Angular Analysis B Kbib-pubdb1.desy.de/record/288940/files/Helmholtz_Wehle... · 2015-11-27 · E2...

Angular Analysis B → K (∗)`+`−.

Overview of the Analysis

Simon Wehle Sergey YashchenkoDeutsches Elektronen-Synchrotron9th Annual Helmholtz Alliance Workshop,November 17, 2015

Table of Contents

I IntroductionI BelleI Motivation

I Full Angular Analysis

I Systematic Uncertainties

I Perspective

S. Wehle | DESY | 9th Annual Helmholtz Alliance Workshop, November 17, 2015 | /16Introduction Full Angular Analysis Systematic Uncertainties Perspective

The Belle Experiment

I The Belle Experiment is located at theKEKB accelerator in Tsukuba, Japan

I It is designed as a “B factory”I 771 million BB meson pairsI World record for integrated luminosity∫

Ldt = 1 ab−1


The Belle Detector


Motivation for B → K (∗)`+`−

I Flavor Changing Neutral Currents are sensitive to new physicsI The interesting process in B → K (∗)`+`− contains the quark

transition b → s`+`−

s

dd

b

W−

γ, Z0ℓ−

ℓ+

u, c, t

B0 K∗0

s

dd

b

W−

γ, Z0ℓ−

ℓ+

u, c, t

K∗0B0

s

dd

b

ℓ−

ℓ+

u, c, t

νℓ

W+ W−

K∗0B0

I Small decay amplitudes BR(B → K ∗``) ∼ 10−6


B → K∗`` - Goals of the Analysis / Status

Goals of the analysis

I Full angular analysis, measurement of P ′iobservablesI The observables P ′4,5,6,8 can be

extracted from the angular decay rate ofB0 → K 0∗`+`−

I In 2013 the LHCb collaborationannounced a local discrepancy of 3.7σfrom Standard Model prediction in oneof 24 measurements (Phys. Rev. Lett.111, 191801 )

Figure : Result of LHCb forP ′5 (2015).

Current Status at Belle

I We have determined our sensitivity in toy studiesI We can use a combination of the electron and muon channelsI The analysis waits for opening the box


http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111.191801

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.111.191801

Reconstruction of B0 → K∗0`+`−

Multivariate approach

I Neural networks for identifying all primaryparticles and K ∗

I K ∗ is reconstructed in K ∗(892)0 → K+π−

I Neural networks for signal selection (onefor each B decay channel)

I Signal is identified in the beamconstrained mass

Mbc ≡√

E 2Beam − |~pB |2

bcM5.22 5.24 5.26 5.28 5.3

Eve

nts

/ ( 0

.008

)

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10

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50

60

70

bcM5.22 5.24 5.26 5.28 5.3

Pul

l

-2

0

2

bcM5.22 5.24 5.26 5.28 5.3

Eve

nts

/ ( 0

.004

4444

4 )

0

20

40

60

80

100

120

bcM5.22 5.24 5.26 5.28 5.3

Pul

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-2

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2


Electron mode

Muon mode

Full Angular Analysis

I This measurement uses the decay channelsB0 → K ∗(892)0(→ K+π−)`+`−

I Difficult to measure with low statistics of ∼ 150 events

Figure : Definition of the angles in thedecay B0 → K∗`+`−. Figure : Binning in q2 ≡ M2

`+`− .


Full Angular Decay Rate

The full angular decay rate for B0 → K ∗`+`− with 8 free parameterscan be written as:

1dΓ/dq2

d4Γ

d cos θL d cos θK dφ dq2 =9

32π

[34

(1− FL) sin2 θK + FL cos2 θK

+14

(1− FL) sin2 θK cos 2θL

− FL cos2 θK cos 2θL + S3 sin2 θK sin2 θL cos 2φ+ S4 sin 2θK sin 2θL cosφ+ S5 sin 2θK sin θL cosφ

+ S6 sin2 θK cos θL + S7 sin 2θK sin θL sinφ

+ S8 sin 2θK sin 2θL sinφ+ S9 sin2 θK sin2 θL sin 2φ],

using definitions of J. High Energy Phys. 01 (2009) 019.


