with the babar detector - university of pennsylvania · 2002-05-22 · with the babar detector...
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![Page 1: with the BaBar Detector - University of Pennsylvania · 2002-05-22 · with the BaBar Detector Shahram Rahatlou University of California, San Diego For the BaBar CollaborationBaBar](https://reader034.vdocuments.net/reader034/viewer/2022042807/5f80a649798ab942a73b3d3f/html5/thumbnails/1.jpg)
Measurement of sin2βwith the BaBar Detector
Shahram RahatlouUniversity of California, San Diego
For the BaBarBaBar Collaboration
Flavor Physics and CP Violation Conference
Philadelphia, 16 May 2002
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FPCP, 16 May 2002 Shahram Rahatlou 2
CP Violation in Standard ModelStandard Model with 3 generations accommodates CP violation through a phase in CKM matrix
Unitarity of the CKM Matrix * * * 0ud ub cd cb td tbV V V V V V+ + =
β
α
γ
VtdVtb*
VudVub*
VcdVcb*
Measure sin2β in B0
� J/ψ KS,L,K*0
B0� χc KS
B0� ηc KS
B0� D*D(*)
B0� Φ Ks
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FPCP, 16 May 2002 Shahram Rahatlou 3
CP Violation due to Mixing and Decay
f f
f
0 | |4
0 |f
|4
( , ) e [1 ]
( , ) e [1 ]
sin( )
sin(
cos( )
cos( ) )
dt
phys CP
tphys CP
d
d d
f B f t
f
C m t
C
S m t
B f S m tm tt
−Γ ∆Γ
−Γ ∆Γ
→ = + −∆
+ ∆∆
∆
→ = −
CP
CP
CP
ff
f
Aqλp A
= ⋅
CP
CP
2f
f 2f
1 | λ |
1 | λ |C
−=
+
Probe of direct CP violation:CPfλ 1≠
CP
CP
ff 2
f
2 Imλ1 | λ |
S =+
Sensitive to phase of λ even without direct CP Violation
B0(t) fCP
B0Initialstate
Flavor eigenstate
B0(t) fCP
B0Initialstate
Flavor eigenstate
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FPCP, 16 May 2002 Shahram Rahatlou 4
Golden Decay Mode: B0 → J/ψ K0S
� Theoretically clean way to measure the phase of λ (sin2β)� Clean experimental signature� Large branching fraction compared to other CP eigenstates
0L,S
2
J/ Kλ i
CPe βψ η −=
Time-dependent CP asymmetry
sin 2( ) sin( )CP CPA t m tβ= −η ∆
0B0B
u,c,t
u,c,t
W−W+
d
b
0 0
0 0
/
/CP S
LCP
B J K
B J K
ψψ
→
→
K0 mixing
�ηCP = +1
� B0 � J/ψ K0
L
� ηCP = -1 � B0
� J/ψ,ψ(2s),χc1 K0S
“Golden Modes”
0K
b
c
s
c
d
ψ/J
d
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FPCP, 16 May 2002 Shahram Rahatlou 5
PEP-II Asymmetric B-Factory at SLAC
9.44 9.46
Mass (GeV/c2)
0
5
10
15
20
25
σ (e
+e- →
Had
rons
)(nb
) ϒ(1S)
10.00 10.020
5
10
15
20
25
ϒ(2S)
10.34 10.370
5
10
15
20
25
ϒ(3S)
10.54 10.58 10.620
5
10
15
20
25
ϒ(4S)
(4 )e e S BB+ − → Υ →B B production threshold
� 9 GeV e- on 3.1 GeV e+
� ϒ(4S) boost in lab frame
� βγ = 0.55
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FPCP, 16 May 2002 Shahram Rahatlou 6
B-Factory Performance
PEP-II delivered: 89.8 fb-1
BABAR recorded: 85.4 fb-1 (includes 8.8 fb-1 off peak)161 million B’s available !!
