Emulsion detector at a Neutrino Factory Detector Working Group, Aug. 21 st, Irvine, California Giovanni De Lellis University of Naples “Federico II” on behalf of the ECC WG

Outline of the talk Revise the potentiality of using an ECC detector to study the silver channel Use nuclear emulsions in a magnetic field MC simulation to validate the perfomances Experimental tests performed Perspectives of the technique Current limitations

The physics case: synergy of golden and silver channels 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. D (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

Golden and silver channels ambiguities Solving the ambiguities

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

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 locate the 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%

Topology and kinematics of signal and background Punch through or decaying Charge misidentification: 1-3 x from oscillation Background 732 km 3000 km signal charm decay in flight and punch-through ++ Signal and background versus E

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

Emulsion Scanning load Boundary conditions: –1 Kton detector located 732 km from the beam source –5 years data taking Scan all events with a negative (wrong sign) µ : –“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 10 kton ECC detector feasible CHORUSDONUTOPERA TS(TTL)NTS(CPLD)UTS(FPGA)S-UTS Scanning System History views/sec ( 1view=120×90  m 2 ) European scanning system

Combining 732km and 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

dE/dx measurement NIM A516 (2004) 436 Pb Film P=1.2GeV/c Hadron dE/dX dE/dx =  measurement ~number of grains  P

Electron energy measurement MC a few GeV Energy determination by calorimetric method Test CERN

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

Position and angular accuracy: NIM A554 (2005) 247 X projectionY projection 0.05 µm Straight tracks (up to 50 mrad) Median ~ 0.4 mrad 200 mrad inclined tracks 0.6 mrad 300 mrad inclined tracks 0.9 mrad Residual of base tracks w.r.t. fitted tracks Using precise meausurements p  measured with 15-20% accuracy up to 6 GeV

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

Emulsion detector in a magnetic field Measure the charge and momentum The charge determination allows the extension of the silver channel to the non-muonic decays (BR gain) Study the feasibility of the “platinum” channel ( µ  e ) by means of the charge determination and electron identification capabilities

Magnetized ECC structure We have focused on the “target + spectrometer” optimization Electronic det: e/  /µ separator & “Time stamp” Rohacell® plate emulsion films 35 stainless steel plates spectrometer target shower absorber 4.5 cm, 2 X0

Structure optimization To be optimized: spacer thickness (2  5 cm) and magnetic field (0.25  1 T) Using muons with momentum from 1 to 10 GeV In the evaluation of the performances, true and reconstructed momentum are compared downstream of the target region (beginning of the spectrometer) except when using the Kalman filter

4 GeV µ momentum resolution

4 GeV µ charge misidentification

µ end electron momentum resolution: 3 gaps (3cm thick) and 0.5 T For the electron only hits associated to the primary electrons used in the parabolic fit (Kalman not used) Given the non negligible energy loss in the target, the electron energy is taken downstream for the comparison of true against reconstructed µelectron

µ and electron charge mis-identification: 3 gaps (3cm thick) and 0.5 T µ electron

Experimental test for a M-ECC Compact ECC structure Chika Fukushima S. Ogawa, M. Kimura, Hiroshi Shibuya, Koichi Kodama, Toshio Hara Dec KEK-PS T1 line Different support used (40 μm polystyrene or 200 μm acrylic plate) 2 GeV  + [without magnet] 3000/cm2 as reference beam 1 T magnetic field Different momentum: 0.5, 1 and 2 GeV, each with 1000/cm2  + (  -)

The sagitta method L = 3 cm in this study

Preliminary experimental results The relative error is roughly ds/s = 0.20  p [GeV/c] ds/s should be about 0.35 in the case of p = 10 GeV/c Assuming a Gaussian distribution, the charge mis- identification probability for a 10 GeV lepton ~ 0.2% N.B. Multiple Coulomb scattering has larger tails  The probability of the charge mis-identification should be somewhat larger Difference with the proposed geometry: Better plate to plate alignment (few µm instead of 10 µm) ++ 2 gaps instead of 3 -- Gap width 1.5 cm instead of 3 cm --

Possible design of a far detector Assume transverse size 15.7x15.7 m 2 (as Nova) A brick contains 35 stainless steel plates 1 mm thick: it corresponds to about 2 X 0 The spectrometer part consists of 3 gaps (3 cm each) and 4 emulsion films Brick weigh 3.5 kg A wall contains bricks  68 tons 60 walls  bricks  4.1 kton Emulsion films are 47.3 M pieces (12 M in OPERA) Assuming as electronic detector 35 Nova planes (5.3 X 0 ) after each MECC wall  2100 planes The total length of the detector would be ~ 150 m Synergy with other detectors for the silver and platinum study Signal (θ 13 =2°,δ=0°) Signal (θ 13 = 2°, δ=90°) Background L=732km old L=3000km old L=732km new L=3000km new Silver channel sensitivity Very preliminary

Conclusion and outlook A hybrid detector for the CP violation study in the leptonic sector is feasible by means of the “silver” channel A magnetized ECC with stainless steel has also been presented Modular structure allows to test it with a single brick First experimental tests are very encouraging A far detector (4 Kton target) with this technique has been presented The choice of the electronic detector brings interesting synergies Big question mark: how to magnetize so large volumes Study the µ identification with the electronic detector Check the sensitivity to the “golden” channel A full simulation of neutrino interactions mandatory to evaluate the oscillation sensitivity