Transcript Brookhaven Super-Neutrino Beam Scenario

A Super-Neutrino Beam From BNL to
Homestake
Steve Kahn
http://pubweb.bnl.gov/people/kahn/talks/bnl2homestake.pdf
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 1
Staging to a Neutrino Factory
• Two feasibility studies for a Neutrino Factory have been concluded.
– These studies indicate a cost of 2-2.5 B$.
• This does not include contingency and overhead.
• This kind of money may not be available in the current climate
– They indicate an optimistic turn-on date of 2012.
• We might like to do some physics before that.
• A staged approach to building a Neutrino Factory maybe desirable.
– First Phase: Upgrade AGS to create a 1 MW Proton Driver and target
station.
– Second Phase: Build phase rotation and part of cooling system.
– Third Phase: Build a pre-acceleration Linac to raise beam momentum to
2.5 GeV/c
– Fourth Phase: Complete the Neutrino Factory.
– Fifth Phase: Upgrade to entry-level Higgs Factory Muon Collider.
• Each phase can support a physics program.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 2
First Phase Super Neutrino Beam
• Upgrade AGS to 1MW Proton Driver:
Machine
Current AGS
AGS Proton Driver
Japan Hadron Facility
Super AGS Prot Driver
Power
0.17 MW
1 MW
0.77 MW
4 MW
Proton/Pulse
6  1013
1  1014
3.3  1014
2  1014
Repetition Rate
0.625 Hz
2.5 Hz
0.29 Hz
5.0 Hz
Protons/SSC year
3.75  1020
2.5  1021
9.6  1020
1.0  1022
– Both BNL and JHF have eventual plans for their proton drivers to
be upgraded to 4 MW.
• Build Solenoid Capture System:
– 20 T Magnet surrounding target. Solenoid field falls off to 1.6 T in
20 m.
– This magnet focuses both + and . Beam will have both  and 
– A solenoid is more robust than a horn magnet in a high radiation.
• A horn may not function in the 4 MW environment.
• A solenoid will have a longer lifetime since it is not pulsed.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 3
Types of Capture/Focus Systems
Considered
• Traditional Horn Focus System
– Uses toroidal magnetic field.
– Focuses efficiently
• B  p
– Conductor necessary along access.
• Concern for radiation damage.
• Cannot be superconducting.
– Pulsed horn may have trouble surviving ~109 cycles that a 1-4 MW
system might require.
• Solenoid Capture System similar to that used by Neutrino
Factory
• Solenoid Horn System
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 4
Simulations to Calculate Fluxes
• Model Solenoid/Horn Magnet in GEANT.
– Use Geant/Fluka option for the particle production model.
– Use 30 cm Hg target ( 2 interaction lengths.)
• No target inclination.
– We want the high momentum component of the pions.
– Re-absorption of the pions is not a problem.
– Solenoid Field profile on axis is B(z)=Bmax/(1+a z)
• Independent parameters are Bmax, Bmin and the solenoid length, L.
– Horn Field is assumed to be a toroid.
– Pions and Kaons are tracked through the field and allowed to decay.
– Fluxes are tallied at detector positions.
• The following plots show  flux and e / flux ratios.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 5
Solenoid Capture
Sketch of solenoid arrangement for
Neutrino Factory
•If only  and not  is desired, then a dipole magnet could be
inserted between adjacent solenoids above.
•Inserting a dipole also gives control over the mean
energy of the neutrino beam.
•Since  and  events can be separated with a modest
magnetic field in the detector, it will be desirable to collect
both signs of  at the same time.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 6
Captured Pion Distributions
PT =225 MeV/c corresponding
to 7.5 cm radius of solenoid
66% of  are lost since
they have PT>225 MeV/c
PT distribution of 
P > 2 GeV/c
Decay Length of Pions
 = 50 m
<L>=7 m
A 15 cm radius of the
solenoid would
capture 67% of the +
PT, GeV/c
February 19, 2001
Neutrino Beams from BNL to
Homestake
L, cm
Stephen Kahn
Page 7
Rate and e/ as a function of Decay
Tunnel Length
num Flux at 0 degrees
nue/num Ratio
0.3
0.25
Ratio, %
Rate
0.2
0.15
10 m
0.1
20 m
0.05
0
0
50
100
150
200
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
250
10 m
20 m
0
50
Decay Path
0.25
Ratio, %
Flux
0.2
0.15
0.1
0 degr
"1.5 degr"
0
50
100
150
200
250
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
250
0 degr
1.5 degr
0
Decay Path, m
February 19, 2001
200
nue/num Ratio for 10 m Solenoid
0.3
0
150
Decay Path, m
num Flux for 10 m Solenoid
0.05
100
50
100
150
200
250
Decay Path, m
