Frontiers of Fundamental Physics 14 CP violation effects in multibody - - PowerPoint PPT Presentation
Frontiers of Fundamental Physics 14 CP violation effects in multibody B decays Jeremy Dalseno on behalf of the LHCb collaboration J.Dalseno [at] bristol.ac.uk 18 July 2014 CP violation effects in multibody B decays 1 Outline 1. Motivation 2.
Jeremy Dalseno
J.Dalseno [at] bristol.ac.uk 18 July 2014
CP violation effects in multibody B decays
1
p and B± → π±p¯ p
Dalitz plot contains all kinematic and dynamic information of decay Amplitude analysis one of the most powerful techniques Extract amplitude-level information rather than amplitude-squared information Interference between intermediate states allows measurement of relative magnitudes and phases
CP violation effects in multibody B decays
2
Charmless B → 3h decay channels provide a rich environment for physics observables Unknown heavy particle in the loop could carry a new CP violating phase
b u s q q u
g
xb
V *
xs
V x x = u, c, t b u s q q u ? g
Tree sensitive to γ = φ3 ≡ − arg
ub
VcdV ∗
cb
u s u u u
γ ∝
ub
V β α γ *
ub
V
ud
V *
cb
V
cd
V *
tb
V
td
V
CP violation effects in multibody B decays
3
In charged B decays, presence of multiple amplitudes may lead to direct CP violation
A(B → f) =
i |Ai|ei(δi+φi)
¯ A( ¯ B → ¯ f) =
i | ¯
Ai|ei(δi−φi)
Strong phase (δ) invariant under CP , while weak phase (φ) changes sign under CP
ACP (B → f) ≡ | ¯ A|2 − |A|2 | ¯ A|2 + |A|2 ∝
sin(δi − δj) sin(φi − φj)
3 conditions required for direct CP violation At least 2 amplitudes Non-zero strong phase difference, δi − δj = 0 Non-zero weak phase difference, φi − φj = 0 Source of weak phase differences come from different CKM phases of each amplitude
CP violation effects in multibody B decays
4
Direct CP violation more complicated in B → 3h decay channels compared to 2-body decays There are at least 4 possible sources of strong phase
BSS mechanism, PRL 43 242 (1979) Penguin diagram (b) contains 3 quark generations in loop If gluon in penguin is timelike (on-shell) Momentum transfer q2 > 4m2
i where i = u, c
Particle rescattering (c) generates a phase difference Tree contribution (a) carries different strong phase
CP violation in 2-body processes caused by this effect
CP violation effects in multibody B decays
5
Remaining sources unique to multibody decays Long-distance contributions (q¯
q level)
Represents intermediate resonance states
F BW
R
(s) = 1 m2
R − s − imRΓR(s)
Phase varies across the Dalitz plot
A(B → f) =
i |Ai|ei(δi+φi)
¯ A( ¯ B → ¯ f) =
i | ¯
Ai|ei(δi−φi)
Related to final state interactions between different resonances
CP violation effects in multibody B decays
6
Each source of strong phase leaves a unique signature in the Dalitz plot Illustrate with series of examples Consider B± → K±π+π− with only 2 isobars
B± → K±ρ0 and non-resonant (NR) component ρ lineshape a Breit-Wigner, F BW
ρ
ρ0 is a vector resonance, so angular distribution follows cos θ
ρ
+
π
+
K θ
A+ = aρ
+eiδρ
+F BW
ρ
cos θ + aNR
+ eiδNR
+ F NR
A− = aρ
−eiδρ
−F BW
ρ
cos θ + aNR
− eiδNR
− F NR
ACP ∝ |A−|2 − |A+|2 ∝ [(aρ
−)2 − (aρ +)2]|F BW ρ
|2 cos2 θ + ... −2(m2
ρ − s)|F BW ρ
|2|F NR|2 cos θ... +2mρΓρ|F BW
ρ
|2|F NR|2 cos θ...
