rare kaon decays -1

July 2005 L. Littenberg – Varenna 1

Rare Kaon Decays -1

Laurence Littenberg

BNL

E. Fermi School, Varenna - 22 July 2005


Organization

• Introduction & general motivation• Lepton Flavor Violation, etc.• Brief review of Unitarity • K++• KL 0• K • KLl+l-

• KL0l+l-


What makes decays rare?

Common decay:

Rare by virtue of kinematics:

Rare since suppressed to 2nd order:


Motivation for rare K decay experiments • Forbidden

– S.M. forbids or greatly inhibits many kinematically possible decay mode

– A number of these are allowed or enhanced by alternative approaches

– Accessible sensitivity to these processes corresponds to very high mass scales

• Discouraged– Certain very inhibited processes cleanly sensitive

to S.M. parameters

• Tolerated– Suppressed processes are a good area for testing

chiral perturbation theory and other approaches to understanding the low energy structure of the S.M.


Rare K decay modes studied recently


Lepton Flavor ViolationPoster child for sensitivity toBSM processes such as Attainable sensitivity correspondingTo MX 100 TeV, clean signatures

Most BSM theories predict some LFV in K decays:— Extended Technicolor— SUSY— heavy neutrinos— horizontal gauge bosons

Problem: s-channel mechanisms tend to give too much K0-K0 mixing

Necessary to measure both 2- and 3-body decays— check Lorentz structure of any new interaction— generation number sensitivity

Process 90% CL Limit Experiment Reference

KLe 4.7 10-12 AGS-871 PRL 81:5734

K+ ++e- 1.2 10-11 AGS-865 PR D in press

K+ +- e+ 5.2 10-10 AGS-865 PRL 85:2877

KL 0 e 3.4 10-10 KTeV Bellavance thesis

Currentstatus

d

s

W

u gsinC


AGS-871

• 15TP AGS p @ 24 GeV • 3.75°, 64sr beam

– 200M KL/1.6sec spill– 6B neutrons

• two- arm d.c. spectrometer– Beamstop in the middle!– US planes straws w/fast gas– Redundant p measurement

p/p ~ 1% m =1.1 MeV/c for KL+-

• Threshold Cerenkov counter + LG array for electrons

• Muon range stack – ~5% momentum resolution


E865

• Unseparated 6 GeV/c positive beam, 70 MHz of K+, 20 more +’s & p’s– 10% of K’s decay in the tank

• Double magnet MWPC spectrometer

• Two stages of threshold Č counters

• Shashlyk calorimeter

• Muon range device

• Did much more than just search for K+++e- (e.g. Ke3, Ke4)


Generic LFV

Adapted from T. Rizzo hep-ph9809526

E871

KTeV

E865

KLe Ke


LFV in the MSSMLepton flavor violation in K decay is allowed in theMSSM by diagrams like those at right (A. Belyaev et al., hep-ph/0008276)

But the rate from such diagrams is very suppressed wrt current experimental sensitivity. The effects in K decay are also suppressed relative to those in rare muon processes such as e and -e- in the field of a nucleus

The can be seen in the plots at right that show the predictions for KL e, e , and -e- conversion assuming the same values of SUSY parameters (<0, tan =20, m½ = 150 & 250GeV, vs m0). The dotted horizontal lines indicate the the current upper limits on e and -e- conversion. There are proposals to push the sensitivity of both muon processes by more than three orders of magnitude.

10-14

10-16

10-18

10-11

10-9

10-13

10-12

10-14

10-16


LFV & LNV in SUSY-2Once R-parity is relaxed, LFV effects in SUSY can be large:

Current LFV data itself gives strictest limits on the couplings.e.g. B(KLe) < 4.7 10-12 gives –

i21’i12 and i12’i21 6.2 10-9(m/100GeV)2

& 2i1’1i2 and 1i1’2i2 1.9 10-7(m/100GeV)2

SUSY can also give like-sign lepton decays like K+-+e+ through b mixing, e.g.:

However the sensitivity for these is much reduced. Even setting the b mixing matrixElement to 1, current limit B(K+-+e+) < 5 10-10 would give

