Final bnl e949 results on the search for the rare decay
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Final BNL E949 results on the search for the rare decay  + →  + . Joss Ives University of British Columbia / TRIUMF. There’s new physics beyond the Standard Model, but we don’t know exactly what it is (yet). Dominance of matter. over antimatter. Dark matter and dark energy.

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Final bnl e949 results on the search for the rare decay

Final BNL E949 results on the search for the rare decay +→ +

Joss IvesUniversity of British Columbia / TRIUMF


There s new physics beyond the standard model but we don t know exactly what it is yet
There’s new physics beyond the Standard Model, but we don’t know exactly what it is (yet)

Dominance of matter

over antimatter

Dark matter and dark energy

Neutrino massand oscillations


To find physics beyond the standard model we need to break the standard model
To find physics beyond the Standard Model, don’t know exactly what it is (yet)we need to break the Standard Model

Energy frontier

Precision/Intensity Frontier

overcompensating.com

Rare decays such as+ → +(E949/E787 @ BNL)

LHC


Quarks cannot decay to another quark of the same charge by a first order process

t don’t know exactly what it is (yet)

u

c

2/3

t

u

c

2/3

First-order weak decaysof quarks

d

b

s

1/3

d

b

s

1/3

Quarks cannot decay to another quark of the same charge by a first-order process


Proceeds very slowly through second order weak processes

c don’t know exactly what it is (yet)

+→ + proceeds very slowly through second-order weak processes

The decay proceeds through second-orderprocesses due to massive top quark

t

u


Observing the rare decay is an enormous experimental challenge

don’t know exactly what it is (yet)+

Observing the rare decay +→ + is an enormous experimental challenge

That’s 1 in 12.5 billion decays!!!

CEX

Standard Model branching ratio is (0.840.7)1010

+-e+

+0

Beam

+

Experimental signature is+ + "nothing"

+0

+0

+

100

10-9

10-6

10-3

10-11

Branching Ratio


A precision measurement of the decay rate probes for new physics

Equivalent Energy (TeV) don’t know exactly what it is (yet)

Relative Error on Measurement

A precision measurement of the +→ + decay rate probes for new physics

Curve assumes a Minimal Flavor Violation (MFV) model

Curve extracted from D.Bryman et al., IJMPA 21, 487 (2006)


The e949 experimental goal is to suppress backgrounds to below the sensitivity level of the signal
The E949 experimental goal is to suppress backgrounds to below the sensitivity level of the signal

TotalBackground

SignalSensitivity


The rest of this talk will look at the e949 experiment in four sections
The rest of this talk will look at the E949 experiment in four sections

Numericaldetails

TheExperiment

Finalresults

Backgrounds


In this section i will discuss the experimental challenge and the blind analysis method
In this section I will discuss the experimental challenge and the blind analysis method

Numericaldetails

TheExperiment

Finalresults

Backgrounds


The experimental challenge is to observe nothing

and the blind analysis method

The experimental challenge is to observe + + "nothing"



K

Neutrinos…not so easy to detect


The 0 decay splits the signal region in two pnn1 and pnn2
The and the blind analysis method0 decay splits the signal region in two:PNN1 and PNN2

Standard Model+ momentumfrom  + →  +


Things get ugly in the pnn2 region
Things get ugly in the PNN2 region and the blind analysis method


E949 e787 have previously observed four candidate events showing that it can be done

PNN1 region and the blind analysis method= 2 E787 events+ 1 E949 event

 Standard Model PNN1 Only

3.5

3

2.5

PNN2 region= 1 E787 event+ ? E949 events

2

Branching Ratio (x10-10)

1.5

1.47

1

0.85

0.5

0

E949 & E787 have previously observed four candidate events showing that it can be done

Refs: PRD70, 037102 (2004), PRD77, 052003 (2008)


How to observe in three easy steps
How to observe and the blind analysis method+→ + in three easy steps

 comes out

K goes in

No additional particles


700 mev c kaon enters and decays at rest in the scintillator fiber target
700 MeV/ and the blind analysis methodc kaon enters and decays-at-rest in the scintillator-fiber target

