searches for cp violation in d decays ... - agenda (indico) · y. grossman, a. l. kagan and y. nir,...
TRANSCRIPT
Searches for CP violation in D0 decays from BABAR and Belle
Maurizio Martinellion behalf of the BABAR Collaboration
Università degli Studi di Bari and INFNFPCP 2010 - May 27 2010, Torino ITALY
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
• Standard Model: CP violation from KM phase in CKM quark mixing matrix:
• Charmed Mesons:
• CP violation is CKM suppressed O(10-3)
• Experimental Sensitivity O(10-2)
CP violation in D0 decays
1% Signal = New Physics2
1− λ2
2 λ Aλ3(ρ− iη + i2ηλ2)
−λ 1− λ2
2 − iηA2λ4 Aλ2(1 + iηλ2)Aλ3(1 − ρ− iη) −Aλ2 1
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
New Physics Scenario
• Direct CP violation at tree level («1%)
• extra quarks in SM vector-like representations• supersymmetry without R-parity models• two Higgs doublet models
• Direct CP violation at one-loop (1%)
• QCD penguin and dipole operators• FCNCs in supersymmetric flavor models.
CPV ~ 1% Strong Evidence for non-SM processes
Details:Y. Grossman, A. L. Kagan and Y. Nir, Phys. Rev. D75, 036008 (2007)I. I. Bigi, hep-ph/0104008 (2001)
Singly Cabibbo Suppressed (CS) decays are uniquely sensitive toCabibbo Favoured and Double CS are not
3
c→ uqq
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Charm & B-factories• Why search for CP violation at B-factories:
• Υ(4S): ccbar cross section = 1/4 total
• require p*(D) > 2.5 GeV/c to reduce background
• D*+→D0π+ provides D0 flavor
• Drawback: Electroweak Forward-Backward asymmetry
4
(GeV/c)lab
sig] p(D*)+-K0, D0D[D*0 1 2 3 4 5
)2Ev
ents
/(100
MeV
/c
0
100
200
300
400
500BBcc
uds
p(D*) > 2.5 GeV/c
MC
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Experimental Searches
• Direct CP violation
• Dalitz Plot analysis
• Time dependent
• T odd correlations
5
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
ACP =RD0 −RD0
RD0 + RD0, with R =
ΓCS
ΓCF
• In asymmetric detectors like BABAR and Belle, forward-backward asymmetry could bias these measurements
• FB asymmetry = EW+EM currents interference
• Two solutions:• estimate FB asymmetry contribution• normalize CP asymmetry to CF channels
Nc/Nc = f(cos θ∗)
ACP =ΓD0 − ΓD0
ΓD0 + ΓD0
Direct CP violation
6
Γ = yields
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
ACP =RD0→K+π−(nπ)
WS −RD0→K+π−(nπ)WS
RD0→K+π−(nπ)WS + RD0→K+π−(nπ)
WS
, with RWS =Γ(K+π−(nπ))Γ(K−π+(nπ))
• D* tagged
• Identification of Right Sign and Wrong Sign decay using K charge