http://iopscience.iop.org/1126-6708/2009/01/019/


The full angular decay rate for B0 → K ∗`+`− with 8 free parameterscan be written as:

1dΓ/dq2

d4Γ

d cos θL d cos θK dφ dq2 =9

32π

[34

(1− FL) sin2 θK + FL cos2 θK

+14

(1− FL) sin2 θK cos 2θL

− FL cos2 θK cos 2θL + S3 sin2 θK sin2 θL cos 2φ+ S4 sin 2θK sin 2θL cosφ+ S5 sin 2θK sin θL cosφ

+ S6 sin2 θK cos θL + S7 sin 2θK sin θL sinφ

+ S8 sin 2θK sin 2θL sinφ+ S9 sin2 θK sin2 θL sin 2φ],

using definitions of J. High Energy Phys. 01 (2009) 019.

S. Wehle | DESY | 9th Annual Helmholtz Alliance Workshop, November 17, 2015 | Page 9/16Introduction Full Angular Analysis Systematic Uncertainties Perspective

http://iopscience.iop.org/1126-6708/2009/01/019/


P ′4, S4 :

φ→ −φ for φ < 0φ→ π − φ for θL > π/2θL → π − θL for θL > π/2,

P ′5, S5 :

{φ→ −φ for φ < 0θL → π − θL for θL > π/2,

P ′6, S7 :

φ→ π − φ for φ > π/2φ→ −π − φ for φ < −π/2θL → π − θL for θL > π/2,

P ′8, S8 :

φ→ π − φ for φ > π/2φ→ −π − φ for φ < −π/2θK → π − θK for θL > π/2θL → π − θL for θL > π/2.

I With a folding of the angles wereduce the dimension of freeparameters

I We perform four measurementswhich are independently sensitiveto three observable Sj ,FL and S3

I The observables

P ′i=4,5,6,8 =Sj=4,5,7,8√FL(1− FL)

,

are considered to be largely freefrom form-factor uncertainties (J.High Energy Phys. 05 (2013) 137).


http://link.springer.com/article/10.1007%2FJHEP05%282013%29137

http://link.springer.com/article/10.1007%2FJHEP05%282013%29137

Fit Procedure

bcM5.22 5.24 5.26 5.28 5.3

Even

ts /

( 0.0

04 )

0

2

4

6

8

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12

14

16

18

20

bcM5.22 5.24 5.26 5.28 5.3

Pull

-202

Signal Sideband Table : Events in q2 bins, MCpredictions for n (nµ

+µ−+ ne+e−

).

bin q2 bin range [GeV2/c4] nsig/bin nbkg/bin

0 1.00− 6.00 37 (24+13) 24 (18+6)1 0.10− 4.00 33 (21+12) 18 (11+2)2 4.00− 8.00 36 (24+12) 33 (20+13)3 10.09− 12.90 29 (23+6) 18 (16+2)4 14.18− 19.00 34 (26+8) 14 (12+2)

I The fit is performed in bins of q2 in θL, θK and φ, each treated asan independent measurement

I We fit Mbc to determine the signal to background fractionI We fit the shape of the background in the Mbc sideband with

smoothed histograms


Fit Example

Kθ0 1 2 3

Eve

nts

/ ( 0

.448

799

)

0

2

4

6

8

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12

14

16

18

20

22

Kθ0 1 2 3

Pul

l

-2

0

2 Lθ0 0.5 1 1.5

Eve

nts

/ ( 0

.224

399

)

0

2

4

6

8

10

12

14

16

18

Lθ0 0.5 1 1.5

Pul

l

-2

0

2φ

0 1 2 3

Eve

nts

/ ( 0

.448

799

)

0

2

4

6

8

10

12

14

φ0 1 2 3

Pul

l

-2

0

2

Figure : Fit example of the extraction of P ′5 ( q2 bin 3) with components:signal, background and total pdf in solid-red, dashed blue and solid black line.

We estimate the efficiency in the angular variables with a spline fit onMC and weight the events by the inverse:

f bineff (cos θL, cos θK , φ, q2) = f θLeff (cos θL)⊗ f θKeff (cos θK )⊗ f φeff (φ)⊗ f q2

eff (q2).


