw tube tracker Crystal calorimeter Particle ID with dE/dx from tracker E/p from ECAL Background study

24. COMET PHASE-I  Cylindrical detector (CyDet) for the μ-e search CDC - cylindrical drift chamber

25. Summary of COMET phase-I/II

26. COMET preparation status Construction of the COMET building is completed! Underground structure, beam line construction is ongoing

27. COMET preparation status Main part of COMET transport solenoid is already installed in the COMET hall

28. COMET preparation status Straw mass production is oingoing at JINR group

29. COMET preparation status

30. COMET collaboration 179 participants from 32 institutes as of July 2015 http://comet.kek.jp

31. COMET collaboration CM15 at KEK/J-PARC, January 2015

32. Belarus activity Beam Test in March 2014 @ Tohoku

33. Belarus activity Beam Test in March 2014 @ Tohoku 2x2x12 cm LYSO (Lu 1.8 Y. 2 SiO 5 :Ce) 2x2x15 cm GSO (Lu 1.8 Y. 2 SiO 5 :Ce)

34. Physics Runs Momentum Scans 65 Mev/c, 85 Mev/c, 105 Mev/c, 125 Mev/c, 145 Mev/c for GSO and LYSO. The incident beam is perpendicular to the center of the crystal array. Beam Belarus activity

35. A scheme of analysis 1. Waveform fitting Get deposit charges. 2. Conversion to energy Calibration factors obtained by cosmic runs 3. Clustering Sum up energy deposits Make energy spectra. Energy resolution GSO (Gaussian fitting)

36. Belarus activity

37. Further we need to find the charge to energy conversion factors for every crystal so-called calibration factors using cosmic data. Example cosmic event. Run 113 Event 244 Bunch 0 GSO Belarus activity Calibration factors

38. Belarus activity Calibration factors We must have a good criterion to exclude these ring noise events. We have found such one based on chi-square parameter. chi2 = Fitting Function ->GetChisquare(); ring noise event

39. Distribution of the total deposit charges in crystals for LYSO (p=105MeV/c) Distribution of the total deposit charges in crystals for GSO (p=105MeV/c) Thus in the first approximation to determine the resolution we can use the box 5x5 in the center of the crystal 24 Belarus activity.Clustering

40. High energy resolution for both crystals without any additional cut to purify data. LYSO has an energy resolution less than 5% for 105 MeV/c ! Calibration factors obtained by fitting with Landau function The comparison of energy resolution for GSO and LYSO Stochastic terms GSO/LYSO: is roughly Belarus activity

41. Japan group result (Kou Oishi)

42. Belarus activity  What cluster is better to use for ECAL pretrigger? Array of 1x1, 2x2 or 3x3 modules ?  What algorithm for choice of a cluster is better for ECAL pretrigger?  What is the average energy deposited in modules ?  What the threshold do we need to use for better results?  We must know answers. We have tried to answer these questions. Simulation of an algorithm for ECAL pretrigger. First step

43. Belarus activity Red - electrons; Green - photons -20 < θ < 20 0 Uniform magnetic field: Bx=By=0,Bz=1T Using Gaussian distribution of noise σ_noise_crystal is 0,4; 0,6 MeV.

44. BINP Algorithm for pretrigger

45. Another an algorithm for pretrigger

46. Deposited energy in 3x3 modules  Generate 1 mln, electron with p =105 MeV/c -20 0 < θ < 20 0 -5 0 < θ < 5 0 -10 < θ < 10 0 97,3775 MeV 97,4956 MeV 97,4991MeV The distribution of total deposited energy in modules for 3x3 array

47. Max energetic module -5 0 < θ < 5 0 -10 < θ < 10 0 -20 < θ < 20 0 Conlusion. One module can't use as the cluster for ECAL pretrigger for ECAL pretrigger

48. Energy leak  Here the energy leak means difference between the total deposited energy in the setup and the total deposited energy in 3x3 & 2x2 modules

49. Why does the another algorithm look so bad? Answer: Because this algorithm does not always correctly reсonstruct crystal with the largest energy deposit for max energetic module. Here you can see the difference between the true value of line for crystal with the largest energy deposit and the reconstructing value. The same picture for raw too. As a result we correctly reconstruct the crystal with max energy deposit for ~60% events only.

50. Threshold  What is the optimal value for threshold energy?  We add the threshold energy for module in our model i.e we take into acount events when total deposited energy in module larger then threshold.  if (Energy_2x2_right_module < threshold) { Energy_2x2_right_module = 0;} and so on. In the case σ_noise_crystal = 0,4 MeV we have Also we consider the case when σ_noise_crystal =0,6 MeV σ_noise_ module = 1,2 MeV We have plotted the dependence of energy resolution on threshold energy (for threshold energy = 0, 0,5σ_noise_ module; 1σ_noise_module; 2σ_noise_module and 3σ_noise_module) Right Module

51. Threshold. Energy resolution. 0,5σ1σ1σ 3σ3σ 2σ2σ0σ 2σ2σ 1σ1σ 0,5σ 0σ 3σ3σ The optimal value for threshold energy is 0,5σ_noise_ module -20 < θ < 20 0 Red color corresponds σ_noise_ module=0.8 MeV Blue color - σ_noise_ module=1.2 MeV

52. Summary CLFV would give the best opportunity to search for BSM. (So far, no BSM signals at the LHC.) Muon to electron conversion could be one of the important CLFV processes in terms of theoretical and experimental points of view The COMET is a search experiment for μ - -e - conversion at J-PARC with sensitivity of O(-17) which is four orders of magnitudes better than the present limit. We’re ready for the COMET Experiment phase-I !!! Thank you !!!