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 8
Comparison of Horn and Solenoid
Focused Beams
•
The Figure shows the spectra at 0º at
1 km from the target.
– Solenoid Focused Beam.
– Two Horned Focused Beam designed for
E889.
– So-called Perfect Focused beam where
every particle leaving the target goes in
the forward direction.
• The perfect beam is not attainable.
It is used to evaluate efficiencies.
•
A solenoid focused beam selects a lower
energy neutrino spectrum than the horn
beam.
– This may be preferable for CP violation
physics
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 9
Horn and Solenoid Comparison (cont.)
• This figure shows a similar
comparison of the 1 km spectra
at 1.25º off axis.
– The off axis beam is narrower
and lower energy.
• Also a curve with the  flux
plus 1/3 the anti- flux is shown
in red.
– Both signs of  are focused by
a solenoid capture magnet.
• A detector with a magnetic
field will be able to
separate the charge current
 and anti-.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 10
 Flux Seen at Off-Axis Angles
•We desire to have Low Energy
 beam.
•We also desire to have a
narrow band beam.
•I have chosen 1.5º off-axis
for the calculations.
Angle
Solenoid  QE evts
Solenoid  QE Events
Horn  QE evts
Horn  evts
0
4.21106
9.86105
1.38107
1.20105
¼
4.11106
9.56105
1.32107
1.06105
½
4.10106
9.46105
1.18107
1.05105
1
3.80106
8.83105
8.69106
8.27104
1.5
3.36106
7.89105
5.98106
7.53104
2
2.88106
6.80105
4.01106
4.76104
3
1.94106
4.64105
1.93106
3.31104
4
1.31106
3.20105
1.02106
2.35104
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 11
e/ Ratio
• The figure shows the e flux
spectrum for the solenoid focused
and horn beams.
• The horn focused beam has a
higher energy e spectrum that is
dominated by Koee
• The solenoid channel is effective in
capturing and holding  and .
– The e spectrum from the solenoid
system has a large contribution at
low energy from ee.
– The allowed decay path can be
varied to reduce the e/ ratio at
the cost of reducing the  rate.
• We expect the e/ ratio to be ~1%
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 12
Running the AGS with 12 GeV Protons
• We could run the AGS with a
lower energy proton beam.
• If we keep the same machine
power level we would run at a
5 Hz repetition rate.
– This would work for a
conventional beam since we
are not concerned with
merging bunches.
•24 GeV protons
•12 GeV Protons
Perfect Beam
• Figure shows Perfect Beam for
12 and 24 GeV incident
protons.
– 12 GeV profile is multiplied by
2 for the higher repetition rate.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 13
12 GeV Protons (cont.)
1.25 degrees off axis
On Axis
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 14
Detector Choices
• The far detector would be placed 350 km from BNL (near Ithica, NY).
– There are salt mines in this area. One could go deep underground if
necessary.
• If a massive detector were built at say 2540 km from BNL (at
Homestake), this would permit the determination of the CP violation
sign using mass effect.
• Two possible detector technologies that can be considered are Liquid Ar
and Water Cherenkov.
– We are considering Liquid Ar TPC similar to Icarus. The far detector
would have 50 ktons fiducial volume (65 ktons total.)
• Provides good electron and o detection.
• The detector will sit between dipole coils to provide a field to
determine the lepton charge.
• This technology is expensive and may not be practical.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 15
Detector Choices (cont.)
– Water Cherenkov technology similar to Super-K may be the only
reasonable way to achieve a Megaton detector.
• Charge determination using a magnetic field may not be
possible with this type of detector. The neutrino source must
sign select the .
• A close-in 1 kton detectors at 1 km and/or 3 km would be needed.
– 1 km detector gives  beam alignment and high statistics for
detector performance.
– 3 km detector is far enough away that  source is a point.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 16
Detectors Are Placed 1.5o Off  Beam
Axis
• Placing detectors at a fixed
angle off axis provides a similar
E profile at all distances.
• It also provides a lower E
distribution than on axis.
•  from  decays are captured
by long solenoid channel. They
provide low E enhancement.
• Integrated flux at each detector:
– Units are /m2/POT
Detector Position
At 1 km
At 3 km
At 350 km

