Jeremy Dalseno on behalf of the LHCb...

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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

Transcript of Jeremy Dalseno on behalf of the LHCb...

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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 multibodyB decays 1

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Outline1. Motivation

2. LHCb Detector

3. B± → K±K+K− and B± → K±π+π− (penguin dominated)

4. B± → π±K+K− and B± → π±π+π− (tree dominated)

5. B± → K±pp and B± → π±pp

6. Summary

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 multibodyB decays 2

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MotivationCharmlessB → 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

qu

-W

gxbV *xsV

x

x = u, c, t

b

u

s

q

qu

?

g

Tree sensitive to γ = φ3 ≡ − arg

(

VudV ∗

ub

VcdV ∗

cb

)

b

u

s

uu

u

-W

γ ∝ ubVβ

α

γ

*ubVudV

*cbVcdV

*tbVtdV

CP violation effects in multibodyB decays 3

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Motivation

In chargedB 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 underCP , while weak phase (φ) changes sign underCP

ACP (B → f) ≡|A|2 − |A|2

|A|2 + |A|2∝

i,j

sin(δi − δj) sin(φi − φj)

3 conditions required for direct CP violation

At least 2 amplitudes

Non-zero strong phase difference, δi − δj 6= 0

Non-zero weak phase difference, φi − φj 6= 0

Source of weak phase differences come from different CKM phases of each amplitude

CP violation effects in multibodyB decays 4

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Motivation

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

1. Short-distance contributions (quark level)

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 > 4m2i 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

eg. B0 → K+π−

CP violation effects in multibodyB decays 5

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MotivationRemaining sources unique to multibody decays

Long-distance contributions (qq level)

2. Breit-Wigner phase

Represents intermediate resonance states

FBWR (s) =

1

m2R − s− imRΓR(s)

Phase varies across the Dalitz plot

3. Relative CP -even phase in the isobar model

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 multibodyB decays 6

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MotivationEach source of strong phase leaves a unique signature in the Dalitz plot

Illustrate with series of examples

ConsiderB± → K±π+π− with only 2 isobars

B± → K±ρ0 and non-resonant (NR) component

ρ lineshape a Breit-Wigner, FBWρ

ρ0 is a vector resonance, so angular distribution follows cos θ

0ρ +π-π

+K

θ

A+ = aρ+e

iδρ+FBW

ρ cos θ + aNR+ eiδNR

+ FNR

A− = aρ−e

iδρ−FBW

ρ cos θ + aNR− eiδNR

− FNR

ACP ∝ |A−|2 − |A+|

2

∝ [(aρ−)2 − (aρ

+)2]|FBWρ |2 cos2 θ + ...

−2(m2ρ − s)|FBW

ρ |2|FNR|2 cos θ...

+2mρΓρ|FBWρ |2|FNR|2 cos θ...

CP violation effects in multibodyB decays 7

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Motivation

ACP ∝ [(aρ−)2 − (aρ

+)2]|FBWρ |2 cos2 θ + ...

−2(m2ρ − s)|FBW

ρ |2|FNR|2 cos θ...

+2mρΓρ|FBWρ |2|FNR|2 cos θ...

Only depends on ρ resonance, maximum difference at ρ pole, quadratic in helicity

(GeV) low-π+πm0 0.5 1 1.5 2 2.5

+ -

B-

B

-400

-300

-200

-100

0

> 0θcos

(GeV) low-π+πm0 0.5 1 1.5 2 2.5

+ -

B-

B

-600

-500

-400

-300

-200

-100

0

< 0θcos

MC

0ρ +π-π

+K

θ

0ρ +π-π

+K

θ

Only short-distance effects can create aρ+ 6= aρ

CP violation effects in multibodyB decays 8

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Motivation

ACP ∝ [(aρ−)2 − (aρ

+)2]|FBWρ |2 cos2 θ + ...

−2(m2ρ − s)|FBW

ρ |2|FNR|2 cos θ...

+2mρΓρ|FBWρ |2|FNR|2 cos θ...