• Both are DCS, using ratio DCS/CF yields
• 2D binned maximum likelihood fit to (m(D0), ∆m)
Doubly Cabibbo Suppressed D0→K+π-(nπ)
ACPKπππ = -0.006±0.053
RS
WS ACPKππ = -0.018±0.044
RS
WS
Phys. Rev. Lett. 95, 231801 (2005)Belle (281fb-1)
syst. < 0.01
NDtot=1978±104 NDtot=1721±757
D0→K+π-π0 D0→K+π-π+π-
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
AhhCP,dir = Ahh
CP + AFB + Aπs
ACP =Γ(D0 → h+h−)− Γ(D0 → h+h−)Γ(D0 → h+h−) + Γ(D0 → h+h−)
= AhhCP,dir + Ahh
CP,ind
Cabibbo Suppressed Decays: D0→h+h-
• Major issue: asymmetry in D0 tagging
• FB asymmetry
• soft pion(πs) reconstruction asymmetry
Need to separate contributions to ACP
from mixing analysis
8
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Cabibbo Suppressed Decays: D0→h+h-
• map the πs asymmetry using D0→K-π+ tagged and untagged data to retrieve the weighting factors to correct D0 yield
• measure ACP in cosθ bins in order to isolate production asymmetry
• measure ACP from χ2 fit over cosθ bins
even: ACP uniform over cosθ
odd: AFB asymmetric over cosθ
9
a±(cos θ∗) =nD0(±| cos θ∗|)− nD0(±| cos θ∗|)nD0(±| cos θ∗|) + nD0(±| cos θ∗|)
ACP �[a+(cos θ∗) + a−(cos θ∗)]/2AFB �[a+(cos θ∗)− a−(cos θ∗)]/2
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Cabibbo Suppressed Decays: D0→h+h-
0 0.2 0.4 0.6 0.8-0.02
-0.01
0
0.01
0.02
0 0.2 0.4 0.6 0.8-0.02
-0.01
0
0.01
0.02
0 0.2 0.4 0.6 0.8-0.02
-0.01
0
0.01
0.02
0 0.2 0.4 0.6 0.8-0.02
-0.01
0
0.01
0.02
0 0.2 0.4 0.6 0.8-0.06
-0.04
-0.02
0
0 0.2 0.4 0.6 0.8-0.06
-0.04
-0.02
0
0 0.2 0.4 0.6 0.8-0.06
-0.04
-0.02
0
0 0.2 0.4 0.6 0.8-0.06
-0.04
-0.02
0
(a) (b)
(c) (d)
aKK
FBaK
KCP
a!! FB
a!!
CP
| cos !CMSD0 | | cos !CMSD0 |
| cos !CMSD0 | | cos !CMSD0 |
BABAR (385fb-1)Phys. Rev. Lett. 100, 061803 (2008)
Category ∆ACPKK ∆ACPππ
2-dim PDF shapes
πs corrections
ACP corrections
Quadrature sum
±0.04% ±0.05%
±0.08% ±0.08%
±0.09% ±0.20%
±0.13% ±0.22%
Systematic errors
ResultsACPKK = (0.00±0.34stat±0.13syst)%
ACPππ = (-0.24±0.52stat±0.22syst)%
two-dimensional fit to D0 and ∆mSample Size
K-π+ untag
K-π+ tag
K+K-
π+π-
6.6x106
1.5x106
130x103
64x103
10
D0→K+K- D0→π+π-
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Cabibbo Suppressed Decays: D0→h+h-
Belle (540fb-1)Phys. Lett. B670.190 (2008)
|cos *|
AC
P
a) K+K-
|cos *|
AC
Pb) + -
|cos *|
AFB c) K+K-
|cos *|
AFB d) + -
-0.04
-0.03-0.02
-0.01
0
0.01
0.020.03
0.04
0 0.2 0.4 0.6 0.8-0.04
-0.03-0.02
-0.01
0
0.01
0.020.03
0.04
0 0.2 0.4 0.6 0.8
