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Measurement of CKM angle φ3 at Belle II
Niharika Rout
(Belle II Collaboration)
IIT Madras, India
Conference on Flavor Physics and CP ViolationMay 7, 2019
Niharika Rout Measurement of CKM angle φ3
Outline
1 Introduction
2 Current status of CKM parameters
3 Extraction of φ3 from B± → D(∗)K (∗)±
4 Belle II outlook
5 Future prospects
6 Summary
Niharika Rout Measurement of CKM angle φ3 2
Introduction
Unitaritycondition
=⇒(1st � 3rd)
Measuring SM CP violation ⇒ Measure complex phase of CKM el-ements.
φ1/β ≡ arg(−VcdV∗cb
VtdV∗tb
)
φ2/α ≡ arg(− VtdV∗tb
VudV∗ub
)
φ3/γ ≡ arg(−VudV∗ub
VcdV∗cb
)
Definition of φ3 does not dependon coupling to top quark.
Thus measurable via treelevel decays ⇒ theoreticallycleaner [O(10−7)] [1].
Precise measurement providesSM benchmark.1
J. Brod, J. Zupan, arxiv:1308.5663
Niharika Rout Measurement of CKM angle φ3 3
Current status of CKM parameters
Figure : Constraints on CKM parameters [2]
Direct measurements
(φ3)combined = (73.5+4.2−5.1)◦
Indirect extrapolation
(φ3)combined = (65.3+1.0−2.5)◦
φ3 is an excellent probe to NP.
Testing of direct vs indirectdisagreement.
Need to improve precision on direct
measurement.
Figure : Constraints on “tree-level” processes (left) and “loop-level” processes (right)
2Image source: http://ckmfitter.in2p3.fr/
Niharika Rout Measurement of CKM angle φ3 4
Extraction of φ3
φ3: Only CKM angle accessible at tree level.
Sensitivity to φ3 arises from the interference of b → u and b → cquark transitions.
Classic mode: B± → DK±.
Interference occurs when D0 and D0
decay to the same final state f .
rB = |Asup
Afav| ∼ |VubV
∗cs
VcbV ∗us| ×CcolorSupp ∼ 0.1 for B± → DK± decays [3].
δB is the strong phase difference between favoured and suppressedmodes; φ3 is the weak phase.
3HFLAV16, Y. Amhis et al. (Heavy Flavor Averaging Group), Eur. Phys. J. C 77 (2017)895 [arXiv:1612.07233 [hep-ex]]
Niharika Rout Measurement of CKM angle φ3 5
Common final states: primary methods
GLW [Phys. Lett. B 253, 483]
Both D0 and D0 decays to same CP eigenstates such as K+K−, π−π+ (CP-even), K0Sπ
0
(CP-odd).4 observables (RCP± ,ACP± )No need of external inputs.
ADS [Phys. Rev. Lett. 78, 3257]
D from a favoured amplitude decays to adoubly-Cabibbo-suppressed state.
2 Observables (RADS,AADS)
External charm factory inputs (rD andδD).
GGSZ [Phys. Rev. D 68, 054018] parameters to extract: φ3 , rB and δB
Uses multi-body D(K0Sh−h+) final states.
Sensitivity to φ3 by comparing D Dalitzdistributions for B+ and B−
Fit D Dalitz plot with full amplitudemodel.
AB = A(m2−,m
2+)+rBe
i(δB+φ3)A(m2+,m
2−)
m2± = squared invariant masses of K0
Sh±
: D Dalitz plot variables.Figure : Dalitz plots of B+ → DK+ (left) and
B− → DK− (right) arXiv:1806.01202v1 [hep-ex]
Niharika Rout Measurement of CKM angle φ3 6
GGSZ: Binned model-independent approachOptimal binning of the D Dalitz plot which gives the maximum sensitivity to φ3.Number of events in ith bin is a function of x±/y±:
N±i = hB [K±i + r2BK∓i +
√KiK−i (x±ci ± y±si )].
hB : Normalization constant. Ki : Number of events in the ith bin of a flavourtagged D decay (obtained using a sample of D∗± → Dπ± decays).Fit simultaneously in each bin,
(x±, y±) = rB(cos(±φ3 + δB), sin(±φ3 + δB))
ci and si : amplitude-averaged strong phase difference between D0 and D0 over ith
bin and are obtained from external charm factories like CLEO and BESIII.
