100830 Neutrino Summer School @Tokai Superbeam long baseline experiments Takashi Kobayashi KEK
ne nm nt 3 flavor mixing of neutrino Flavor eigenstates Mass eigenstates m1 Unitary matrix m2 m3 6 parameters q12, q23, q13, d Dm122, Dm232, Dm132 Dmij=mi2-mj2 2
Known and Unknowns • Solar & Reactor • q12~33o • Dm122~0.00008eV2 • Atomspheric + Acc • q23~45o • Dm232~0.0025eV2 • Unknown! • q13<10o • (Dm132~Dm232)? • d ??? ne?? n3 n2 OR n1 Mass hierarchy
Unknown properties of neutrino q13? Last unknown mixing angle T2K, NOvA, Double Chooz, RENO, DayaBay CP invariance ? Mass hierarchy ? Absolute mass Tritium beta decay, double-beta Majorana or Dirac? Double-beta Next generation accelerator based expriemtns 4
Sakharov’s 3 conditions To generate Baryon asymmetry in the unverse • There is a fundamental process that violates Baryon number • C and CP invariance is violated at the same time • There is a deviation from thermal equilibrium acting on B violating process
Toward origin of matter dominated universe • Quark sector CPV is found to be not sufficient for reproducing present baryon content • Scenario for baryogenesis through lepton CP violation: Leptogenesis • CPV in lepton sector is responsible for B genesis • CPV in neutrino oscillation could provide a key to unravel mystery of origin of matter
Let’s find CPV in lepton sector Let’s design an experiment to search for CPV in lepton sector • I give you • 1000億円 or • 1.2 Billion USD • 755M GBP • 55 Billion INR • 1,401 Billion Won • 2,130 Billion Peso • 7.9 Billion 元 • 918 Million Euro • 35 Billion Ruble • 1.2 Billion CHF If you find any good idea, let’s write a paper! One condition: Within 10years
How? …. : Q1 • Do we really need oscillation phenomena to probe CPV?? • Can’t we attack CPV in an experiment which fit in an experimental hall like such as Kaon CPV or B CPV • Why??
Measuring CPV in quark sector • Through loop diagram • Amplitude ∝ (mu,c,t/MW)2 • Please calculate • Since quark is heavy (especially top), this process becomes measureable VCKM u,c,t VCKM s,b W W W u,c,t d s,b VCKM VCKM VCKM u,c,t VCKM
How about lepton sector? g Example: meg • Amplitude ∝ (mn/MW)2 • Standard model process STRONGLY suppressed • Thus, good field to search for physics beyond standard model W ne,nm,nt m e VMNS VMNS
Oscillation n1 nl n2 nl’ n3
Oscillation (cont) If Ei are same for all mass eigenstates E Ei’s are same, no oscillation, in other word, Ei’s are different, we can probe mixing matrix through oscillation Difference of Ei, ie, phase advance difference is essential For Dm2~10-3eV2
Q2: What oscillation process is best? • OK, now, we somehow understand we need (long baseline) oscillation phenomena to probe matrix elements and attack CPV. • What type of oscillation is best? • Fundamental physics reason • Experimental feasibility
Disappearance ? Appearance? Oscillation probability Disappearance case There is no place for complex phase d in UMNS to appear Disappearance has no sensitivity on (standard) CPV
Appearance • Conventional nm beam (~GeV) • nm ne • Not yet discovered • nm nt • Dominant oscillation mode • Neutrino factory/Beta beam (~10GeV) • ne nm • ne nt Next talks
ne vsnt appearance Oscillation probability (w/ CPV) • nm ntcase, • probability A∝sin22q23, is known to be large, relative effect of CPV becomes small • Also experimentally, identification of nt (out of lots of nm interactions ) is not easy • For nue appearance, A∝sin22q13 is known to be small • Large CPV effect expected CP conserved part CPV part Relative effect of CPV
