# Presentation: 770494

## The kaon physics programme outside CERN

- L. Littenberg - BNL

- Villars sur Ollon                                                                         26 Sept 2004

## Closeup of excluded area

## Context for a possible CERN program
Express tour around the outside facilities
K  ll central
A comment or two on related processes
Some comments on BSM processes
Mainly BNL, FNAL, & KEK/J-PARC
Extra emphasis on the BNL program
A conclusion or two

- Express tour around the outside facilities
- K  ll central
- A comment or two on related processes
- Some comments on BSM processes
- Mainly BNL, FNAL, & KEK/J-PARC
- Extra emphasis on the BNL program
- A conclusion or two

- Plan of talk

- _

## IHEP

-   Present: a couple of experiments with unseparated K beams
-  precision studies of common modes + medium rare decays
-   Future: OKA
-  separated beam 5106 12-18 GeV/c K+, 75% pure
-  spectrometer, partID, lead glass, -ID, etc.
-  few  10-11/event sensitivity
-  high-precision studies of common to medium-rare decays

## The KLOE experiment at DANE

**Be beam pipe** (0.5 mm thick)
**Instr. permanent magnet quads**
**Drift chamber** (4 m   3.3 m)
**Scifi electromagnetic calorimeter**
**Superconducting coil** (5 m bore)
*B* = 0.52 T  (  *B dl*  = 2 T·m)

**Present: **Precision studies of common modes; KS, K sensitivity @ 10-7 level
**Future: 5 ** more sensitivity by end 2005.  Another factor 100 with DANE upgrade (by 2011 or 12?)

## AGS/RHIC Accelerator Complex

- 25 GeV

## AGS Experimental Hall

## Fermilab Accelerator Complex

- 120 GeV

## FNAL Fixed Target Experimental Halls

## J-PARC

## J-PARC Hadron Hall

- Phase 1
- Hall

## Comparison of Facilities

| Facility | AGS  | KEK | J-PARC | FNAL MI |
| --- | --- | --- | --- | --- |
| Pproton | 2--28 | 12 | 30-50 | 90-120 |
| p/cycle (TP) | 65--100 | 2 | 100--200 | 30 |
| cycle time (s) | 3-10 | 4 | 3.4-5.6 | 2.9-4 |
| spill length (s) | 1-7 | 2 | 0.75-3 | 1-2 |
| duty factor | up to ~0.70 | 0.50 | .22-.53 | .33-.50 |
| K utilization factor | 0.8/0.4 | 0.3 | 0.3 | 0.40 |
| Share with  | RHIC/MECO |   |   | collider, |

## Beyond the Standard Model

- A number of dedicated BSM experiments (mainly LFV) ran for a decade starting in the late 1980’s
- BSM limits also produced by other experiments of the period
- Very impressive limits set (BRs as low as 4.7  10-12)
- But theoretical impetus ran dry
- Now a few results still trickling out, but almost no new initiatives on the horizon (one exception)
- Results were at or near background limit
- Should new experiments be considered?
- Some theorists think it interesting
- Advances in beams/detectors could make possible further progress.

## 90% CL upper limits on non-SM Decays

- T-viol K3

## 90% CL upper limits on non-SM Decays

## Rare K decay & the Unitarity Triangle

- 

- 

- 1

- BSD(KL*+**-*)

## KL0 Experimental Issues

- All-neutral initial & final state, ’s make 0
- Expected BR ~ 3  10-11
- need high flux of KL
- Largest background KL0 0, BR ~ 10-3
- need excellent vetoes, other handles if possible
- Background from n-produced 0’s, ’s
- need 10-7 Torr vacuum
- need a way to be sure decay vertex was in the beam

## E391a detector system

- Pencil
- beam

## E391a status & prospects

- First physics run Feb-June this year
- 2.21012 12 GeV _x0013_POT, 50% duty factor
- 5 105 KL/pulse
- Detector worked well
- Nominal s.e.s. 410-10
- Analysis underway
-  first sight of the enemy
- Halo neutrons, self-vetoing, etc.
- Second run proposed for next year

## KEK-PS to J-PARC

**100******** more K****L**

**Thicker photon vetoes**

**Deeper, more granular crystals**

**Faster electronics**

## KL0 Experiment

- prod.
- tgt

- veto

- calor.

- beam veto

## KL0 Experiment

- prod.
- tgt

- veto

- calor.