PEP-II top luminosity: 4.60 x 1033cm-2s-1
(design 3.0 x 1033)
Top recorded Lumi/week: 1.8 fb-1
Top recorded Lumi/24h: 303 pb-1
Top recorded Lumi/8h: 105 pb-1
BABAR logging efficiency: > 96%
56 fb-1 analyzedfor CP
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FPCP, 16 May 2002 Shahram Rahatlou 7
The BaBar Detector
Cerenkov Detector(DIRC)
1.5 T solenoid Electromagnetic Calorimeter
Drift Chamber
Instrumented Flux ReturnSilicon Vertex Tracker
e+ (3.1 GeV)
e-(9 GeV)
SVT: 97% efficiency, 15 µm z hit resolution (inner layers, perp. tracks)SVT+DCH: σ(pT)/pT = 0.13 % ×××× pT + 0.45 %DIRC: K-π separation 4.2 σ @ 3.0 GeV/c � 2.5 σ @ 4.0 GeV/cEMC: σE/E = 2.3 %⋅E-1/4 ⊕⊕⊕⊕ 1.9 %
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FPCP, 16 May 2002 Shahram Rahatlou 8
+e-e Tag vertex
reconstructionTag vertex
reconstruction
FlavorTaggingFlavor
Tagging
Exclusive B Meson and Vertex Reconstruction
Exclusive B Meson and Vertex Reconstruction
Event Topologyz
∆z∆t βγ c≈ < >
Brec
Btag( )4sΥ
βγΥ(4S) = 0.55
z∆Start the Clock
-π
0sK
+π
+µ-µ
Coherent BB pair
B0
B0
µ−
Κ−
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FPCP, 16 May 2002 Shahram Rahatlou 9
Ingredients for Time-Dependent sin2β Analysis
B vertex ReconstructionFlavor Tagging
B0 B0 Mixing CP Asymmetries
Reconstruction of neutral B mesons in flavor eigenstates
Reconstruction of neutralB mesons in CP eigenstates
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FPCP, 16 May 2002 Shahram Rahatlou 10
Cabibbo-favored hadronic decays
“Open Charm” decays
Fully Reconstructed B sample
B0
ducb→
( )b c c s→
0 *0/ ( )B J K Kψ π+ −→/ , (2 )B J K S Kψ ψ+ + +→
0( )B D π− ∗ −→0
1( )B D π /ρ /a +∗ − + +→
Hadronic decays into final stateswith Charmonium
cm 2 cm 2ES beam Bm = (E ) - (p ) [GeV]
~21000 signalPurity: 85%
~20000 signalPurity: 85%
B+
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FPCP, 16 May 2002 Shahram Rahatlou 11
Vertex and ∆t Reconstruction
� Reconstruct Brec vertex fromcharged Brec daughters
� Determine BTag vertex from � charged tracks not
belonging to Brec
� Brec vertex and momentum
� beam spot and Υ(4S) momentum
� High efficiency: 97%
� Average ∆z resolution is 180 µm (<|∆z|> ~ βγcτ = 260 µm)
� ∆t resolution function measured from data
Beam spot
Interaction Point
BREC Vertex
BREC daughters
BREC direction
z BTAG directionTAG Vertex
TAG tracks
V0s
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FPCP, 16 May 2002 Shahram Rahatlou 12
NN output
Not U
s ed
B Flavor Tagging Methods
For electrons, muons and Kaons use the charge correlation
b c
d d
l-
ν
B0 D, D*
W-
0
0
l
l
B
B
−
+
→
→
Lepton Tag
Each category is characterized by the probability of giving the wrong answer (mistag fraction w)
Multivariate analysis exploiting the other kinematic information of the event, e.g.,� Momentum spectrum of the charged particles� Information from non-identified leptons and kaons� Soft π from D* decay Neural Network
Hierarchical Tagging CategoriesHierarchical Tagging Categories
b
d
B0
W- W+
c sK-
d
0
0
0
0
kaons
kaons
Q
Q
B
B>
�<
�
�
�
Kaon Tag
uu
