Superbeams plus neutrino factory: the golden path to leptonic CP violation

Burguet–Castell, J.; Gavela, M.B.; Gómez-Cadenas, J.J.; Hernández, P.; Mena, Olga

doi:10.1016/s0550-3213(02)00872-6

Cited by 111 publications

(119 citation statements)

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“…A new source of CP -violation or a new mechanism is necessary, and CPviolation in the lepton sector [6] is a good candidate. Leptonic CP -violation has not yet been observed despite many studies at various neutrino factories [7].Positronium (Ps) is a neutral system comprising an electron and a positron and is the analogue of the neutral meson. If CP is violated in the lepton sector, such neutral systems (e.g.…”

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confidence: 99%

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Search forCPViolation in Positronium Decay

et al. 2010

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CP -violation in the quark sector has been well established over the last decade, but has not been observed in the lepton sector. We search for CP -violating decay processes in positronium, using the angular correlation of ( S · k1)( S · k1 × k2), where S is the the positronium spin and k1, k2 are the directions of the positronium decay photons. To a sensitivity of 2.2 × 10 −3 , no CP -violation has been found, which is at the level of the CP -violation amplitude in the K meson. A 90% confidence interval of the CP -violation parameter (CCP ) was determined to be −0.0023 < CCP < 0.0049. This result is a factor 7 more strict than that of the previous experiment.The material state of the universe results only because of its matter-antimatter asymmetry. To understand the origin of this asymmetry is one of particle physics' most urgent goals. One cause could be the CPviolation (charge conjugation and parity) in the quark sector, which was found both in the K [1] and B [2] mesons. The CP -violating processes in B mesons have been measured precisely [3] using its various decay processes at KEKB and PEP-II and they can be well described with the Kobayashi-Maskawa theory [4]. While understanding the origin of CP -violation in the quark sector is a great achievement, the resulting asymmetry may be too small to result in the amount of matter in the Universe [5]. All CP -violating observables in the Standard Model are proportional to the Jarlskog invariance, J= s 2 1 s 2 s 3 c 1 c 2 c 3 sin(δ) ∼ 3 × 10 −5 , where c i are s i are the mixing angles in the KM matrix, and δ is the CP -violating phase. The CP -violating observables are also suppressed by the Higgs vacuum expectation value, 1/v 12 , since non-equilibrium can occur in the electroweak phase transition in the Standard Model. It seems that these violations alone are too small to accout for the observed baryons in the universe. A new source of CP -violation or a new mechanism is necessary, and CPviolation in the lepton sector [6] is a good candidate. Leptonic CP -violation has not yet been observed despite many studies at various neutrino factories [7].Positronium (Ps) is a neutral system comprising an electron and a positron and is the analogue of the neutral meson. If CP is violated in the lepton sector, such neutral systems (e.g. Ps, muonium) are good test candidates since the admixture of opposite CP eigenstates will occur. The search for CP -violation in Ps has been performed previously and no CP violation was found at the 1.5% level of uncertainty [9].If CP -symmetry is not conserved in Ps, the decay rate of the triplet Ps (o-Ps) is dependent on the CP -violating term. The number of o-Ps decay events would be expressed as (1) where S is the spin of the o-Ps, k i is the direction of the i-th energetic γ-ray from the decay (| k i |=1), and τ is the lifetime of o-Ps. C CP is the amplitude of the CP -violation. The Standard Model prediction for C CP is of the order of 10 −10 [10]. This is due to photonphoton interactions in the final state. Another exotic decay cont...

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“…The situation, however, is confounded by the existence of various degeneracies amongst the parameters [14,15] which can render ambiguous their extraction from experiments. To break the degeneracies, one needs to combine the results of experiments, e.g., superbeams, operating at different energies and/or baselines [14,[16][17][18][19][20][21][22][23][24][25][26][27]. In the near future, the T2K [28] and NOνA [29] experiments may be able to determine the hierarchy [30][31][32][33].…”

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Impact of hierarchy upon the values of neutrino mixing parameters

