measurements of the cp angle with the babar...
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Princeton University, Department of PhysicsJadwin Hall, Washington Rd.
Princeton, NJ 08542-0708, U.S.A.
E-mail: [email protected]
XXXIII International Conference on High Energy PhysicsMoscow, Russia
Session 8: CP violation, Rare decays, CKMFriday, July 28, 2006, 10:06
Alexandre V. TelnovPrinceton University
for the BaBar Collaboration
Measurements of the CP angle Measurements of the CP angle αα
with the BaBar experimentwith the BaBar experiment
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 2
Current BaBar dataset: 347 million BB pairs (±1.1%)_
Theoretical and experimental introduction to the CKM angle α
New BaBar results; their interpretation and implications for α :
B → π+π−, π±π0 , π0π0
B → ρ0ρ0, ρ±ρ0, ρ+ρ−
B0 → (ρπ)0
Summary and outlook
OutlineOutline
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 3
g
u
u
−− ρπ ,d
++ ρπ ,d
−W
0B d
b
Penguin
Measuring Measuring αα
ACP(t) in decay to a CP eigenstate at the tree level :duub →
Measure SM)(in arg 180 *
*
⎥⎦
⎤⎢⎣
⎡−≡=−−°
ubud
tbtd
VVVVαγβ
Penguins: ACP (t ) ⇒ sin(2αeff); αeff = α−∆α; direct ACP ≠ 0
0B ++ ρπ ,
−− ρπ ,
uud
d
−Wb
d
Tree
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 4
IsospinIsospin analysis in analysis in B B →→ ππππ , , ρρρρ
−+A2
1−+A~
21
00 ~ −+ = AA
00~A00A
α∆2
)(~)()(~)()(~)(
00
00
00000
00000
0
0
ππ
ππ
ππ
ππ
ππ
ππ
−−−
+++
−+−+
−+−+
→=
→=
→=
→=
→=
→=
BAA
BAABAA
BAABAA
BAA
In B → ρρ, there are 3 such relations (one for each polarization)
M. Gronau, D. London, Phys. Rev. Lett. 65, 3381 (1990)
PeTeA
PeTeAii
hh
iihh
βγ
βγ
+−
−+
+=
+=~
21)22sin( CS −∆+= αα
000
000
~~2
1~2
1
AAA
AAA
+=
+=
−+−
−++
)(~)( 00 hhBAhhBA −−++ →=→
Neglecting EW penguins, ±0 is a pure tree mode, and so the two triangles share a common side:
4-fold ambiguity in 2∆α : either triangle can flip up or down
6 unknowns, 6 observables in ππ (there is no vertex to measure Sπ0π0)5 observables in ρρ (or 7, when both Cρ0ρ0 and Sρ0ρ0 are measured)
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 5
TheThe BB00 →→ ππ++ππ−− analysisanalysisSimultaneous ML fit to B0 → π+π−, K+π−, π+K−, K+K−
Using DIRC Cherenkov angle to separate pions and kaonsAdditional ππ /Kπ /KK separation from ∆E
1.8 2.2 2.6 3.0 3.4 3.8 4.2
pLAB
0
2
4
6
8
10
12
DIR
C π
/K s
epar
atio
n, s
tand
ard
devi
atio
ns
Also measure AK+π− : see talk by Emanuele Di Marco at 12:12 today
DIRC: 144 quartz bars 0.84 x 4π coverage; 97% eff. @ 3 GeV/c
12σ π /K separation at 1.5 GeV/c, 2σ at 4.5 GeV/cCalibration sample: B− → π−D0, D0 → π+K−
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 6
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BABARPreliminary
New New BaBarBaBar results: results: BB00 →→ ππ++ππ−− (1)
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signalbackground
mES
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∆t ∆t
M. Pivk and F. R. Le Diberder, “sPlot: a statistical tool to unfold data distributions,”
Nucl. Instrum. Meth. A 555, 356 (2005) [arXiv:physics/0402083].
