大阪大学大学院理学研究科 久野良孝 ミューオン科学と加速器研究 Neutrino Factory RCNP 研究会 平成 20 年 10 月 21 日
Neutrino Factory Overview
Neutrinos from Pion Decay and Muon Decay • Pion-decay based neutrino beam • Muon-decay based Neutrino beam • prompt decays • delayed decay after all pions π + → µ + ν µ and kaons decay. π − → µ − ν µ + → e + ν e ν µ µ µ − → e − ν • backgrounds (electron neutrino) e ν µ K → µ ν , K → π l ν • four different neutrino falvors are available. µ → e νν • Less beam backgrounds • Beam normalization ~ 10% • Beam normalization can be better known.
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 d 2 N ν µ , ν µ 2 = 4 n µ by Lorentz boosting. N ∝ E 4 y 2 (1 − β cos ϕ ) 6 E µ 2 m µ dyd Ω π L • Pion has too short lifetime of 26 2 − 4 E µ { } 2 y (1 − β cos ϕ × [ 3 m µ nsec. 2 − 4 E µ m P { } ] 2 y (1 − β cos ϕ ) µ m µ • Only muon live long enough to 2 N ν e , ν e d = 24 n µ accelerate (lifetime = 2.2 micro 4 y 2 (1 − β cos ϕ ) 6 E µ π L 2 m µ dyd Ω sec. 2 − 2 E µ { } 2 y (1 − β cos ϕ × [ m µ • pion production is peaked 2 − 2 E µ m P { } ] 2 y (1 − β cos ϕ ) µ m µ around 200 MeV. y = E 2 / E µ 2 ; n µ = #of muons; ν ; β = 1 − m µ E µ 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. θ ∝ 1 • Two straight sections give γ automatically two experiments (with different 2 N ∝ γ baselines) at a time. At 50 GeV, γ =500 and beam spread is 2 mrad. (At 100m, +-20cm beam size.)
Neutrino Cross Sections • Deep Inelastic Scattering Processes at High Energy. ν µ + N → µ + X 2 × E ν ( GeV ) − 38 cm σ ( ν ) ≈ 0.67 × 10 σ ( ν ) ≈ 0.34 × 10 − 38 cm 2 × E ν ( GeV ) σ ( ν ) / σ ( ν ) ≈ 0.5 • Quasi Elastic Scattering Processes at 1 GeV ν µ + N → µ + N ' σ ( ν ) / σ ( ν ) ≈ 1
Lepton Spectra from CC events • neutrino CC events − ( l + ) + X ν ( ν ) + N → l • different for neutrinos and antineutrinos • low energy region is important for neutrino events (not antineutrino events.) • Detector threshold issue.
Advantages of Neutrino Factory • Very highly intense neutrino source • Extremely low backgrounds • a few orders of magnitude higher • for wrong signed muon at a few 10 GeV energy range. detection, a background level would be less than 10 -4 . • intensity proportional to E 2 • Precise Knowledge on Neutrino Flux • Both muon (anti-)neutrinos and electron (anti-)neutrinos are available. • Neutrino flux normalization can be done at the level of 0.1%. • Many variety of oscillation modes can be studied. • 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 + ν e ν µ µ − → e − ¯ µ − → e − ν e ν e ν µ disappearance ν µ → ν µ ν µ → ν µ platinum appearance (challenging) ν µ → ν e ν µ → ν e appearance (atm. oscillation) ν µ → ν τ ν µ → ν τ disappearance ν e → ν e ν e → ν e golden appearance: “golden” channel ν e → ν µ ν e → ν µ silver appearance: “silver” channel ν e → ν τ ν e → ν τ
Event Rates • Charged Current (CC) Event Rates • Oscillation Event Rates N osc ( ν � → � � ) N CC ( ν � → � ) ∝ N ν · σ ∝ E 2 L 2 · E = E 3 ∝ N ν · σ · P ( ν � → ν � � ) L 2 ∝ E 3 L 2 · L 2 E 2 = E • example • 10 21 muons decay /year with a 10 kton detector L ＝１５００ km L ＝１０００ km E µ =20 GeV 3.2x10 5 1.4x10 5 E µ =30 GeV 1.1x10 6 4.8x10 5 MINOS (low energy 3GeV, 732 km) : 5000 CC events/10 kton/year