Beam instrumentation is used to identify a single K+ from the beam

Kaon comes to rest in the target and we wait at least 2 ns for K+ to decay


Decay pion comes to rest in the range stack and undergoes the e decay sequence
Decay pion comes to rest in the range-stack and undergoes the   e  decay sequence

  momentum is measured in the drift chamber

  e  decay sequence is observed in the range-stack scintillator

  range and energy are measured target and range-stack


Veto the photons and any addition charged particle activity
Veto the photons and any addition charged particle activity the

The photon veto gives full 4 sr coverage

Pattern recognition is used in the target, drift chamber and range-stack to identify additional charged tracks


Final bnl e949 results on the search for the rare decay

The blind analysis technique can be summed up as eliminating everything that is not +→ + without directly examining the signal region

“How often have I said to you that when you have eliminated the impossible,

whatever remains, however improbable, must be the truth?”

- Sherlock Holmes to Watson

In The Sign of Four

*Thanks Benji


Backgrounds that can mimic are identified a priori
Backgrounds that can mimic everything that is not +→ + are identified a priori


Final bnl e949 results on the search for the rare decay
The bifurcation method uses two uncorrelated high-rejection cuts to estimate each background using information outside of the signal region

Measure B:Invert CUT1 and apply CUT2

Measure D:Invert CUT2 andapply CUT1

B

D

CUT1

A

C

CUT2

Measure C+D:Invert CUT2

Estimate A:A = BC/D

A is the signalregion

Background estimate = A!


Background estimates are performed using data different from those used to develop cuts
Background estimates are performed using data different from those used to develop cuts

EntireData Set

2/3

1/3

BackgroundEstimates

CutDevelopment

Compare background estimates


Signal region is only examined once all background estimates have been finalized
Signal region is only examined once all background estimates have been finalized

“Open the box”


Final bnl e949 results on the search for the rare decay
In this section I will detail the suppression of various backgrounds and reveal the total background

Numericaldetails

TheExperiment

Finalresults

Backgrounds


The number one enemy is 0 when the scatters in the target

Regular backgrounds and reveal the total background0



K

The number one enemy is 0 when the  scatters in the target

Target Scatter



K

Target

Target

 and  0 are back to back so photons are directed to efficient part of the photon veto

When the  scatters in the target it loses energy and the photons lose directional correlation with the  


This background is suppressed by the photon veto and identification of scattering
This background is suppressed by the photon veto and identification of  scattering



K

Target

KaonPionCombined

A scatter can also be identified by large energy deposits in a pion fiber or hidden energy in a kaon fiber

A scatter can be identified by finding a kink in the  track


The bifurcation cuts used for target scatters are the photon veto and the target scatter cuts
The bifurcation cuts used for identification of + target-scatters are the photon veto and the target-scatter cuts

Target-scatter cuts are inverted (black curve) and the photon veto is applied (red curve)

Photon veto is inverted (black curve) and the target cuts are applied (blue curve)

B

D

Photon Veto

C+D

A

C

Target-scatter ID

B

BackgroundA = BC/D

C


In practice the three 0 backgrounds have to be disentangled

identification of Target Scatter



0

K

Range-Stack Scatter





In practice the three 0 backgrounds have to be disentangled

The + target scatter sample made by inverting the photon veto has contamination from + range-stack scatter and K + →  +  0  processes


The e decay can mimic signal when the and e have low kinetic energies
The identification of e decay can mimic signal when the  and e have low kinetic energies

Simulated K     e 

+ momentum (MeV/c)

SignalRegion

ekinetic energy (MeV)


Use target pattern recognition to isolate sample and estimate rejection power using simulation
Use target pattern recognition to isolate sample and estimate rejection power using simulation

Estimate the rejection power of the target pattern recognition using simulated data supplemented by the measured   energy deposit in scintillator

K    e sample is isolated using target pattern recognition



K s is suppressed by k decay time condition and k l by gaps between the k and tracks

Gaps Between kaon decay K &  Tracks

K Decay Time





K

K

l

KS is suppressed by K decay time condition and KL by gaps between the K and  tracks

KL lifetime is 50 ns so target pattern recognition is used to identify gaps between the K+ and + tracks

KS lifetime is only 0.1 ns so the K decay time condition suppresses KS decays

Additional suppression is provided by detecting the negatively charged lepton


Due to kinematic constraints the troublesome decays are the multi body ones
Due to kinematic constraints, the troublesome kaon decay  decays are the multi-body ones

Not a big deal in the PNN2 region

!