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0 0.2 0.4 0.6 0.8-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0 0.2 0.4 0.6 0.8
Category ∆ACPKK ∆ACPππ
Signal Counting
πs corrections
ACP extraction
Quadrature sum
±0.04% ±0.06%
±0.10% ±0.10%
±0.03% ±0.04%
±0.11% ±0.12%
Systematic errors
ResultsACPKK = (-0.43±0.30stat±0.11syst)%
ACPππ = (+0.43±0.52stat±0.12syst)%
one-dimensional fit to D0 mass spectrum
Sample Size Purity
K-π+ untag
K-π+ tag
K+K-
π+π-
6.3x106 80%
1.3x106 99%
120x103 97%
51x103 91%
11
D0→K+K- D0→π+π-
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Dalitz Plot Analysis
• Quantities that can be measured:
• Asymmetry on the Dalitz Plot
• Asymmetry in the angular moments
• Asymmetry in the amplitudes (model dependent)
• Phase Space integrated asymmetry
12
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Cabibbo Suppressed Decay D0→π+π-π0
Belle (532fb-1)Phys. Lett. B662.102 (2008)
Source MC stat. Tracking Fit KS veto PID Binning AFB Total
σ(%) 0.24 1.01 0.58 0.23 0.15 0.05 0.15 1.23
ACP = (0.43±0.41stat±1.30syst)%
Phase Space integrated asymmetry measurement
Sample Yields
π+π-π0 2.4x106
13
peaking background from D0+random πs
fit PDF from MC
Systematics
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
χ2/ν =
�ν�
i=1
∆2i
�/ν
Cabibbo Suppressed Decay D0→h+h-π0
BABAR (385fb-1)Phys. Rev. D78, 051102(R) (2008)
) 4/c2) (GeV0-(2m0 1 2 3
) 4/c2
) (G
eV0
+(2
m
1
2
3
-4
-3
-2
-1
0
1
2
3
4
(a)
) 4/c2) (GeV0-(K2m1 2
) 4/c2
) (G
eV0
+(K2
m
0
1
2
-4
-3
-2
-1
0
1
2
3
4
(b)
∆ ∆
|0DCM| cos
0 0.2 0.4 0.6 0.8
CP
0a
-0.01
0
0.01 (a)
|0DCM| cos
0 0.2 0.4 0.6 0.8
CP
0K
Ka
-0.02
0
0.02
0.04 (b)
Normalized Residuals
R = efficiency corrected ND0bar/ND0
CL(no CPV) = 32.8% CL(no CPV) = 16.6%
average on cosθ to cancel FB asymmetry
Search for asymmetries in the Dalitz plot
ACPKKπ=(1.00±1.67stat±0.25syst)%ACPπππ=(-0.31±0.41stat±0.17syst)%
Sample Size Purity
K+K-π0
π+π-π0
11x103 98%
82x103 98%
14
∆ =(nD0 −R · nD0)�
σ2nD0+R2·σ2
nD0
CL = one sided gaussian Confidence Level for consistency with no CPV hypothesis
(b)D0→K+K-π0(a)D0→π+π-π0
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Cabibbo Suppressed Decay D0→h+h-π0
BABAR (385fb-1)Phys. Rev. D78, 051102(R) (2008)
No CPV found in Dalitz amplitudes comparing amplitudes, phases and fractions
Study of the Angular Moments to search for asymmetries
15
continued
)2) (GeV/c-+m(0.26 1.01 1.76
0X
-2
0
2
)2) (GeV/c-+m(0.26 1.01 1.76
1X
-2
0
2
)2) (GeV/c-+m(0.26 1.01 1.76
2X
-2
0
2
