Rare kaon physics from 30,000’ and other perspectives

1. Rare kaon physics from 30,000’ and other perspectives L. Littenberg 29 April 2013

2. Outline • Some things can best be appreciated from 30,000 feet • What do we have to do to get some respect? • What does N events buy us? • Lightening review of K ® pnnexperimentalsituation • Real ghosts • Any alternatives? • A challenge • Cycling back to the beginning

3. Some things you can only appreciate from 30,000’

4. Like the Nasca lines in Peru

5. It’s clear they were trying to perfect them

6. Could have been a contender • Almost as old as the Nasca pix: • Green dashed line is supposed to be the usual unitarity triangle • Red solid line is a triangle from rare kaon information alone • If SM is the whole story the vertices at the upper left should meet

7. What do we have to do to get some respect? • Evolution in what qualifies as a discovery. • Now 5s demanded before people believe something. • It’s kind of interesting, 3s means there’s a 1 in 770 chance of being wrong • But that’s not good enough, we demand a 1 in 3.5M chance! • Note that in the US, there are 1.1 deaths/108 highway miles • So if you drive 10,000 miles/year, your chance of dying is 1 in 9000. • So you will bet your life on 3.7s, much less than you demand of a physics result! • Seems like we don’t trust our own systematic errors • Let me pose the question – how close could one come to the Standard Model, and have a five sigma deviation from it? Even though we experimentalists couldn’t possibly make a >5s mistake!

8. What do we have to do to get some respect? • Evolution in what qualifies as a discovery. • Now 5s demanded before people believe something. • It’s kind of interesting, 3s means there’s a 1 in 770 chance of being wrong • But that’s not good enough, we demand a 1 in 3.5M chance! • Note that in the US, there are 1.1 deaths/108 highway miles • So if you drive 10,000 miles/year, your chance of dying is 1 in 9000. • So you will bet your life on 3.7s, much less than you demand of a physics result! • Seems like we don’t trust our own systematic errors • Let me pose the question – how close could one come to the Standard Model, and have a five sigma deviation from it?

9. How many events you need to have 5s? Ratio to SM @ 5s Equivalent Events

10. Zeroing in D.M. Straub arXiv:1012.3893

11. Zeroing in – 10 event experiments

12. Zeroing in – 100 event experiments

13. Zeroing in – 100 event experiments

14. Zeroing in – 1000 event experiments

15. More realistically … 1000 evts _ _ A. Buras et al., General MSSM, tanb = 20 hep-ph/0408142

16. More recent theory example “Trivially Unitary Model” from A. Buras et al. arXiv:1301.5498v1

17. Primary K ® pnn experimental technique

18. Veto System

19. Vetoed Event

20. Ghosts of Experiments Past: E949 @ BNL • Proved K+® p+nn could be done in the “traditional” way • Designed to be a 10-event experiment by my criterion • But killed in the prime of life so ended up a two-event experiment

21. Ghosts of Experiments Past: E391a @ KEK • First dedicated KL® p0nn experiment • High energy approach performed at low energy • Need another factor 1000

22. Ghosts of Experiments Present: KOTO @ J-PARC • High energy technique for KL® p0nn at even lower energy • Scheduled for 1st long physics run any minute • Much experience, improved technology • First stage is a 1.5 event experiment by my criterion • Step-by-step approach has a lot going for it • Next step, get rid of some unnecessary constraints

23. Ghosts of Experiments Present: NA62@ CERN • First to use in-flight technique for K+® p+nn • Physics run scheduled for 2014 • Designed to leap 11 orders of magnitude in a single bound • 75-event class experiment

24. Ghosts of Experiments Future: ORKA@FNAL • Lineal descendent of previous K+® p+nn experiments • 10x the exposure of E949 • 10x better acceptance • Scientific approval December 2011 • Would be a 400-event experiment by my criterion

25. Ghosts of Experiments Future: KOPIO-like experiment for Project-X2 • True 1000-event class experiment • Really requires 3 GeV Stage 2 of Project-X

26. Once and future K experiments Events LL Evts Events E391a KOTO E949 NA62 ORKA P-X K0

27. True Ghost Experiments KOPIO – NSF pulled the plug on RSVP E949 - killed in its prime by DOE KaMI - rejected by the Fermilab PAC CKM - murdered by P5

28. Another Look at KL0l+l- • KL0l+l- has several kinds of bad-luck and trouble. • NA48 observed KS0l+l- at higher end of expectation • & arguments for constructive interference between mixing & direct CP-violating components strong as ever • SM expectation for KL0l+l- rather large: • B(KL0e+e-) = (41)10-11 • B(KL0+-) = (1.50.3)10-11 • Compare with KLl+l- background (worst one):

