T2K and Aggressive Oscillation

Transcription

1 Can the hint of δ CP from T2K also indicate the hierarchy and octant? Monojit Ghosh Physical Research Laboratory Ahmedabad XXI DAE-BRNS High Energy Physics Symposium IITG, 8-12 December, 214

2 Introduction In neutrino oscillation one flavor evolves into another. This is because the flavor eigenstates and mass eigenstates are not same and related by ν α = N U αi ν i i=1 Where U is the unitary PMNS matrix which diagonalize the neutrino mass matrix m ν = Umν diag U T where m diag ν = diag(m 1, m 2, m 3 ) In standard three generation framework U can be parametrized by three mixing angles i.e θ 12, θ 13, θ 23 and one phase δ CP.

3 Continue... Neutrino oscillation also involves two independent mass squared difference i.e the solar mass square difference (m 2 2 m2 1 = 21) and the atmospheric mass squared difference (m 2 3 m2 1 = 31). The undetermined sign of 31 give rise to two possible mass orderings i.e. Normal Hierarchy(NH i.e m 3 > m 1 ) and Inverted hierarchy(ih i.e m 3 < m 1 )

4 Unknowns Hierarchy(NH or IH) Octant of θ 23 (LO: θ 23 < 45 or HO: θ 23 < 45) δ CP (violation and precision)

5 Current status of δ CP Recently, an indication for δ CP = -9 o has been obtained from T2K data This hint comes from T2K running in the neutrino mode with 8% of the expected total flux of T2K ( protons on target (pot))

6 The question In this work we ask the following questions: If the T2K hint of -9 o is confirmed by the further T2K neutrino runs, then can it indicate the true hierarchy and true octant? what are the role of anti-neutrinos?

7 The T2K experiment T2K is a long-base experiment in Japan currently running in neutrino mode ν µ s are shot from J-PARC towards 295 km away Super-Kamiokande detector, which is a Water Cerenkov detector having mass 22.5 kt. The flux peaks sharply at the first oscillation maxima around.6 GeV

8 The appearance channel For T2K, the probability relevant for the measurement of CP can be expressed in terms of α = 21 / 31 as P µe = 4s13s sin 2 [(1 Â) ] + (1 Â)2 sin  sin [(1 Â) ] α sin 2θ 13 sin 2θ 23 cos ( + δ CP )  (1 Â) = 31 L/4E = +ve for NH & -ve for IH A =  31 = ρ(gm/cc)e(gev ) For anti-neutrinos( ν) both  and δ CP changes sign

9 Degeneracies in P µe The determination of CP in T2K is affected by degeneracies: a)hierarcy-δ CP degeneracy i.e P µe (δ CP, NH) = P µe (δ CP, IH) b)octant-δ CP degeneracy i.e P µe (LO, δ CP ) = P µe (HO, δ CP ) Due to (a) and (b) there exist 3 fake solutions: i)wrong hierarchy-right octant ii)right hierarchy-wrong octant iii)wrong hierarchy-wrong octant As for ν, Â and δ CP both changes sign, addition of ν resolves (b) but not (a) which in turn removes (ii) and (iii) but not (i)

10 CP Precision True value: -9 o (motivated by T2K hint)-(39 o ), (= (N true N test ) 2 /N true ) vs δ CP (test) for different test combinations of hierarchy and octant 8+ correspond to running T2K in only ν mode with total POT True NH,True LO δ CP (True)=-9 o T2K(8+) best fits: -9,, 135, 135 arises due to the fake and solutions(wrong octant i.e HO(51 o )) Conclusion: If true combination is, then clear hint at -9 is not possible.

11 Continue... The same fig plotted for all 4 possible true combinations i.e,,, T2K config: True NH, True LO δ CP (True) = -9 o 2 True NH, True HO δ CP (True) = -9 o 2 True IH, True LO δ CP (True) = -9 o 2 True IH, True HO δ CP (True) = -9 o Only gives clear hint at -9 This is because for ν, -9- give to highest event rates Conclusion: If T2K runs only in ν and gives δ CP = -9, then true hierarchy = NH, true octant = HO

12 Impact of anti-neutrino run T2K config: True NH, True LO δ CP (True) = -9 o 2 True NH, True HO δ CP (True) = -9 o 2 True IH, True LO δ CP (True) = -9 o 2 True IH, True HO δ CP (True) = -9 o ν removes the wrong octant fits but not wrong hierarchy fits 2nd panel remains unaltered as it does not have any wrong octant best fit Conclusion: If T2K runs in equal ν- ν and gives δ CP = -9, then true hierarchy = NH, true octant =LO, HO

13 The CP violation discovery To quantify the ν run we study CPV discovery The CPV discovery is defined as = min (N ex(δ tr CP ) N th(δ test CP =, 18o )) 2 N ex (δ tr CP ) = at δcp tr = &18(CP conserving values) = max at δcp tr

14 Continue... CPV discovery is plotted vs δ CP (true) for all 4 possible true combinations 8 NH, LO NH, HO IH, LO IH, HO δ CP (True) δ CP (True) δ CP (True) δ CP (True) For and, 8+ is best: addition of ν reduce sensitivity For, 5+3 and for 6+2 is best: further addition of ν reduce sensitivity Conclusion: ν only removes wrong octant solution if it is present otherwise it reduces sensitivity

15 The Answer In conclusion we give the following answers: If T2K runs only in ν mode and gives δ CP = -9, then true hierarchy is NH and true octant is HO If T2K runs in equal ν- ν mode and gives δ CP = -9, then true hierarchy is NH ν only removes wrong octant solution if it is present otherwise it reduces sensitivity Ghosh, Goswami, Raut : arxiv

16 The Answer In conclusion we give the following answers: If T2K runs only in ν mode and gives δ CP = -9, then true hierarchy is NH and true octant is HO If T2K runs in equal ν- ν mode and gives δ CP = -9, then true hierarchy is NH ν only removes wrong octant soluion if it is present otherwise it reduces sensitivity Thank You