Neutrino Factory RCNP 20 10 21 Neutrino Factory Overview - - PowerPoint PPT Presentation

Neutrino Factory

大阪大学大学院理学研究科 久野良孝 RCNP研究会 ミューオン科学と加速器研究 平成20年10月21日

Neutrino Factory Overview

Neutrinos from Pion Decay and Muon Decay

• Pion-decay based neutrino beam
• prompt decays
• backgrounds (electron neutrino)
• Beam normalization ~ 10%
• Muon-decay based Neutrino

beam

• delayed decay after all pions

and kaons decay.

• four different neutrino falvors

are available.

• Less beam backgrounds
• Beam normalization can be

better known.

π + → µ +ν µ π − → µ−ν

µ

K → µν,K → πlν µ → eνν

µ + → e+νeν µ µ− → e−ν

eν µ

Accelerate to Get More Neutrinos !

• Given the proton beam power,

numbers of pions and muons are similar.

• Acceleration of the parent

particles gives more neutrinos by Lorentz boosting.

• Pion has too short lifetime of 26

nsec.

• Only muon live long enough to

accelerate (lifetime = 2.2 micro sec.

• pion production is peaked

around 200 MeV.

N ∝ E

2

d2Nν µ ,ν µ dydΩ = 4nµ πL

2mµ 6 Eµ 4y2(1−β cosϕ)

×[ 3mµ

2 − 4Eµ 2y(1−β cosϕ

{ }

mP

µ mµ 2 − 4 Eµ 2y(1− βcosϕ)

{ }]

d

2Nν e,ν e

dydΩ = 24nµ πL2mµ

6 Eµ 4y 2(1−β cosϕ)

×[ mµ

2 −2Eµ 2y(1−β cosϕ

{ }

mP

µ mµ 2 − 2Eµ 2y(1− βcosϕ)

{ }]

y = E

ν

Eµ ; β = 1− mµ

2 / Eµ 2 ; nµ =#of muons;

ϕ = angle between beam and detector; L = distance

Storage Ring is Needed !

• Muons accelerated at high

energy do not decay quickly !

• at 10 GeV, muon lifetime is

about 200 microseconds.

• A storage ring is needed with

long straight sections.

• Two straight sections give

automatically two experiments (with different baselines) at a time.

At 50 GeV, γ=500 and beam spread is 2 mrad. (At 100m, +-20cm beam size.)

θ ∝ 1 γ N ∝γ

2

Neutrino Cross Sections

• Deep Inelastic Scattering

Processes at High Energy.

• Quasi Elastic Scattering

Processes at 1 GeV

ν µ + N → µ + X

σ(ν) ≈ 0.67 ×10

−38cm 2 × Eν (GeV )

σ(ν ) ≈ 0.34 ×10−38cm2 × Eν(GeV ) σ(ν ) /σ(ν) ≈ 0.5

νµ + N → µ + N'

σ(ν ) /σ(ν) ≈1

Lepton Spectra from CC events

• neutrino CC events
• different for neutrinos and

antineutrinos

• low energy region is important

for neutrino events (not antineutrino events.)

• Detector threshold issue.

ν(ν ) + N → l

−(l +) + X

Advantages of Neutrino Factory

• Very highly intense neutrino source
• a few orders of magnitude higher

at a few 10 GeV energy range.

• intensity proportional to E2
• Both muon (anti-)neutrinos and

electron (anti-)neutrinos are available.

• Many variety of oscillation

modes can be studied.

• Extremely low backgrounds
• for wrong signed muon

detection, a background level would be less than 10-4.

• Precise Knowledge on Neutrino

Flux

• Neutrino flux normalization can

be done at the level of 0.1%.

• polarization, beam divergence

12 Oscillation Processes in a Neutrino Factory

12 Oscillation Processes from (simultaneous) beams of positive and negative muons in a neutrino Factory.

Table 6: Oscillation processes in a Neutrino Factory µ+ → e+νeνµ µ− → e−νe νµ → νµ νµ → νµ disappearance νµ → νe νµ → νe appearance (challenging) νµ → ντ νµ → ντ appearance (atm. oscillation) νe → νe νe → νe disappearance νe → νµ νe → νµ appearance: “golden” channel νe → ντ νe → ντ appearance: “silver” channel

