mixing and cp violation in beauty and charm at...

Mixing and CP violation in beauty and charm at LHCb

Jinlin Fu INFN e Università di Milano

On behalf of the LHCb collaboration

Moriond QCD 2017 La Thuile, March 25–April 1, 2017

Introduction

J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 2

Violation of CP symmetry (CPV) is a necessary condition for the Baryon Asymmetry of the Universe [1]

CPV is present only in the weak interactions via CKM mechanism in the SM, but is too small to explain the absence of antimatter in the universe

[1] A. D. Sakharov, “Violation of CP invariance, C asymmetry, and baryon asymmetry of the universe,”JETP Lett. 5, 24-27 (1967), Sov. Phys. Usp. 34, 392-393 (1991)

Possibly there are other sources of CPV beyond SM. B and D hadrons are a fantastic laboratory to search for CPV effects extensively.

Overview


• Combined measurement of CKM angle 𝛾

• Search for CPV in , decays⇤0b ! p⇡�h+h� h = K,⇡

• Search for CPV in decays ⇤0b ! pK�µ+µ�

• Charm mixing and CPV in decaysD0 ! K±⇡⌥

• measurement in and decaysA� D0 ! K+K� D0 ! ⇡+⇡�

JHEP 12(2016) 087

Nature Physics(2017) DOI:10.1038/nphys4021

arXiv:1703.00256, submitted to JHEP

arXiv:1611.06143, submitted to PRD

arXiv:1702.06490, submitted to PRL

Combined measurement of CKM angle 𝛾


• Direct measurement: measured in the interference between b→cand b→u transitions.

• Indirect measurement: extracted from global fits to CKM triangle

theoretically clean measurement: 𝛿𝛾/𝛾 ≲ O(10-7)J. Brod, J. Zupan, JHEP 1401(2014)051

• Discrepancies between direct and indirect measurements could indicate new physics.

but single measurement not very sensitive, due to small BR ~10-7

need to combine many decay modes

JHEP 12(2016) 087⌘ �arg(VudV

⇤ub

VcdV ⇤cb)

Combined measurement of CKM angle 𝛾


• Most precise measurement

• Consistent with B factory with better precision

� = (69+17�16)

�

� = (68+15�14)

�BaBarBelle

PRD 87, 052015 (2013)

arXiv:1301.2033 (2013)

� = (72.2+6.8�7.3)

o

• Combine observables from a wide range of decays with run 1 dataset ( ), use a frequentist approachLint = 3fb�1

JHEP 12(2016) 087⌘ �arg(VudV

⇤ub

VcdV ⇤cb)

Search for CPV in ,


⇤0b ! p⇡�h+h�

• Transitions governed by b→udu tree and b→duu penguin amplitudes of similar magnitude. Large relative weak phase in SM from CKM elements, arg( VtbVtd*/VubVud* ) = 𝛼

• Potential non negligible CPV effects in SM

I.I. Bigi, arXiv:1608.06528M. Gronau, J. Rosner, PLB749(2015) 104-107

W. Bensalem et al.,PLB538(2002) 309-320W. Bensalem et al.,PRD66(2002) 094004

h = K,⇡Nature Physics(2017) DOI:10.1038/nphys4021

Triple product asymmetries


• Use 4-body topology to build triple products

/ sin�

/ sin�

, for

, for

⇤0b

⇤0b

• P-odd ( ) asymmetries:ˆT -odd

, for ⇤0b

, for ⇤0b

AT (CT ) =N(CT>0)�N(CT<0)N(CT>0)+N(CT<0)

AT (C T ) =N(�CT>0)�N(�CT<0)

N(�CT>0)+N(�CT<0)

⇤0b rest frame

aˆT -odd

P =1

2(A

ˆT + AˆT )

P-violating variable CP-violating variable


production/reconstruction asymmetries don’t affect results

Signal yields


]2c) [GeV/−π+π−πp(m5.2 5.4 5.6 5.8 6

)2 cEv

ents/

(9 M

eV/

0

500

1000

1500

Full fit−π+π−πp →0bΛ

Part-rec. bkg.Comb. bkg.

+π−π−π+K →0B−π+π−pK →0bΛ

LHCb(a)

]2c) [GeV/−K+K−πp(m5.2 5.4 5.6 5.8 6

)2 cEv

ents/

(9 M

eV/

0

200

400

Full fit−K+K−πp →0bΛ

Part-rec. bkg.Comb. bkg.