Muon processes are suppressed kinematically and by identification of the decay
Muon processes are suppressed kinematically and by identification of the  decay

decay sequence: e

Range in plastic scintillator

Momentum

Pulse shape in the range-stackstopping counter

Muons have different kinematic signature in the detector than pions


Beam backgrounds come from events other than a single kaon decaying at rest in the target
Beam backgrounds come from events other than a single kaon decaying at rest in the target

Single-beam

Double-beam


Final bnl e949 results on the search for the rare decay
Compared to the E787-PNN2 analysis, our total background was decreased by 24% and total acceptance increased by 63%

1.4

1.2

+0

Target-Scatters

1.0

E787Total

0.8

0.6

Background Estimate (Events)

+-e+

Total

0.4

+0

0.2

Muon

Beam

0

+0

Range-StackScatters

ChargeExchange

E787-PNN2 This AnalysisTotal kaons 1.73  1012 1.70  1012Total acceptance 0.84  103 1.37  103

Only 20% of the approved beam time


In this section i will discuss some last numerical details before getting to the grand opening
In this section I will discuss some last numerical details before getting to the grand opening

Numericaldetails

TheExperiment

Finalresults

Backgrounds


Final bnl e949 results on the search for the rare decay

D' before getting to the grand opening

B'

Loosen CUT1 

A'

C'

Loosen CUT2 

Outside-the-box studies compare background estimates to direct measurements just outside the signal region

Signal region is masked out; the background estimate and direct measurement for region Aare compared directly

If CUT1 and CUT2 are uncorrelated, the two values will agree


Final bnl e949 results on the search for the rare decay
The outside-the-box results demonstrate that the systematic uncertainties assigned to the backgrounds were reasonable


By further tightening four of the cuts the signal region was divided into nine cells

+ uncertainties assigned to the backgrounds were reasonable

+

Decay Time

Decay Time

K

K

º

+

K

p

+

By further tightening four of the cuts, the signal region was divided into nine cells


The relative signal to background levels of the nine cells varied by about a factor of 4

Estimated uncertainties assigned to the backgrounds were reasonableBackground

The relative signal-to-background levels of the nine cells varied by about a factor of 4

1

0.9

0.038

0.152

0.8

0.019

Signal-to-Background

0.7

0.005

0.6

0.059

0.027

0.5

0.243

0.007

0.4

0.3

0.2

0.379

0.1

0

Cell


Now it s time to open the box
Now it’s time to open the box… uncertainties assigned to the backgrounds were reasonable


And three events were observed

1 uncertainties assigned to the backgrounds were reasonable

0.9

3 events

0.038

0.152

0.8

0.019

Signal-to-Background

0.7

0.005

0.6

0.059

0.027

0.5

0.243

0.007

0.4

0.3

0.379

0.2

0.1

0

Cell

Measured branching ratio is

The probability that all three eventswere due to background only is 3.7%

…and three events were observed


Final bnl e949 results on the search for the rare decay

3.5 uncertainties assigned to the backgrounds were reasonable

 Standard Model PNN1 Only ALL E787/E949

3

2.5

Branching Ratio (x10-10)

2

1.73

1.5

1.47

1

0.85

0.5

0

The probability that all seven eventswere due to background only is 0.1%

The combined E787/E949 branching ratio is twice as high, but consistent with Standard Model expectation

Despite the sizes of the boxesPNN1 analyses are 4.2 times more sensitive than PNN2 analyses


The e787 e949 collaboration a k a the fine folks behind these results
The E787/E949 collaboration uncertainties assigned to the backgrounds were reasonablea.k.a. the fine folks behind these results


The next measurements of are just around the corner

NA62 (formerly NA48/3) uncertainties assigned to the backgrounds were reasonablein preparation at CERN

Letter of intent for using best E949 bits in Japan

The next measurements of +→ + are just around the corner

Future experiments

Fermilab Project X?

Ref: FlaviaNet - http://www.lnf.infn.it/wg/vus/


Thank you questions

3.5 uncertainties assigned to the backgrounds were reasonable

 Standard Model PNN1 Only ALL E787/E949

3

2.5

Branching Ratio (x10-10)

2

1.73

1.5

1.47

1

0.85

0.5

0

Thank you…questions?

Thank you to David Jaffe for the resources that made this talk possible