# Presentation: 024528

## Measuring Rare Kaon Decays with KOPIO:Summary of Workshop

**2005 RHIC & AGS Users’ Meeting**
**Brookhaven National Laboratory**
**June 24, 2005**
**Michael Sivertz**

## Poor kinematic signature: 3-body decay.
Neutral initial and final states.
Only outgoing 0 is observable.
SM prediction Br(KL0) = 3x10-11 with a primary background decay KL0 0  which needs a suppression of ~108.

Large window of opportunity for discovering new physics!

- Neutral initial and final states.
- Only outgoing** ********0******** **is observable.
- SM prediction Br**(K****L********0********) = 3**x**10****-11**** **with a primary background** **decay** K****L********0 ********0****  **which needs a suppression of ~108.
- Large window of opportunity for discovering new physics!

**Observing K****L********0******

**“****Experimentally, the problems are perhaps best represented by the statement that nobody has shown that a measurement of this decay is ****absolutely**** impossible” F.J.Gilman, “CP violation in Rare K Decays”, ***Blois CP Violations*** 1989:481-496**

## KOPIO Detector

**Proton Beam**
**100TP/spill (upgraded from present 70TP)**
**~5s spill, 2.3s interspill**
**Microbunching**
**Extract debunched beam resonantly between empty buckets**
**25MHz frequency**
**200ps bunch width**
**10****-3**** interbunch extinction**
**Kaon Beam (Pancake)**
**42.5****o**** take-off angle**
**Soft momentum spectrum**
**0.5-1.5 GeV/c**
**3********10****8**** K****L****/spill**
**8% decay in decay region**
**10 GHz neutrons**

**Need AGS to provide**

- =200 ps

**Notes:**
Mostly soft  n < 10 MeV, soft K suppresses bkgs. From hyperons,etc.

## KOPIO Technique

**Measure everything! (energy, position, angle, time)**
**Eliminate extra charged particles and extra photons**
**KOPIO Veto inefficiencies: ********0**** < 10****-8**** ; ********+**** < 2**x**10****-5****; ********-**** < 1.2**x**10****-4**
**Suppress backgrounds**
**Predict backgrounds *****from data*****:dual cuts**
**Use “blind” analysis techniques**
**Test predictions “outside the box”**
**Weight candidate events with S/N likelihood function**

## Kinematic Separation of Signal &Backgrounds

-  **Signal**

**Backgrounds**

- Pion kinetic energy squared (T*2) vs Ln(Missing Energy)

## _

**	****(based on ****K****+**** ******** ********+**** ******** ******** and isospin) **
**Experimental Searches for ****K****L**** ******** ********0**** ******** ******
**KTeV (FNAL): ****B(K****L********0********) < 5.9********10****-7**** (90% CL)**
**E391a (KEK): Expects sensitivity ~few **x** 10****-9****   **
****** ****J-PARC LOI submitted, proposal anticipated**
**KOPIO (BNL): **
**-****	****proposed single event sensitivity <10****-12**
***-*****	****Discovery (5********) for B(K****L********0********)>5********10****-11 ****or <1.8 ********10****-11**
**-****	****If no new physics, Standard Model gives ~150 events**
**Rule out BRs outside of (1********0.24)BR****SM**** @ 95%CL**
**Bound non-SM operators (B-system can’t access)**

## Experimental Search for KL0 

## KL0 Beyond the Standard Model

**K****L********0********  ****is unique because**
** ****it retains its clean connection to short distance parameters BSM **
**NOT the case for e.g. B********J/********K****S**** where new physics can be seen but not interpreted.**
** ****it**** ****probes the flavor structure of any new physics**
**a 10% deviation in B-physics translates into an ****O****(1) deviation in this decay.**
**even if result agrees with B-physics prediction, it gives unique constraint on new physics operators **
**a 10% measurement can probe new physics mass scales to > 1000 TeV!**

## Slide 10

## New Physics Potential - Early

**New Physics Potential - Early**

## Additional Measurements

- Search for Neutral long-lived (invisible) particles: X
- e.g. sGoldstino** K**L** ******** ******o** X****S****,      K**L** ******** ******o** ******o** X****P**
- Limits <5.9x10-11 (E949)     <9x10-6 ISTRA
**K****L************o**** **(10-7 KTEV) **K****L************o********o**(5.6x10-6 NA31)
****PT predictions inconsistent (10-8 or 7 x 10-11)
- Radiative Decays:**K****L******** ****, K****L******** ****K****L******** ****K****L******** **
- Improve on ****, ****e**+**e**-**, ******+********-**, e**+**e**-********+********-**, e**+**e**-**e**+**e**-**, ****
- **********–**************scattering length from **K****L******** **************************decays
**K****L**** **beta decay: Predictions for**  K****L**** ******** K e **are** **~10**-8****. **
**- Proportional to ****m****5**** where ****m is the K**L**-K****+**** mass difference.**
- Tagged** ********o**** **decays: o ****** e**+** ****e**-**  (6.2 ****± 0.5) ****x 10****-8**** **
- o ****** ********      <1.7 x 10****-6**
- KL Lifetime: Measured to 1% currently.

## Discovering/Constraining New Physics

**Discovering/Constraining New Physics**

**KOPIO Proposal**

## KL modes simulated for bkgnd studies

- Largest back-grounds

## Other Backgrounds

**K****+**** contamination of beam: <0.001 of signal rate**
**K****L********K****+****e****-********, K****-****e****+********: ~ 0.001 of signal rate**
**nN ************N:  negligible production from residual gas in decay volume if pressure<10****-6**** Torr. Requirements  on reconstructed Z****V****(K****L****) suppress rate from US wall to <0.01 of signal rate**
**n: far smaller than neutron background**
**Hyperons: <10****-5**** of signal rate**
**Fake photons < 0.05 of signal rate assuming ~10****-3******** 10****-3**** suppression from (vetoing) ******** (********/n discrimination)**
**Two K****L**** giving single candidate: negligible due to vetoes**
**(K****L**** ************X) ******** (********************e ************): ~0.01 of signal rate**
**K****S**** ************************ 10****-4**** of K****L**** ******************** background rate**

- _

## KOPIO Operations Plan

**-****	****2010 Test Run – partial detector**
**-****	****2011 Engineering Run – full detector**
**	****	****“****Discovery phase” **
**	****	****Sensitivity goal:~10****-10**
**2012-16 Data Accumulation**
**	****	****~3 x 10****20**** protons delivered in 5700 hours**

## Summary & Outlook

**Unique connection with underlying parameters**
**Extremely rapid progress in first part of KOPIO run**
**5******** ****discovery if  BR**** 0.6< BR****SM**** or >1.7 BR****SM**
**If find Br ~ Br****SM**
**Likelihood analysis using ~150 evts**** **
**Precision on BR: ********14%;****   Im ********t****: ********7%**
**Rule out non-SM effects outside (1 ******** 0.24)********BR****SM**
**Unique constraint on some BSM operators**

**Summary & Outlook**