- beam
- veto

- prerad

## In the KLCoM

- In the KLCoM

-  Bckgnd mainly in discrete areas
-  Obvious for KL00 “even”
-  But even “odd” case not ubiquitous

-  K3 infests slightly different area

-  Even after all bckgrnds accounted for, still some clear space for signal
-  Can get factor 50-100

## KOPIO KL0 Experiment

- KOPIO KL0 Experiment

- BNL AGS experiment
- Aim: to get >40 evts
-          with S:B ~2:1
- Use the AGS between RHIC fills
- Capitalize on the experience of previous AGS rare K decay experiments

##  Detect  and nothing
                   veto
Measure everything possible
KL TOF : to work in KL CMS
bunch AGS protons
Large angle (soft) beam
Asymmetric beam profile
2  detection, timing of KL
 Reconstruct 0 decay from 
Measure  directions & positions in PR
Measure energy in PR+CAL
Veto : cover 4  solid angle
Photon veto
Charged particle veto

-  Detect __ and _nothing_
-                    veto
- Measure everything possible
- KL TOF : to work in KL CMS
- bunch AGS protons
- Large angle (soft) beam
- Asymmetric beam profile
- 2  detection, timing of KL
-  Reconstruct 0 decay from 
- Measure  directions & positions in PR
- Measure energy in PR+CAL
- Veto : cover 4  solid angle
- Photon veto
- Charged particle veto

- KOPIO Concept

## KOPIO Requirements

- 100 TP/AGS pulse (requires upgrade from 70TP)
- 250 ps bunch width, every 40 ns, with <10-3 between bunches
- Beamline at 42.5o, 100 mr   5mr, halo 10-4
- Gives 3  108 KL/spill, (12% decay), but 100  more n’s)
-  timing commensurate with bunching
-  veto inefficiency of ~ 10-4, ***~ 10******-3*** ***in beam***
-  energy resolution of ~3%/E
-  angular resolution of ~ 30mr
- Charged particle inefficiencies 10-4

## Microbunched Beam 

-   Based on CERN technique
-  Used for smoothing beam
-  Cappi & Steinbach 1981
-  Achieved 244ps bunch rms with 93MHz cavity
-  Recent tests with main AGS cavities showed extinction of ~ 10-5
-   25 MHz cavity in design
-  based on RHIC 28 MHz

## Preradiator

- 2 X0 alternating DC & scint. planes
- 4m  4m (four quadrants)
-  200,000 channels

-  ~ 25 mr @ 250MeV

-  angular resolution measured at NSLS

## Shashlyk Calorimeter

- 2500 11cm2 modules, 16 X0 deep
- Pmt or APD readout
- Prototype tests have achieved
- Energy resolution ~ 3%/ E
- Time resolution ~ 90ps/E

- Shashlyk  calorimeter

## KOPIO Charged Particle Veto

- Thin scintillator directly read out by pmts in vacuum
- Tests of achievable inefficiency at PSI
- Note  vetoes back up CPV
- Prototype tests at PSI

## KOPIO Beam Catcher Veto

- Photon veto which covers beam core region
- in fierce_x0013_ neutron rate
- Needs to be...
- _efficient for ____rays_
- _insensitive to neutrons_
- Aerogel Cherenkov + distributed geometry
- Prototypes tested in p beams:

- Catcher Module

## Status of KOPIO

- RSVP approved all the way up the NSB
- Received $6M in R&D funds in FY04
- In the President’s FY05 budget for $30M
- In the House Appr. Sub-committee markup
- Waiting for Congress to complete its process
- All requirements shown to be met by prototype tests or performance of other experiments (e.g. E949).
-  In late stage R&D, initial engineering
-  **Still seeking collaborators!**

## Experimental considerations for K++

- 3-body decay, only 1 visible
- + common K decay product
- BR ~ few  10-11
- Backgrounds:
- K++()
- K+ + 0
- Beam
- Beam + mis-ID as K+, then fakes K decay at rest
- K+ decay in flight
- 2 beam particles
- K+nK0p; KL  + l-, lepton missed

- _

- pnn1

- pnn2

## E787/949 Detector

##  E787/949 Technique

-  Incoming 700MeV/c beam K+: identified by Č, WC, scintillator hodoscope (B4). Slowed down by BeO

-  K+ stops & decays at rest in scintillating fiber target – measure delay (2ns)

-  Outgoing π+ : verified by IC, VC, T counter. Momentum measured in UTC, energy & range in RS and target           (1T magnetic field parallel to beam)

-  π+ stops & decays in RS – detect π+μ+e+ chain

-  Photons vetoed hermetically in BV-BVL, RS, EC, CO, USPV, DSPV

** **E787/949 Technique

## E787 Events

- Candidate E787A

- Candidate E787C

## E787 Results 

- E787 Results

|  | PNN1 | PNN2 |
| --- | --- | --- |
| Pπ (MeV/c) | [211,229] | [140,195] |
| Years  | 1995-98 | 1996-97 |
| Stopped K+  | 5.91012  | 1.71012  |
| Candidates  | 2 | 1 |
| Background  | 0.150.05 | 1.220.24 |
| BR(K+ π+νν)  |  | < 2210-10 (90% CL) |

- 1995-97
- 1998
- Monte Carlo

## E787  E949

-  Much higher proton flux (65 TP)
-  Improved tracking and energy resolution
-  Higher rate capability due to DAQ, electronics and trigger improvements
-  Lower beam duty factor (Siemans  Westinghouse)
-  Lower proton energy    (by 10%, cost 10% in flux)
-  Problematic separators, worse K/π ratio (4 3), fewer K/proton (factor ~1.5)
-  **Total cost, factor 2**

- E787  E949

##  Upgrades in E949

-  Upgrades in E949

**Notes:**
RSSC: the yellow histogram is  for the modified RSSC in E949 and the blacked dots are for the previous RSSC in E787. 
Histogram is for the muon scattering events. The two arrows indicate the current cut positions.