29. Motivation for KL0l+l- Add to this, now we are interested in bigger game than Imt. E.g., from Isidori, et al., hep-ph/0404127  • Take KaMI as example of a next-generation experiment with sensitivity to KL0+-. In 3 years, KaMI would have reached a s.e.s of 410-13. • In the example above, would collect 110±13 signal events (with 70 events of background) compared with a SM expectation of 37 events. • KL0e+e- case left for homework

30. Why not KL® m+m-? K ® pnn KL® m+m- BR ~ 7´10-9 Beautiful signature 1% background • BR ~ few´10-11 • Very poor signature • Background 10% or worse

31. Here’s Why The fundamental irony of rare kaon physics: The very interactions that make the the process detectable, introduce obfuscating long-distance effects! The above process introduces an absorptive part that is many times larger than the short-distance contribution plus a dispersive part that can interfere with it.

32. A long distance to go • We start off with what I’d classify as a 3700 event experiment. • The absorptive piece can be well-determined by measuring KL® gg • Subtracting it gives Bdisp(KL+-)= (3.2±1.2)´10-10 • I.e. a number ~20 times smaller than the absorptive part • And ~3 times smaller than SM fits to the short-distance part! • This corresponds to a 7 event experiment! Nature is a real killjoy. • And this is before trying to untangle the dispersive interference. • Where there’s agreement from all sectors of the theory world that this is very difficult! • What could possibly be done? • The experiment can be done better – I never imagined it would be worth it. • Could imagine 5´smaller errors, would correspond to a ~200 event experiment for the dispersive part. • Then the theorists could do their part. If they were perfect, and the true value was ~ the SM-predicted one, could get to 500 event equivalent. So it might be worth considering • But theorists really have to do well. A 10% error on the dispersive amplitude degrades it to a 100 equivalent event experiment

33. What about KS® m+m-? • In this case the short distance piece is CP-violating! • In the SM µh2. • BR = 1.7 ´ 10-13, exp as sensitive as the KL one would see 1.5 evts • Moreover the long distance parts are tractable • Don’t interfere with the SM • Well-calculable – maybe the lattice could improve further • But LD parts are still 25´ bigger than SD (~5´10-12). • Note Isidori & Unterdorfer (hep-ph/0311084) point out that K+® p+nncurrentlylimits SD BR to ~10-11 in most BSM models. • So any sensitivity exceeding that limit is interesting. • Starts to limit K ® pnn, also Grossman-Nir bound • Present limit, 9x10-9 @ 90%CL, is from LHCb! (arXiv 1209.4029) • How much better could a fixed-target experiment do?

34. Limits on the K unitarity triangle (Isidori & Unterdorfer) Corresponds to B(KS® m+m-)<1.7´10-11 KS ® m+m- K®m+m- events for a 10-13/evt experiment. At the SM level, KL dominates. Green curve corresponds to the BR at which KS®m+m- becomes a stronger constraint on KL®p0nn than the Grossman-Nir bound. Could get >6s separation from SM for green curve at this sensitivity. Evts/0.1tS KS + KL (SM) KL®m+m- Time (tS)

35. Is the Unitarity Triangle Melting?

36. Is the Unitarity Triangle Melting? For a 100 evt KL experiment this distance is >6s!

37. Take-away Thoughts • The virtue of the golden twins is safe for at least another generation. There’s a huge range of BR in which to prospect for BSM effects. • If new physics shows up, can further refine its properties by studying other rare modes. • But what’s really strange is that the golden twins may be essential for cleaning up what’s now considered the SM CKM triangle, for which they were proposed 25 years ago! • Editorial: rare process experiments thrive in a programmatic, rather than a project environment. • Homework: beat LHCb in KS® m+m- • Appreciate that your work may be have uses you never thought of…

38. Limit on heavy photons from K+® p+X0

39. Backup Slides

40. What I mean by “equivalent events” • If you had a perfect experiment, with no background and no systematic errors, a given number of events gives a fractional uncertainty = 1/sqrt(S), where S is the number of signal events. • So I’m really talking about a certain sensitivity • If one had a perfectly determined background B, the equivalent number of events would be S/(1+B/S). • If the background had an uncertainty sB, then the equivalent number of events would be S/(1+B/S + sB2/S) • This gets increasingly complicated as more realism is inserted, but the basic idea should be clear.