µ− → e−¯ νeνµ

golden silver platinum

Event Rates

• Charged Current (CC) Event Rates
• example
• 1021 muons decay /year with a

10 kton detector

• Oscillation Event Rates

L＝１０００km L＝１５００km Eµ=20 GeV 3.2x105 1.4x105 Eµ=30 GeV 1.1x106 4.8x105

MINOS (low energy 3GeV, 732 km) : 5000 CC events/10 kton/year

NCC(ν → ) ∝ Nν · σ ∝ E2 L2 · E = E3 L2

Nosc(ν → ) ∝ Nν · σ · P(ν → ν) ∝ E3 L2 · L2 E2 = E

Neutrino Oscillation Signature at NuFact

• The signature of neutrino
• scillation is wrong-signed

leptons.

• Charge identification of the

lepton(s) is needed.

• Muons are easy.
• Electrons are difficult.

µ

− → e − ν e ν µ

ν

µ

µ

−

µ

+

• scillation

µ

+ → e + ν e ν µ

ν µ µ

+

µ

−

• scillation

Look for wrong signed Muons.

Neutrino Factory Complex

Neutrino Factory Components

• Proton Driver
• 1 - 4 MW beam power
• Pion Capture
• high acceptance
• Phase Rotation and bunching
• narrow energy spread
• Muon Ionization Cooling
• reduce beam emittance
• Muon Acceleration
• accelerate muons
• Muon Storage Ring
• store muons to decay

Proton Drivers

• 1 - 4 MW proton beam power is

needed.

• only beam power matters.
• Proton energy is not important

(next slide), but 5-15 (about 10) GeV would be the best.

• Considerations
• slow repetition rate with many

protons in each pulse (0.1 - 1 Hz).

• high repetition with less protons

in each pulse. (10-100 Hz)

• Options
• 200 MeV Linac + 3 GeV

Booster synchrotron + Proton FFAG (10 GeV)

• 8 GeV Fermilab

superconducting LINAC (20 Hz upgrade) + accumulator buncher

• SPL at CERN (50 Hz) +

accumulator/buncher

• or existing machines (BNL,

Japan, etc.)

Optimum Proton Energy

Simulation by MARS14

Optimum proton energy for high-Z target is broad, but drops at low-energy

2.2 GeV 4 MW

Protons Current of 300 kA π B∝1/R B = 0

Target and Pion Capture

• Achieve highly intense muon

beam by maximizing pion production and collecting as many of them as possible.

• soft pion production
• high Z material
• sustain high beam power

(1-4 MW)

• Neutrino Factory Concept
• Liquid mercury target ?
• Pion capture system
• 20 T superconducting

magnet, then reduced.

• Magnetic horn system

horn capture (EU) solenoid capture (US,Japan)

Tests of Mercury Liquid Target

Issues : Jet disperse by proton beam ? How does a magnetic field affect ?

E951

• 1 cm
• v=2.5 cm/s
• 24 GeV 4 TP p beam
• No B field

CERN/Grenoble

• 4 mm
• v=12 m/s
• No p beam
• 0,10,20T B field

Hg jet dispersal properties :

• proportional to beam intensity
• velocities ~½ times that of “confined thimble” target
• largely transverse to the jet axis
• delayed 40 ms
• The Hg jet is stabilized by the 20 T B field
• Minimal jet deflection for 100 mrad angle of entry
• Jet velocity reduced upon entry to B field

Bunching and Phase Rotation

• bunching to fit in an RF system

(200 MHz?).

• originally muon beam

spread longitudinally due to different energy.

• Phase rotation : accelerate slow

muons and decelerate fast muons to align muon beam energy.

Bunched Beam Rotation with 200 MHz RF (Neuffer)

dt dE

Drift RF Buncher RF Rotate

Reduction of Beam Emittance (Cooling)

• Emittance = a volume in phase

space occupied by beam particles

• for transverse
• Reduce the muon beam

emittance so that as many muons as possible can be accepted in the following accelerating system (Cooling)

Accelerator acceptance R ≈ 10 cm, x’ ≈ 0.05 rad rescaled @ 200 MeV π and µ after focalization

(x, dx dz , y, dy dz )

Ionization Cooling

• Ordinary beam cooling

(stochastic cooling etc.) is too

• slow. A novel method for

muons are needed.

• ionization cooling system

consists of degraders (absorber) and accelerating RF cavities.