Matter effect Interactions through propagation in matter nt ne nm e- nt nm ne ne NC W Z Z Z X X X ne e- X X X CC
Relative size of effect ∝ E Change sign when Dm2 sign change: Can probe sign Change sign when n⇔nbar: Fake CPV effect Matter effect
Oscillation probabilities 3 Dm232 2 1 when contribution from Dm12 is small (No CPV & matter eff. approx.) nm disappearance (LBL/Atm) q23 and Dm232 ~1 ne appearance (LBL/Atm) q13 and Dm132 ~0.5 Pure q13 and Dm132 ne disappearance (Reactor) ≪1
d-d, a-a for nmne appearance & CPV Main CP-odd Solar Matter Matter eff.: Sensitivity indep. from q13 (if no BG & no syst. err) # of signal ∝ sin2q13 (Stat err∝sinq13), CP-odd term ∝ sinq13
All mixing angle need to be non-zero Leading CP-odd d-d, a-a for + other terms.. Matter eff.: CPV effect (where sinq12~0.5, sinq23~0.7, sinq13<0.2) Same as Kobayashi-Maskawa model which require 3x3 to incorporate CPV 23 Takashi Kobayashi (KEK), PAC07
CPV vs matter effect nmne osc. probability w/ CPV/matter 295km 730km @sin22q13=0.01 Smaller distance/lower energy small matter effect Pure CPV & Less sensitivity on sign of Dm2 Combination of diff. E&L help to solve.
Lepton Sector CP Violation Effect of CP Phase δ appear as • νe Appearance Energy Spectrum Shape *Peak position and height for 1st, 2nd maximum and minimum *Sensitive to all the non-vanishing δincluding 180° *Could investigate CP phase with νrun only • Difference between νe and νeBehavior
How to do experiment? OK, we now understand • Importance of CPV in lepton sector • Necessity of oscillation to probe CPV • What process is suited for CPV measurement • Behavior of oscillation probabilities and relevant physics So, now, let’s consider more on experimentation!
Decay Pipe Focusing Devices Proton Beam Target m nm p,K Beam Dump Super Beam Conventional neutrino beam with (Multi-)MW proton beam (nFact) • Pure nm beam (≳99%) • ne (≲1%) from pme chain and K decay(Ke3) • nm/nm can be switched by flipping polarity of focusing device Strongly motivated by high precision LBL n osc. exp.
Far Det. q Decay Pipe Horns Target En(GeV) En(GeV) Ep(GeV) High intensity narrow band beam-- Off-axis (OA) beam -- (ref.: BNL-E889 Proposal) nm flux Decay Kinematics 1 2 5 1/gp~q • Increase statistics @ osc. max. • Decrease background from HE tail
nm -15%@peak nm 1021POT/yr nm/nm flux for CPV meas. Example Sign flip by just changing horn plarity 50GeV proton At 295km
Cross section ∝ E Higher energy higher statistics Anti-neutrino cross section smaller than neutrino by ~1/3 Why? Take ~3 times more time for anti-neutrino measurements to acquire same statistics as neutrino Cross sections
ne appearance search m e p0 • Back ground for ne appearance search • Intrinsic ne component in initial beam • Merged p0 ring from nm interactions 31
“Available” technologies for huge detector Good at low E (<1GeV) narrow band beam LiqAr TPC • Aim O(100kton) • Electronic “bubble chamber” • Can track every charged particle • Down to very low energy • Neutrino energy reconstruction by eg. total energy • No need to assume process type • Capable upto high energy • Good PID w/ dE/dx, pi0 rejection • Realized O(1kton) Water Cherenkov • Aim O(1000kton) • Energy reconstruction assuming Ccqe • Effective < 1GeV • Good PID (m/e) at low energy • Cherenkov threshold • Realized 50kton Good at Wideband beam
