Hybrid Emulsion Detector for Neutrino Factory: Recalling the Physics Case and Future Prospects

1. Hybrid emulsion detector for the neutrino factory • Recall the physics case • The detector technology • Future prospects Giovanni De Lellis University of Naples“Federico II”

2. Recalling the physics case • Study the CP violation in the leptonic sector: e µ the most sensitive (“golden”) channel • In the (13,) measurement, ambiguities arise • Intrinsic degeneracy [Nucl. Phys. B608 (2001) 301] • m2 sign degeneracy [JHEP 0110 (2001) 1] • [23, /2 -23] symmetry [Phys. Rev. D65 073023 (2002)] • The “silver” channel (e  and   µ) is one way of solving the intrinsic degeneracy at the neutrino factory • A. Donini et al., Nucl. Phys. B646 (2002) 321. • An hybrid emulsion detector is considered • D. Autiero et al., Euro. Phys. J. C33 (2004) 243

3. Golden and silver channels ambiguities Solving the ambiguities

4. 10 X0 1 mm t 8.3kg n Pb Emulsion layers A hybrid emulsion detector • Target based on the Emulsion Cloud Chamber (ECC) concept • Emulsion films (trackers) interleaved by lead plates (passive) • At the same time capable of large mass (kton) and high spatial resolution (<1mm) in a modular structure The basic unit : the « brick » • ECC topological and kinematical measurements • Neutrino interaction vertex and decay topology • reconstruction • Measurement of hadron momenta by Multiple scattering • dE/dx for /µ separation at the end of their range • Electron identification and energy measurement • Visual inspection at microscope replaced • by kinematical measurements in emulsion 10.2 x 12.7 x 7.5 cm3 ECC technique successfully used in cosmic rays (X-particle discovery in 1971) and by DONUT for the direct observation 8 GeV

5. 8 cm 8 m Electronic detector task • trigger and location of neutrino interactions • muon identification and momentum/charge measurement ECC emulsion analysis: Vertex, decay kink e/g ID, multiple scattering, kinematics Electronic detectors: Target Trackers Pb/Em. target Spectrometer supermodule Link to muon ID, Candidate event Pb/Em. brick Basic “cell” 1 mm Pb Emulsion Extract selected brick Brick finding, muon ID, charge and p p/p < 20%

6. Punch through or decaying Topology and kinematics of signal Muon identification Background Charge misidentification: 1-3 x 10-3 from oscillation

7. Signal and background versus E charm decay in flight and punch-through 732 km t+ signal 3000 km

8. Emulsion scanning • Real time analysis: several tens of bricks extracted/day • High speed (20 cm2/h) fully automatic scanning systems (one order of magnitude faster than previous generation) • independent R&D in Europe and Japan based on different approaches • First prototype developed and tuned in Europe • Successfully running since Summer 2004 with high efficiency (>90%), high purity (~2 tracks/ cm2 /angle) and design speed • 2 mrad accuracy at small incident angles  Fast CCD camera (3 k frames/sec)  Continuous movement of the X-Y stage

9. Emulsion Scanning load • Boundary conditions: • detector located 732 km from the beam source • 5 years data taking • Scan all events with a negative (wrong sign) µ (#evts per kton): • “silver” ~ 30 events and “golden” ~ 310 • Anti-µ with misidentified charge: ~ 2200 • Charm background: ~ 80 events •  NC with punch-through or decaying h: ~ 4800 • ~ 8 x 103 events in 5 years • 510 kton ECC detector feasible

10. Combining ECC @ 732km and iron @ 3000km Allowed regions from the analysis of simulateddata for 13 = 1°,  = 90°. The bestfit is13 = 0.9°, = 80°. 5 kton ECC + 40 kton Iron No clone regions for 13>1°, for 13=1° they show-up in less than 10% of the experiments Both at 3000 km • Large reduction of all backgrounds ( 1/L2) except the muonic decay of + events from anti-µ anti-  • scanning load reduced by about a factor of 20

11. Precision measurements Position measurement of particle trajectories 0.05 µm 0.06 µm Nucl. Instr. Meth. A in press RMS distribution of fitted angular trajectories Median 0.4 mrad Median 0.64 mrad Inclined (200 mrad) particles Perpendicular particles

12. Momentum measurement by Multiple Scattering Routine scanning performed 2 GeV pions 3 GeV pions 22% resolution with 5 X0 30% resolution with 3 X0 Nucl. Instr. Meth. A512 (2003) 539

13. IN HID OUT dqav dXav porm ( ) eVolav  /µ separation using neural network (multiple scattering and energy deposit) Exposure at PSI (Zurich) with pure  and µ beams  (P=202MeV) and  (P=120MeV) follow tracks till they stop and characterize them according to the energy deposition per unit length and the scattering angle Data µ PRELIMINARY 

14. 4 GeV : data 6 GeV : data-MC comparison 2 GeV : data /e separation study:2 = 2e-2separator

15. R0: sheet normally developed after the exposure R0 R1 R2 R1: sheet refreshed after the exposure (3 days, 300C, 98% R.H.) LEXAN LEXAN LEXAN R2: sheet refreshed after the exposure (3 days, 380C, 98% R.H.) Exposure of an ECC to 400 Mev/u C ions at NIRS Cell structure ECC structure: emulsions and Lexan (C5H8O2) target sheets ( = 1.15 g/cm3) 1 mm thick (73 consecutive “cells”) 12C

16. Ionization ( only 3 mm chamber– R0 versus R1)  Z > 2 R0 p Ionization (8 cm chamber– R1 versus R2) Z = 6 Z = 5 Z = 3 Z = 4 Z = 2 R1

17. Conclusions • A hybrid detector for the study of CP violation in the leptonic sector by means of the “silver” channel is feasible • The OPERA experiment with the same technology will be running from next year and demonstrate it • The scanning load is feasible already now • Possible improvements • dE/dx measurement to reduce the charm background (already shown by test-beam data) • increase the mass of the detector and/or the exposure • Different strategy: scan > 1 brick per event  increase the signal detection efficiency by about 20% (increase in the brick finding efficiency) • The emulsion technology is improving in different contexts