Anything but... Leptogenesis. Sacha Davidson IPN de Lyon/CNRS, France

Transcription

1 Anything but... Leptogenesis Sacha Davidson IPN de Lyon/CNRS, France

2 CP Violation in µ e Conversion Sacha Davidson IPN de Lyon/CNRS, France 1. Why is CP in muon physics interesting? in general leptogenesis 2. CP in triple products rappelle CPT, unitarity and all that... looking for CP in rare muon decays 3. µ e conversion 4. Simple Dirac algebra (even I can do by hand) 5. Summary and things to do

3 Why is µ physics interesting, in the shadow of the LHC? Assume find new physics (... LHC?), precision low energy data can be useful for 1. obtaining model parameters (eg to which LHC is not sensitive) BR(µ eγ) angular distributions in µ eγ,, model testing ( analogy: inputs to the electroweak fit of LEP data : the SM, G F, α em, m Z ) (g 2) µ LHC µ eγ µn en...and if LHC does not find BSM, most low energy experiments still could... (But must check which area of parameter space excluded by LHC).

4 Why is CP interesting? CP : particules anti-particles In Lagangian L implemented by taking complex conjugate of all coupling constants CP unremoveable phases quark sector of the SM: one O(1) CKM phase IF new physics at the weak scale: no electric dipole moments observed combinations of the new physics phases 1 Enigmatic origin of CP Violation : are all coupling constants equiped with O(1) phases, or is CPV a particularity of the quark sector?

5 Why is CP in muon physics interesting? baryon asymmetry of the U CP (but all mechanisms need more than CKM) IF baryogenesis via leptogenesis (e.g. in the seesaw) CP sector phases in the lepton!! third generation ν beam (νfact, β-beam or superbeam) sensitive to the phase δ of the lepton mixing matrix!! these are expensive machines (10 9 $,e for δ?) can leptonic CP Violation can be found somewhere else?

6 Outline (again) 1. Why is CP in general leptogenesis 2. CP in muon physics interesting? in triple products (LR, FB asyms. No antiparticle process...) rappelle CPT, unitarity and all that... looking for CP in rare muon decays 3. µ e conversion 4. Simple Dirac algebra (even I can do by hand) 5. Summary and things to do

7 Discrete symmetries... In a local Lorentz-invariant theory, described by a unitary S-matrix (and respecting spin-stats), CPT is a symmetry. (Not quite : CP = T 1 ) CP : particle( p, s) antipart( p, s) For example, matrix element for µ eγ ( ) CP : M µ( p µ, s µ ) e( p e, s e )+γ( p γ, s γ ) ( ) : M µ( p µ, s µ ) e( p e, s e )+γ( p γ, s γ ) T : particle( p, s) particle( p, s) ( ) M µ( p µ, s µ ) ē( p e, s e )+γ( p γ, s ( M e( p e, s e )+γ( p γ, s γ ) µ( p µ, s µ

8 CP triple products CP : particle( p, s) antipart( p, s) T : particle( p, s) particle( p, s) ««CP : M µ( p µ, s µ ) e( p e, s e ) + γ( p γ, s γ ) M µ( p µ, s µ ) ē( p e, s e ) + γ( p γ, s γ ) «T : M µ( p µ, s µ ) e( p e, s e ) + γ( p γ, s γ ) If triple products appear in M 2 ( can arise from Tr M e( p e, s e ) + γ( p γ, s γ ) µ( p µ, s µ )»γ 0 γ i γ j γ k γ 5 = 4iǫ 0ijk ) «M [...] p b ( s c p d ) + [...] p b ( s c s d ) +... and if they are multiplied by complex coupling constants could be a T (maybe CP) odd term in the differential rate! need to measure spin, p... not need to measure process involving antiparticles not need loop/strong and weak phases

9 Unitarity, loops and all that... Recall (from leptogenesis), that a CP asym in an integrated partial decay rate requires loop(s), whose on-shell intermediate state particles give strong phase, that multiplies phase of coupling constants. This follows from 1. unitarity of S = I + i(2π) 4 δ 4 (P i P f )M(i f): ( SS = [1 + it][1 it ]) M(µ eγ) M(eγ µ) = M M(µ eγ) M(µ eγ) 2 M(eγ µ) 2 = O(MM M)(µ eγ) CPT: ( ) 2 ( M M e(p e, s e )+γ(p γ,s γ ) µ(p µ,s µ ) = µ(p µ, s µ ) ē(p e, s e )+γ(p γ, s γ... unitarity + CPT say that a CP asymmetry where spins, momenta are summed over, is higher order in coupling constant/loop expansion obtain phases of coupling constants at tree level by measuring asymmetries associated with triple products (FB asyms, spin asyms, etc)

10 Triple products in rare muon decays µ(p µ,s µ ) eēe triple products galore... Okada Okumura Shimizu BR(µ eēe) < no new experiments planned...?psi thinking? difficulty: multiple final state particles, accidental coincidence backgrounds

11 Triple products in rare muon decays µ(p µ,s µ ) eēe triple products galore... Okada Okumura Shimizu BR(µ eēe) < no new experiments planned...?psi thinking? difficulty: multiple final state particles, accidental coincidence backgrounds µ(p µ,s µ ) e(p e,s e ) + γ(q) BR(µ eγ) < MEG@PSI soon only possible triple product: s µ ( s e p e ),... but multiplied by q 2 = 0 if measure also photon polarisation, there is sensitivity to CP phases Farzan backgrds:...+ accidental coincidences, increase as (rate) 2 µ e conversion on nuclei: one outgoing e, q 2 0.