CP violation effects in multibody B decays
7
ACP ∝ [(aρ
−)2 − (aρ +)2]|F BW ρ
|2 cos2 θ + ... −2(m2
ρ − s)|F BW ρ
|2|F NR|2 cos θ... +2mρΓρ|F BW
ρ
|2|F NR|2 cos θ...
Only depends on ρ resonance, maximum difference at ρ pole, quadratic in helicity
(GeV)
lowm
0.5 1 1.5 2 2.5 +> 0 θ cos
(GeV)
lowm
0.5 1 1.5 2 2.5 +< 0 θ cos
MC
ρ
+
π
+
K θ ρ
+
π
+
K θ
Only short-distance effects can create aρ
+ = aρ −
CP violation effects in multibody B decays
8
ACP ∝ [(aρ
−)2 − (aρ +)2]|F BW ρ
|2 cos2 θ + ... −2(m2
ρ − s)|F BW ρ
|2|F NR|2 cos θ... +2mρΓρ|F BW
ρ
|2|F NR|2 cos θ...
Interference term from real part of Breit-Wigner, zero at ρ pole, linear in helicity
(GeV)
lowm
0.5 1 1.5 2 2.5 +> 0 θ cos
(GeV)
lowm
0.5 1 1.5 2 2.5 +< 0 θ cos
MC
ρ
+
π
+
K θ ρ
+
π
+
K θ
Caused by long distance effects from final state interactions
CP violation effects in multibody B decays
9
ACP ∝ [(aρ
−)2 − (aρ +)2]|F BW ρ
|2 cos2 θ + ... −2(m2
ρ − s)|F BW ρ
|2|F NR|2 cos θ... +2mρΓρ|F BW
ρ
|2|F NR|2 cos θ...
Interference term from imaginary part of Breit-Wigner, maximum at ρ pole, linear in helicity
(GeV)
lowm
0.5 1 1.5 2 2.5 +> 0 θ cos
(GeV)
lowm
0.5 1 1.5 2 2.5 +< 0 θ cos
MC
ρ
+
π
+
K θ ρ
+
π
+
K θ
Caused by long distance effects from Breit-Wigner phase and final state interactions
CP violation effects in multibody B decays
10
Last source of strong phase
Can occur between decay channels with the same flavour quantum numbers
CPT conservation constrains hadron rescattering
For given quantum numbers, sum of partial widths equal for charge-conjugate decays
KK ↔ ππ rescattering generates a strong phase
Look into rescattering region If rescattering phase in one decay channel generates direct CP violation in this region, Rescattering phase should generate opposite sign direct CP violation in partner decay channel
CP violation effects in multibody B decays
11
pp collisions b quark tends to foward/backward direction
Data set: 1 fb−1 @ 7 TeV and 2 fb−1 @ 8 TeV Forward spectrometer Vertex Locater (VeLo) Precision tracking Tracker Turicensis (TT) Tracking, p measurement Ring Imaging Cherenkov (RICH) Particle identification Electromagnetic Calorimeter (ECAL)
e, γ ID
Hadronic Calorimeter (HCL) Hadronic showers Muon Detector Magnet polarity reversal
CP violation effects in multibody B decays
12
B− → K−π+π− B+ → K+π+π− B− → K−K+K− B+ → K+K+K− NSig = 181069 ± 404 (stat) NSig = 109240 ± 354 (stat)
]
2
c [GeV/
−π
+π
−K
m 5.1 5.2 5.3 5.4 5.5 × )
2
c Candidates / (0.01 GeV/ 2 4 6 8 10 12 14 16 18
3
10 ×
LHCb
]
2
