Studies of CP violation in B0sJ/+ /f0...

Studies of CP violation inB0

s → J/ψ + φ/f0 decay

R. Magaña 1 on behalf of the DØ Collaboration.

1Cinvestav, México

The 19th Particles and Nuclei International ConferencePANIC 2011

R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 1 / 22

Motivation

• The mass eigenstates of the B0s

system have sizeable mass anddecay width difference ∆Ms and∆Γs

• The CP-violating mixing phaseis predicted to beΦ

J/ΨΦs = −2βs =−2 arg[−VtbV ∗ts/VcbV ∗cs] =−0.038± 0.002

• New phenomena may alter thephase Φ

J/ΨΦs ≡ −2βs + φ∆

s

• We measure ∆Γs and ΦJ/ΨΦs


Event distribution

• Bs → J/ΨΦ admixture of CP-even/odd states• Can be described by 3 polarization amplitudes• Transversity basis ~ω = (ψ, θ, ϕ):

• CP-odd (l=1): A⊥• CP-even (l=0,2): A0, A‖

y

x

z

θ

φ

J/ψ

µ+

−

−

K

K

µ

frameψ rest J/

+

x-y plane

y

x

K

K

J/ψ

+

−

ψ

φ

φ rest frame


DØ Detector

• Excellent muon detection to |η| < 2.2, lowpunch-through

• Fiber and Silicon Tracker in 2T Solenoid

Calorimeter

Shielding

Toroid

MuonChambers

MuonScintillators

η = 0 η = 1

η = 2

η = 3

Solenoid

Preshower

FiberTracker

SiliconTracker

η = 0 η = 1

η = 2

η = 3

1.2m

• Single and dimuontriggers


Data Samples


Event Selection

• We require two reconstructedmuons of opposite charge.

• Form J/Ψ candidates• Form Φ candiates from opposite

charged tracks assuming thetracks are kaons.

• Form Bs candidates from J/Ψand Φ candidates.

• Make cuts in the kinematic andthe mass windows:

• Pt (K±) > 0.4GeV• 2.84 < M(µ+µ−) < 3.35GeV• 0.98 < M(K +K−) < 1.04GeV• 5.0 < M(µ+µ−K +K−) <

5.8GeV

p p_


Background suppression

• BDT used to suppress background.• Prompt pp → J/ΨX

PromptBDTOutput-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

N(events)(Normalized)

0

1

2

3

4

5SignalBackground DØRun II,MC

PromptBDTOutput-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8


0

1

2

3

4

5Preliminary

• b-inclusive pp → bb → J/ΨX

InclusiveBDTOutput-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8


0

0.5

1

1.5

2

2.5

3

3.5SignalBackground DØRun II,MC

InclusiveBDTOutput-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8


0

0.5

1

1.5

2

2.5

3

3.5

Preliminary

• Simple-Cut as in 2008 PRL, forcross-check and systematicuncertainties.

Mass (GeV)5.2 5.3 5.4 5.5

N(events)/0.004

GeV

0

200

400

600

800

1000

1200

1400

1600

1800

Mass (GeV)5.2 5.3 5.4 5.5

N(events)/0.004

GeV

0

200

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600

800

1000

1200

1400

1600

1800-1Run II, 8fb∅DPreliminary

Mass (GeV)5.2 5.3 5.4 5.5

N(events)/0.004

GeV

0

200

400

600

800

1000

Mass (GeV)5.2 5.3 5.4 5.5

N(events)/0.004

GeV

0

200

400

600

800

1000-1Run II, 8fb∅DPreliminary


Optimizing selection

S+B200 400

310×

S

4000

5000

6000

7000 -1D Run II, 8fbPreliminary

S5000 6000

rad

)φψ

J/ sφ(σMean

0.25

0.27

0.29

0.31

0.33

0.35-1D Run II, 8fb Preliminary

• Tight cuts implies better signal significance but less signal events• Optimized selection cuts using toy montecarlo studies


Probability Distribution Function

ε(~ω)×(Bs(λ; t , ~ω)

1− D2

+ Bs(λ; t , ~ω)1 + D

2

)⊗ R(t)

where:• ~ω = (ψ, θ, ϕ)− angles• D− initial flavor tagging dilution• ε(~ω)− acceptance• R(t)−resolution.