B0 tags
B0 tags_
asymmetry
BaBar-CONF-06/039
Nπ+π− = 675 ± 42
sPlot:Builds a histogram of x excluding it from the Maximum-Likelihood fit, assigning a weight to each event, keeping all signal events, getting rid of all background events, and keeping track of the statistical errors in each x bin
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 7
ππS-1 -0.5 0 0.5 1
ππC
-1
-0.5
0
0.5
1
CL=0.6827
CL=0.9545
CL=0.9973
CL=0.999937
BABARpreliminary
CL=0.9997
New New BaBarBaBar results: results: BB00 →→ ππ++ππ−− (2)
BaBar has observed a 3.63.6σσ evidence for CP violation in B0 → π+π−
SSππππ = = −−0.53 0.53 ±± 0.14 0.14 ±± 0.020.02
CCππππ = = −−0.16 0.16 ±± 0.11 0.11 ±± 0.030.03
(S,C) = (0.0, 0.0) is excluded at a confidence level of 0.99970 (3.6σ)
BaBar-CONF-06/039
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 8
TheThe B B →→ ππ±±ππ00, , ππ00 ππ00 analysisanalysis
Simultaneous fit to B0 → π+π0, K+π0 (using DIRC Cherenkov angle to separate pions and kaons)B0 → π0π0: branching fraction and time-integrated direct CP asymmetry
new: in addition to π0 → γγ, we use merged π0 and γ → e+e− conversions⇒ 10% efficiency increase per π0 (4% from merged π0 , 6% from γ conversions)
merged π0 :
the two photons are too close to one another in the EMC to be reconstructed individually; can be recovered using
,
where S is the second EMC moment of the merged π0 → γγ
The control sample: τ → ρν
)( 00022
γπππSSEM −≈
γ → e+e− conversions: result from interactions with detector elements
beam pipebeam pipebeam pipe
inner SVT layersinner SVT layersinner SVT layers DCH inner wallDCH inner wall
SVT outer layersSVT outer layers
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 9
New New BaBarBaBar results: results: B B →→ ππ±±ππ00, , ππ00 ππ00
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BABARPreliminary
mES π0π0
Nπ0π0 = 140 ± 25Nπ±π0 = 572 ± 53
CCππ00ππ00 = = −−0.33 0.33 ±± 0.36 0.36 ±± 0.080.08
BrBrππ00ππ00 = = (1.48 (1.48 ±± 0.26 0.26 ±± 0.12) 0.12) ×× 1010−−66
BrBrππ±±ππ00 = = (5.12 (5.12 ±± 0.47 0.47 ±± 0.29) 0.29) ×× 1010−−66
B± → ρ±π0 background
BaBar-CONF-06/039
sPlot
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 10
Here is one of the possible solutions to the Gronau-London isospin triangle in B →ππ according to the
central values of the latest BaBar results:
An interpretation An interpretation of the new of the new B B →→ ππππ resultsresults
∆∆αα αα
This is a frequentist interpretation: we use only the B →ππ isospin-triangle relations in arriving at these constraints on ∆α = α − αeff
and on α itself
|∆α | < 41º at 90% C.L.
BaBar-CONF-06/039
α = 0 excluded at 1−C.L. = 4.4 × 10−5
α near 0 can be disfavored by additional experimental information
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 11
B B →→ ρρρρ angular analysisangular analysis
DSA32
31 :alLongitudin 0 +−=
PDSA
PDSA
21
61
31 :Transverse
21
61
31 :Transverse
1
1
−+=
++=
−
+
pure CP = +1
transverse is not a CP eigenstate
π 0
π +
ρ+
0π
θ 2
ρ_
_
π
θ 1
φ
“helicity frame”
B → ρρ is a vector-vector state; angular analysis is required to determine CP content:
Fortunately, the fraction fL of the helicity-zero state in B → ρρ decays is very close to 1:
Heavy Flavor Averaging Group, April 2006 update: http://www.slac.stanford.edu/xorg/hfag/rare/winter06/polar/index.html
fL(B0 → ρ+ρ−)WA= 0.967+0.023−0.028
fL(B± → ρ±ρ0)WA= 0.96 ± 0.06
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 12
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∆ΕmES ρ0f0
ρ0ρ0
New New BaBarBaBar results: results:
Incremental improvements in the event selection and the analysis techniqueResults are statistically consistent with the previous BaBar analyses
Nρ0ρ0 = 98+32 ± 22−31
Brρ0ρ0 = (1.16+0.37 ± 0.27) × 10−6−0.36 fL(B0 → ρ0ρ0)= 0.86+0.11 ± 0.05−0.13
3.03.0 σσ evidence forevidence for BB00 →→ ρρ00ρρ00
The systematic error is dominated by interference with B0 → a± (1260)πm and by PDF parameter uncertainties1
BaBar-CONF-06/027
hep-ex/0603050,accepted by PRLBr (B0 → a± (1260)πm ) × Br (a± (1260) → πm π± π± ) = (16.6 ± 1.9 ± 1.5) × 10−6
1 1
Br (B0 → ρ0f0 ) × Br ( f0 → π+ π−) < 0.68 × 10−6 (at 90% C.L.)