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FPCP, 16 May 2002 Shahram Rahatlou 13
( )( )UnmixMix
f (∆ t) 1 1 2 cos( )4
Bd
d
|∆ t |/τ
Bd
e ∆t∆mw Rτ
−� �� �� �� �� �
= × ± − ⊗
Fit Parameters∆md 1Mistag fractions for B0 and B0 tags 8Signal resolution function 2 x 8Empirical description of background ∆t 16+3B lifetime fixed (PDG 2000) τB = 1.548 ps
Mixing Likelihood Fit
Unbinned maximum likelihood fit to flavor-tagged B0 sample
44 total free parameters
All ∆t parameters extracted from data
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FPCP, 16 May 2002 Shahram Rahatlou 14
B0B0 Mixing Fit Result
∆∆∆∆∆∆∆∆mmd d = 0.516 ± 0.016 (stat) ± 0.010 (syst) ps= 0.516 ± 0.016 (stat) ± 0.010 (syst) ps--11
( )unmixed mixedAsymmetry( ) 1 2 cos( )
unmixed mixed d
N( ) N( )t w ∆m ∆t
N( ) N( )
−∆ = ≈ − ×+
hep-ex/0112044Accepted by PRL
29.7 fb-1
World Average: 0.496 ± 0.007 ps-1
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FPCP, 16 May 2002 Shahram Rahatlou 15
Yields for modes with Ks
94%995Total
94%60χc1 Ks
89%119Ψ(2S) Ks
89%123J/Ψ Ks(π0π0)
96%693J/Ψ Ks(π+π-)
PurityNtaggedSample
cm 2 cm 2ES beam Bm = (E ) -(p )
J/Ψ Ks(KS → π+π-)
J/Ψ Ks(KS → π0π0)
χc1 Ks
Ψ(2S) Ks
1999-2001 data62 x 106 BB pairs56.4 fb-1 on peak
Energy-substituted mass
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FPCP, 16 May 2002 Shahram Rahatlou 16
J/Ψ KL and J/Ψ K*0 Yields
Signal
J/ψ Bkg
Fake J/ψ Bkg
• Data
79%1850All CP83%113J/Ψ K*0
57%742J/Ψ KL
94%995(cc)Ks
PurityNtaggedMode
J/ψ background composition and CP contentfrom inclusive J/ψ Monte CarloFake J/ψ background from data sidebands
J/Ψ K*0
(K*0 → KSπ0)
Full angular analysis
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FPCP, 16 May 2002 Shahram Rahatlou 17
00tag BB = 00
tag BB =
perfectflavor tagging & time resolution
∆t Spectrum of CP Events
Mistag fractions wAnd resolution function R
1 (1 2 )sin4
sin2 ( )d
d
B
B|∆t|/τ
f def (∆t) η ∆mτ w ∆β t
� �� �� �� �� �� �� � �� �� �
�� �� ��
−= × − ⊗� R
CP PDF
00tag BB = 00
tag BB =
realistic mis-tagging & finite time resolution
1 (1 2 )cos( )4
dB
Bd|∆t|/τ
mixing, dwef (∆t) ∆m ∆tτ
� �� �� �� �� �� � �� � �� ��
−± = × ± − ⊗R
Mixing PDFdetermined byflavor sample
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FPCP, 16 May 2002 Shahram Rahatlou 18
sin2β Likelihood Fit
Combined unbinnedmaximum likelihoodfit to ∆t spectra of flavor and CP sample
35 total free parameters
� All ∆t parameters extractedfrom data
� Correct estimate of the error and correlations
Fit Parameterssin2β 1cos2β 1
Mistag fractions for B0 and B0 tags 8Signal resolution function 8Empirical description of background ∆t 17B lifetime fixed (PDG 2000) τB = 1.548 psMixing Frequency fixed (PDG 2000) ∆md = 0.472 ps-1
tagged flavor sample
tagged CP samplesFrom J/ψ K*0 sample
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FPCP, 16 May 2002 Shahram Rahatlou 19
Null Test in B Flavor Sample
B flavor sample as control sample for CP analysis
-0.01 ± 0.03B-� D(*)0 π−
-0.05 ± 0.08B-� J/ψ,χc K-
0.00 ± 0.09B0� J/Ψ K*0(K+π-)
-0.01 ± 0.03B0� D(*)- π+, ρ+, a1
+
“sin2β”Sample
No asymmetry where noneis expected!