)2) (GeV/c0+m(0.26 1.01 1.76
0X
-2
0
2
)2) (GeV/c0+m(0.26 1.01 1.76
1X
-2
0
2
)2) (GeV/c0+m(0.26 1.01 1.76
2X
-2
0
2
)2) (GeV/c-K+m(K1 1.5
0X
-2
0
2
)2) (GeV/c-K+m(K1 1.5
1X
-2
0
2
)2) (GeV/c-K+m(K1 1.5
2X
-2
0
2
)2) (GeV/c0+m(K0.6 1 1.4
0X
-2
0
2
)2) (GeV/c0+m(K0.6 1 1.4
1X
-2
0
2
)2) (GeV/c0+m(K0.6 1 1.4
2X
-2
0
2
D0→π+π-π0 D0→K+K-π0
particlecombination π+π- π+π0 K+K- K+π0
CL (No CPV) 28.2% 28.4% 63.1% 23.8%
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
∆Y =τKπ
τhhAτ
τhh =τ+hh + τ−hh
2Aτ =
τ+hh − τ−hh
τ+hh + τ−hh
τ+hh =τKπ [1 + rm (y cosϕf − x sin ϕf )]−1
τ−hh =τKπ
�1 + r−1
m (y cosϕf − x sin ϕf )�−1
Time Dependent (TD)
• D0 mixing affects D0 decay times (h=K,π)
• defining
• ∆Y is a probe for CP violation in decay times
(SM: ∆Y=0)16
for a definition of x, y, rm and φf see Nicola’s talk on D0 mixing
(rm=1,φf =0)
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
t = mD0�L · �p/p2
Cabibbo Suppressed Decay D0→h+h- (TD)Belle (540fb-1)Phys. Rev. Lett. 98.211803 (2007)
Source Acceptance Equal t0 M window Sig/SB bkg Bkg B(t) Res Func Selection Binning Total
σ(%) 0.07 0.08 <0.01 0.06 0.07 0.01 0.05 0.01 0.15
Aτ = (0.01±0.30stat±0.15syst)%
• D* tagged events• many systematics cancel in lifetime ratio
t (fs)
Even
ts p
er 6
1.5
fs (a) KK
t (fs)
Even
ts p
er 6
1.5
fs (b) K
t (fs)
Even
ts p
er 6
1.5
fs (c)
t (fs)
(NK
K+N
)/NK (d)
1
10
10 2
10 3
10 4
-2000 0 2000 400010
10 2
10 3
10 4
10 5
-2000 0 2000 4000
1
10
10 2
10 3
-2000 0 2000 40000.1
0.11
0.12
0.13
0.14
0.15
0.16
0 2000 4000
Sample Size Purity
K-π+
K+K-
π+π-
111x103 98%
1220x103 99%
49x103 92%
AτKK=(0.15±0.35stat)%Aτππ=(-0.28±0.57stat)%
yCP≠0
17
Systematics
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Cabibbo Suppressed Decay D0→h+h- (TD)
17
Aτ = (-0.26±0.36stat±0.08syst)%
BABAR (385fb-1)Phys. Rev. D78.011105 (2008)
Source Sig Model Charm Bkg Comb Bkg Selection Detector Model Total
σ(%) KK
σ(%) ππ
σ(%) average
0.072 0.001 0.001 0.083 0.054 0.122
0.265 0.002 0.005 0.172 0.040 0.318
0.062 0.001 0.002 0.011 0.054 0.083
t (ps)-2 -1 0 1 2 3 4
Nor
m.
Res
idua
l
-22
Even
ts/0
.06
ps
1
10
210
310
1
10
210
310
DataSignal
Charm
Comb.
*-D+K-K
t (ps)-2 -1 0 1 2 3 4
Nor
m.
Res
idua
l
-22
Even
ts/0
.06
ps
1
10
210
310
1
10
210
310
DataSignal
Charm
Comb.
*+D+K-K
t (ps)-2 -1 0 1 2 3 4
Nor
m.
Res
idua
l
-22
Even
ts/0
.06
ps
1
10
210
310
1
10
210
310DataSignal
Charm
Comb.
*-D+-
t (ps)-2 -1 0 1 2 3 4
Nor
m.
Res
idua
l
-22
Even
ts/0
.06
ps
1
10
210
310
1
10
210
310DataSignal
Charm
Comb.