Bs =∣∣∣[√1− Fsg(µ)A + e−iδs

√Fsh(µ)B

]× n̂∣∣∣2

• A(λ; t, ~ω)− P-Wave• B(λ; t, ~ω)− S-Wave.• λ = (τs,∆Γs, φ

J/Ψφs , |A0|2, |A⊥|2,Fs, δs, δ‖, δ⊥,∆ms)


Real Measurables

• Two constraints:• ∆ms ≡ 17.77± 0.12• cos(δ⊥) < 0

Parameter Definition|A0|2 P-wave amplitude squared|A‖|2 P-wave amplitude squaredτ s (ps) B0

s mean lifetime∆Γs (ps−1) Heavy-light decay width difference

FS K +K− S-wave fractionφ

J/ψφs CP-violating phaseδ‖ arg(A‖/A0)δ⊥ arg(A⊥/A0)δs arg(As/A0)


Acceptance, Resolution and Flavor Tagging

θcos-1 -0.5 0 0.5 1-3

-2

-1

0

1

2

3

0.65

0.7

0.75

0.8

0.85

0.9

0.95D Run II,MC Preliminary

• Data selectioncriteria wereapplied to flat MC

• 2D cos(θ), φacceptance

(t) (ps)σ0 0.1 0.2 0.3 0.4

10

210

310

(t) (ps)

dN(events)/d

σ(t)

σ0 0.1 0.2 0.3 0.4

10

210

310-1D Run II, 8fb

Preliminary

• Event-by-Eventresolution width

• Distribution ofproper decay timeresolution

• MC - Dots• Data - Crosses

|ost|d0 0.2 0.4 0.6 0.8 1

|D|

0

0.1

0.2

0.3

0.4

0.5

0.6

(IIa)*0D+µ→0Data: B

(IIb1)*0D+µ→0Data: B



Data:WeightedAve.

FittoData

Uncertainty

-1Run II, 8fbDPreliminary

• Opposite Flavortagging using:

• Muon• Electron• Jet Charge


Maximum Likelihood Fit

ProperDecayTime(ps)0 2 4 6

N(events)/0.075ps

10

210

310

410


N(events)/0.075ps

10

210

310

410 -1Run II, 8fb∅DPreliminary

)ψcos(-1 -0.5 0 0.5 1

N(events)/0.1

0

1000

2000

3000

4000

5000 -1Run II, 8fb∅DPreliminary

)θcos(-1 -0.5 0 0.5 1

N(events)/0.1

0

1000

2000

3000

4000

5000-1Run II, 8fb∅D

Preliminary

φ-3 -2 -1 0 1 2 3

N(events)/0.314

0

1000

2000

3000

4000


Preliminary


Maximum Likelihood Fit (Signal Enriched)


N(events)/0.075ps

10

210

310

410


N(events)/0.075ps

10

210

310

410 -1Run II, 8fb∅D

t>1 ps

Preliminary

)ψcos(-1 -0.5 0 0.5 1

N(events)/0.1

0

50

100

150

200

250

300

350


Preliminary

)θcos(-1 -0.5 0 0.5 1

N(events)/0.1

0

50

100

150

200

250

300

350


Preliminary

φ-3 -2 -1 0 1 2 3

N(events)/0.314

0

50

100

150

200

250

300

350


Preliminary


Fit Results

Parameter BDT Sample Simple Cut Sampleτ s 1.426+0.035

−0.032 ps 1.444+0.041−0.033 ps

∆Γs 0.129+0.076−0.053 ps−1 0.179+0.059

−0.060 ps−1

φJ/ΨΦs −0.49+0.48

−0.40 −0.56+0.36−0.32

|A0|2 0.552+0.016−0.017 0.565± 0.017

|A‖|2 0.219+0.020−0.021 0.249+0.021

−0.022

δ‖ −3.15± 0.27 −3.15± 0.19cos(δ⊥ − δs) −0.06± 0.24 −0.20+0.26

−0.027

FS(eff ) 0.146± 0.035 0.176± 0.036


Independent determination of Fs• The invariant mass distribution of B0

scandidates with ct > 0.02cm in twoslices of M(K +K−)

