Measurements of the CP angle with the BaBar...
Transcript of 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
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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
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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
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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)
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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−
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Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 6
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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
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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
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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
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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
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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
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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
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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:
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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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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
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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
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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
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|∆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
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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
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Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 16
0
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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
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Alexandre V. Telnov (Princeton University)Measurements of the CP angle α with the BaBar experiment 17
∆t/σ(∆t)
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nts
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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
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data
projection of the fit result
signal misreconstructionexpected B backgroundcontinuum background
minimum of the three di-pion invariant masses
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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
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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
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[5, 63]ºat 68.3% C.L.
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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!
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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
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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
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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)