1.40105
1.49106
1.101010
February 19, 2001
Anti 
1.22105
1.30106
9.391011
e
2.40108
2.42109
1.781013
Anti e
1.33108
1.31109
9.621014
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 17
Neutrino Oscillation Physics
• The experiment would look at the following channels:
–  disappearance -- primarily  oscillations.
• Sensitive to m232 and 23
• Examine ratio of np (QE) at 350 km detector to 3 km
detector as a function of E.
– NoN events
• These events are insensitive to oscillation state of 
Ratio of QE D350/D3
• Can be used for normalization.
10
– e appearance
1
• (continued on next transparency)
0.1
0.01
0
1
2
3
Enu, GeV
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 18
4
e Appearance Channel
• There are several contributions to P(e):
– Solar Term: Psolar=sin2212 cos213cos223sin2(m2solL/4E)
• This term is very small.
– Tau Term: P=sin2213sin223sin2 (m2atmL/4E)
• This is the dominant term.
• This term is sensitive to 13 and would allow us to measure it with the
1 MW proton driver.
– Terms involving the CP phase :
• There are both CP conserving and violating terms involving .
• The CP violating term can be measured as
ACP 
P(    e )  P(    e )
P(    e )  P(    e )

m122 L sin 212
4 E
sin 13
sin 
• This asymmetry is larger at lower E. This could be ~25% of the total
appearance signal at the optimum E
• The 4 MW proton driver would be necessary for this asymmetry
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 19
Event Estimates Without Oscillations
• Below is shown event estimates expected from a solenoid capture
system
– The near detectors are 1 kton and the far detector is 50 kton.
– The source is a 1 MW proton driver.
– The experiment is run for 5 Snowmass years. This is the running period
used in the JHF-Kamioka neutrino proposal.
– These are obtained by integrating the flux with the appropriate cross
sections.
Detector Position
At 1 km
At 3 km
At 350 km
np
3.87107
4.17106
15539
pn
8.82106
9.44105
3455
NNo
3.87106
4.28105
1618
enep
1.32106
1.31105
455
epen
3.18105
3.20104
150
• Estimates with a 4 MW proton driver source would be four times
larger.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 20
Determination of m223
•
Consider a scenario where
–
–
–
–
–
m212=5105 eV2
23=/4
m231=0.0035 eV2 (unknown)
Sin2 213=0.01
(unknown)
This is the Barger, Marfatia, and
Whisnant point Ib.
•
<E> =0.8 GeV is not optimum since I
don’t know the true value in advance.
• I can determine m223 from
1.27 m223L/E0=/2
Where E0 is the corresponding null point
• Note that these figures ignore the effect
of Fermi motion in the target nuclei.
/2
– This would smear the distinct 3/2
minimum.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 21
m232 with Errors
•Same plot as
previously shown.
•
•
The near detector at 3 km and the far detector is at 350 km.
The plot is made comparing quasi-elastic events only.
– E is well measured for these events. No corrections are necessary.
•
This should produce a solid measurement of m232.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 22
Barger, Marfatia and Whisnant Table
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 23
Oscillation Signal
•The following transparencies will show Quasi-Elastic event
numbers for Solenoid and Horn capture systems. They assume:
•1 MW Proton Driver
•50 kton detector at 350 km with charge determination (Liquid Ar)
•5107 second running period.
•For comparison we have 28% of the flux used in Barger et al.
•We do not use a necessarily optimum L/E fixed configuration
for all cases since the true oscillation parameters are not known
in advance.
•We use the actual flux distribution, not a monochromatic 
beam (as used in Barger et al.).
•The size of the e appearance signal will give a 13 measurement since
m132  m232 is measured independently by the  disappearance.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 24
Going to Homestake
• Most of the transparencies
shown are based on Snowmass
calculations for a far detector
placed near Cornell.
• We can scale the number of
events from these calculations
to estimate signals that would
be seen at Homestake.
– Scale with detector mass
– Scale with 1/r2.
Distance
Detector mass
Proton Driver Power
Scale Factor
Cornell
350 km
50 ktons
1 MW
1.0
Homestake
2540 km
1000 ktons
4 MW
1.52
0.38 if 1 MW
•With the eventual upgrade to a
neutrino factory, the Homestake
detector would have a significant
event rate.
• Increasing the Proton Driver
Power to 4 MW would be very
advantageous to a detector at
Homestake.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 25
Solenoid Capture System with
230 m Decay Tunnel
Table 1: Oscillation Signal:
 Consider m212=510-5 eV2, 23=/4 and sin2 213=0.01
· Using a 1 MW proton driver and a 50 kton detector 350 kilometers away.
· Experiment running for 5107 seconds.
· Solenoid capture system with e/ flux ratio=1.9 %