Escamilla-Roa¹,

Latimer²,

Ernst³

2010

Phys. Rev. C

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A neutrino-oscillation analysis is performed of the more finely binned Super-K atmospheric, MI-NOS, and CHOOZ data in order to examine the impact of neutrino hierarchy in this data set upon the value of θ13 and the deviation of θ23 from maximal mixing. Exact oscillation probabilities are used, thus incorporating all powers of θ13 and ε := θ23 − π/4. The extracted oscillation parameters are found to be dependent on the hierarchy, particularly for θ13. We find at 90% CL are ∆32 = 2.44 +0.26 −0.20 and 2.48 +0.25 −0.22 × 10 −3 eV 2 , ε = θ23 − π/4 = 0.06 +0.06 −0.16 and 0.06 +0.08 −0.17 , and θ13 = −0.07 +0.18 −0.11 and −0.13 +0.23 −0.16 , for the normal and inverted hierarchy respectively. The inverted hierarchy is preferred at a statistically insignificant level of 0.3 σ.PACS numbers: 14.60.Pq Keywords: neutrino oscillations, three neutrinos, mixing angles, mass-squared differences, mass hierarchyThe field of neutrino oscillations has progressed rapidly over the past fifteen years. The data can largely be understood by the oscillation of the three known neutrinos [1, 2]. Oscillation phenomenology invokes a unitary matrix that relates the flavor basis, in which the neutrinos are created or destroyed, to the mass basis, in which the neutrinos propagate through vacuum. This matrix can be written in terms of three real mixing angles, θ 12 , θ 23 , and θ 13 , and a phase δ that determines CP violation. Oscillations also require nonzero neutrino mass differences, being dependent upon the difference of the square of the masses, ∆ ij := m 2 i − m 2 j with m i the mass of neutrino i. A recent analysis [3] reports the present knowledge of the values of the oscillation parameters. In particular, we note that only an upper limit exists on the size of the "reactor" mixing angle |θ 13 | = 0.19 +0.12 −0.19 (1σ), a constraint which arises, in part, from the null oscillation result of the CHOOZ experiment [4]. A nonzero value of θ 13 is requisite for the existence of CP violation in neutrino oscillations; hence, we presently have no knowledge of the value of δ. We also have no knowledge of the ordering of the neutrino mass eigenstate; namely, is m 3 greater or less than m 1 and m 2 ? The former (latter) situation is termed the normal (inverted) hierarchy.Recently, hints of nonzero θ 13 have been reported as a means by which to ease the tension between the determination of the oscillation parameters θ 12 and ∆ 21 by the solar and KamLAND experiments [5,6]. At a smaller significance, analyses of atmospheric data also hint at nonzero θ 13 [7,8], though one study shows that the significance of the results are dependent upon the precise nature of the statistical analysis [9]. Furthermore, an analysis of the updated atmospheric data finds no preference for nonzero θ 13 [10]; however, this analysis employs approximate oscillation formulae and cannot be directly compared to these other works. Should these various hints be cleanly confirmed in current neutrino oscillation experiments [11-13], then one might be able to attack the issue of C...

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“…Our understanding of the ν-Factory physics reach is practically still the one presented in ref. [13] (and graphically summarized in Fig. 8) with the addition of the ν e → ν τ "silver" appearance channel ref.…”

Section: Physics Reach Of the ν-Factorymentioning

confidence: 99%

Physics reach of β-beams and ν-factories: the problem of degeneracies

Rigolin¹

2006

Nuclear Physics B - Proceedings Supplements

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We discuss the physics reach of β-Beams and ν-Factories from a theoretical perspective, having as a guideline the problem of degeneracies. The presence of degenerate solutions in the measure of the neutrino oscillation parameters θ13 and δ is, in fact, the main problem that have to be addressed in planning future neutrino oscillation experiments. If degeneracies are not (at least partially) solved, it will be almost impossible to perform, at any future facility, precise measurements of θ13 and/or δ. After a pedagogical introduction on why degenerate solutions arise and how we can get rid of them, we analyze the physics reach of current β-beam and ν-factory configurations. The physics reach of the "standard" β-Beam is severely affected by degeneracies while a better result can be obtained by higher-γ setups. At the ν-Factory the combination of Golden and Silver channels can solve the eightfold degeneracy down to sin 2 θ13 ≤ 10 −3 .

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Superbeams plus neutrino factory: the golden path to leptonic CP violation

Cited by 111 publications

References 24 publications

Search forCPViolation in Positronium Decay

Search forCPViolation in Positronium Decay

Impact of hierarchy upon the values of neutrino mixing parameters

Physics reach of β-beams and ν-factories: the problem of degeneracies

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