Toy Study - Results for P ′5

0 5 10 15 20

q2 [GeV2 /c4 ]

1.5

1.0

0.5

0.0

0.5

1.0

1.5

2.0

P′ 5

Belle MC preliminary

9th Annual Helmholtz Alliance Workshop Ongoing Belle analysis, theoretical predicitons by Javier Virto

LHCb (2011)SM from DHMV Expected Statistical Error µExpected Statistical Error e+µ

Figure : Result of the MC toy studies with the expected signal and backgroundyields, each data point represents the averaged result of 10000 fits.


Sources for Systematic Uncertainties

For the angular analysis we consider sources of systematic uncertainty ifthey introduce an angular or q2 dependent bias to the distribution ofsignal or background candidates.

We consider

I Fit bias (dominant systematic error)I Data/MC discrepancyI K ∗ S-Wave contribution (negligible)I CP Asymmetries (negligible)I Cross-Feed (negligible)


Perspective

Resume

I We could show that we can perform the measurementI Even with lower total signal yield than LHCb we

might compare electron and muon channels

Outlook

I Will we also see a deviation in P ′5?I We hope to get the permission for a box opening very

soonI The result is targeted to be shown at the winter

conferences


Thank you for your Attention!

Thank you!S. Wehle | DESY | 9th Annual Helmholtz Alliance Workshop, November 17, 2015 | Page 16/16

Introduction Full Angular Analysis Systematic Uncertainties Perspective

Toy Study - Results for P ′4

0 5 10 15 20

q2 [GeV2 /c4 ]

2.0

1.5

1.0

0.5

0.0

0.5

1.0

1.5

2.0

P′ 4

Belle MC preliminary

9th Annual Helmholtz Alliance Workshop Ongoing Belle analysis, theoretical predicitons by Javier Virto

LHCb (2011)SM from DHMV Statistical Sensitivity µStatistical Sensitivity e+µ

Figure : Result of the MC toy studies with the expected signal and backgroundyields, each data point represents the averaged result of 10000 fits.

S. Wehle | DESY | 9th Annual Helmholtz Alliance Workshop, November 17, 2015 | Page 1/3Additional Material

Background estimation on Mbc sideband

We check the correlation of the angular variables with the Mbc sideband:

5.22 5.24 5.25 5.27 5.29

Mbc

-1.00

-0.50

0.00

0.50

1.00

cosθK

Probability of flat hypothesis: 58.79%

5

4

3

2

1

0

1

2

3

4

5

(a) cos θK vs. Mbc

5.22 5.24 5.25 5.27 5.29

Mbc

-1.00

-0.50

0.00

0.50

1.00

cosθL

Probability of flat hypothesis: 0.02%

5

4

3

2

1

0

1

2

3

4

5

(b) cos θL vs. Mbc

5.22 5.24 5.25 5.27 5.29

Mbc

-3.14

-1.57

-0.00

1.57

3.14

φ

Probability of flat hyopthesis 26.97%

5

4

3

2

1

0

1

2

3

4

5

(c) φ vs. Mbc

Figure : Flat correlation plot of Mbc with the angular variables and q2. Thecolor represents the deviation of the expected bin-content for a flat distributionin σ.


Efficiency estimation

We estimate the efficiency in the angular variables and weight the eventsby the inverse of the it:

f bineff (cos θL, cos θK , φ) = f fiteff (cos θL)⊗ f fiteff (cos θK )⊗ f fiteff (φ).

This procedure is valid as there is no correlation in the efficiency amongthe angular variables.

-1.00 -0.50 -0.03 0.45 1.00

cosθK

-1.00

-0.41

0.00

0.42

1.00

cosθL

Probability of flat hypothesis 2.43%

5

4

3

2

1

0

1

2

3

4

5

(a) cos θL vs. cos θK

-1.00 -0.41 0.00 0.42 1.00

cosθL

-3.14

-1.58

0.00

1.58

3.14

φ


5

4

3

2

1

0

1

2

3

4

5

(b) φ vs. cos θL

-1.00 -0.50 -0.03 0.45 1.00

cosθK

-3.14

-1.58

0.00

1.58

3.14

φ


5

4

3

2

1

0

1

2

3

4

5

(c) φ vs. cos θK

Figure : Flat correlation plots of the reconstruction efficiency among theangular variables.


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