Mixing and CP violation in beauty and charm at...
Transcript of 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
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 3
• 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
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 4
• 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
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 5
• 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 ,
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 6
⇤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
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 7
• 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
Nature Physics(2017) DOI:10.1038/nphys4021
production/reconstruction asymmetries don’t affect results
Signal yields
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 8
]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
Nature Physics(2017) DOI:10.1038/nphys4021
First evidence for CPV in baryons
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 9
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
Nature Physics(2017) DOI:10.1038/nphys4021
∆++,N*,ρ0(770),|𝚽|
Search for CPV in
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 10
⇤0b ! pK�µ+µ�
arXiv:1703.00256, submitted to JHEP
• 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
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 11
• 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/ )
arXiv:1703.00256, submitted to JHEP
�ACP
Asymmetry measurements
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 12
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
arXiv:1703.00256, submitted to JHEP
consistent with CP symmetry
Charm mixing and CPV in
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 13
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±⇡⌥
Charm mixing and CPV in
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 14
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
Charm mixing and CPV in
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 15
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
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 16
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.
J. FU (UNIMI & INFN) Moriond QCD 2017 2017.03.27 17
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
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• 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.