• Fits to a sum of a Gaussian functionand a polynomial are used to extractthe B0

s yield in each slice.• Fs = 0.14± 0.01

M(KK)(GeV)1 1.01 1.02 1.03 1.04 1.05

Events/(0.002GeV

)

0

200

400

600

800

M(KK)(GeV)1 1.01 1.02 1.03 1.04 1.05

Events/(0.002GeV

)

0

200

400

600

800 Preliminary

KK)(GeV)µµM(5.2 5.3 5.4 5.5

N(events)/0.01

GeV

0

20

40

60

80

100

120 -1D Run II, 8fb Preliminary

1.018 < M(K +K−) < 1.020

5.2 5.3 5.4 5.5

N(events)/0.01

GeV

0

2

4

6

8

10

12

14

16

K K)(GeV)µµM(

-1D Run II, 8fb Preliminary

1.048 < M(K +K−) < 1.050

·R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 15 / 22

Systematic Uncertainties

• Acceptance systematic from differences between BDT andSimple-cut samples

• Variation in resolution parameters• Random variations in the resolution parameters

• Different widths of Φ• Different resolution for the Φ mass, important since s-wave is

around 15%

• Variation OST calibration curve• Markov Chain thechique for contours and systematics


B0s → J/ΨΦ Result

P xτ s 1.443+0.038

−0.035 ps

∆Γs 0.163+0.065−0.064 ps−1

φJ/ΨΦs −0.55+0.38

−0.36

|A0|2 0.558+0.017−0.019

|A‖|2 0.231+0.024−0.030

δ‖ −3.15± 0.22(δ⊥-δs) −0.11+0.027

−0.025

FS(eff ) 0.173± 0.036

SMp-value=29.8%

−10.12ps±17.77≡sMΔ

SM

68%CL

90%CL

95%CL

−3 −2 −1 2 30 1−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4 −1D Run II, 8fb

(rad)φψJ /sφ

)−1

(ps

sΓΔ

Preliminary


B0s → J/Ψf0(890)

• CP-odd final state, no angular analysis• Independent information on ∆Γs

• First step is measure the branching ratio


B0s → J/Ψf0(890) Branching ratio

(GeV)-π+π-µ+µM5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8

Eve

nts

/ 28

MeV

0

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200

300

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500

600

700

(GeV)-π+π-µ+µM5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8

Eve

nts

/ 28

MeV

0

100

200

300

400

500

600

700-1 Run II, Preliminary, 8 fb∅D

• Muon trigger• Identical selection criteria

for J/Ψf0 and J/ΨΦ

• BDT to reduce background• 478± 76J/Ψf0(980) events

(GeV)-π+πM0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2

Eve

nts

/ 20

MeV

0

50

100

150

200

250

300

350

400

450

(GeV)-π+πM0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2

Eve

nts

/ 20

MeV

0

50

100

150

200

250

300

350

400

450

-1 Run II, Preliminary, 8 fb∅D

Branching Ratio:

R =B(B0

s → J/Ψf0(980); f0 → π+π−)

B(B0s → J/ΨΦ; Φ→ K +K−)

= 0.210±0.032(stat)±0.036(sys)


Summary

• Measurement of B0s mixing parameters, polarization amplitudes

and phases in the B0s → J/ΨΦ analysis using 8fb−1 data sample.

• Inclusion of K +K− s-wave• Measurement of the branching fraction of B0

s → J/Ψf0(980) inagreement with other experiments.

• Next step is to use in CP-Violation measurements

• Combination with other DØ measurements of CP-Violationparameters will be performed soon

Stay tuned !


Backup Slides

·


Markov Chain technique

• Since φs is very correlated with ∆Γs we want to know how thelikelihood depends on these variables.

• Start from some point µ. I use the minimum obtained from the fit.

• Generate a multivariate gaussian (e−12 (x−µ)·Σ1·(x−µ).) point x ′

• Where Σ is the covariance matrix.• Calculate α = L(x ′)/L(µ)

• Generate a random number r = U(0,1)

• If r < α accept the new point µ = x• And continue until reach the amount of points desired.• We generate 1M events for each Markov Chain


Studies of CP violation in B0sJ/+ /f0...

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