Experimental Opportunities in Kaon Decays At the Proton Driver

Fermilab Workshop 9 October 2004

Y. Wah, U of Chicago

Underlying dictum is to confront current knowledge with “precision” measurements:An obvious way:

One of the best examples is the search of edm of spin particles. Why ? Any particle with spin do not have edm unless P/T symmetries are violated.The physics is clean and clear and the effect, if observed, is an unambiguous indication beyond current knowledge.(history of neutron edm)

Another obvious way:With precision measurement of paramters that can be calculated precisely. The physics is clean and clear and if observed deviated, is an unambiguous indication beyond current knowledge.

(g-2 of electron, muon)

K These are special decays that belongs to the same class.

B (K= 4.1 x 10-10 A4

(<1% theoretical)

B (K+=8.9 x 10-11 A4 f ()

(5% theoretical)

How to get there ? What to do on the way ?

Now (2004/5):E391 ~0.1 evt

~2010:JPARC ~ few tens evtsKPOIO ~ few tens evtsK+ ~ few tens evts

O(103) events will be a reasonable goal in 2015.

A Scenario: (Yr data collected)

2004: K E391: 0.1 events sensitivity

2010: KKOPIO: few tens events

2010: KJPARC: few tens events

What are the worries for Kto collect few thousand events ?

(1) Acceptance is low :

Typically only forward calorimeter as detector, all else in veto to suppress background. Typical acceptance 5%.

Answer: Veto detector could be detector calorimeter also. Everybody is working on this obvious path. This also implies relatively low energy kaon beam (1 - 5 GeV) to be economical.

(2) Kinematics is not favorable

Neutral beam, two unmeasurable neutrinos.

Answer: KOPIO: microbunching neutral beam;

directions of gamma for decay vertex. This implies relatively lower kaon energy. Everybody

is working on these also. This particular issue also ties with the photon veto inefficiencies, in

particular, the K2obackground.

Veto inefficiencies improves as E Resolutions of direction and vertex as E

(c) Accidentals due to beam neutrons

KOPIO: n/K ~ O(102) Ek~.5 GeV

E391 : n/K ~ O(101-2) Ek~1.5 GeV

Fermilab neutral K : n/K ~ 3 Ek~70 GeV

The accidental loss and background is the limitation factor of high rate experiments. For example, a unique and key feature of CKM is to have a pure K+ beam (via rf separator) to eliminate the accidental background.

The proton driver is needed to largely reduce this effect with the following scheme:

A neutral kaon beam with K/n ~ O(100-1)

Step1: Use proton driver to deliver max intensity proton beam to >100 GeV , hit a target to produce charged K+

(and +), focused ; then use rf separator to make a “pure” K+ beam (~ few tens GeV) very much like CKM method.

(30 MHz for CKM, few GHz possible ??)

Step 2: Take this strangeness enriched charged beam and hit a secondary target to produce neutral kaon beam (~few GeV). Q : what’s the resulting K rate and E spectrum ? what’s the K/n ratio ? In principle should be favorable, but ?

test beam measurements to confirm

P + P K0 + Anything Cross section

1 mb

10 mb

10 GeV 100 GeV

K- + P K0 + Anything Cross section

10 mb

10 Gev 100 GeV

2010: K+CERN/FNAL few tens to perheps hundred evts

2015: Assuming a “pure” K+ secondary beam is viable, tertiary Ks experiments should be done.

000= ? (should = if QM is right [the same box diagram])Basically a 10-9 rare decay. Make me very happy to see the interference of 3 decay. Critical to have a clean beam (ie k/n>1). Similarly for +-0.

There are compelling arguments that a (’/)ee should be done with Ks to measure both the phase and amplitude. Proton driver will provide such oppuntunity.

Conclusions:• Proton driver will be ideally suited to provide high

intensity and clean kaon beams for the unique K experiments, particular the pure tertiary beams as discussed. And because of their pure short distance nature, these decays provide discovery potential on the fundemental level.

• These experiments are hard, and will need step-by-step approach. We need to start and protect them now so that by the time the proton driver arrives in 2015, we will be able to exploit fully it’s potential. There is some kind of old saying : “To do well in future, we need to do good now.”