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

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] –  m 2 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. A hybrid emulsion detector 8.3kg 10 X 0 Pb Emulsion layers  1 mm 10.2 x 12.7 x 7.5 cm 3 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 (<1  m) 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 8 GeV ECC technique successfully used in cosmic rays (X-particle discovery in 1971) and by DONUT for the  direct observation

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

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

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

8. Emulsion scanning Real time analysis: several tens of bricks extracted/day High speed (20 cm 2 /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/ cm 2 /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 10 3 events in 5 years 5  10 kton ECC detector feasible

10. Combining ECC @ 732km and iron @ 3000km No clone regions for  13 >1°, for  13 =1° they show-up in less than 10% of the experiments 5 kton ECC + 40 kton Iron Allowed regions from the analysis of simulated data for  13 = 1°,  = 90°. The best fit is  13 = 0.9°,  = 80°. Both at 3000 km Large reduction of all backgrounds (  1/L 2 ) 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 RMS distribution of fitted angular trajectories Perpendicular particles Inclined (200 mrad) particles Median 0.4 mradMedian 0.64 mrad Nucl. Instr. Meth. A in press

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

13.  X av INHIDOUT  or   av eVol av ()  /µ separation using neural network (multiple scattering and energy deposit) Data µ  PRELIMINARY 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

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

15. Results –  exposure at CERN P P     e

16. Exposure of an ECC to 400 Mev/u C ions at NIRS ECC structure: emulsions and Lexan (C 5 H 8 O 2 ) target sheets (  = 1.15 g/cm 3 ) 1 mm thick (73 consecutive “cells”) Cell structure LEXAN R0R1R2 R0: sheet normally developed after the exposure R1: sheet refreshed after the exposure (3 days, 30 0 C, 98% R.H.) R2: sheet refreshed after the exposure (3 days, 38 0 C, 98% R.H.) 12 C

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

18. 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