New Views on the Problem of CP Violation

New Views on the New Views on the Problem of CP ViolationProblem of CP Violation

H. MinakataH. Minakata

Tokyo Metropolitan University Tokyo Metropolitan University (TMU)(TMU)

Dec. 3-5, 2003 Neutrino Oscillation in Venice Hisakazu Minakata

Why do we look for leptonic CP violation?


Lepton-quark correspondence

• Quantum anomaly tells us that leptons and quarks are related with each other in a deeper level => we want to know if leptonic KM phase is unsuppressed

“lepton-quark correspondence” in the spirit of Nagoya model (Sakata et al., ‘60th) Shoichi SakataShoichi Sakata


Leptogenesis• Lepton # asymmetry g

enerated by Majorana converted to baryon # asym. by “spharelon”

• => standard model for baryogenesis?

• Need CP violating phases

• Related with leptonic KM phase

(Buchmuller et al.)(Buchmuller et al.)

(Fukugita-Yanagida ‘86)(Fukugita-Yanagida ‘86)


Good old way


Good-old way of measuring CPV

P(->e) = P

P(bar->ebar)

= CP[P]P = P - CP[P] = nonz

erogives you CP violation

A useful tool for --> representation: Bi-probability plot H.M. & H. Nunokawa (=MN), JHEP 10 (2001) 001

A useful tool for --> representation: Bi-probability plot H.M. & H. Nunokawa (=MN), JHEP 10 (2001) 001

N. Cabibbo …N. Cabibbo …


P = P - CP[P]; sign of m2 or CPV?P = P - CP[P] = P(->e; m2, , a) - P(bar->ebar; m2, , a)

= P(->e; m2, , a) - P(->e; - m2, -, a) If P is insensitive to =>

= P(->e; m2) - P(->e; -m2) = m2-odd P measures sign of m2 in -insensitive region P measures in matter-insensitive region

= P(->e; m2, -, -a)= P(->e; - m2, -, a) (if m2

solar /m2atm << 1)

= P(->e; m2, -, -a)= P(->e; - m2, -, a) (if m2

solar /m2atm << 1)

Low-E superbeam; MN, Sato, Richter, …

Low-E superbeam; MN, Sato, Richter, …


TV; Cleanest way of measuring CPV

P(->e)=P

P(e->)=T[P]

PT = P - T[P]

gives you T (=CP under CPT) violation

P = Acos + Bsin + CT[P] = Acos - Bsin + CPT = P - T[P] = 2 Bsin

If = 0 => PT = 0

Experimentally, it is NOT easy => beta beam!

Experimentally, it is NOT easy => beta beam! MN-Parke, hep-ph/0204171MN-Parke, hep-ph/0204171


New ways


New ways of measuring CPV?• Reactor-LBL combination• BNL strategy with several

oscillation maxima (neutrino only)

• Its low-energy version?


Reactor measurement of 13

• Independent of , matter effect, 23, 12, solar m2

=> Pure measurement of 13

e disappearance probabilitye disappearance probability

(H.M. Sugiyama, Yasuda, Inoue, Suekane, hep-ph/0211111)



Reactor-LBL combination

• JPARC-HK neutrino mode, 2 years (4 MW & 540 kton, s/bg accounted)

• 50 ton detectors @Kashiwazaki-Kariwa NPP, 1-10 years

• CP violation can be detected by reactor-LBL combination ! (H.M. H.Sugiyama, hep-ph/0309323 v2 -> PLB)

Principle very simple ! => e appearance at OM + reactor 13 measurement gives you

Principle very simple ! => e appearance at OM + reactor 13 measurement gives you


Detecting CPV by reactor-LBL combination; details

Realisticdb crucial in sensitivity estimate in phase II

Realisticdb crucial in sensitivity estimate in phase II


Can Super-K Do the Job?

• JPARC-SK neutrino mode, 10 years (0.75 MW & 22.5 kton, s/bg accounted)

• 50 ton detectors @Kashiwazaki-Kariwa NPP, 1-10 years

• Though less sensitive, Though less sensitive, SK can do a job !SK can do a job !

In the case of “C-evaluation” by the HK review committee

In the case of “C-evaluation” by the HK review committee

the only way to detect CPV without HK?

the only way to detect CPV without HK?


We must know sign of m2 in advance, otherwise …

This is nothing but Parameter Degeneracy due to sign (m2)!

MN, JHEP 10 (2001) 001

This is nothing but Parameter Degeneracy due to sign (m2)!

MN, JHEP 10 (2001) 001


Why so much ambiguity by sign-m2 degeneracy?

The reason is:• Large 2 - 1 (=

/2 ~ in overlapping region of different-sign m2 ==>

• CPC-CPV confusion


BNL strategy (hep-ex/0211001)


JPARC-HK vs. BNL proposal• L=295 km/E=0.7 GeV vs. L=2540 km/E=0.5-5GeV==> 1st oscillation maximum vs. 1st-3rd oscillation max. • Clean environment for CPV vs. exploring oscillation pattern, sign of m2

13, can prove solar m2, can run with only

<=background ?

<=background ?

1 1


Low-energy version of BNL strategy?• JPARC accelerator com

plex funded => we will have low-energy neutrino superbeam

• Low-energy beam cannot see 2nd OM because of Fermi motion

• Depend onm2 L/2E => , 3 means the detectors placed at L and 3L =>

• 300 km: Kamioka• 900 km: Seoul, Korea!

Similar to 2-detector strategy in: MN hep-ph/9706281

Similar to 2-detector strategy in: MN hep-ph/9706281


Shooting Korea


Bi-probability plot for JPARC-Korea

• Korean detector more important for accurate determination of (steeper slope)

• It is hard to determine sign(m2) from neutrino run only

• Mathematically, there is no degeneracy apart from -> similar to

MN to appear =>

MN to appear =>


anti run at the oscillation maximum (reminder)

In the thinnest ellipse limit (KMN)

• There is no degeneracy apart from ->

• sin2is the “distance to the origin”

Kajita-MN, hep-ph/0112345Kajita-MN, hep-ph/0112345


Conclusion• Real alternative to good-old -anti low-E super

beam does not appear to show up yet• Reactor-LBL may work but confidence level les

s than 2 even with Hyper-K

• BNL strategy interesting to explore but CP sensitivity less than 1 => very long-baseline setting loses statistics

(in conventional beams)• Need to determine sign m2, otherwise CPV-CP

C confusion

<= the only way to detect CPV without HK?

<= the only way to detect CPV without HK?

Low-E version exists but expensive

Low-E version exists but expensive


LBL measurement of 13

JPARC-SK 13 sensitivity; OA2°, 5 years

Very simple form!Very simple form!Very simple form !Very simple form !


Reactor-LBL complementarity I

• Pure measurement of 13 by reactors help resolve (2323) degeneracy• If lucky, one may see CP & mass hierarchy



New Views on the Problem of CP Violation

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