Br (B0 → f0 f0) × Br 2( f0 → π+ π−) < 0.33 × 10−6 (at 90% C.L.)Also measure:
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 13
New New BaBarBaBar results: results: BB±± →→ ρρ±±ρρ00
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Brρ±ρ0 = (16.8 ± 2.2 ± 2.3) × 10−6
The systematic error is dominated by modeling of backgrounds, signal misreconstruction, and by statistical PDF uncertainties
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Nρ±ρ0 = 390 ± 49 BABARpreliminary BABAR
preliminary
Based on 232 million BB pairs; BaBar-PUB-06/052 _
Phys. Rev. Lett. 91, 221801 (2003)Phys. Rev. Lett. 91, 171802 (2003)
PDG 2004: (26 ± 6) × 10−6
Belle: (31.7 ± 7.1+3.8) × 10−6
Previous BaBar : (22.5+5.7 ± 5.8 ) × 10−6−6.7
−5.4}
+0
00+−/√2“before”:
old ρ±ρ0 WA
isospin prediction
fL(B± → ρ±ρ0) = 0.905 ± 0.042+0.023−0.027
The new BaBar measurement in B± → ρ±ρ0 allows the ρρ isospin triangle to close
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 14
Br (B0 → a±ρm ) × Br (a± → π+ π−π± ) < 30 × 10−6 (90% C.L.)1 1
B0 tags
B0 tags_
asymmetry
∆t (ps)
New New BaBarBaBar results:results: BB00 →→ ρρ++ρρ−−
Nρ+ρ− = 615 ± 57
fL(B0 → ρ+ρ−) = 0.977 ± 0.024+0.015−0.013
Slong = −0.19 ± 0.21+0.05−0.07Br ρ+ρ− = (23.5 ± 2.2 ± 4.1) × 10−6
Clong = −0.07 ± 0.15 ± 0.06
dominated by self-crossfeed
distributions for the highest-purity tagged events
mES sum of backgrounds
∆Ε
mπ±π0ρ helicity
BaBar-CONF-06/016
BABARpreliminary
reduced systematics thanks to hep-ex/0605024,accepted by PRD
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 15
As datasets increase, determination of both C and S will become possible in B0 →ρ0ρ0, leading to an improvement in the precision of the the ρρ isospin analysis
BaBar-CONF-06/27, BaBar-CONF-06/016
An interpretation An interpretation of the new of the new B B →→ ρρρρ resultsresults
This is a frequentist interpretation: we use only the B →ρρ branching fractions, polarization fractions and isospin-triangle relations in
arriving at these constraints on ∆α = α − αeff and α
(deg)ρρα∆ -30 -20 -10 0 10 20 30
2χ
∆
0
5
10
15
20
25
∆∆αα
|∆α | < 21º at 90% C.L.
|∆α | < 18º at 68% C.L.
BABARpreliminary
(deg)α 0 20 40 60 80 100 120 140 160 180
1-C
.L.
0
0.2
0.4
0.6
0.8
1
αα
[74, 117]ºat 68.3% C.L.
BABARpreliminary
Due to the new B0 →ρ0ρ0 BF result, the constraint on α from B →ρρ has become less stringent
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 16
0
5
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0 5 10 15 20 25 30
s+ (GeV2/c4)
s –
(G
eV2 /c
4 )
0
1
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22 23 24 25 26 27
Interference
√s0 = 1.5 GeV/c 2
√s+
= 1.
5 G
eV/c
2
√s– = 1.5 GeV/c2
BB00 →→ ((ρπρπ))00: : DalitzDalitz--plot analysisplot analysisBaBar-CONF-06/037 and references therein
0B
0B
−+πρ+−πρ
ρπ is not a CP eigenstateAn isospin-pentagon analysis method exists but is not fruitful
⇒ Time-dependent Dalitz-plot analysis assuming isospin symmetry,measuring 26 coefficients of the bilinear form factors
ρ0π0
ρ−π+
ρ+π−
The ρ(1450) and ρ(1700) resonances are also included in this analysis
Interference in the corners of the Dalitz plot provides information on strong phases between resonances
)(~)(~)(~)(~)()()()(
000
00
000
00
πρπρπρπππ
πρπρπρπππ
AfAfAfBA
AfAfAfBA
++=→
++=→+−
−−+
+−+
+−−
−++
−+
A. Snyder and H. Quinn, Phys. Rev. D, 48, 2139 (1993)
⊕ π0
π+
ρ−π−π− ρ0
π0
π+
Monte Carlo
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 17
∆t/σ(∆t)
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2 BABARP R E L I M I N A R Y
New New BaBarBaBar results: results: BB00 →→ ((ρπρπ))00 (1)
mES
∆t/σ(∆t)
BaBar-CONF-06/037
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NN output
m' θ'
data
projection of the fit result
signal misreconstructionexpected B backgroundcontinuum background
minimum of the three di-pion invariant masses
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 18
New New BaBarBaBar results: results: BB00 →→ ((ρπρπ))00 (2)
Sρπ = 0.01 ± 0.12 ± 0.028
Cρπ = 0.154 ± 0.090 ± 0.037
∆Sρπ = 0.06 ± 0.13 ± 0.029∆Cρπ = 0.377 ± 0.091 ± 0.021
parameters from the quasi-two-body description of B → ρπ :
a more physically intuitive way to represent direct-CP quantities:
Aρπ = −0.142 ± 0.041 ± 0.015
Aρπ = 0.03 ± 0.07 ± 0.03+−
Aρπ = −0.38+0.15 ± 0.07−0.16−+
BaBar-CONF-06/037
For results on Direct CP Violation, attend talk by Emanuele Di Marco at 12:12 today
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 19
An interpretation An interpretation of the new of the new BB00 →→ ((ρπρπ))00 resultsresults
0
0.25
0.5
0.75
1
-100 0 100
δ+- (deg)
C.L
.