Interference term from real part of Breit-Wigner, zero at ρ pole, linear in helicity

(GeV) low-π+πm0 0.5 1 1.5 2 2.5

+ -

B-

B

-400

-200

0

200

400

> 0θcos

(GeV) low-π+πm0 0.5 1 1.5 2 2.5

+ -

B-

B

-600

-400

-200

0

200

400

600

800

< 0θcos

MC

0ρ +π-π

+K

θ

0ρ +π-π

+K

θ

Caused by long distance effects from final state interactions

CP violation effects in multibodyB decays 9

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Motivation

ACP ∝ [(aρ−)2 − (aρ

+)2]|FBWρ |2 cos2 θ + ...

−2(m2ρ − s)|FBW

ρ |2|FNR|2 cos θ...

+2mρΓρ|FBWρ |2|FNR|2 cos θ...

Interference term from imaginary part of Breit-Wigner, maximum at ρ pole, linear in helicity

(GeV) low-π+πm0 0.5 1 1.5 2 2.5

+ -

B-

B

-400

-300

-200

-100

0

> 0θcos

(GeV) low-π+πm0 0.5 1 1.5 2 2.5

+ -

B-

B

0

100

200

300

400

500

600

700

< 0θcos MC

0ρ +π-π

+K

θ

0ρ +π-π

+K

θ

Caused by long distance effects from Breit-Wigner phase and final state interactions

CP violation effects in multibodyB decays 10

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Motivation

Last source of strong phase

4. Final state KK ↔ ππ rescattering

Can occur between decay channels with the same flavour quantum numbers

eg. B± → K±K+K− and B± → K±π+π−

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 multibodyB decays 11

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LHCb Detectorpp 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 multibodyB decays 12

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B± → K±h+h−, π±h+h−

B− → K−π+π− B+ → K+π+π− B− → K−K+K− B+ → K+K+K−

NSig = 181069 ± 404 (stat) NSig = 109240 ± 354 (stat)

]2c [GeV/−π+π−Km

5.1 5.2 5.3 5.4 5.5×

)2 cC

andi

date

s / (

0.01

GeV

/

02468

1012141618

310×

LHCb

]2c [GeV/−π+π+Km5.1 5.2 5.3 5.4 5.5

×

model−π+π± K→ ±B

combinatorial 4-body→B

±)Kγ0ρ’(η → ±B ±π−π+π → ±B

]2c [GeV/−K+K−Km5.1 5.2 5.3 5.4 5.5

×

)2 cC

andi

date

s / (

0.01

GeV

/

0

2

4

6

8

10

12

310×

LHCb

]2c [GeV/−K+K+Km5.1 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

]2c [GeV/-π+π-πm5.1 5.2 5.3 5.4 5.5

×

)2 cC

andi

date

s / (

0.01

GeV

/

0

0.5

1

1.5

2

2.5

3

310×

LHCb

]2c [GeV/-π+π+πm5.1 5.2 5.3 5.4 5.5

×

model±π−π+π → ±B

combinatorial 4-body→B

−π+π± K→ ±B

]2c [GeV/-π+K-Km5.1 5.2 5.3 5.4 5.5

×

)2 cC

andi

date

s / (

0.01

GeV

/

0

0.2

0.4

0.6

0.8

1310×

LHCb

]2c [GeV/-π+K+Km5.1 5.2 5.3 5.4 5.5

×

model±π−K+ K→ ±B

combinatorial 4-body→ SB

4-body→B −K+K± K→ ±B−π+π± K→ ±B

Prelim

inary

LHCb-

PAPER-2

014-

044

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 multibodyB decays 13

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B± → K±h+h−, π±h+h−

Global direct CP asymmetry

ARawCP =

NB− −NB+

NB− +NB+

Correct for B± production asymmetry and unpaired hadron (eg. B± → K±π+π−) detection

asymmetry

ACP = ARawCP −AP −Ah

D

AP and AKD from B± → J/ψ[µ+µ−]K±, PRL 108 201601 (2012)

AπD from promptD+ 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)

Prelim

inary

LHCb-

PAPER-2

014-

044

CP violation effects in multibodyB decays 14

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B± → K±h+h−, π±h+h−

Dalitz plot background subtracted and effiency corrected with ∼ (NB+ +NB−) in each bin