c [GeV/
−π
+π
+K
m 5.1 5.2 5.3 5.4 5.5 ×
model
−
π
+
π
±
K →
±
B combinatorial 4-body → B
±
)K γ ρ ’( η →
±
B
±
π
−
π
+
π →
±
B
]
2
c [GeV/
−K
+K
−K
m 5.1 5.2 5.3 5.4 5.5 × )
2
c Candidates / (0.01 GeV/ 2 4 6 8 10 12
3
10 ×
LHCb
]
2
c [GeV/
−K
+K
+K
m 5.1 5.2 5.3 5.4 5.5 ×
model
−
K
+
K
±
K →
±
B combinatorial 4-body → B
±
π
−
K
+
K →
±
B
−
π
+
π
±
K →
±
B
]
2
c [GeV/
π
m 5.1 5.2 5.3 5.4 5.5 × )
2
c Candidates / (0.01 GeV/ 0.5 1 1.5 2 2.5 3
3
10 ×
LHCb
]
2
c [GeV/
π
+π
m 5.1 5.2 5.3 5.4 5.5 ×
model
±
π
−
π
+
π →
±
B combinatorial 4-body → B
−
π
+
π
±
K →
±
B
]
2
c [GeV/
K
m 5.1 5.2 5.3 5.4 5.5 × )
2
c Candidates / (0.01 GeV/ 0.2 0.4 0.6 0.8 1
3
10 ×
LHCb
]
2
c [GeV/
K
+K
m 5.1 5.2 5.3 5.4 5.5 ×
model
±
π
−
K
+
K →
±
B combinatorial 4-body →
S
B 4-body → B
−
K
+
K
±
K →
±
B
−
π
+
π
±
K →
±
B
P r e l i m i n a r y
L H C b
A P E R
1 4
4 Penguin Tree B− → π−π+π− B+ → π+π+π− B− → π−K+K− B+ → π+K+K− NSig = 24907 ± 222 (stat) NSig = 6161 ± 172 (stat)
CP violation effects in multibody B decays
13
Global direct CP asymmetry
ARaw
CP = NB− − NB+
NB− + NB+
Correct for B± production asymmetry and unpaired hadron (eg. B± → K±π+π−) detection asymmetry
ACP = ARaw
CP − AP − Ah D
AP and AK
D from B± → J/ψ[µ+µ−]K±, PRL 108 201601 (2012)
Aπ
D from prompt D+ studies, PLB 713 186 (2012)
ACP (B± → K±π+π−) = +0.025 ± 0.004 (stat) ± 0.004 (syst) ± 0.007 (J/ψK±) (2.8σ) ACP (B± → K±K+K−) = −0.036 ± 0.004 (stat) ± 0.002 (syst) ± 0.007 (J/ψK±) (4.3σ) ACP (B± → π±π+π−) = +0.058 ± 0.008 (stat) ± 0.009 (syst) ± 0.007 (J/ψK±) (4.2σ) ACP (B± → π±K+K−) = −0.123 ± 0.017 (stat) ± 0.012 (syst) ± 0.007 (J/ψK±) (5.6σ)
P r e l i m i n a r y
L H C b
A P E R
1 4
4
CP violation effects in multibody B decays
14
Dalitz plot background subtracted and effiency corrected with ∼ (NB+ + NB−) in each bin
B± → K±π+π− B± → K±K+K−
0.2 0.4 0.6 0.8 1
]
4
c /
2
[GeV
π 2
m 5 10 15 20 ]
4
c /
2
[GeV
K 2
m 5 10 15 20 25
0.2 0.4 0.6 0.8 1
LHCb (a)
0.2 0.4 0.6 0.8 1
]
4
c /
2
[GeV
low
K 2
m 2 4 6 8 10 12 14 ]
4
c /
2
[GeV
high
K 2
m 5 10 15 20 25
0.2 0.4 0.6 0.8 1
LHCb (b)
0.2 0.4 0.6 0.8 1
]
4
c /
2
[GeV
low
π 2
m 2 4 6 8 10 12 14 ]
4
c /
2
[GeV
high
π 2
m 5 10 15 20 25
0.2 0.4 0.6 0.8 1
LHCb (c)
0.2 0.4 0.6 0.8 1
]
4
c /
2
[GeV
K 2
m 5 10 15 20 25 ]
4
c /
2
[GeV
K 2
m 5 10 15 20 25
0.2 0.4 0.6 0.8 1
LHCb (d)
P r e l i m i n a r y
L H C b
A P E R
1 4
4 Penguin Tree
B± → π±π+π− B± → π±K+K− CP violation effects in multibody B decays
15
Project onto mππ of B± → π±π+π− ]
2
c [GeV/
low
−
π
+
π
m
0.5 1 1.5
)
2
Yield/(0.05 GeV/c
