february 19, 2001neutrino beams from bnl to homestake stephen kahn page 1 a super-neutrino beam from...

February 19, 2001 Neutrino Beams from BNL to Homestake

Stephen Kahn

A Super-Neutrino Beam From BNL to Homestake

Steve Kahnhttp://pubweb.bnl.gov/people/kahn/talks/bnl2homestake.pdf


Stephen Kahn

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.


Stephen Kahn

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.

Machine Power Proton/Pulse Repetition Rate Protons/SSC year Current AGS 0.17 MW 6 1013 0.625 Hz 3.75 1020

AGS Proton Driver 1 MW 1 1014 2.5 Hz 2.5 1021

Japan Hadron Facility 0.77 MW 3.3 1014 0.29 Hz 9.6 1020

Super AGS Prot Driver 4 MW 2 1014 5.0 Hz 1.0 1022


Stephen Kahn

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


Stephen Kahn

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.


Stephen Kahn

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.


Stephen Kahn

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 +


Stephen Kahn

Rate and e/ as a function of Decay Tunnel Length

num Flux at 0 degrees

0

0.05

0.1

0.15

0.2

0.25

0.3

0 50 100 150 200 250

Decay Path

Ra

te

10 m

20 m

nue/num Ratio

00.20.40.60.8

11.21.41.61.8

2

0 50 100 150 200 250

Decay Path, m

Ra

tio

, %

10 m

20 m

num Flux for 10 m Solenoid

0

0.05

0.1

0.15

0.2

0.25

0.3

0 50 100 150 200 250

Decay Path, m

Flu

x

0 degr

"1.5 degr"

nue/num Ratio for 10 m Solenoid

0

0.2

0.4

0.6

0.81

1.2

1.4

1.6

1.8

0 50 100 150 200 250

Decay Path, m

Ra

tio

, %

0 degr

1.5 degr


Stephen Kahn

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


Stephen Kahn

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-.


Stephen Kahn

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 4.21106 9.86105 1.38107 1.20105

¼ 4.11106 9.56105 1.32107 1.06105

½ 4.10106 9.46105 1.18107 1.05105

1 3.80106 8.83105 8.69106 8.27104

1.5 3.36106 7.89105 5.98106 7.53104

2 2.88106 6.80105 4.01106 4.76104

3 1.94106 4.64105 1.93106 3.31104

4 1.31106 3.20105 1.02106 2.35104


Stephen Kahn

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 Koee

• 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%


Stephen Kahn

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


Stephen Kahn

12 GeV Protons (cont.)

On Axis 1.25 degrees off axis


Stephen Kahn

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.


Stephen Kahn

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.


Stephen Kahn

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 Anti e Anti e

At 1 km 1.4010 5 1.2210

5 2.4010 8 1.3310

8 At 3 km 1.4910

6 1.3010 6 2.4210

9 1.3110 9

At 350 km 1.1010 10 9.3910

11 1.7810 13 9.6210

14


Stephen Kahn

Neutrino Oscillation Physics

• The experiment would look at the following channels: disappearance -- primarily oscillations.

• Sensitive to m232 and 23

• Examine ratio of np (QE) at 350 km detector to 3 km detector as a function of E.

NoN events

• These events are insensitive to oscillation state of • Can be used for normalization.

e appearance

• (continued on next transparency)

Ratio of QE D350/D3

0.01

0.1

1

10

0 1 2 3 4

Enu, GeV


Stephen Kahn

• There are several contributions to P(e):– Solar Term: Psolar=sin2212 cos213cos223sin2(m2

solL/4E)• This term is very small.

– Tau Term: P=sin2213sin223sin2 (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

sinsin

2sin

4)()(

)()(

13

12

212

E

Lm

PP

PPA

ee

eeCP


Stephen Kahn

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.

Detector Position n p p

n NNo en e

p

ep en

At 1 km 3.87107 8.82106 3.87106 1.32106 3.18105 At 3 km 4.17106 9.44105 4.28105 1.31105 3.20104

At 350 km 15539 3455 1618 455 150


Stephen Kahn

Determination of m223

• Consider a scenario where m2

12=5105 eV2 23=/4 m2

31=0.0035 eV2 (unknown)– Sin2 213=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


Stephen Kahn

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.


Stephen Kahn

Barger, Marfatia and Whisnant Table


Stephen Kahn

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)

•5107 second running period.

•The size of the e appearance signal will give a 13 measurement since m13

2 m232 is measured independently by the disappearance.


Stephen Kahn

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.

Cornell Homestake Distance 350 km 2540 km

Detector mass 50 ktons 1000 ktons Proton Driver Power 1 MW 4 MW

Scale Factor 1.0 1.52

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

0.38 if 1 MW


Stephen Kahn

Table 1: Oscillation Signal: Consider m2

12=510-5 eV2, 23=/4 and sin2 213=0.01

Using a 1 MW proton driver and a 50 kton detector 350 kilometers away. Experiment running for 5107 seconds. Solenoid capture system with e/ flux ratio=1.9 %

m213 eV2 e signal e background Anti Anti e signal Anti e BG

No Oscillation 15539 455 3455 150

0.002 5065 76 455 1096 18.5 150

0.0035 5284 70 455 1283 16.2 150

0.005 7722 55 455 1762 13.1 150

Solenoid Capture System with 230 m Decay Tunnel

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.


Stephen Kahn


12=510-5 eV2, 23=/4 and sin2 213=0.01

Using a 1 MW proton driver and a 50 kton detector 350 kilometers away. Experiment running for 5107 seconds. Solenoid capture system with e/ flux ratio=1.1 %


No Oscillation 10582 249 2560 47

0.002 3600 58 249 878 14.4 47

0.0035 4282 50 249 1090 12.3 47

0.005 5283 43 249 1303 10.6 47

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


Stephen Kahn


12=510-5 eV2, 23=/4 and sin2 213=0.01

Using a 1 MW proton driver and a 50 kton detector 350 kilometers away. Experiment running for 5107 seconds. Horn capture system with e/ flux ratio=1.08 %


No Oscillation 21645 272 228 5.4

0.002 8317 83 272 115 1 5.4

0.0035 5165 95 272 84 1 5.4

0.005 9966 69 272 90 1 5.4

Horn Beam 200 m Decay Tunnel



Significance:

e signal: 5.8 s.d.

E889 Horn Design


Stephen Kahn


12=510-5 eV2, 23=/4 and sin2 213=0.01

Using a 1 MW proton driver and a 50 kton detector 350 kilometers away. Experiment running for 5107 seconds. Horn capture system with e/ flux ratio=1.04 %


No Oscillation 691 19 4354 65

0.002 506 4 19 1576 19.7 65

0.0035 305 4.7 19 1018 17.8 65

0.005 331 4.5 19 2074 13.9 65

Anti Horn Beam 200 m Decay Tunnel



Significance:

e signal: 2.2 s.d.

E889 Horn Design


Stephen Kahn

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.

Muons NeutronsRaw Rate (kHz) 81.7 2.7

Beam Time Correlation Reduction 2.5 10 7 2.5 10

7

Passive/Active Shielding 0.001 0.18Energy Cuts 0.47 0.26

Vertex and Direction Info 0.0033 0.062Total Reduction 3.9 10

13 7.2 10 10

Background in 5 107 sec 34 2280


Stephen Kahn

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.


Stephen Kahn

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!

february 19, 2001neutrino beams from bnl to homestake stephen kahn page 1 a super-neutrino beam from...

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