Neutrino Oscillation Signature at NuFact − → e − ν e ν µ µ • The signature of neutrino oscillation is wrong-signed − µ oscillation leptons. + ν µ µ • Charge identification of the + → e + ν e ν µ lepton(s) is needed. µ oscillation + µ • Muons are easy. ν µ − µ • Electrons are difficult. 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 • Options needed. • 200 MeV Linac + 3 GeV • only beam power matters. Booster synchrotron + Proton • Proton energy is not important FFAG (10 GeV) (next slide), but 5-15 (about 10) • 8 GeV Fermilab GeV would be the best. superconducting LINAC (20 Hz upgrade) + accumulator • Considerations buncher • slow repetition rate with many • SPL at CERN (50 Hz) + protons in each pulse (0.1 - 1 accumulator/buncher Hz). • or existing machines (BNL, • high repetition with less protons Japan, etc.) in each pulse. (10-100 Hz)
Optimum proton energy for high-Z target is broad, but drops at low-energy Optimum Proton Energy Simulation by MARS14
solenoid capture (US,Japan) 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 horn capture (EU) • sustain high beam power (1-4 MW) • Neutrino Factory Concept Current of 300 kA • Liquid mercury target ? π • Pion capture system Protons • 20 T superconducting 2.2 GeV B = 0 4 MW magnet, then reduced. B ∝ 1/R • Magnetic horn system
E951 CERN/Grenoble •1 cm •4 mm •v=2.5 cm/s •v=12 m/s •24 GeV 4 TP p beam •No p beam •No B field •0,10,20T B field • The Hg jet is stabilized by the 20 T B field Hg jet dispersal properties : • Minimal jet deflection for 100 mrad angle of entry • proportional to beam intensity • Jet velocity reduced upon entry to B field • velocities ~ ½ times that of “confined thimble” target • largely transverse to the jet axis • delayed 40 ms Issues : Jet disperse by proton Tests of beam ? How does a magnetic Mercury Liquid Target field affect ?
Bunching and Phase Rotation Bunched Beam Rotation with 200 MHz RF (Neu ff er) • bunching to fit in an RF system (200 MHz?). dE • originally muon beam Drift RF Buncher RF Rotate spread longitudinally due to dt different energy. • Phase rotation : accelerate slow muons and decelerate fast muons to align muon beam energy.
Reduction of Beam Emittance (Cooling) Accelerator acceptance • Emittance = a volume in phase R ≈ 10 cm, x’ ≈ 0.05 rad space occupied by beam rescaled @ 200 MeV particles ( x, dx dz , y, dy • for transverse dz ) • Reduce the muon beam emittance so that as many muons as possible can be accepted in the following accelerating system (Cooling) π and µ after focalization
principle Ionization Cooling reduce p t and p l • Ordinary beam cooling (stochastic cooling etc.) is too heating slow. A novel method for muons are needed. increase p l • ionization cooling system consists of degraders (absorber) and accelerating RF cavities. • to minimize heating, degrader should have a large radiation length (X 0 ) and strong focusing dE 2 d 1 1 ( 0 . 014 ) � � � n µ n � = � + system make the beta function 2 3 ds ds E 2 E m X � � 0 small. µ µ µ cooling heating
Scaling FFAG Acceleration • Rapid Acceleration (to 20-50 GeV) is needed. • a synchrotron not work. Non-Scaling FFAG • Options 1.Scaling FFAG (Fixed Field Alternating Gradient) accelerator • Japanese design 2.Non-Scaling FFAG • US Study 2A 3.RLA (Recirculating Linear RLA Accelerator ) • racetrack or dog-bone • US Study 2
Storage Ring • Triangle Ring µ - • more fraction of straight µ + sections (up tp 48 %), but less flexibility • two rings in single tunnel • Racetrack Ring • less fraction of straight Two identical rings, one for µ + , one for µ - , stacked µ + µ - section (up to 38 %), but vertically side by side in µ - same tunnel. Muon more flexibility to beam bunches interleaved in time directions. µ + µ + • one rings in two tunnels. • Both signed muons are circulated with timing µ - discrimination. • Dependent on accelerator and µ - µ - µ + µ + detector locations. 400ns 400ns 100ns
Neutrino Factory CERN Layout
Recommend
More recommend