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FPCP, 16 May 2002 Shahram Rahatlou 20
CP Asymmetry in ηCP=-1 and ηCP=+1 Samples
471 events
sin2β = 0.76 ± 0.10
524 events
sin2β = 0.73 ± 0.19
392 events
350 events
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FPCP, 16 May 2002 Shahram Rahatlou 21
sin2β Results
Consistency of CP channels P(χ2) = 70%
sin2sin2ββ = 0.75 = 0.75 ±± 0.090.09
Goodness of fit(CP Sample): P(Lmax>Lobs) > ~50%
cos2β = +3.3+0.6-1.0
+0.6-0.7
• Using theoretically preferredchoice of strong phases
• Need more statistics!
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FPCP, 16 May 2002 Shahram Rahatlou 22
Sources of Systematic Error
� Description of background events 0.019� CP content of background components� Event-by-event signal probability
� ∆t resolution and detector effects 0.015� Silicon detector misalignment� ∆t resolution model
� Fixed lifetime and oscillation frequency 0.014
� Monte Carlo statistics 0.014
� Composition and content of J/ψ KL background 0.013
Total systematic error: 0.04
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FPCP, 16 May 2002 Shahram Rahatlou 23
Search for Direct CP in Golden Modes
� In the Standard Model |λ| = 1
� Probe New Physics beyond the Standard Model� No constraint on |λ|
CP
CP
CP
ff 2
f
2 Imλ0.76 0.10
1 | λ |S = = ±
+
CP
CP
CP
ff
f
Aqλp A
= ⋅ Amplitude ratio
Weak Phase
CPf 0.93 0.06| λ | 0.03= ± ±
f f cos() )( sin( )dC dP C m tSA t m t= ∆∆ −
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FPCP, 16 May 2002 Shahram Rahatlou 24
The Unitarity Triangle
Method as in Höcker et al, Eur.Phys.J.C21:225-259,2001(also other recent global CKM matrix analyses)
One solution for β is consistent with
measurements of sides of Unitarity
Triangle
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FPCP, 16 May 2002 Shahram Rahatlou 25
New sin2β World Average
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FPCP, 16 May 2002 Shahram Rahatlou 26
New Modes to Measure sin2β
� Enlarge b � ccs sample� B0
� ηc Ks
� Hadronic decays of J/ψ
� New tests of the Standard Model� Cabibbo suppressed modes in b � ccd: B�D*D(*)
� Same weak phase but unknown contribution from penguins� Not pure CP eigenstate
� Pure penguin b � sss modes: B0 � φ Ks
� Experimentally clean� Small branching fraction: O(10-5)
� Cabibbo suppressed mode: B0 � J/ψ π0
� Experimentally more challenging� Provides valuable information on penguin contribution
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FPCP, 16 May 2002 Shahram Rahatlou 27
New Charmonium mode
B0→ ηc Ks
ηηηηc → KsK±π+,K+K-π0
sin2sin2ββ = 0.43 = 0.43 ±± 0.46 0.46 ±± 0.080.08
∆t (ps)∆t (ps)
112 events71% purity
Higher multiplicity in the final state
Asym
met
ry
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FPCP, 16 May 2002 Shahram Rahatlou 28
CP Asymmetry in D*D* and D*D
� Vector-Vector final state� Mixture of CP-odd and CP-even final states
� Fit only for coefficients
ACP(∆t) = SD*D* sin(∆m∆t) + CD*D* cos(∆m∆t)
SD*D* = -0.05 ± 0.45 ± 0.07
CD*D* = 0.12 ± 0.30 ± 0.03
D*D*
Ntag = 76Purity = 80%
D*DNtag = 85Purity = 52%
� Different time distribution for D*+D- and D*-D+
SD*+D- = -0.43 ± 1.41 ± 0.20
CD*+D- = 0.53 ± 0.74 ± 0.13
SD*-D+ = 0.38 ± 0.88 ± 0.05
CD*-D+ = 0.30 ± 0.50 ± 0.08
See Yury Kolomensky’s talk on Saturday for more details
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FPCP, 16 May 2002 Shahram Rahatlou 29
Conclusions and Prospects
� Updated measurement of sin2β with BaBar
� Going towards a precision measurement with 500 fb-1
� Systematic error to shrink with enlarged data sample
� Comparable statistical and systematic error of ≤ 0.03
sin2sin2ββ = 0.75 ± 0.09 (stat) ± 0.04 (syst)= 0.75 ± 0.09 (stat) ± 0.04 (syst)
hephep--ex/0203007ex/0203007 PreliminaryPreliminary