−π+K+K−K →0B+π−π+K−K →0sB−K−K+pK →0bΛ−π+π−pK →0bΛ

LHCb(b)

• First observation of and decays

=6646±105 =1030±56Nsig(p⇡�⇡+⇡�) Nsig(p⇡�K+K�)

⇤0b ! p⇡�⇡+⇡� ⇤0

b ! p⇡�K+K�

Lint = 3fb�1


First evidence for CPV in baryons


Asy

mm

etrie

s [%

]

Phase space bin5 10

20 0

20− /ndf=21.1/122χ CP

-oddTa

5 10

20 0

20−

LHCb Scheme A

/ndf=27.9/122χ P-oddTa

Asy

mm

etrie

s [%

]

| [rad]Φ|1 2 3

20 0

20− /ndf=30.5/102χ CP

-oddTa

1 2 3

20 0

20−

LHCb Scheme B

/ndf=20.7/102χ P-oddTa

• For decays:Global measurements consistent with CP symmetry

⇤0b ! p⇡�⇡+⇡�

Local measurements: combined 2 binning results, CP symmetry 3.3σ deviation.

• For decays:⇤0b ! p⇡�K+K�

Global and local measurements consistent with CP symmetry


∆++,N*,ρ0(770),|𝚽|

Search for CPV in


⇤0b ! pK�µ+µ�


• b→sµ+µ- FCNC process, limited amount CPV predicted in SM makes it particularly sensitive to New Physics

R. Gauld, F. Goertz and U. Haisch, arXiv:1310.1082, JHEP01(2004) 069M. A. Paracha, I. Ahmed, and M. J. Aslam, arXiv:1408.4318, PTEP 2015(2015) 033B04A. K. Alok et al., arXiv:1103.5344, JHEP11(2011) 122

CP–odd observables


• Triple product asymmetries to built

CT = ~pµ+ · (~pp ⇥ ~pK�) / sin�

C T = ~pµ� · (~pp ⇥ ~pK+) / sin�

• measurements

aT�odd

CP

Araw = N(⇤0b!pK�µ+µ�)�N(⇤

0b!pK+µ�µ+)

N(⇤0b!pK�µ+µ�)+N(⇤

0b!pK+µ�µ+)

⇡ ACP (⇤0

b ! pK�µ+µ�) +Aprod

(⇤0

b)�Areco

(K+) +Areco

(p)

�ACP = ACP (⇤0b ! pK�µ+µ�)�ACP (⇤0

b ! pK�J/ )

⇡ Araw(⇤0b ! pK�µ+µ�)�Araw(⇤0

b ! pK�J/ )


�ACP

Asymmetry measurements


Lint = 3fb�1

• First observation of ⇤0b ! pK�µ+µ�

Nsig = 600 ± 44

= (–3.5 ± 5.0stat ± 0.2syst ) x 10-2

= ( 1.2 ± 5.0stat ± 0.7syst ) x 10-2

�ACP

aT�odd

CP


consistent with CP symmetry

Charm mixing and CPV in


arXiv:1611.06143, submitted to PRD

• Mass eigenstates ≠ flavour eigenstates ⇒ D0–D0 mixing

• CPV in charm expected < 10-3 in SM, and not yet observed.

x = 2(m1 �m2)/(�1 + �2) y = (�1 � �2)/(�1 + �2)

D0 mixing well established with very slow rate: x, y < 10-2

|D1,2i = q|D0i± p|D0i |p|2 + |q|2 = 1

CPV and mixing parameters extracted by measuring time-dependent ratio R(t) = WS/RS

R(t)± = R±D

+q

R±D

y0±( t

⌧

) + (x0±)2+(y0±)2

4 ( t

⌧

)2

x

0= x cos �K⇡ + y sin �K⇡ y

0= y cos �K⇡ � x sin �K⇡

DCS interference mixing

R+D 6= R�

D

x

0+ 6= x

0�

y0+ 6= y0�

⇒

⇒

direct CPV

CPV in mixing and interference

D0 ! K±⇡⌥



D0 ! K±⇡⌥arXiv:1611.06143, submitted to PRD

]2) [MeV/csπ0m(D

2000 2005 2010 2015 2020 2025

)2Ev

ents

/ ( 0

.05

MeV

/c

10000

20000

30000

40000

50000

60000

70000LHCb

Data

Fit

Background

(a)

