hybrid emulsion detector for the neutrino factory giovanni de lellis university of naples“federico...
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Hybrid emulsion detector for the neutrino factory
Giovanni De Lellis
University of Naples“Federico II”
•Recall the physics case•The detector technology•Future prospects
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
Golden and silver channels
truemeas
90,1:parametersInput 13
ambiguities
Solving the ambiguities
A hybrid emulsion detector
8.3kg
10 X0
Pb
Emulsion layers
1 mm
10.2 x 12.7 x 7.5 cm3
• 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 (<1m) 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 GeVECC 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 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%
Topology and kinematics of signal
edunidentifi
C
Muon identification
Punch throughor decaying
NC
iedmisidentif
Charge misidentification: 1-3 x 10-3
from oscillation
Background
Signal and background versus E
732 km
3000 km
signal
charm
decay in flightand
punch-through
+
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
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• 510 kton ECC detector feasible
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/L2) except the muonic decay of + events from anti-µ anti- •scanning load reduced by about a factor of 20
Precision measurementsPosition 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 mrad Median 0.64 mrad
Nucl. Instr. Meth. A in press
Momentum measurement by Multiple Scattering
Nucl. Instr. Meth. A512 (2003) 539
3 GeV pions 2 GeV pions
30% resolutionwith 3 X0
22% resolutionwith 5 X0
Routine scanning performed
Xav
IN HID OUT
orav
eVolav( )
/µ separation using neural network (multiple scattering and energy deposit)
Dataµ
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
12
2
/
/
2
/
/
/2
N
i
ii
i
ii
e
ey
e
ex
e
2 GeV : data
4 GeV : data
2
0/
2
/ )(
6.132
X
d
zPee
/e separation study:2 = 2e -2
separator
6 GeV : data-MC comparison
Exposure of an ECC to 400 Mev/u C ions at NIRS ECC structure: emulsions and Lexan (C5H8O2) target sheets
( = 1.15 g/cm3) 1 mm thick (73 consecutive “cells”)Cell structure
LE
XA
N
LE
XA
N
LE
XA
N
R0 R1 R2
R0: sheet normally developed after the exposure
R1: sheet refreshed after the exposure (3 days, 300C, 98% R.H.)
R2: sheet refreshed after the exposure (3 days, 380C, 98% R.H.)
12C
Ionization ( only 3 mm chamber– R0 versus R1)
p
Z > 2
R0
R1
Z = 6
Z = 5
Z = 4Z = 3
Z = 2
Ionization (8 cm chamber– R1 versus R2)
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