Figure : Optimal binning of D Dalitz plot and comparison of phase terms ci , si measured by CLEO and Belle [4]
4Phys. Rev. D 85, 112014 (2012)
Niharika Rout Measurement of CKM angle φ3 7
φ3: world averages (HFLAV)
From all measurements of B → D(∗)K (∗) from GLW, ADS, and GGSZ
(Belle + BaBar + LHCb)
0
0.2
0.4
0.6
0.8
1
CL
−1
0 50 100 150]° [γ
GLW
ADS
GGSZ
Combined
GLW
ADS
GGSZ
Combined
68.3%
95.5%
HFLAVCKM 2018
0
0.2
0.4
0.6
0.8
1
CL
−1
0 50 100 150]° [γ
+K−sD→0
sB+*K0D→+B+K0*D→+B0*K0D→0B
+K0D→+BCombined
+K−sD→0
sB+*K0D→+B+K0*D→+B0*K0D→0B
+K0D→+BCombined
68.3%
95.5%
HFLAVCKM 2018
(φ3)combined = (73.5+4.2−5.1)◦ [8]
(φ3)Belle = (73+13−15)◦
(φ3)BaBar = (69+17−16)◦ [6]
(φ3)LHCb = (74+5.0−5.8)◦ [7]
6[PRD 87 052015 (2013)]
7[LHCb-CONF-2017-004]
8http://www.slac.stanford.edu/xorg/hflav/triangle/moriond2018/index.shtml
Niharika Rout Measurement of CKM angle φ3 8
Belle II @SuperKEKB
Super KEKB: 4 GeV e+ and 7 GeV e− asymmetric collider at KEK, Japan.Belle II detector is at the interaction point.
The center-of-mass energy is close to the mass of Υ(4S), which decays to BB pair.
Figure : Belle II detector [9]
9Image source: PoS EPS-HEP2017 (2017) 223
Niharika Rout Measurement of CKM angle φ3 9
Status of Belle II experiment
Phase I (complete)
Accelerator commissioningwith single beam.
Phase II (complete)
Taken data with partialdetector (with small part ofvertex detector).Accumulated ∼ 0.5 fb−1
data.Physics studies are going on.
Phase III (“Run I” started)
SuperKEKB becameoperational on March 11th forphase III data taking.First collision was on March25th.
Ultimate goal: 50 ab−1 Figure : SuperKEKB luminosity projection
Niharika Rout Measurement of CKM angle φ3 10
Glimpse from phase II data taking
D∗± → D0(K0Sπ
0)π±
M∆
0.14 0.142 0.144 0.146 0.148 0.15 0.152 0.154 0.156 0.158 0.16
)2E
ntrie
s/ (
0.00
06 G
eV/c
0
5
10
15
20
25
30
35 +π)0π0
S(K0 D→ *+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
0π0SK
M
1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1
)2E
ntrie
s/ (
0.01
33 G
eV/c
0
5
10
15
20
25
30 +π)0π0
S(K0 D→ *+D
Belle II 2018 (preliminary)
-1 L dt = 472 pb∫
D∗± → D0(K0Sπ
+π−)π±
M∆
0.14 0.142 0.144 0.146 0.148 0.15 0.152 0.154 0.156 0.158 0.16
)2E
ntrie
s/ (
0.00
06 G
eV/c
0
20
40
60
80
100 +π)+π-π0
S(K0 D→ *+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
0π0SK
M
1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1)2
Ent
ries/
(0.
0133
GeV
/c0
20
40
60
80
100
120+π)+π-π0
S(K0 D→ *+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
Better reconstruction, selection and tagging algorithm.Improved PID performance.Good neutral (K 0
S , π0) reconstruction efficiency.
Niharika Rout Measurement of CKM angle φ3 11
Glimpse from phase II data taking
Mbc =√
E2beam − (Σ−→pi )2, Mbc > 5.27 GeV/c2, ∆E = ΣEi − Ebeam, |∆E | < 0.05 GeV.
E (GeV)∆-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2
Ent
ries
/ (16
MeV
)
0
10
20
30
40
50
60
70
80
90±π)ππ0
S,K0π
S,KK,K0ππ,Kπ,K3π->D(K±B
±ρ)π, K3π->D(K±B±π)0ππ, Kπ, K3π(K*0->D±B
±
π)0ππ, Kπ, K3π(K±*
->D0B
±
ρ)π, K3π(K±*
->D0B
±
π)ππ(K±->D0B
±
ρ)ππ(K±->D0B
(S)
(*)) K-µ+µ, -e+(eψ->J/0B
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
)2 (GeV/cbcM5.2 5.21 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29
)2E
ntrie
s /
(4 M
eV/c
0
20
40
60
80
100
120
140 ±π)ππ0S
,K0πS
,KK,K0ππ,Kπ,K3π->D(K±B±ρ)π, K3π->D(K±B
±π)0ππ, Kπ, K3π(K*0->D±B
±
π)0ππ, Kπ, K3π(K±*
->D0B
±
ρ)π, K3π(K±*
->D0B
±
π)ππ(K±->D0B
±
ρ)ππ(K±->D0B
(S)
(*)) K-µ+µ, -e+(eψ->J/0B
Belle II 2018 (preliminary)
L dt ∫ -1= 472 pb
More than 200 B candidates from hadronic modes!!
