Oo ~ )À *Ó ²Þ)O~Þ) Þcds.cern.ch/record/2710585/files/Poster-2020-1030.pdf · CPV in...
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Measurement of CP violation in B 0 → D ∗± D ∓ decays [1] Philipp Ibis on behalf of the LHCb collaboration Introduction: CP violation in B 0 mixing Oscillation between B 0 and B 0 states. W u,c,t ¯ u, ¯ c, ¯ t W d B 0 ¯ b b B 0 ¯ d Decay of a neutral B meson into the final state f or ¯ f : directly or after oscillation → four time-dependent decay rates. dΓ(t ) dt = e -t/τ d 8τ d (1 + r A D * D )× h 1 - d (S D * D + r ΔS D * D ) sin(Δmt )+ d (C D * D + r ΔC D * D ) cos(Δmt ) i d = 1, B 0 -1, B 0 r = 1, f -1, ¯ f B 0 B 0 f = D * + D – f = D * – D + CP violation in B 0 → D *± D ∓ • First measurement of CP violation in B 0 → D *± D ∓ at LHCb • Former measurements by Belle and BaBar [2,3] D* +- D -+ S HFLAV Summer 2016 -1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 BaBar PRD 79, 032002 (2009) -0.68 ± 0.15 ± 0.04 Belle PRD 85 (2012) 091106 -0.78 ± 0.15 ± 0.05 Average HFLAV -0.73 ± 0.11 HFLAV HFLAV Summer 2016 D* +- D -+ C HFLAV Summer 2016 -0.2 -0.1 0 0.1 0.2 BaBar PRD 79, 032002 (2009) 0.04 ± 0.12 ± 0.03 Belle PRD 85 (2012) 091106 -0.01 ± 0.11 ± 0.04 Average HFLAV 0.01 ± 0.09 HFLAV HFLAV Summer 2016 D* +- D -+ A HFLAV Summer 2016 -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 BaBar PRD 79, 032002 (2009) 0.01 ± 0.05 ± 0.01 Belle PRD 85 (2012) 091106 0.06 ± 0.05 ± 0.02 Average HFLAV 0.03 ± 0.04 HFLAV HFLAV Summer 2016 [4] • b → c cs decays are sensitive to weak phase 2β • Measured by several experiments in different chan- nels [4] • Same phase appears in b → c cd transitions • For B 0 → D *± D ∓ decays higher-order diagrams con- tribute to CP violation. Instrumental asymmetries • Overall asymmetry is corrected for instrumental asymmetries from reconstruction, detection and par- ticle identification • B 0 → D *± D ∓ decay is charge-balanced, asymme- tries only due to different momentum spectra of pos- itive and negative pions and kaons • 6 million prompt D ± → K ∓ π ± π ± decays reweighted to signal D *- or D - distributions • Split into four subsamples: One sample per D 0 decay mode and one for D *- and D - , respectively • Asymmetries A D *- det and A D - det calculated with D + and D - yields from fits to the mass distributions Final state A D *- det A D - det A D *- D + det [%] K - π + 0.0169 0.0158 0.11 ± 0.40 ± 0.30 K - π - π + π + 0.0146 0.0138 0.09 ± 0.26 ± 0.51 Signal extraction Reconstruction • D *+ → D 0 π + D 0 → K - π + D 0 → K - π - π + π + • D - → K + π - π - Full LHCb dataset • 1 fb -1 at 7 TeV • 2 fb -1 at 8 TeV • 6 fb -1 at 13 TeV Multivariate Selection • Further reduction of combinatorial background • Boosted Decision Tree (BDT) • Signal proxy: signal MC • Background proxy: upper mass sideband from data • Kinematic, topological and particle identification variables used • BDT cut point minimises uncertainties of CP parameters Mass Fit • Disentangle