• to minimize heating, degrader

should have a large radiation length (X0) and strong focusing system make the beta function small.

principle reduce pt and pl increase pl heating

2 3 2

2 ) 014 . ( 1 1 X m E E ds dE ds d

n n µ µ µ µ

• +
• =

cooling heating

Acceleration

• Rapid Acceleration (to 20-50

GeV) is needed.

• a synchrotron not work.
• Options

1.Scaling FFAG (Fixed Field Alternating Gradient) accelerator

• Japanese design

2.Non-Scaling FFAG

• US Study 2A

3.RLA (Recirculating Linear Accelerator )

• racetrack or dog-bone
• US Study 2

Scaling FFAG Non-Scaling FFAG RLA

µ+ µ-

Storage Ring

• Triangle Ring
• more fraction of straight

sections (up tp 48 %), but less flexibility

• two rings in single tunnel
• Racetrack Ring
• less fraction of straight

section (up to 38 %), but more flexibility to beam directions.

• one rings in two tunnels.
• Both signed muons are

circulated with timing discrimination.

• Dependent on accelerator and

detector locations.

µ+ µ+ µ+ µ+ µ+ µ- µ- µ- µ- µ-

400ns 400ns 100ns

Two identical rings, one for µ+, one for µ-, stacked vertically side by side in same tunnel. Muon bunches interleaved in time

Neutrino Factory

CERN Layout

• Proton Driver
• primary beam on production

target

• Target, Capture, Decay
• capture pions, which decay

into muons.

• Bunching, Phase Rotation
• reduce energy spread of

bunch

• Cooling
• reduce transverse

momentum

• Acceleration
• from 200 MeV to 20-50 GeV
• Decay Ring
• store for about 500 turns
• long straight sections

Decay Channel Linear Cooler Buncher 1-4 MW Proton Source Hg-Jet Target Pre-Accelerator

Acceleration Decay Ring ~ 1 km

5-10 GeV 10-20 GeV 1.5-5 GeV

ν

US Neutrino Factory

Neutrino Factory at J-PARC

FFAG-based Scenario

4 FFAG rings + storage ring

Neutrino Factory Detector Options

• Segmented Magnetized Detector
• Totally Active Scintillator Detector
• Liquid Ar Detector
• Emulsion Detector

iron (4 cm) scintillators (1cm)

ν beam

20 m 10 m 10 m B=1 T

15 m 15 m 1 m

Neutrino Factory Sensitivities And Optimization

limit for (sin22θ13)eff sin22θ13 systematics correlations degeneracies

statistical limit

(all parameters fixed)

limit for sin22θ13 from *THIS* experiment only

precise knowledge of some parameter combination = precision of the experiment synergies = combine with other experiments  gain more than statistics

Comments : Definitions of Sensitivity Plots with Systematics, Correlations, degeneracies

a la M. Lindner et al.

Exclusion Sensitivity to

sin2 2θ13

T2K T2K+NOvA T2HK 5E20 decays 50 kton, 8 years, golden mode only

Huber, Lindner, Winter, hep-ph/0204352

Exclusion Sensitivity to Mass Hierarchy

T2K NOvA T2HK 5E20 decays 50 kton, 8 years, golden mode only 1E20 decays 10 kton, 5 years, golden mode only

Huber, Lindner, Winter, hep-ph/0204352

CP (anti-) Coverage for Different

Sin22θ13=10-1

T2HK and NF Comparable

Sin22θ13=10-3

Synergy between T2HK and NF

Sin22θ13=10-4

NF outperforms

sin2 2θ13

CP violation sin22θ13 Mass hierarchy

Summary of Neutrino Factory Optimization

• A lot of works have been done and more works are being undertaken.
• For there is a strong case for a neutrino factory, which

gives the best sensitivity of CP violation.

• For , T2HK and a neutrino factory are comparable. For a

neutrino factory, systematic uncertainty, in particular from matter density, is important and should be reduced. (The study is going.)

sin2 2θ13 < 0.01

sin2 2θ13 > 0.01

Summary

• Neutrino Oscillation Physics
• Objectives are
• Eight-fold Degeneracies
• Future Neutrino Facilities
• Superbeams
• Beta beam
• Neutrino factory
• Neutrino Factory

Complex and R&D

• New physics beyond the

standard neutrino oscillation

θ13

Search for Mass Hierarchy

δ

Discovery of Leptonic CP Violation