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

 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

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

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

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

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 crystals in a film 6

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

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

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

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

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

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

Flux measurement Reconstructed tracks – Angular acceptance tan  <0.3 – Efficiency correction applied – Negligible BG from cosmic ray For 250 kA, 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

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

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

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: – Submitted to PTEP, under revision 16

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

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Backup 19

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

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)

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 May Fit peak Mar May

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