Jusak Tandean National Taiwan University · Jusak Tandean National Taiwan University 7 July 2019 Based on XG He, JT, G Valencia, arXiv:1806.08350 [JHEP 10 (2018) 040] arXiv:1903.01242

Rare hyperon decays in and beyond the standard model

Jusak Tandean

National Taiwan University

7 July 2019

Based on

XG He, JT, G Valencia, arXiv:1806.08350 [JHEP 10 (2018) 040]arXiv:1903.01242 [JHEP 07 (2019) 022]

JT, arXiv:1901.10447 [JHEP 04 (2019) 104]G Li, JY Su, JT, arXiv:1905.08759

Workshop on form factor, polarization and CP violation in quantum-correlated hyperon-anti-hyperon production

Fudan University, Shanghai, China

Outline

❑ Introduction

❑ +p+– & +pe+e–

❑ Lepton-flavor-violating hyperon decays

❑ Hyperon decays with missing energy

❑ Conclusions

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Rare hyperon decays

❑ In the standard model (SM) they receive a short-distance contribution induced by loop diagrams and also a long-distance contribution.

❑ SD-dominated modes

such as +p

❑ LD-dominated modes

such as +p+–

➢ Negligible SDSM contribution

❑ There are also modes forbidden in the SM, such as +pe+–

SM:

SM:

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Outline

❑ Introduction

❑ +p+– & +pe+e–



❑ Conclusions

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He, JT, Valencia, 1806.08350

LD-dominated +p+−

❑ The LD dominance leads to significant uncertainties in the predicted rate.

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Lyagin & Ginzburg, 1962Bergstrom, Safadi, Singer, 1988

He, JT, Valencia, 2005

LD-dominated +p+−

❑ The LD dominance leads to significant uncertainties in the predicted rate.

❑ Nevertheless, one can construct observables which are sensitive to terms in the amplitude not dominated by LD contributions.➢ Such observables are then potentially sensitive to SD effects beyond the SM.

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Lyagin & Ginzburg, 1962Bergstrom, Safadi, Singer, 1988

He, JT, Valencia, 2005

Differential rate of +p+− in SM

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Branching fraction of +p+− in SM

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Muon asymmetries in +p+−

❑ Look for observables sensitive to the small SD contribution.

❑ One of them turns out to be the muon forward-backward asymmetry.

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Muon asymmetries in +p+−



Branching fraction & muon asymmetries of +p+− in SM

❑ Some of the asymmetries are tiny in the SM.➢ They are potentially sensitive to NP effects.


+pe+e−

❑ The existing data translates into

❑ The SM predicts

❑ The Dalitz decay contribution

accounts for more than 88% of .


He, JT, Valencia, hep-ph/05060671806.08350

Ang et al., 1969

Outline

❑ Introduction

❑ +p+– & +pe+e–



❑ Conclusions



Lepton flavor violation in kaon & hyperon decays

❑ Charged-lepton-flavor violation (CLFV) has been much searched for in |S|=1 kaon decays (with negative outcomes so far), but not yet been pursued experimentally in the hyperon sector.

❑ The situation may change in the near future if LHCb starts to look for CLFV in |S|=1 hyperon decays.

❑ To explore hyperon and kaon decays manifesting CLFV and how their experimental constraints may complement each other, it is useful to perform a model-independent study using the SM-gauge-invarianteffective Lagrangian.


Effective interactions

❑ The most general SM-gauge-invariant effective Lagrangian of lowest dimension contributing to dse interactions

❑ In the mass basis of the down-type fermions


❑ terms

❑ parity even & odd

Effective Lagrangian for dse interactions

J Tandean 182019/7/7

Constraints

❑ Kaon constraints

❑ Constraints from other processes which get contributions from some of the same [SU(2) gauge-invariant] operators, especially

➢ K

➢e conversion in nuclei


PDG

J Tandean 20

J Tandean 21

Complementarity of kaon & hyperon measurements


Complementarity of koan, hyperon, and other measurements


Outline

❑ Introduction

❑ +p+– & +pe+e–



❑ Conclusions


JT, 1901.10447Li, Su, JT, 1905.08759

Available data on |S|=1 neutral-current decays with missing energy

❑ 1

❑ 2

❑ 3

❑ No data yet in the baryon sector.


Gninenko, 2015

E787, 2001

E391a, 2011

E949 2008, PDG 2019

KOTO, 2019

Data available

❑ 1

❑ 2

❑ 3

❑ No data yet in the baryon sector.

❑ BESIII is going to search for hyperon decays with missing energy.


E949 2008, PDG 2019

KOTO, 2019

Gninenko, 2015

E787, 2001

E391a, 2011

Contributions of invisible spin-½ fermions

272019/7/7J Tandean

Contributions of invisible spin-½ fermions

282019/7/7J Tandean

Hadronic matrix elements

❑ Mesonic matrix elements which don’t vanish:

❑ Vanishing ones:


Hadronic matrix elements

❑ The baryonic matrix elements are estimated with aid of chiral perturbation theory (PT) at leading order:

❑ Most of them don’t vanish in leading-order PT.


Contributions of various couplings to kaon & hyperon modes


❑ Lf

❑ couplings

SM predictions for hyperon decays with missing energy


HB Li, 1612.01775

Constraints from kaon sector


PDG 2019

KOTO, 2019

Bobeth & Buras, 2018

Constraints from kaon sector

J Tandean 342019/7/7

PDG 2019

Littenberg & Valencia, 1996Chiang & Gilman, 2000Kamenik & Smith, 2012

Gninenko, 2015

NP-enhanced hyperon rates (mf = 0)

❑ NP contributing only via operators with pseudocalar ds part.

❑ constraints

❑ These numbers are still 2 to 3 orders of magnitude beyond the expected BESIII reach.


NP-enhanced hyperon rates (mf = 0)

❑ NP contributing only via operators with axial-vector ds part➢ with the couplings assumed to be real.

❑ constrants

❑ The upper values of these limits exceed the BESIII sensitivity levels.


NP-enhanced hyperon rates (mf 0)

❑ With mf > 0, more possibilities could arise.

❑ possibilities




Li, Su, JT, 1905.08759


❑ With mf > 0, even more interesting possibilities could arise.

❑ possibilities


Li, Su, JT, 1905.08759



Li, Su, JT, 1905.08759

Contributions of invisible spin-0 bosons


NP-enhanced hyperon rates (m 0)

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Li, Su, JT, 1905.08759

J Tandean

Outline

❑ Introduction

❑ +p+– & +pe+e–



❑ Conclusions


Conclusions

❑ After a long hiatus, in the near future we can expect to see new results on rare hyperon decays from at least two ongoing major experiments.

❑ LHCb will likely produce improved data on +p+– soon and perhaps also a new finding on its muon forward-backward asymmetry. In addition, LHCb may eventually provide the first limit on CLFV in the hyperon sector.

❑ BESIII will hopefully supply the first results on rare hyperon decays with missing energy. Under certain conditions, the acquired data may test parts of the potential NP parameter space better than what present kaon data can offer.

❑ These efforts will yield long-awaited important information which will be complementary to that gained from kaon measurements.


Documents

Jusak Tandean National Taiwan University · Jusak Tandean National Taiwan University 7 July 2019 Based on XG He, JT, G Valencia, arXiv:1806.08350 [JHEP 10 (2018) 040] arXiv:1903.01242