B±→ K±π+π− B±

→ K±K+K−

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

]4c/2 [GeV -π+π2m

0 5 10 15 20

]4 c/2 [G

eV - π+

K2m

0

5

10

15

20

25

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

LHCb (a)

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

]4c/2 [GeVlow-

K+K2m

0 2 4 6 8 10 12 14

]4 c/2 [

GeV

high

-K+

K2m

0

5

10

15

20

25

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

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1

LHCb (b)

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

]4c/2 [GeVlow-π+π2m

0 2 4 6 8 10 12 14

]4 c/2 [G

eVhi

gh- π+ π2

m

0

5

10

15

20

25

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

LHCb (c)

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

]4c/2 [GeV-π+K2m

0 5 10 15 20 25

]4 c/2 [G

eV-

K+K2

m

0

5

10

15

20

25

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

LHCb (d)Prelim

inary

LHCb-

PAPER-2

014-

044

Penguin

Tree

B±→ π±π+π− B±

→ π±K+K−

CP violation effects in multibodyB decays 15

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CP Asymmetry by InterferenceProject onto mππ of B± → π±π+π−

]2c[GeV/ low−π+πm0.5 1 1.5

)2Y

ield

/(0.

05 G

eV/c

0

200

400

600

800 LHCb +B−

B

]2c[GeV/ low−π+πm0.5 1 1.5

+ -

B-

B

-200-100

0100200300 LHCb

]2c[GeV/ low−π+πm0.5 1 1.5

)2Y

ield

/(0.

05 G

eV/c

0

0.5

1

1.5310×

LHCb +B−

B

]2c[GeV/ low−π+πm0.5 1 1.5

+ -

B-

B

-1000

100200300 LHCbPre

limina

ry

LHCb-

PAPER-2

014-

044

0 ρ+ π

- π

+K

θ0 ρ

+ π- 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 multibodyB decays 16

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CP Asymmetry by Rescatteringππ ↔ KK rescattering region: 1.0 − 1.5 GeV/c2

B± → K±π+π− B± → K±K+K−

]2c [GeV/−π+π−Km

5.1 5.2 5.3 5.4 5.5×

)2 cC

andi

date

s / (

0.01

GeV

/

00.20.40.60.8

11.21.41.61.8

310×

LHCb

]2c [GeV/−π+π+Km5.1 5.2 5.3 5.4 5.5

×

model−π+π± K→ ±B

combinatorial 4-body→B

±)Kγ0ρ’(η → ±B ±π−π+π → ±B

]2c [GeV/−K+K−Km5.1 5.2 5.3 5.4 5.5

×

)2 cC

andi

date

s / (

0.01

GeV

/

00.20.40.60.8

11.21.41.61.8

22.22.4

310×

LHCb

]2c [GeV/−K+K+Km5.1 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

Prelim

inary

LHCb-

PAPER-2

014-

044

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 multibodyB decays 17

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B± → K±pp and B± → π±ppAnother new preliminary result based on full data set

B± → K±pp penguin dominated

B± → π±pp tree dominated

Similar physics to non-baryonic 3-body charmless decays

pp ↔ h+h− rescattering expected to be smaller than

KK ↔ ππ rescattering

CP asymmetry could be less pronounced

Threshold enhancement in low mpp typical in B → ppX

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 uud

p

du p

b

+B

d,su

u

+π,+K

W

u uud

p

du pb

+B

d,s

u

u

+π,+KW

CP violation effects in multibodyB decays 18

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Signal Yield

B± → K±pp

NSig = 18721 ± 142 (stat)

]2 [GeV/c±Kppm5.1 5.2 5.3 5.4 5.5

)2C

and

idat

es /

(0.0

1 G

eV/c

0

500

1000

1500

2000

2500

3000

3500

4000

4500

LHCb

Blue: Signal

Red: Combinatorial

B± → π±pp

NSig = 1988 ± 74 (stat)