signal from remaining background • Shapes of the signal and background components based on sim- ulated data Signal Candidates K - π + K - π - π + π + Run 1 856 ± 32 469 ± 28 Run 2 3265 ± 61 1570 ± 48 Candidates / (6 MeV /c 2 ) 200 400 600 800 1000 1200 m D *± D ∓ [MeV /c 2 ] 5000 5200 5400 5600 -5 0 5 Pull LHCb Run 2 Total B 0 → D *± D ∓ B 0 s → D *± D ∓ B 0 → D + s D *- B 0 → D *+ D *- B 0 s → D *+ D *- Comb. bkg. Candidates / (6 MeV /c 2 ) 100 200 300 400 500 600 m D *± D ∓ [MeV /c 2 ] 5000 5200 5400 5600 -5 0 5 Pull LHCb Run 2 Total B 0 → D *± D ∓ B 0 s → D *± D ∓ B 0 → D + s D *- B 0 → D *+ D *- B 0 s → D *+ D *- Comb. bkg. Flavour Tagging Knowledge of b quark flavour at produc- tion is essential for measurements of time- dependent CP asymmetries. PV SV b → c b → Xl - SV c → s same side opposite side b b D *± D ∓ d d u d u u π + p x l - K - B 0 h b SS pion SS proton OS muon OS electron OS kaon OS vertex charge OS charm Tagging Algorithms • OSμ, e , K , vtx Charge • SSp and SSπ Calibration Channels • B 0 → D + s D - • B 0 → D *- D + s Tagging Power m D + s D - ( MeV /c 2 ) 5300 5400 5500 Candidates / (2.8 MeV /c 2 ) 0 500 1000 1500 2000 2500 LHCb Total B 0 → D + s D - B 0 s → D - s D + Comb. bkg. [5] Sample ε tag [%] ε tag D 2 [%] Run1 K - π + 80.2 ± 1.4 5.61 ± 0.36 K - π - π + π + 88.8 ± 1.9 6.25 ± 0.55 Run2 K - π + 93.5 ± 0.5 6.61 ± 0.19 K - π - π + π + 92.7 ± 0.8 7.05 ± 0.29 Decay-time fit CP observables are extracted via fit to decay time. 1 10 2 10 Signal Yield / ( 0.125 ps ) LHCb 2 4 6 8 10 Decay time [ps] 5 - 0 5 Pull • Decay-time acceptance: cubic splines • Decay-time resolution: triple Gaussian, σ t ≈ 60 fs References [1] LHCb collaboration, R. Aaij et al., submitted to JHEP [arXiv:1912.03723] [2] Belle collaboration, M. Röhrken et al., Phys. Rev. Lett. 108 (2012) [arXiv:1201.4643] [3] BaBar collaboration, B. Aubert et al., Phys. Rev. D79 (2009) [arXiv:0808.1866] [4] Heavy Flavor Averaging Group, Y. Amhis et al. [arXiv:1612.07233] [5] LHCb collaboration, R. Aaij et al., Phys. Rev. Lett. 117 (2016) [arXiv:1608.06620] Results Dominant systematic uncertainties: • S D * D , ΔS D * D , C D * D and ΔC D * D : FT calibration and signal mass model • A D * D : prompt D ± meson mass shape S D * D = -0.861 ± 0.077 (stat) ± 0.019 (syst) ΔS D * D = 0.019 ± 0.075 (stat) ± 0.012 (syst) C D * D = -0.059 ± 0.092 (stat) ± 0.020 (syst) ΔC D * D = -0.031 ± 0.092 (stat) ± 0.016 (syst) A D * D = 0.008 ± 0.014 (stat) ± 0.006 (syst) • Most precise measurement in B 0 → D *± D ∓ decays • Precision of C D * D and ΔC D * D comparable with pre- vious measurements • Precision of world average for S D * D , ΔS D * D and A D * D significantly improved
Transcript of Oo ~ )À *Ó ²Þ)O~Þ) Þcds.cern.ch/record/2710585/files/Poster-2020-1030.pdf · CPV in...
Measurement of CP violation in B0→ D∗±D∓ decays [1]
Philipp Ibis on behalf of the LHCb collaboration
Introduction: CP violation in B0 mixingOscillation between B0 and B0 states.
