# Presentation: 813173

## A Super-Neutrino Beam From BNL to Homestake

- Steve Kahn
- http://pubweb.bnl.gov/people/kahn/talks/bnl2homestake.pdf

## 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.

## First Phase Super Neutrino Beam

- Upgrade AGS to 1MW Proton Driver:
- 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.

## 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

##  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.

## 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.

## Captured Pion Distributions

- PT distribution of 

- PT  =225 MeV/c corresponding to 7.5 cm radius of solenoid

- 66% of  are lost since they have PT>225 MeV/c

- PT, GeV/c

- Decay Length of Pions

- <L>=7 m

- L, cm

- P > 2 GeV/c

-  = 50 m

- A 15 cm radius of the solenoid would capture 67% of the +

## Rate and e/ as a function of Decay Tunnel Length

## 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

## 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-.

##  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.

## 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%

## 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.
- Figure shows *Perfect Beam *for 12 and 24 GeV incident protons.
- 12 GeV profile is multiplied by 2 for the higher repetition rate.

- 24 GeV protons

- 12 GeV Protons

- Perfect Beam

## 12 GeV Protons (cont.)

- On Axis

- 1.25 degrees off axis

## 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.

## 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.

## 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

## 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 
- Can be used for normalization.
- e appearance
- (continued on next transparency)

## 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

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

- 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
- 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

- e Appearance Channel

## 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.
- Estimates with a 4 MW proton driver source would be four times larger.

## 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.
- This would smear the *distinct* 3/2 minimum.

- /2

## m232 with Errors

- 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.

- Same plot as previously shown.

## Barger, Marfatia and Whisnant Table

## Oscillation Signal

- 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 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.

- The size of the e appearance signal will give a 13 measurement since m132  m232 is measured independently by the  disappearance.

## 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.
- Increasing the Proton Driver Power to 4 MW would be very advantageous to a detector at Homestake.

- With the eventual upgrade to a neutrino factory, the Homestake detector would have a significant event rate.

- 0.38 if 1 MW

## Solenoid Capture System with 230 m Decay Tunnel

-         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 %

- 

- e Signal

- e BG

- 

- e signal

- e BG

- Ignores e BG oscillations

- Significance:
- 	e signal:  3.3 s.d.
- 	e signal:  1.3 s.d.

## 

-         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

- 

- e signal

- e BG

- Ignores e BG oscillation

- Significance:
- 	e signal: 3.2 s.d.
- 	e signal: 1.8 s.d.

- Solenoid Capture System with 100 m Decay Tunnel

## Horn Beam 200 m Decay Tunnel

-         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 %

- 

- e Signal

- e BG

- 

- e signal

- e BG

- Ignores e BG oscillations

- Significance:
- 	e signal:  5.8 s.d.

- E889 Horn Design

## Anti  Horn Beam 200 m Decay Tunnel

-         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 %

- Anti  Horn Beam 200 m Decay Tunnel

- 

- e Signal

- e BG

- 

- e signal

- e BG

- Ignores e BG oscillations

- Significance:
- 	e signal:  2.2 s.d.

- E889 Horn Design

## 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.
- 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.

## 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.

## 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 JHF-Kamioka neutrino project.
- Do we need two such projects?  I will not answer that!