1. OPERETTE TEST BEAM EXPERIMENT :
C. HERITIER on behalf of operette working group

2. USING FREE NEUTRINO BEAM
OPERETTE
WHY?
The main aim of Operette is to prepare OPERA for what concerns the scanning of emulsion films with neutrino events.
to check and improve on vertex finding efficiency.
to check the validity of the brick finding efficiency
to check the back scattering contribution.
USING FREE NEUTRINO BEAM

3. The beam layout 400 GeV p SPS cycle=16.8s/Slow spill 5.2 s
p(+K) beam 9.6 mrad upwards/0.3 mrad spread
Muons at EHN2= 2x108 /1013 pot(cycle)
Neutrinos 2x109/cycle
Narrow radial distribution => small size detector
Strong correlation between neutrino energy and radial position (CC/NC)

4. Predicted energy from radius
vs true energy
Mean Energy vs Radius

5. shielding
beam
# 1 m
emulsion
bricks TT
dummy
bricks
SFT
RPC

6. SFT

7. Neutrinos
On-axis
1020 m
GeV
4 events/brick/month

8. Physics Strategy
Run during 1-2 months with bricks kept in place
Events triggered are recorded from both TT and SFT
SFT will be used to estimate the brick finding efficiency
based on TT information
(information from SFT seems enough to locate, at very high efficiency, the brick)
SFT will be used to estimate the back-scattering
After the run  develop and scan all the bricks
 compare with TT, SFT

9. BRICK FINDING EFFICIENCY WITH SFT
We are developping an algorithm using information
of SFT detectors to find the brick. This algorithm uses a
barycentric method (possible reconstruction of particles
direction using the 2 doublets of each station).
For the Charged Current events, we have a resolution
about 95% and for the Neutral Current events, 92%.

10. BACKGROUND:
muons produced by neutrino interactions in
the earth in front of the detector. The first two
RPC stations and the first plane of scintillators
allow to improve the rejection efficiency of
those muons.
cosmics: some preliminary results concerning this point (Trigger study).

11. Produced by neutrino interaction in the rock
Rock Muons
Produced by neutrino interaction in the rock
GeV
6 105 muons/month

12. TRIGGER Rock muons: Cosmics :
Using the veto system (2 RPC stations +first TT)
6.105 muons/month  2 muons escaping detection for 1 month.
Cosmics :
A complete trigger scheme is under study using TT & RPC informations (at present only the TT information is used)
Furthermore the use of the SFT requires a fast hard trigger (due to the acquisition rate of the CCD reading out the SFT : 30 fps)

13. The experimental set-up was simulated in the Geant3 code.
COSMICS
The experimental set-up was simulated in the Geant3 code.
We used the same neutrino events generator as for OPERA to produce CC events with the expected energy spectrum given by the halo code.
For the generation of cosmics muons, we use a generator provided by M. Sioli.
* data1 : 1 minute of cosmics flux in the energy range GeV and for zenith angles greater than 70 degrees (10 h CPU time);
* data2 : 10 seconds of cosmics flux in the energy range GeV but for all zenith angles (more than 20 h CPU time);

14. 

15. Energy spectrum of cosmics muons.
data1
data2

16. Energy spectrum of neutrino events generated(CC)
 from  interaction
The interaction vertex are distributed randomly inside the emulsion bricks.

17. Number of scintillator planes per event
cosmics
neutrinos

18. Number of strips per event
muons
neutrinos

19. Number of photoelectrons per event
cosmics
neutrinos
The digitization takes into acount the response of PM.

20. Number of RPC stations per event
neutrinos
cosmics
Station 1
Station 2
Station 3
Station 4

21. BUT we can improve by: FIRST RESULTS:
Using a cut at 25 strips per event:
we have 98% of rejection for cosmics and 90% of
efficiency for neutrino events.
BUT we can improve by:
* using information from RPC stations in front of the detector
* using the information on the number of photoelectrons.

22. CONCLUSION Operette can be a real test for different sub-detectors:
Emulsion, Scintillators, RPC, Electronics , Scanning.
Acquisition (electronics, scanning) can be tested and
strategies can be decided accordingly.
Many studies are done and an OPERA note will be soon
available
Expected time to start in 2004

23. Installation Strategy
TT planes with endcaps and electronic readout
should be assembled in one lab.
Bricks should be prepared and put in their walls
at CERN (aleph pit?)
The set-up should then be completed quickly
on the detector place before the run
It is possible to run one month with only fake bricks to test electonics

24. Needs List
Mechanical structure men during 1 month
TT planes construction men during 1 month
Bricks man during 15 days
installation man during 1 week
Shift men for one month
developement men for one month

25. SFT+Emul. Bricks
56.3 K €
PMT (22)
OPERA
Scint. Strips 800X1 m
2 K €
Fibers X3 m
4.8 K €
Scint. Endcaps
11 K €
Scint. Readout
OPERA?
RPC + Readout
3 K €
Lead
Mechanical structure
2 K €
Infrastructure
100 K €
TOTAL
180 K €