CT&S Meeting | Status of Simulation Group | MC liaisons: Alex Birnkraut, Margarete Schellenberg 1
u, c, t
W W
u, c, t
d
B0
b
b
B0
d
W
u, c, t u, c , t
W
d
B0
b
b
B0
d
ޠ
u, c, t
W W
u, c, t
d
B0
b
b
B0
d
W
u, c, t u, c , t
W
d
B0
b
b
B0
d
ޠ
Decay of a neutral B meson into the final state f or f : directly or after oscillation→ four time-dependent decay rates.
dΓ(t)
dt=e−t/τd
8τd(1 + rAD∗D)×[
1− d(SD∗D + r∆SD∗D) sin(∆mt) + d(CD∗D + r∆CD∗D) cos(∆mt)]
d =
{1, B0
−1, B0
r =
{1, f−1, f
B2OC TD Meeting | Status of B0→D*D | Margarete Schellenberg
Motivation‣ aim: first measurement of CPV in B0→D*±D∓ decays at LHCb
‣ former measurements by BaBar/Belle
‣ CPV in interference of decay and decay after B0B0 mixing
‣ time dependent CP asymmetries:
‣ b → ccd decay: • higher order contributions are not suppressed
• CPV in B0→D*±D∓ is sensitive to sin(2βeff), βeff (≈β)
‣ measurement of decay-time-dependent decay rate can be performed
2
B0
B0f = D*+D–
f = D*–D+
ACP,f (t) =�(B0(t)� f )� �(B0(t)� f )
�(B0(t)� f ) + �(B0(t)� f )
= Sf sin(�mt)� Cf cos(�mt)
ACP,f (t) =�(B0(t)� f )� �(B0(t)� f )
�(B0(t)� f ) + �(B0(t)� f )
= Sf sin(�mt)� Cf cos(�mt)
d�(t, d, q,�)dt � e�t/� [1 + d(1� 2�) ((S + q�S) sin(�mt)� (C + q�C) cos(�mt))]
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S =1
2(Sf + Sf )
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�S =1
2(Sf � Sf )
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CP violation in B0→ D∗±D∓• First measurement of CP violation in B0→ D∗±D∓at LHCb
• Former measurements by Belle and BaBar [2,3]
D*+- D-+ S
HFL
AV
Sum
mer
201
6
-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4
BaBarPRD 79, 032002 (2009)
-0.68 ± 0.15 ± 0.04
BellePRD 85 (2012) 091106
-0.78 ± 0.15 ± 0.05
AverageHFLAV
-0.73 ± 0.11
HFLAVHFLAVSummer 2016
D*+- D-+ C
HFL
AV
Sum
mer
201
6
-0.2 -0.1 0 0.1 0.2
BaBarPRD 79, 032002 (2009)
0.04 ± 0.12 ± 0.03
BellePRD 85 (2012) 091106
-0.01 ± 0.11 ± 0.04
AverageHFLAV
0.01 ± 0.09
HFLAVHFLAVSummer 2016
D*+- D-+ A
HFL
AV
Sum
mer
201
6
-0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
BaBarPRD 79, 032002 (2009)
0.01 ± 0.05 ± 0.01
BellePRD 85 (2012) 091106
0.06 ± 0.05 ± 0.02
AverageHFLAV
0.03 ± 0.04
HFLAVHFLAVSummer 2016
[4]
• b→ ccs decays are sensitive to weak phase 2β
• Measured by several experiments in different chan-nels [4]
• Same phase appears in b→ ccd transitions
• ForB0→ D∗±D∓ decays higher-order diagrams con-tribute to CP violation.
Instrumental asymmetries• Overall asymmetry is corrected for instrumentalasymmetries from reconstruction, detection and par-ticle identification
• B0→ D∗±D∓ decay is charge-balanced, asymme-tries only due to different momentum spectra of pos-itive and negative pions and kaons
• 6 million prompt D±→ K∓π±π± decays reweightedto signal D∗− or D− distributions
• Split into four subsamples: One sample perD0 decaymode and one for D∗− and D−, respectively
• Asymmetries AD∗−det and AD−
det calculated with D+ andD− yields from fits to the mass distributions
Final state AD∗−det AD−det AD∗−D+det [%]
K−π+ 0.0169 0.0158 0.11± 0.40± 0.30K−π−π+π+ 0.0146 0.0138 0.09± 0.26± 0.51
Signal extractionReconstruction• D∗+→ D0π+
D0→ K−π+D0→ K−π−π+π+
• D−→ K+π−π−
Full LHCb dataset• 1 fb−1 at 7TeV• 2 fb−1 at 8TeV• 6 fb−1 at 13TeV
Multivariate Selection• Further reduction of combinatorial background
• Boosted Decision Tree (BDT)
• Signal proxy: signal MC
• Background proxy: upper mass sideband from data
• Kinematic, topological and particle identification variables used
• BDT cut point minimises uncertainties of CP parameters
Mass Fit• Disentangle signal from remaining background
• Shapes of the signal and background components based on sim-ulated data
Signal CandidatesK−π+ K−π−π+π+
Run 1 856± 32 469± 28Run 2 3265± 61 1570± 48
Can
didates/(6
MeV/c
2)
200
400
600
800
1000
1200
mD∗±D∓ [MeV/c2]
5000 5200 5400 5600−5
0
5
Pull
LHCbRun 2
Total
B0→ D∗±D∓
B0s→ D∗±D∓
B0→ D+s D
∗−
B0→ D∗+D∗−
B0s→ D∗+D∗−
Comb. bkg.