B A B A RP R E L I M I N A R Y δδ++−−
[5, 63]ºat 68.3% C.L.
0
0.25
0.5
0.75
1
0 50 100 150
α (deg)
C.L
.
B A B A RP R E L I M I N A R Y
αα[75, 152]º
at 68.3% C.L.
no constraint at 2σ level
BaBar-CONF-06/037
δ+ − = arg(A+*A−) :the relative phase between the amplitudes of
B0 → ρ−π+ and B0 → ρ+π−
The constraint on α from B0 → (ρπ)0 is relatively weak – but free from ambiguities!
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 20
Recap of new resultsRecap of new results
Br (B0 → a± (1260)πm ) × Br (a± (1260) → πm π± π± ) = (16.6 ± 1.9 ± 1.5) × 10−61 1
Br (B0 → a±ρm ) × Br (a± → π+ π−π± ) < 30 × 10−6 (90% C.L.)1 1
Brρ0ρ0 = (1.16 +0.37 ± 0.27) × 10−6
First evidence, at 3.0σ−0.36 fL(B0 → ρ0ρ0)= 0.86+0.11 ± 0.05−0.13
Brρ±ρ0 = (16.8 ± 2.2 ± 2.3) × 10−6 fL(B± → ρ±ρ0) = 0.905 ± 0.042+0.023−0.027
Sππ = −0.53 ± 0.14 ± 0.02Cππ = −0.16 ± 0.11 ± 0.03
CP violation at 3.6σ
Brπ±π0 = (5.12 ± 0.47 ± 0.29) × 10−6
Brπ0π0 = (1.48 ± 0.26 ± 0.12) × 10−6
Cπ0π0 = −0.33 ± 0.36 ± 0.08
fL(B0 → ρ+ρ−) = 0.977 ± 0.024+0.015−0.013
Br ρ+ρ− = (23.5 ± 2.2 ± 4.1) × 10−6
BB00 →→ ((ρπρπ))00:: see page 18see page 18
Slong = −0.19 ± 0.21+0.05−0.07
ρρ
Clong = −0.07 ± 0.15 ± 0.06ρρ
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 21
(deg)α0 20 40 60 80 100 120 140 160 180
1 -
CL
(deg)α0 20 40 60 80 100 120 140 160 180
1 -
CL
CKM fit meas. in fitαno
BABARρ ρ →B π ρ →B
π π →B
Combined
0
0.2
0.4
0.6
0.8
1
ICHEP 2006
CKMf i t t e r
CKM fitno α in fit
169.7°
α ∈ [164, 176]º at 68.3% C.L.
Global fits for the value ofGlobal fits for the value of αα
CKMfitter Group (J. Charles et al.), Eur. Phys. J. C41, 1-131 (2005), [hep-ph/0406184], updated results and plots available at http://ckmfitter.in2p3.fr
M. Ciuchini, G. D'Agostini, E. Franco, V. Lubicz, G. Martinelli, F. Parodi, P. Roudeau, A. Stocchi, JHEP 0107 (2001) 013 [hep-ph/0012308],
updated results and plots available at http://utfit.roma1.infn.it
Please see talks by S. Please see talks by S. T'JampensT'Jampens ((CKMfitterCKMfitter) and V. ) and V. VagnoniVagnoni ((UTfitUTfit) for details) for details
97.5°
α ∈ [86, 114]ºat 68.3% C.L.
Two interpretations currently exist that convert the B → ππ, ρπ, ρρ measurements to constraints on α :
CKMfitter talk: 17:30 tomorrow UTfit talk: 17:48 tomorrow
Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 22
Summary and outlookSummary and outlook
The ability of existing B-meson factories to measure the angle α with a precision
of a few degrees crucially depends on the developments in measuring the
branching fractions and CP parameters in B0 → ρ0ρ0 and B0 → π0π0
The BaBar experiment has observed evidence of
• Time-dependent CP violation in B0 → π+π−
• The decay process B0 → ρ0ρ0
and improved the precision of other measurements related to the extraction of α.
The extraction of α depends significantly on the statistical and theoretical treatment; The larger of the CKMfitter and UTfit 68.3% C.L. intervals is α ∈ [86, 114]º (CKMfitter)