m- m- nm+ n→ m+ p+ p nm+n→m + p (Em, pm) (Em, pm) ql qm n n p p inelastic QE Neutrino Energy En reconstruction in Water Cherenkov CC quasi elastic reaction p
2 approaches for CPV (and sign(Dm2) ) • Energy spectrum measurement of appeared ne • Only w/ numu beam (at least early part) • Measure term ∝ cosd (and sind) • Assume standard source of CPV (d in MNS) • Cover 2nd oscillation maximum (higher sensitivity on CPV) • Higher energy = longer baseline favorable • Wideband beam suited • LiqAr TPC is better suited • Difference between P(numunue) and P(numubar nuebar) • Measure term ∝ sind • Not rely on the standard scenario
Angle and Baseline • Off-axis angle • On-Axis: Wide Energy Coverage, ○Energy Spectrum Measurement ×Control of π0 Background • Off-Axis: Narrow Energy Coverage, ○Control of π0 Background ×Energy Spectrum Measurement → Counting Experiment • Baseline • Long: ○ 2ndOsc. Max. at Measurable Energy × Less Statistics ? Large Matter Effect • Short: ○ High Statistics × 2ndOsc.Max.Too Low Energy to Measure ? Less Matter Effect dCP=0 OA0° dCP=90 nm flux OA2° dCP=270 OA2.5° OA3° νμ νeoscillation probability Oscillation probability Dm312 = 2.5x10-3 eV2 sin22q13 = 0.1 No matter effects (E/L)
CERN future possibilities Present accelerator complex Various POSSIBLE scenarios • Under discussion
Possible scenarios in Japan Okinoshima Kamioka Korea 295km 2.5deg. Off-axis 658km 0.8deg. Off-axis 1000km 1deg. Off-axis
Scenario 1 νeSpectrum sin22θ13=0.03,Normal Hierarchy • Cover 1st and 2nd Maximum • Neutrino Run Only 5Years×1.66MW • 100kt Liq. Ar TPC • -Good Energy Resolution • -Good e/π０discrimination • Keeping Reasonable Statistics δ=0° δ=90° δ=180° δ=270° CP Measurement Potential Okinoshima Beam νe Background 3s 658km 0.8deg. Off-axis NP08, arXiv:0804.2111
Scenario 2 • Cover 1st Maximum Only • 2.2Years Neutrino+7.8Years anti-Neutrino Run 1.66MW • 540kt Water Cherenkov Detector 295km 2.5deg. Off-axis <En>~0.6GeV Kamioka Tokai sin22θ13=0.03,Normal Hierarchy d=0 d=p/2 CP sensitivity signal+BG 3s nm+nm+ne+neBG nm sin22q13 nm+nmBG deg. Enrec Enrec 3s Fraction of d nm sin22θ13 Enrec Enrec K.Kaneyuki @NP08
FNAL possibilities NOvA 700kW 15kt Liquid Scintillator Under construction NSF’s proposed Underground Lab. DUSEL 735 km 2.5 msec 810 km MiniBooNE SciBooNE MINOS NOvA MINERvA MicroBooNE 1300 km ~300 kton Water Cerenkov ~50 kton Liquid Ar TPC Project X: ~2 MW Combination of WC and LAr US Superbeam Strategy: Young-Kee Kim, Oct. 1-3, 2009
To realize the experiments Need • Finite (reasonable) q13 T2K, NOvA, Reactors! • High power (>MW) neutrino beam • Huge high-sensitivity detector • YOUR CHALLENGE • OR YOUR NEW IDEA!
Summary • Properties of neutrino are gradually being revealed • However still yet far unknown than quarks • CPV, mass hierarchy, etc. • Especially, CP symmetry could be a critical key to answer the fundamental question: What is the origin of matter in the universe • Future superbeam long baseline oscillation experiments have chance to discover CPV effect (if q13 is large enough to be detected in present on-going experiments) • Already many studies and developments (beam, detectors) are being made around the world to realize the experiments • Lot’s of challenges and funs forseen • Let’s enjoy!