Niharika Rout Measurement of CKM angle φ3 12
B± → DK± @Belle II
ADS, GLW and GGSZ can all bereproduced at Belle II.
Ongoing analyses (D final states)
KK , ππ: CP-even.K0Sπ
0: CP-odd.
K0Sππ: GGSZ
Need to focus on:
PID improvements.Continuum suppression.
Tracking, K0S selection.
Figure : K0S reconstruction at Belle II
E (GeV)∆
0.2− 0.1− 0 0.1 0.2
Ent
ries
/ 4 M
eV
0
100
200
300
400
500
600
700mixedcharged bkgudscharmsignal
Belle II MC Continuumsuppression
=⇒95% bkg rej30% sig loss
E (GeV)∆
0.2− 0.1− 0 0.1 0.2
Ent
ries
/ 4 M
eV
0
20
40
60
80
100
120
140
160
180
200
220mixedcharged bkgudscharmsignal
Belle II MC
Niharika Rout Measurement of CKM angle φ3 13
Future prospects
Expect Belle II and LHCb upgrade to match each other’sperformance!δ(φ3) < 2◦ by 2027.
Due to Belle II unbiased trigger it will be better in Dalitz plot analysisand sensitivity to the neutrals will allow to include more D modes.LHCb will clearly have more precise results in fully-charged finalstates.
Niharika Rout Measurement of CKM angle φ3 14
Summary
Precision measurement of φ3 is very crucial.
Current uncertainty on φ3 ∼ 5◦
Combined sensitivity of 1.6◦ isexpected:
Including more D(∗) modes!Integrated luminosity = 50ab−1
Input from Charm factory Figure : fit extrapolated to the 50 ab−1 for anSM-like scenario [B2TIP report]
Assuming BESIII will collect 10 fb−1, D0 hadronic parametersmeasured at BESIII will play vital role.
Uncertainty on indirect prediction of φ3 already ∼ 1◦
Many modes can be added to improve the uncertainity.
Niharika Rout Measurement of CKM angle φ3 15
Niharika Rout Measurement of CKM angle φ3 16
Backup
Niharika Rout Measurement of CKM angle φ3 17
φ3 sensitivity studies with Belle II
Goal is to go up-to precision ≈ 1◦.B± → D0(K 0
Sπ−π+)K±: Golden mode to determine φ3!
Large branching fraction involved.
Significant overlap between D0 and D0 amplitudes which gives a large interferenceterm sensitive to φ3.
Rich resonant structure which provides large variations of the strong phase in D
decay: sesnsitive to φ3.
* GLW like states: Interference of B− → DK− , D → K 0Sρ
* ADS like states: Interference of B− → DK− , D → K∗π
Figure : Expected uncertainty on φ3 (based on toy MonteCarlo studies) versus luminosity
Figure : Dalitz binning used for D → K0Sππ analysis
δ(φ3)50ab−1= 1.6◦ when Belle GLW
+ ADS + GGSZ extrapolated.Niharika Rout Measurement of CKM angle φ3 18
Glimpse from phase II data taking
D∗± → D0(K−π+)π±
0.14 0.145 0.15 0.155 0.16)2 M (GeV/c∆
0
20
40
60
80
100
120
140
160
180
200
220
)2E
ntrie
s / (
0.42
MeV
/c
+π)+π-(K0D→*+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
1.75 1.8 1.85 1.9 1.95 2)2) (GeV/c+π-M(K
0
20
40
60
80
100
120
140
160
180
200
)2E
ntrie
s / (
5 M
eV/c +π)+π-(K0D→*+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
D∗± → D0(K−π+π0)π±
0.14 0.145 0.15 0.155 0.16)2 M (GeV/c∆
0
100
200
300
400
500
600
700
800
)2E
ntrie
s / (
0.42
MeV
/c
+π)0π+π-(K0D→*+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
1.75 1.8 1.85 1.9 1.95 2)2) (GeV/c0π+π-M(K
0
50
100
150
200
250
300
350
400
450
500)2E
ntrie
s / (
5 M
eV/c
+π)0π+π-(K0D→*+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
D∗± → D0(K−π+π−π+)π±
0.14 0.145 0.15 0.155 0.16)2 M (GeV/c∆
0
50
100
150
200
250
)2E
ntrie
s / (
0.42
MeV
/c
+π)+π-π+π-(K0D→*+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
1.75 1.8 1.85 1.9 1.95 2)2) (GeV/c+π-π+π-M(K
0
20
4060
80
100
120140
160
180200
220
)2E
ntrie
s / (
5 M
eV/c +π)+π-π+π-(K0D→*+D
Belle II 2018 (preliminary)
-1L dt = 472 pb∫
Niharika Rout Measurement of CKM angle φ3 19