12 µ e conversion on nuclei Kuno Okada,... µ captured by nucleus, cascades down to 1s state, then (in SM) beta decay of nucleus by muon capture (emit ν).

13 µ e conversion on nuclei Kuno Okada,... µ captured by nucleus, cascades down to 1s state, then (in SM) beta decay of nucleus by muon capture (emit ν). Or: Beyond the SM, could have Lepton Flavour Violation. Parametrise BSM in off-shell effective field theory, µe conversion mediated by 4G Fm µ µσ αβ (A L P R + A R P L )ef αβ + h.c + four fermion(ēµ qq) 2 Γ(µTi eti) Γ(µTi capture) < , Γ(µAu eau) Γ(µAu capture) < µ2e(fnal), COMET/PRISM (J-PARC) 10 16,10 18 backgrds: muon decay in orbit, in flight... Improve beam quality with intensity, can improve sensitivity... disciminate operators via rate diff on various nuclei?

14 µ e conversion on nuclei Kuno Okada,... µ captured by nucleus, cascades down to 1s state, then (in SM) beta decay of nucleus by muon capture (emit ν). Or: Beyond the SM, could have Lepton Flavour Violation. Parametrise BSM in off-shell effective field theory, µe conversion mediated by 4G Fm µ µσ αβ (A L P R + A R P L )ef αβ + h.c + four fermion(ēµ qq) 2 Γ(µTi eti) Γ(µTi capture) < , Γ(µAu eau) Γ(µAu capture) < µ2e(fnal), COMET/PRISM (J-PARC) 10 16,10 18 triple product s µ ( s e p e ) in µe conversion? Need µ polarisation... 16% after cascade? Worse for target with spin, better for polarised target. Kuno, Nagamine, Yamazaki

15 CP in µ e conversion to calculate 1)From operators : 4G Fm µ µσ µν (A L P R + A R P L )ef µν + h.c 2 M = M L + M R = 4G Fm µ 2 ( ) d 3 xe i k x A Lu(k)2σ 0i E i P L ψ (µ) 1s + A Ru(k)2σ 0i E i P R ψ (µ) 1s 2)Define average over muon wavefunction : d 3 xψ (µ) 1s Ei E i, 1 and recall spin proj. operator : 2 (I + γ 5s/ ) { M 2 =...+ 2G 2 Fm 2 µa L A R (I + γ 5 s/ e )k/ γ 0 E/ P R (I + γ 5 s / µ ) γ 0 P R γ 0 E/ } 2G 2 Fm 2 µa LA R {(I + γ 5 s/ e )k/ γ 0 E/ P L (I + γ 5 s / µ ) γ 0 P L γ 0 E/ } = G 2 Fm 2 µim{a L A R} E 2 s µ ( s e k)

16 The asymmetry For 100% polarised muons, the asymmetry (normalised to conversion rate) between electrons polarised ± in direction perpendicular to momentum: Im[A L A R] 8( A L 2 + A R 2 ) (recall : 4G Fm µ µσ µν (A L P R + A R P L )ef µν + h.c) 2 maximised for extensions of the SM that give similar, and complex, contributions to A L and A R (relative magnitude of A L and A R can be determined by the angular distribution of the electron, in µ eγ, or µ e conversion providing the muon is polarised) For 16 % µ polarisation, 10 % efficiency for detecting e polarisation, need > 10 3 events?... BR(µ e conversion) > for exptal sensitivity > But Γ(µ eγ) Γ(µeconversion) 1 α need BR(µ eγ) PSI??

17 Summary, Prospects... If there is new flavoured physics at the TeV, it could mediate LFV such as µ eγ, µ 3e, µ e conversion. The greatest planned sensitivity is BR (µ e conversion) Asymmetries in these processes, including µ e conversion, are sensitive to CP phases (of effective operators) To do: what is relation of the effective operator phases to phases (flavour-diagonal, flavoured) in BSM Lagrangians in SUSY seesaw can I relate this phase to leptogenesis? what are asymmetries generated by all those four fermion ēµ qq operators, which contribute to µ e conversion(but not to µ eγ, µ 3e)? Arise (in off-shell effective field theory) from box diagrams. Small in many SUSY models. Not small in, eg Little Higgs. final state interactions? better nuclear physics...