1. Characterization of muon beam in T2K with emulsion detectors A. Ariga, T. Ariga, C. Pistillo AEC-LHEP University of Bern 1

2.  Understanding of muon flux leads to understand neutrino beam  Muon monitor (MUMON): direction and stability of the muon beam (spill-by-spill)  Si PIN Photodiode + Ionization Chamber (IC) (7x7 sensors each, 25-cm spacing) The T2K Muon monitor INGRID 2

3. MUMON phase space coverage Phase space contributed to the fluxes – beam dump of T2K corresponds to 5 GeV energy loss Parent pion p-  distribution contributing to neutrino flux at SK Parent pion p-  distribution contributing to muon flux at muon pit 3

4. Particle components The beam is a mixture of muons and low energy components (electrons)  Charged particle flux is predicted to be ∼ 90% muons  Difficult to quantify by Si or IC detectors  Emulsion detectors 4

5. Emulsion detectors at the muon pit  Si, IC measure the integrated ionization, while emulsion can reconstruct individual tracks (positions and angles).  Small contamination from low energy component (~1%)  Absolute muon flux measurement  Momentum measurements through multiple Coulomb scattering Reconstructed data 5

6. 20μm π-10GeV/c Electron ～ 100keV intrinsic resolution 50nm! Photographic emulsion detectors (ex. OPERA film by Fuji Film) The best among the detectors! sensitivity 36grains/100micron 6 Cross-sectional view (SEM) Plastic Base (200micron) Emulsion Layer Emulsion Layer (44micron)  minimal detectors AgBr Cristal, Size = 0.2micron 10 14 crystals in a film 6

7. 7 How the tracks are seen 80 micron 1MeV/c electron 1MeV/c 10MeV/c 100MeV/c 1GeV/c 飛跡の再構成 track reconstruction filmbetween films between lead 1MeV/c ＸＸＸ 10MeV/c○ △Ｘ 100MeV/c○○ △ 1GeV/c○○○ △： possible to reconstruct, tuning parameters film (300  m) film lead 0.5~1mm 7

8. Module structures Flux module: Only trackers, up to 10 6 particles/cm 2 Momentum module: Trackers and scattering material, measure the momentum by multiple Coulomb scattering. Up to 5x10 4 particles/cm 2 Flux module 8 films Momentum module 25 x (films + 1mm-lead) MUMON Beam Momentum module Flux modules MUMON 8

9. Detection efficiency (MC) Reconstruction in 8 films – Angular acceptance: tan  <0.3 low energy component has wide angular distribution – Request an O(mrad) angular matching between segments in different films Electron contamination reduced to 1% level, while muon efficiency kept ~98% 9

10. Emulsion exposure (2010) 7 flux modules + 1 momentum module for each shot. 2 horn configurations (0kA, 250kA) Dedicated low intensity shots, O(10 11 ) POT  O(10 4 ) tracks / cm 2 at emulsion Emulsion modules Vertical support Horizontal aluminum support 10

11. Emulsion scanning at LHEP Bern 24 modules (226 plates) were scanned. Scanning and reconstruction took net 3 weeks using 1 automatic microscope. 6 microscopes with automatic plate changers in Bern. The largest scanning lab in Europe for OPERA event analysis We used 1 of the OPERA microscopes dedicated to T2K. 11

12. Reconstructed tracks ~2x10 4 tracks/cm 2 tracks reconstructed in the 1mm x 1mm area in the center module (250kA) (animation) mm mm 1cm x 1cm 12

13. Flux measurement Reconstructed tracks – Angular acceptance tan  <0.3 – Efficiency correction applied – Negligible BG from cosmic ray For 250 kA, 4.06 +- 0.05 +- 0.10 x 10 4 tracks/cm 2 /4x10 11 p.o.t. Stat. error only for MC Data/ MC comparison MC: FLUKA Tuned MC with systematic error 13

14. Angular distribution High precision mechanical support – 1 mrad accuracy with laser alignment Angular resolution 2mrad for each track Rich information – origin of muon – momentum component Stat. error only for MC  x (rad)  between plates RMS 2.5 mrad Center module Left module 14

15. Momentum distribution Momentum is estimated by Multiple Coulomb Scattering track by track Resolution ~ 30% Nice probe for hadron production model Reconstruction efficiency with 1- mm lead (MC) Momentum resolution (MC) Stat. error only for MC 15

16. Summary T2K employed a series of emulsion detectors to characterize the muon beam. – Number of muons, rejecting low energy components (2% error) – Angular distribution (2mrad for each track) – Momentum distribution (30% for each track) –  Check of hadron production model A reasonable agreement between data and prediction is found after a dedicated tuning. – More detail: http://arxiv.org/abs/1412.0194http://arxiv.org/abs/1412.0194 – Submitted to PTEP, under revision 16

17. Outlook for BNB In case you deem possible and useful such a measurement at BNB, we would be happy to discuss it further – Where to place the detector – Feasibility of low intensity run (~ 10 4 particle /cm 2 at emulsion) – Horn setup We would make available emulsions (detector assembling and operations), chemicals (emulsion development), microscopes (scanning) We would need – Support on site (dark room for emulsion handling and development, site definition and surveying) – MC simulation – Contribution for emulsion scanning and/or analysis 17

18. End 18

19. Backup 19

20. Measure position, angle and momentum of muons. Beam dump Emulsion tracker 20   Transverse momentum by scattering ~250MeV/c Emulsion tracker Measurement - Position - 3D angle (  =~3mrad) - Momentum ~150X 0 energy loss 5GeV P T =30MeV/c Muon Pit MUMON Decay volume Reconstructed data MUMON Beam Momentum module Flux modules MUMON

21. DAQ (scanning) and processing RAW tracks on each surface. Reconstructed tracks between base. base em Computing ~5min Computing 5~30min Reconstructed tracks between films Analysis Scanning 10min/cm 2 film Scanning of 1 module takes 2 hours. Most time consuming. 21 Basetrack (Segment)

22. Reproducibility check (0kA data) 22 2 measurements for 0kA were compared. – 1 st exposure (May 2009) and 2 nd exposure (Mar 2010) Shots with 0kA is less sensitive to horn changes. 2 independent measurements show good agreement.  (cm) Mar 2010121.8 +- 6.5 May 2009131.0 +- 7.6 Fit peak Mar 201010940 +- 128 May 200910740 +- 117

23. Parent P-  distribution (MC) parent of muons 0kA 273kA Difference between 273kA and 0kA Difference between 273kA and 0kA By taking the difference, possible to analyze the large  components. rad 23 MC 09c Emu