Can
didates/(6
MeV/c
2)
100
200
300
400
500
600
mD∗±D∓ [MeV/c2]
5000 5200 5400 5600−5
0
5
Pull
LHCbRun 2
Total
B0→ D∗±D∓
B0s→ D∗±D∓
B0→ D+s D
∗−
B0→ D∗+D∗−
B0s→ D∗+D∗−
Comb. bkg.
Flavour TaggingKnowledge of b quark flavour at produc-tion is essential for measurements of time-dependent CP asymmetries.
PV
SV
b→ cb→ X l−
SVc→ s
same side
opposite side
b
b
D∗±
D∓
d
du
duu
π+
p
x
l−
K−
B0
hb
SS pion
SS proton
OS muonOS electron
OS kaon
OS vertex chargeOS charm
Tagging Algorithms• OSµ, e , K, vtx Charge• SSp and SSπ
Calibration Channels• B0→ D+s D−• B0→ D∗−D+s
Tagging PowermD+
s D−(MeV/c2)5300 5400 5500C
andidates/(2.8
MeV/c
2)
0
500
1000
1500
2000
2500 LHCb TotalB0→ D+
s D−
B0s → D−
s D+
Comb. bkg.
[5]
Sample εtag [%] εtagD2 [%]
Run1 K−π+ 80.2± 1.4 5.61± 0.36K−π−π+π+ 88.8± 1.9 6.25± 0.55
Run2 K−π+ 93.5± 0.5 6.61± 0.19K−π−π+π+ 92.7± 0.8 7.05± 0.29
Decay-time fitCP observables are extracted via fit to decay time.
1
10
210
Sign
al Y
ield
/ (
0.12
5 ps
)
LHCb
2 4 6 8 10Decay time [ps]
5−
0
5
Pull
• Decay-time acceptance: cubic splines• Decay-time resolution: triple Gaussian, σt ≈ 60 fs
References[1] LHCb collaboration, R. Aaij et al., submitted to JHEP
[arXiv:1912.03723][2] Belle collaboration, M. Röhrken et al., Phys. Rev. Lett. 108 (2012)
[arXiv:1201.4643][3] BaBar collaboration, B. Aubert et al., Phys. Rev. D79 (2009)
[arXiv:0808.1866][4] Heavy Flavor Averaging Group, Y. Amhis et al. [arXiv:1612.07233][5] LHCb collaboration, R. Aaij et al., Phys. Rev. Lett. 117 (2016)
[arXiv:1608.06620]
ResultsDominant systematic uncertainties:• SD∗D , ∆SD∗D , CD∗D and ∆CD∗D : FT calibration andsignal mass model
• AD∗D : prompt D± meson mass shape
SD∗D = −0.861± 0.077 (stat)± 0.019 (syst)∆SD∗D = 0.019± 0.075 (stat)± 0.012 (syst)CD∗D = −0.059± 0.092 (stat)± 0.020 (syst)∆CD∗D = −0.031± 0.092 (stat)± 0.016 (syst)AD∗D = 0.008± 0.014 (stat)± 0.006 (syst)
• Most precise measurement in B0→ D∗±D∓ decays
• Precision of CD∗D and ∆CD∗D comparable with pre-vious measurements
• Precision of world average forSD∗D ,∆SD∗D andAD∗Dsignificantly improved
1
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