200 400 600 800
LHCb
+
B
−
B ]
2
c [GeV/
low
−
π
+
π
m
0.5 1 1.5
+
100 200 300
LHCb ]
2
c [GeV/
low
−
π
+
π
m
0.5 1 1.5
)
2
Yield/(0.05 GeV/c
0.5 1 1.5
3
10 ×
LHCb
+
B
−
B ]
2
c [GeV/
low
−
π
+
π
m
0.5 1 1.5
+
100 200 300
LHCb
P r e l i m i n a r y
L H C b
A P E R
1 4
4
ρ
+
π
+
K θ ρ
+
π
+
K θ
Sign-flip and zero around ρ0 pole, CP asymmetry may be dominated by real part of Breit-Wigner
CP violation effects in multibody B decays
16
ππ ↔ KK rescattering region: 1.0 − 1.5 GeV/c2 B± → K±π+π− B± → K±K+K−
]
2
c [GeV/
−
π
+
π
−
K
m 5.1 5.2 5.3 5.4 5.5 × )
2
c Candidates / (0.01 GeV/ 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
3
10 ×
LHCb
]
2
c [GeV/
−
π
+
π
+
K
m 5.1 5.2 5.3 5.4 5.5 ×
model
−
π
+
π
±
K →
±
B combinatorial 4-body → B
±
)K γ ρ ’( η →
±
B
±
π
−
π
+
π →
±
B
]
2
c [GeV/
−
K
+
K
−
K
m 5.1 5.2 5.3 5.4 5.5 × )
2
c Candidates / (0.01 GeV/ 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
3
10 ×
LHCb
]
2
c [GeV/
−
K
+
K
+
K
m 5.1 5.2 5.3 5.4 5.5 ×
model
−
K
+
K
±
K →
±
B combinatorial 4-body → B
±
π
−
K
+
K →
±
B
−
π
+
π
±
K →
±
B
P r e l i m i n a r y
L H C b
A P E R
1 4
4
ACP (B± → K±π+π−) = +0.121 ± 0.012 (stat) ± 0.017 (syst) ± 0.007 (J/ψK±) ACP (B± → K±K+K−) = −0.211 ± 0.011 (stat) ± 0.004 (syst) ± 0.007 (J/ψK±)
Clear opposite sign CP asymmetry in KK/ππ - related channels
KK ↔ ππ rescattering would require this by CPT conservation
CP violation effects in multibody B decays
17
Another new preliminary result based on full data set
B± → K±p¯ p
penguin dominated
B± → π±p¯ p
tree dominated Similar physics to non-baryonic 3-body charmless decays
p¯ p ↔ h+h− rescattering expected to be smaller than KK ↔ ππ rescattering CP asymmetry could be less pronounced
Threshold enhancement in low mp¯
p typical in B → p¯
pX
decays Need to better understand dynamics of these decays Previous publication based on 1 fb−1 No evidence of CP violation PRD 88 052015 (2013)
u u u d p d u p b
+
B d , s u u
+
π ,
+
K W u u u d p d u p b
+
B d , s u u
+
π ,
+
K W
CP violation effects in multibody B decays
18
B± → K±p¯ p NSig = 18721 ± 142 (stat)
]
2
[GeV/c
±
K p p
m
5.1 5.2 5.3 5.4 5.5
)
2
Candidates / (0.01 GeV/c
500 1000 1500 2000 2500 3000 3500 4000 4500
LHCb
Blue: Signal Red: Combinatorial
B± → π±p¯ p NSig = 1988 ± 74 (stat)
]
2
[GeV/c
±
π p p
m
5.1 5.2 5.3 5.4 5.5
)
2
Candidates / (0.01 GeV/c
100 200 300 400 500 600 700
LHCb
Green: Partially reconstrcuted Purple: Cross-feed
P r e l i m i n a r y
L H C b
A P E R
1 4
4
CP violation effects in multibody B decays