## E949 Event

## Combined E787/949 Result

- (68% CL interval)
- E787 result:

## Acceptance larger than for pnn1 (in principle)
E787 bkgnd-limited at  ~10-9, another factor 10 needed to get to S:B ~ 1

Main background from 
   K2 w/nasty correlation                   	
Improved photon vetoing in E949 very encouraging.
Answer expected in a few months.

- E787

- Acceptance larger than for pnn1 (in principle)
- E787 bkgnd-limited at  ~10-9, another factor 10 needed to get to S:B ~ 1
- Main background from
-    K2 w/nasty correlation
- Improved photon vetoing in E949 very encouraging.
- Answer expected in a few months.

- pnn2

- E949

## Status & prospects for E949

* *E949 detector worked well
-  Obtained ~2/3 sensitivity of E787 in 12 weeks (1/3 pnn1+1/3 pnn2)
-  Found one new pnn1 candidate
-  pnn2 analysis currently in progress – looks promising
-   AGS & beamline problems cost a factor ~2 in sensitivity/hour
-   DOE cut off experiment after 12 of 60 promised weeks
-   Currently seeking NSF support

## J-PARC K++ LOI

-  Stopped K+ experiment
-  Builds on E787/949 experience
-  Lower energy separated beam
-  Higher B spectrometer
-  More compact apparatus
-  Better resolution
-  Finer segmentation
-  Improved  veto (crystal barrel)
-  Aims for 50 events
-  Not an early experiment for J-PARC
-  Needs beamline
-  place on the floor
-  $ for detector

## Pros & cons of stopped-K technique

- PROs
- Long history
- The enemies are known
- Well-honed methods
- S/B good enough!
- Effective particle ID
- Easy to be hermetic
- Very pure beam
- In CM right away
- Clean separation of kinematics/part-ID

- CONs
- Decay in matter
- Nuclear effects
- Require ’s to stop
- ID sensitive to rates
- 3 timescales (up to s)
- Need low veto thresholds
- Limited K flux
- Most K’s interact (typ 4/5)
- Correlation of detector geometry w/CM system

## Fermilab in-flight initiative

- Unseparated beam
- 10MHz K+/230MHz
- 1cm  1cm
- 37-53 GeV/c
- 17% decay
- K &  spectrometers
- RICH particle ID
-  &  vetoes
- 10-6/ 
- pnn1 & pnn2
- 100 evts/2 years/10-10
- Hope to run by 2009

## How to pursue K++?

- In-flight has the “appeal of the new”
- The only way to get >100 events
- But requires 11 O.M. leap!
- Watch out for tails, acceptance losses, the unexpected
- Stopping experiment very well understood
- Technique shown to have sufficient S/B
- Any further improvements can increase acceptance
- Note acceptance of 787/949 is ~0.002
- Plenty of room for improvement!
- Could ***really know*** if 50-100 events possible

## World enough & time for K

- _

- SM

## KL0l+l-

- KL0l+l-

- KL0e+e-
- ’97+’99

- KL0+ -
- ’97

## KL+-

-  **But** BR dominated by abs contrib:
-   >5 larger than SD
-   can be measured from KL
-   uncertainty > that on KL+-)  meas.
-  Subtraction can be addressed by other BR meas.
-  **But** LD dispersive contribution of similar size to SD
-  interferes with SD
-  can get information from KL l-l+, etc.
-  good progress, **but **would need 1000  KTeV to go further
-  in the hands of theorists
-  Better precision would be hard to get.

- KL+-

- K3

## Do we need multiple experiments?

- If we can’t get a 4  10-1 BR right to 5%

- Are we really going to get a **few ******** 10****-11** BR right to 10% the first time?

-   & we can’t get a 2  10-1
-    BR right to 8%

## Conclusions

- K++ seen, BR 2ce SM, but consistent with it
- Could go at least 10 further with same technique
- Initiative to go 100 further with in-flight technique
- KL0 experiment aiming to w/i factor 10 of SM level, w/i some BSM predictions
- Two initiatives to go >100 further
- Situation rife with uncertainty!
- J-PARC accelerator will be there, but experiments?
- Is FNAL really in the game?
- BNL K++ experiment stalled by DOE, future unclear
- BNL KL0 experiment probably has best prospects but not guaranteed (US Senate not helpful)

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## Gratuitous Advice

- Don’t worry too much about what others will or won’t do.
- If you are going to do it, don’t scrimp!
- Allow enough running time (years) for development, mid-course corrections, upgrades, and learning as you go.