# Presentation: 149106

## Horn and Solenoid Capture Systems for a BNL Neutrino Superbeam 

- Steve Kahn
- 21 December 2001

## 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

##  Super Neutrino Beam from Solenoid Capture

- 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.

## 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.

## A Solenoid as a Horn

- A horn system can be imagined as 3 thin lenses.  (Simplistic Model of course.)
- A similar arrangement could be made using multiple short solenoids as thin lenses.
- This is being investigated.  We do not have results yet.

- 10 m

- 1.5 m

- 0.3 m

- The first 2 lenses form the 1st horn and the 3rd lens forms the 2nd horn.

##  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.

## 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 for a Solenoid Capture System

## 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%

## 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

## 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

## 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