’2k2’11k 10(md/100GeV)2k

~

~

~


LNV & Majorana NeutrinosExplanations of neutrino mixing tend to involve Majorana neutrinos. These can mediate processes like K+-+ + that violate LNV as well as LFV

Tends to be undetectably small, but there’s a possibility of “resonant enhancement” of the left-hand diagram for heavy neutrinos in the mass range 245-389 MeV. Present limit (from AGS-865) is B(K+-+ +) < 3 10-9 @ 90% CL. This gives a constraint |Uj

|2(5.61) 10-9 (see Dib et al., hep-

ph/0011213)

Appel et al.PRL 85 2877 (2000)


Prospects for LFV Experiments• Last round of

experiments pretty much killed the most promising theoretical predictions.– Theorists now pointing

at rare muon processes• There are exceptions,

e.g. Frère et al. hep-ph/0309014, large extra dimensions

• Future progress on LFV kaon decays likely to be slow– No dedicated

experiments on the horizon

– Background getting harder to fight:

KL0e


Materials and Life ScienceExperimental Facility

Hadron Experimental Facility

Neutrino to Kamiokande

Nuclear Transmutation

J-PARC Facility

J-PARC = Japan Proton Accelerator Research Complex

50 GeV Synchrotron(0.75 MW)

3 GeV Synchrotron(25 Hz, 1MW)

Linac(350m)

500 m

January, 2005


J-PARC: Accelerator complex

– Phase 1 + Phase 2 = 189 billion Yen (= $1.89 billion if $1 = 100 Yen).

– Phase 1 = 151 billion Yen for 7 years.

– Construction budget does not include salaries.


Construction Schedule

ConstructionStart

Phase 1Completion


Proton accelerator in the world


Expected intensity of charged K beam

• Relatively larger increase for K- and K0 of higher momentum ( 1 GeV).≧

• Factor 5-10 increase from BNL AGS intensities.

• Issues - duty factor, competition for protons (from )


T-violation in K3• Look for polarization asymmetry of + polarization in K+0+

• Interference of SM and new physics magnifies effects (i.e. a 10-6 effect in the BR 10-3 effect in this polarization)

• Particularly sensitive to multi-Higgs models, some SUSY, LQ, etc.


KEK-246 Detector

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.


Muon Polarimeter




E246 Method




Progress in T-violation

J-PARC

PT = -0.00180.023stat0.0011syst

(|PT| < 0.0051 @ 90% C.L.)

Im = -.00550.0073stat0.0036syst

(|Im| < 0.016 @ 90% C.L.)

E246:In 3 HD Model, corresponds to neutron EDM < 910-27 (cf 6.310-26)


K3 Polarization at J-PARC

Goal: measurementof PT in K3 and in K++ to 10-4


90% CL upper limits on non-SM Decays

K++

T-viol K3


90% CL upper limits on non-SM Decays

T-viol K3

LIMIT

K++


K++Violates angular momentum conservation, etc. Who would even bother thinking about it?



B(K++) = 810-17(1TeV/NC)4 (hep-ph/0507231)

C.f. E949 search for K++ near the m=0 endpoint, see no events, extract B(K++) <2.310-9 @ 90% C.L. (hep-ex/0505069).Would give NC>14 GeV, not competitive with LEP Z. which gives NC>118 GeV. (would need to get below 4 10-13)




Summary of BSM Searches• Dedicated experiments at BNL brought sensitivities in LFV

processes to 10-11.– More or less wiped out the theories that motivated them

– MSSM tends to predict very small BR’s• Looking under the lampost

– New theoretical motivation developing slowing

– Further progress would require substantial investment• Although 5-10 more incident protons available

– Developed techniques in beams and detectors that will be useful in Kll

• Other BSM searches mainly by-products of experiments dedicated to other processes– E.g. KTeV gets KLe e from KL+-e+e- (not main object)

– The one exception is T-violating + polarization in K3 decay likely to be pursued at J-PARC

± ±

rare kaon decays -1

Documents

decays rare

pressk e

e conversion

rare muon processes

rare kaon decays

sensitivity tobsm processes

ks decay

decay modes