19
Background subtracted and efficiency corrected using calibrated MC
B± → K±p¯ p
]
4
/c
2
[GeV
2 p p
m
5 10 15 20
]
4
/c
2
[GeV
2 Kp
m
2 4 6 8 10 12 14 16 18 20
)
8
/c
4
Signal yield /(0.16 GeV
2000 4000 6000 8000 10000 12000
LHCb
B± → π±p¯ p
]
4
/c
2
[GeV
2 p p
m
5 10 15 20 25
]
4
/c
2
[GeV
2 p π
m
2 4 6 8 10 12 14 16 18 20
)
8
/c
4
Signal yield /(0.20 GeV
500 1000 1500 2000 2500 3000 3500
LHCb
✻ ✁ ✁ ✁ ✁ ✁ ✁ ✕
✏✏✏✏✏✏✏ ✶
Low mp¯
p threshold enhancement
Charmonimum resonances Define mp¯
p < 2.85 GeV/c2 as charmless region
Λ(1520) → pK
P r e l i m i n a r y
L H C b
A P E R
1 4
4
CP violation effects in multibody B decays
20
AFB = N(cos θ > 0) − N(cos θ < 0) N(cos θ > 0) + N(cos θ < 0)
Meausure forward-backward asymmetry in bins of mp¯
p
Gives hint on p¯
p waves that might contribute
p p
+
h θ
B± → K±p¯ p
]
2
[GeV/c
p p
m
2 2.2 2.4 2.6 2.8
FB
A
0.2 0.4 0.6 0.8 1
LHCb
B± → π±p¯ p
]
2
[GeV/c
p p
m
2 2.2 2.4 2.6 2.8
FB
A
0.2 0.4 0.6 0.8 1
LHCb
Ap¯
pK FB (mp¯ p < 2.85 GeV/c2) = +0.495 ± 0.012 (stat) ± 0.007 (syst)
Ap¯
pπ FB (mp¯ p < 2.85 GeV/c2) = −0.409 ± 0.033 (stat) ± 0.006 (syst)
Large asymmetries indicate dominance of non-resonant p¯
p scattering, J Phys G 34 283 (2007)
P r e l i m i n a r y
L H C b
A P E R
1 4
4
CP violation effects in multibody B decays
21
Measure ACP in Dalitz plot bins Same number of events in each bin
ACP (mp¯
p < 2.85 GeV/c2, m2 Kp > 10 GeV2/c4)
= +0.096±0.024 (stat)±0.004 (syst) (4.0σ)
First evidence of CP violation in any B decay involving baryons
B± → K±p¯ p
]
2
)
2
[(GeV/c
p p 2
m
5 10 15 20
]
2
)
2
[(GeV/c
Kp 2
m
2 4 6 8 10 12 14 16 18 CP
Raw A
0.05 0.1 0.15 0.2
✟✟✟✟✟✟✟✟✟✟ ✯ ✻
)
4
/c
2
(GeV
p p 2
m
4 6 8
)
4
/c
2
)/(0.33 GeV
+
)-N(B
50 100 150
)
4
/c
2
(GeV
p p 2
m
4 6 8
)
4
/c
2
)/(0.33 GeV
+
)-N(B
50 100 150
P r e l i m i n a r y
L H C b
A P E R
1 4
4
CP violation effects in multibody B decays
22
New preliminary results with the full LHCb data set
B± → K±h+h− and B± → π±h+h−
Evidence of global direct CP violation Large localised CP asymmetries across the Dalitz plot Long-distance effects play an important role in generating a strong phase
B± → h±p¯ p
Large forward-backward asymmetries indicate dominance of non-resonant p¯
p scattering
First evidence CP violation in decays involving baryons Sign-flip of CP asymmetry probably generated by interference of long-distance p¯
p waves
Look forward to amplitude analyses on all these channels
CP violation effects in multibody B decays
23
CP violation effects in multibody B decays
24