m213 eV2

No Oscillation
15539
0.002
5065
0.0035
0.005
e Signal e BG
e signal

e signal
Anti e signal
e BG
e background
Anti 
Anti e BG
455
3455
76
455
1096
18.5
150
5284
70
455
1283
16.2
150
7722
55
455
1762
13.1
150
150
Ignores e BG
oscillations
Significance:
e signal: 3.3 s.d.
e signal: 1.3 s.d.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 26
Solenoid Capture System
with 100 m Decay Tunnel
Table 1: Oscillation Signal:
 Consider m212=510-5 eV2, 23=/4 and sin2 213=0.01
· Using a 1 MW proton driver and a 50 kton detector 350 kilometers away.
· Experiment running for 5107 seconds.
· Solenoid capture system with e/ flux ratio=1.1 %
 e signal e BG
m213 eV2

e signal
No Oscillation
10582
0.002
3600
0.0035
0.005

e signal
Anti e signal
e BG
e background
Anti 
Anti e BG
249
2560
58
249
878
14.4
47
4282
50
249
1090
12.3
47
5283
43
249
1303
10.6
47
47
Ignores e BG
oscillation
Significance:
e signal: 3.2 s.d.
e signal: 1.8 s.d.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 27
Horn Beam 200 m Decay Tunnel
E889 Horn Design
Table 1: Oscillation Signal:
 Consider m212=510-5 eV2, 23=/4 and sin2 213=0.01
· Using a 1 MW proton driver and a 50 kton detector 350 kilometers away.
· Experiment running for 5107 seconds.
· Horn capture system with e/ flux ratio=1.08 %

m213 eV2

No Oscillation
21645
0.002
8317
0.0035
0.005
e Signal e BG
e signal

e signal
Anti e signal
e BG
e background
Anti 
Anti e BG
272
228
83
272
115
1
5.4
5165
95
272
84
1
5.4
9966
69
272
90
1
5.4
5.4
Ignores e BG
oscillations
Significance:
e signal: 5.8 s.d.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 28
Anti  Horn Beam 200 m Decay Tunnel
E889 Horn Design
Table 1: Oscillation Signal:
 Consider m212=510-5 eV2, 23=/4 and sin2 213=0.01
· Using a 1 MW proton driver and a 50 kton detector 350 kilometers away.
· Experiment running for 5107 seconds.
· Horn capture system with e/ flux ratio=1.04 %

m213 eV2

No Oscillation
691
0.002
506
0.0035
0.005
e Signal e BG
e signal

e signal
Anti e signal
e BG
e background
Anti 
Anti e BG
19
4354
4
19
1576
19.7
65
305
4.7
19
1018
17.8
65
331
4.5
19
2074
13.9
65
65
Ignores e BG
oscillations
Significance:
e signal: 2.2 s.d.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 29
Cosmic Ray Background
• This table shows the cosmic ray rates for a detector placed on the
surface.
– The rate reduction factors come from the E889 proposal.
– The events shown are scaled to the 350 km detector mass and 5 Snowmass
year running period.
Muons
Neutrons
Raw Rate (kHz)
Beam Time Correlation Reduction
Passive/Active Shielding
Energy Cuts
Vertex and Direction Info
Total Reduction
Background in 5  107 sec
81.7
2.5  107
0.001
0.47
0.0033
3.9  1013
34
2.7
2.5 107
0.18
0.26
0.062
7.2  1010
2280
– The neutron background could be significantly reduced by going 50-100
m underground if it is a problem.
• Placing the detector deep below ground in a mine would be more
advantageous for proton decay experiments.
– The residual cosmic ray background could be reduced to ~0.002 events at
~600 m below ground.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 30
Backgrounds to e Appearance Signal
• The largest backgrounds to the e signal are expected to
be:
– e contamination in the beam.
• This was ~1% e/ flux ratio in the capture configuration that
was used in this study. This yields a ~2% in the event ratio.
– Neutral Current oN events where the o are misidentified as an
electron.
• If a  from the o converts close to the vertex (Dalitz decay) and
is asymmetric.
• The magnetic field and dE/dx will be helpful in reducing this
background. Simulation study is necessary.
• I estimate (guess) that this background is ~0.001 of the oN
signal.
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 31
Conclusions
• A high intensity neutrino super beam maybe an extremely
effective way to study neutrino oscillations.
– In particular the 4 MW version of the super beam may be the only
way to observe CP violation in neutrino oscillations without a
Muon Ring Neutrino Factory.
• This experiment is directly competitive with the JHFKamioka neutrino project.
– Do we need two such projects? I will not answer that!
February 19, 2001
Neutrino Beams from BNL to
Homestake
Stephen Kahn
Page 32