]2 [GeV/c±πppm5.1 5.2 5.3 5.4 5.5

)2C

and

idat

es /

(0.0

1 G

eV/c

0

100

200

300

400

500

600

700

LHCb

Green: Partially reconstrcuted

Purple: Cross-feed

Prelim

inary

LHCb-

PAPER-2

014-

034

CP violation effects in multibodyB decays 19

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Dalitz PlotBackground subtracted and efficiency corrected using calibrated MC

B± → K±pp

]4/c2 [GeV2ppm

5 10 15 20

]4/c2

[G

eV2 K

pm

2

4

6

8

10

12

14

16

18

20 )8/c4

Sig

nal

yie

ld /(

0.16

GeV

0

2000

4000

6000

8000

10000

12000LHCb

B± → π±pp

]4/c2 [GeV2ppm

5 10 15 20 25

]4/c2

[G

eV2 pπ

m

0

2

4

6

8

10

12

14

16

18

20 )8/c4

Sig

nal

yie

ld /(

0.20

GeV

0

500

1000

1500

2000

2500

3000

3500

LHCb

6

�������

��

��

��

�������1

Low mpp threshold enhancement

Charmonimum resonances

Definempp < 2.85 GeV/c2 as charmless region

Λ(1520) → pK

Prelim

inary

LHCb-

PAPER-2

014-

034

CP violation effects in multibodyB decays 20

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Forward-Backward Asymmetry

AFB =N(cos θ > 0) −N(cos θ < 0)

N(cos θ > 0) +N(cos θ < 0)

Meausure forward-backward asymmetry in bins of mpp

Gives hint on pp waves that might contributepp

+h

θ

B± → K±pp

]2 [GeV/cppm2 2.2 2.4 2.6 2.8

FB

A

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

LHCb

B± → π±pp

]2 [GeV/cppm2 2.2 2.4 2.6 2.8

FB

A

-1

-0.8

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-0.2

0

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0.8

1

LHCb

AppKFB (mpp < 2.85 GeV/c2) = +0.495 ± 0.012 (stat) ± 0.007 (syst)

AppπFB (mpp < 2.85 GeV/c2) = −0.409 ± 0.033 (stat) ± 0.006 (syst)

Large asymmetries indicate dominance of non-resonant pp scattering, J Phys G 34 283 (2007)

Prelim

inary

LHCb-

PAPER-2

014-

034

CP violation effects in multibodyB decays 21

Page 22: Jeremy Dalseno on behalf of the LHCb collaborationffp14.cpt.univ-mrs.fr/DOCUMENTS/SLIDES/DALSENO_Jeremy.pdf · Vertex Locater (VeLo) Precision tracking Tracker Turicensis (TT) Tracking,

Direct CP Asymmetry

Measure ACP in Dalitz plot bins

Same number of events in each bin

ACP (mpp < 2.85 GeV/c2,m2Kp > 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±pp

]2)2 [(GeV/cpp2m

5 10 15 20

]2 )2 [

(GeV

/cK

p2

m

2

4

6

8

10

12

14

16

18

CP

Raw

A

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

����������*

6

)4/c2 (GeVpp2m

4 6 8

)4/c2

)/(0

.33

GeV

+)-

N(B

-N

(B

-150

-100

-50

0

50

100

150

)4/c2 (GeVpp2m

4 6 8

)4/c2

)/(0

.33

GeV

+)-

N(B

-N

(B

-150

-100

-50

0

50

100

150

Prelim

inary

LHCb-

PAPER-2

014-

034

CP violation effects in multibodyB decays 22

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Summary

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±pp

Large forward-backward asymmetries indicate dominance of non-resonant pp scattering

First evidenceCP violation in decays involving baryons

Sign-flip of CP asymmetry probably generated by interference of long-distance pp waves

Look forward to amplitude analyses on all these channels

CP violation effects in multibodyB decays 23

Page 24: Jeremy Dalseno on behalf of the LHCb collaborationffp14.cpt.univ-mrs.fr/DOCUMENTS/SLIDES/DALSENO_Jeremy.pdf · Vertex Locater (VeLo) Precision tracking Tracker Turicensis (TT) Tracking,

Backup

CP violation effects in multibodyB decays 24