1. Low Z Detector Simulations
Off-Axis Detector Workshop
Stanley Wojcicki
Stanford University
January 24, 2003
Stanford, Ca
( Work done in collaboration with Tingjun Yang )

2. Stan Wojcicki, Low Z Detector Simulations
Outline
Introductory Comments
Parameters/Issues
Few “Typical” Events
Methodology and Initial Results
Plans for the Future

3. Experimental Challenge
Stan Wojcicki, Low Z Detector Simulations
Experimental Challenge
(visible E)
5 times below
CHOOZ limit

4. NuMI Off-axis Detector
Stan Wojcicki, Low Z Detector Simulations
NuMI Off-axis Detector
Different detector possibilities are currently being studied
The goal is an eventual >20 kt fiducial volume detector
The possibilities are:
Low Z target with RPC’s, drift tubes or scintillator
Liquid Argon (a large version of ICARUS)
Water Cherenkov counter
One can do relatively generic simulations for the first category of detectors

5. Detector(s) Challenge
Stan Wojcicki, Low Z Detector Simulations
Detector(s) Challenge
Surface (or light overburden)
High rate of cosmic m’s
Cosmic-induced neutrons
But:
Duty cycle 0.5x10-5
Known direction
Observed energy > 1 GeV
LoDen R&D project
Principal focus: electron neutrinos identification
Good sampling (in terms of radiation/Moliere length)
Large mass:
maximize mass/radiation length
cheap

6. A possible low Z detector
Stan Wojcicki, Low Z Detector Simulations
A possible low Z detector
The absorber medium can
be cheap recycled plastic
pellets
The active detector in this
version are RPC chambers

7. Stan Wojcicki, Low Z Detector Simulations
Relative electron/muon (pion)
appearance
Fuzzy track = electron
Clean track = muon (pion)

8. No of hits/plane for m and e
Stan Wojcicki, Low Z Detector Simulations
No of hits/plane for m and e

9. Stan Wojcicki, Low Z Detector Simulations
Examples of Backgrounds
NC - p0 - irreducible (PH?)
NC - p0 - initial gap

10. Stan Wojcicki, Low Z Detector Simulations
Backgrounds (ctd)
NC - p0 - 2 tracks
nm CC - with p0 - muon

11. Stan Wojcicki, Low Z Detector Simulations
Aims of the studies
Understand ne detection efficiency that is possible
Understand background contributions
Devise optimum algorithms
Understand detector optimization:
Strip width
Possible gain from pulse height
Benefits of 2D readout

12. Stan Wojcicki, Low Z Detector Simulations
Electron Criteria
FH = Hits in road/planes hit is high (~>1.4)
FH also high on each half (~>1.15)
No gap between vertex and 1st hit on track
No gaps early in the track
Minimum track length (~>8 planes)
Not accompanied by a muon
No converted gamma “in vicinity”

13. Muon and gamma definitions
Stan Wojcicki, Low Z Detector Simulations
Muon and gamma definitions
What is a muon?
FH is low (~<1.2)
Curvature is small
Minimum track length
What is a converted gamma “in vicinity”?
FH is high (~>1.4)
Some distance from “vertex”
Gap(s) early in the track
Makes a relatively small angle wrt “primary” track

14. Overall Event Criteria
Stan Wojcicki, Low Z Detector Simulations
Overall Event Criteria
Total energy in the event (as measured by total number of hits) within some limits
Overall asymmetry of the event wrt beam direction is low

15. Stan Wojcicki, Low Z Detector Simulations
Energy Resolution
ne CC events
passing all cuts
1 < En < 3 GeV
s = 15.1 %
Oscillated ne spectrum
at 715 km, 9 km
for Dm2 = 3 x 10-3
s = 15.9 %

16. Initial “practice” analysis
Stan Wojcicki, Low Z Detector Simulations
Initial “practice” analysis
Toy beam - gaussian distribution, centered at 2 GeV with a width of 0.4 GeV and truncated at 1 and 3 GeV
Relatively monolithic detector, mean density somewhat smaller than what is currently proposed
Early version of the analysis algorithms based on using the longest track only
Standard NuMI neutrino interaction generator is used; is it correct for the tails?

17. Initial Results (4 cm strips)
Stan Wojcicki, Low Z Detector Simulations
Initial Results (4 cm strips)
Assumed same number of oscillated ne’s
Assumed same ratio of beam to oscillated ne’s
Figure-of-merit (FOM) defined as signal/sqrt(backround)
Neutrino beam
Signal
ne CC
Beam ne NC
nm CC
(ND)
Effic
FOM
JHF OAB 20
123 11
9.3
1.8
40.7 %
26.2
GeV
112 10
3.1
15.4
37.1 %
29.0

18. Stan Wojcicki, Low Z Detector Simulations
Issue of Rates
At 9 km and 715 km, medium energy NuMI beam, 3.7 x 1020 p/yr, produce in 5 yrs, 20 kt detector, 400 oscillated ne evts (CHOOZ limit, Posc=0.05, Ue32=0.025)
For 37.5 % detection efficiency, Ue32=.0025, we get 15 events in that time
The beam ne background should be comparable or smaller than that

19. Relative Effectiveness of Cuts (an example)
Stan Wojcicki, Low Z Detector Simulations
Relative Effectiveness of Cuts (an example)
ne CC
nm CC NC
All
151.5
436.8
917.5
After 1st cuts
86.6
7.2
28.3
After 2nd cuts
59.0
1.01
2.0
1st cuts: gaps in front, hits/50% of planes (>1.06,1.29)
2nd cuts: hits/all planes (>1.42), no of planes(>9)

20. Track Length Distributions
Stan Wojcicki, Low Z Detector Simulations
Track Length Distributions

21. Stan Wojcicki, Low Z Detector Simulations
Plans for the Future
Make simulation more realistic:
Use NuMI offaxis beam (9 and 11 km)
Make detector geometry more realistic
Use full fledged analysis programs
Optimize reconstruction/event selection algorithms:
Roads around the tracks
Values of cuts used
Maximum likelihood or neural network

22. Plans for the Future (ctd)
Stan Wojcicki, Low Z Detector Simulations
Plans for the Future (ctd)
Optimize the design of the detector:
Determine strip width tradeoffs
Determine possible gain from pulse height information
Determine loss of sensitivity from 1D readout
Understand fiducial volume issues
Understand impact of beam parameters:
Dependence on transverse distance
Possible gain from shorter decay pipe
Dependence on target position and (?) location of 2nd horn
Understand ND -> FD extrapolation (nm CC issue)

23. Stan Wojcicki, Low Z Detector Simulations
Conclusions
The initial studies show that a low Z calorimeter, with fine granularity, can accomplish desired aims
The efficiency/background rejection should be competitive or maybe better than that of JHF/SuperK
The realistic quantitative studies are just beginning