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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 2 / 22
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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 3 / 22
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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 4 / 22
Data Samples
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 5 / 22
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_
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 6 / 22
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
N(events)(Normalized)
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
N(events)(Normalized)
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
N(events)(Normalized)
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
400
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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 7 / 22
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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 8 / 22
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)
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 9 / 22
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)
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 10 / 22
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
(IIb2)*0D+µ→0Data: B
(IIb3)*0D+µ→0Data: B
Data:WeightedAve.
FittoData
Uncertainty
-1Run II, 8fbDPreliminary
• Opposite Flavortagging using:
• Muon• Electron• Jet Charge
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 11 / 22
Maximum Likelihood Fit
ProperDecayTime(ps)0 2 4 6
N(events)/0.075ps
10
210
310
410
ProperDecayTime(ps)0 2 4 6
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
5000-1Run II, 8fb∅D
Preliminary
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 12 / 22
Maximum Likelihood Fit (Signal Enriched)
ProperDecayTime(ps)0 2 4 6
N(events)/0.075ps
10
210
310
410
ProperDecayTime(ps)0 2 4 6
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
400-1Run II, 8fb∅D
Preliminary
)θcos(-1 -0.5 0 0.5 1
N(events)/0.1
0
50
100
150
200
250
300
350
400-1Run II, 8fb∅D
Preliminary
φ-3 -2 -1 0 1 2 3
N(events)/0.314
0
50
100
150
200
250
300
350
400-1Run II, 8fb∅D
Preliminary
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 13 / 22
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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 14 / 22
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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 16 / 22
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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 17 / 22
B0s → J/Ψf0(890)
• CP-odd final state, no angular analysis• Independent information on ∆Γs
• First step is measure the branching ratio
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 18 / 22
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
100
200
300
400
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)
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 19 / 22
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 !
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 20 / 22
Backup Slides
·
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 21 / 22
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
R. Magaña (DØ/ Cinvestav) CP Violation on Bs → J/Ψ + φ/f0 PANIC11 July, 25 22 / 22
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