*+D+-
Sample Size Purity
K-π+
K+K-
π+π-
731x103 99.9%
67x103 99.6%
31x103 98.0%
AτKK=(-0.40±0.44stat±0.12syst)%Aτππ=(0.05±0.64stat±0.32syst)%
• D* tagged events• many systematics cancel in lifetime ratio
18
Systematics
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
AT =Γ(�v1 · (�v2 × �v3) > 0)− Γ(�v1 · (�v2 × �v3) < 0)Γ(�v1 · (�v2 × �v3) > 0) + Γ(�v1 · (�v2 × �v3) < 0)
T odd correlations
• Asymmetry in T-odd observable→T violation→CPV (assuming CPT invariance)
• T-odd observable (v = spin or momentum)
• Final State Interactions could fake the measure producing AT≠0
• Remove FSI effects
AT =12
�AT − AT
�
W. Bensalem, A. Datta and D. London, Phys. Rev. D66, 094004 (2002)W. Bensalem and D. London, Phys. Rev. D64, 116003 (2001)W. Bensalem, A. Datta and D. London, Phys. Lett. B538, 309 (2002)
T violating observable
19
measured on D0
measured on D0
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
CT = �pK+ · (�pπ+ × �pπ−)
D0→K+K-π+π-
• T-odd correlation observable (CT) can be built using final state particle momenta:
I. I. Bigi, hep-ph/0107102 (2001)
-p
+p
+Kp
-Kp
-p × +pTC
rest frame0D
20
AT =Γ(D0, CT > 0)− Γ(D0, CT < 0)Γ(D0, CT > 0) + Γ(D0, CT < 0)
AT =Γ(D0,−CT > 0)− Γ(D0,−CT < 0)Γ(D0,−CT > 0) + Γ(D0,−CT < 0)
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
AT = (1.0± 5.1stat ± 4.4syst)× 10−3
AT =(−68.5± 7.3stat ± 5.8syst)× 10−3
AT =(−70.5± 7.3stat ± 3.9syst)× 10−3
)2Ev
ents
/ ( 0
.8 M
eV/c
0
200
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800
1000)2Ev
ents
/ ( 0
.8 M
eV/c
0
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0
dataSignalBackground
>0)T
(C0D <0)T
(C0D
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
Pull
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
Pull
-3 0
+3
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
)2Ev
ents
/ ( 0
.8 M
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ents
/ ( 0
.8 M
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>0)TC (0D <0)TC (0D
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
Pull
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
Pull
-3 0
+3
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
BABAR
Pre
limin
ary
BABAR (470fb-1)hep-ex/1003.3397 (submitted to PRL)
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
Even
ts/ (
0.8
0 M
eV/c
^2)
0
1000
2000
3000
4000
)2) (GeV/c-+-K+m(K1.84 1.86 1.88 1.9
Even
ts/ (
0.8
0 M
eV/c
^2)
0
1000
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3000
4000dataSignal
peaking0Dm peaking
Combinatoric+sD
BABARpreliminary
)2 m (GeV/c0.14 0.145 0.15
Even
ts/ (
0.1
5 M
eV/c
^2)
0
5000
10000
)2 m (GeV/c0.14 0.145 0.15
Even
ts/ (
0.1
5 M
eV/c
^2)
0
5000
10000dataSignal
peaking0Dm peaking
Combinatoric+sD
BABARpreliminary
Pull
Pull
-3 0+3
Pull
Pull
-3 0+3
• D* tagged events• 2D fit to (m(D0), ∆m)• 47000 signal events
Effect signal PDF ∆m peak PDF bin size PID p*(D0) cosθ* fit bias mistag det asym Total
σ(x10-3) 0.2 0.5 0.2 3.5 1.7 0.9 1.4 0.0 1.1 4.4
fit projections signal region
21
Cabibbo Suppressed Decay D0→K+K-π+π-
Systematics:
Maurizio Martinelli - CP violation in D0 decays - BABAR and Belle mini reviewMay 27, 2010
Conclusions• D0 and charm decays provide a
powerful probe for non SM processes involving CPV
• Experimental sensitivity comparable to higher SM predictions
• Many experimental techniques developed by BABAR and BELLE
• No evidence of CPV found yet
• Is the best yet to come?
22
)-2 10× (CPA-10 -8 -6 -4 -2 0 2 4 6 8 10
Belle(2005) 0-+ K 0DBelle(2005) -+-+ K 0DBelle(2007) -+ 0DBelle(2007) -K+ K 0DBaBar(2008) -+ 0DBaBar(2008) -K+ K 0DBaBar(2008) -+ 0DBaBar(2008) -K+ K 0DBelle(2008) -+ 0DBelle(2008) -K+ K 0DBelle(2008) 0-+ 0DBaBar(2008) 0-+ 0DBaBar(2008) 0-K+ K 0DBaBar(2010) -+-K+ K 0D