]2) [MeV/csπ0m(D

2000 2005 2010 2015 2020 2025

σ/∆

4−2−024

]2) [MeV/csπ0m(D

2000 2005 2010 2015 2020 2025

)2Ev

ents

/ ( 0

.05

MeV

/c

100

200

300

400

500

600

700 LHCbData

Fit

Background

(b)

]2) [MeV/csπ0m(D

2000 2005 2010 2015 2020 2025

σ/∆

4−2−024

Lint = 3fb�1

1.7x106 RS 6.7x103 WS

• The double-tagged (DT) selection ( B→D*+(→D0π+)µ–X, D0→Kπ ) leads to very pure samples

• DT allows better measurements at lower decay time than “prompt” selection ( D*+→D0π+, D0→Kπ ) from previous measurement.

arXiv:1309.6534, PRL111(2013) 251801



D0 ! K±⇡⌥arXiv:1611.06143, submitted to PRD

τ t/0 D0 5 10

]-3

[10

+ R

3

3.5

4

4.5

5

5.5

6 LHCb

PromptDoubly Tagged

0D

τ t/0 D0 5 10

]-3

[10

- R

3

3.5

4

4.5

5

5.5

6

No CPVNo Direct CPVAll CPV allowed

0D

τt/0 5 10

]-3

[10

- -

R+

R

0.8−0.6−0.4−0.2−

00.20.40.60.8

0D−0D

R(t)± = R±D

+q

R±D

y0±( t

⌧

) + (x0±)2+(y0±)2

4 ( t

⌧

)2

• World’s best measurements on charm mixing parameters, consistent with CP symmetry.

• Results with DT samples consistent with the prompt

• Simultaneous fit to DT and prompt samples improve precision by 10~20%

measurement in and


A� D0 ! K+K� D0 ! ⇡+⇡�arXiv:1702.06490, submitted to PRL

• Given small mixing parameters (x, y < 10-2), the time-dependent asymmetry approximated as:

ACP (t) ⌘ �(D0(t)!f)��(D0(t)!f)

�(D0(t)!f)+�(D0(t)!f)

' afdir �A�t⌧D

afdirNeglecting sub-leading amplitudes, =0 and independent of

PRD85(2012) 012009

PRD75(2007) 036008EPJC50(2007) 579

A� , the asymmetry between the D0 and D0 effective decay widths

A� ⌘�D0!f��

D0!f

�D0!f+�D0!f

A�

the final state.


A�

0 2 4 6 8�1

0

1

2

A(t

)[%

]

LHCb D0 ! K+K� DataFit

20t/⌧D

0 2 4 6 8�2

�1

0

1

2

A(t

)[%

]

LHCb D0 ! ⇡+⇡� DataFit

20t/⌧D

• Extract by linear fit of the asymmetryA� ACP (t) = afdir �A�t⌧D

A�(K+K�)

A�(⇡+⇡�)

= (–0.30±0.32±0.10)x10-3

= ( 0.46±0.58±0.12)x10-3

as function of the proper decay time

• Assuming only indirect CPV contributes

consistent with CP symmetry

to , two values can be averaged A�

to one single value: A� = ( –0.13±0.28±0.10)x10-3

consistent with results using µ-tagged sample at LHCb.

A� = ( –0.29±0.28)x10-3Combine two results:

JHEP1504(2015)043

PRD75(2007) 036008

most precise measurement

Lint = 3fb�1

measurement in and D0 ! K+K� D0 ! ⇡+⇡�arXiv:1702.06490, submitted to PRL

Summary


• First evidence for CPV in baryons found in decays with a statistical significance of 3.3σ

⇤0b ! p⇡�⇡+⇡�

• No CPV found in and decays ⇤0b ! p⇡�K+K� ⇤0

b ! pK�µ+µ�

• Most precise measurement � = (72.2+6.8�7.3)

o

• World’s best measurements on Charm mixing parameters in D0 ! K±⇡⌥ decays, no CPV found.

• Most precise measurement of in and A� D0 ! K+K� D0 ! ⇡+⇡�

decays, no CPV found.

mixing and cp violation in beauty and charm at...

Documents