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1Mahalaxmi Krishnamurthy Beauty 2003
Measurement of time dependentCP violation in B → φKs
Measurement of time dependentCP violation in B → φKs
Mahalaxmi KrishnamurthyUniversity of Tennessee
BaBar CollaborationBeauty 2003
CMU, Pittsburgh
2Mahalaxmi Krishnamurthy Beauty 2003
• Decays dominantly through penguin amplitudes (gluonic & EW), tree small:
e.g.
• CP violation from interference of decay amplitudes into CP eigenstate: B0 → φKs and B0 → B0-bar → φKs
b-> sss Decays
• Estimate hadronic pollution (rescattering) using flavor SU(3) relations (30% breaking) between (measured) decay rates of charmless quasi-twobody decays e.g. [Grossman, Ligeti, Nir, Quinn, hep-ph/0303171] worst case scenario today: | sin2β(φKs) – sin2β(J/ψKs) | < 25%
• Decay exclusively through penguin : | sin2β(φKs) – sin2β(J/ψKs) | < 4%
With more data, smaller bounds: 1 ab-1 expect ~10%
3Mahalaxmi Krishnamurthy Beauty 2003
BaBar Detector
110 fb-1
Lum
inos
ity f
b-1
deliv
ered
reco
rded
Off Peak
EMC
DCH
SVT
IFR
1.5T Magnet
DIRC
e-
e+
4Mahalaxmi Krishnamurthy Beauty 2003
Measuring sin(2ββββ) at the Asymmetric B-Factory
Time dependent asymmetry:
µ+, e+, K++++
e- : 9 GeV
φ φ φ φ
K+
K−
KS
π−
π+
Btag
∆z
e+ 3 GeV B-Flavor Tagging
ExclusiveB Meson
Reconstruction
BCP : φKs, φKl, J/ψ Ks ..
BCP
Btag : Xl+, XK+, Xπs-
(B flavor sample)
)sin()cos()()( tmStmCtRR
RRta ddf ff ∆+∆−=
+−= C S
5Mahalaxmi Krishnamurthy Beauty 2003
Event Variables
Energy-substituted mass:MES= [s/2 + pΥpB)2/EΥ
2-pB2]1/2
Energy difference: ∆∆∆∆E = EB* - s0.5/2
signal events : 70 ±±±±9.0purity : 61 ±±±±0.1%
MES (GeV/c2) ∆E (GeV)
Number of signal events is consistent with published branching fraction.
(EΥ, pΥΥΥΥ), (EB,pB) 4 momenta of Υ(4S) and B in laboratory frame, EB* reconstructed B energy in center of mass frame
Eve
nts
/(2.
5 M
eV/c
2 )
abs(∆E)< 0.06 GeV 5.27<MES< 5.29 GeV/c2
6Mahalaxmi Krishnamurthy Beauty 2003
Event Variables
Helicity angle: - angle(K, B) in φ-rest frame
*Υ(4S) rest frame
Fisher discriminant: linear combination of - cosθT (thrust angle*) - cosθB (emission angle* w.r.t. z-axis) - momentum-weighted Legendre polynomials
side band data
SignalMC
F = a0cosθT+ a1cosθB + a2ΣpiL0(θi ) + a3ΣpiL2(θi )
7Mahalaxmi Krishnamurthy Beauty 2003
• Tagging performance evaluated from data using B flavor sample
• Tags grouped into 4 mutually exclusive categories:
Q = Σ ε(1-2ω)2
8.10.8 3.9 9.5Lepton
10.71.1 9.616.3Kaon I
7.33.419.319.4Kaon II
2.7 4.031.820.5Inclusive
65.7
ε (%) ω (%) ∆ ω (%)
28.7 ±±±± 0.7Total
Q (%)Categoryefficiency mistag rate tag difference
6.8
11.7
13.9
14.6
φKs signal events
Tagging
Tagging optimized for maximal value of Q
σσσσ(S) ~ 1/√√√√ N Q
8Mahalaxmi Krishnamurthy Beauty 2003
J/ψ Ks
φφφφKs
Vertexing (ΦΦΦΦK % J/ΨΨΨΨ K)
φ→ Κ+Κ−
J/ψ → l+l−
Opening angles quite different:
φ in B (Y(4S) )
K+
K-
θH
B->φ K : - large Q-value - helicity angle ~ cos2θ
B vertex z resolutions :Bcp ~ 50 µmBtag ~ 170 µm
Resolution dominated by the tag side
cosθH
9Mahalaxmi Krishnamurthy Beauty 2003
• Comparable σ(∆t) distributions in J/ψ Ks and φKs
• Background Resolution Function:
)}()1()/({
)];8,0()));((,([)(
tftExpf
tpspsGttscalebiasGtR
B
outliericore
∆•−+∆•⊗
∆+∆∆=∆
δτ
σ
∆∆∆∆t Resolution
• Signal Resolution Function:
);8,0()3,(
)));((,()1()(
tpspsGfpsbiasGf
ttscalebiasGfftR
outlieroutliertailtail
itagcoreoutliertail
∆++
∆∆−−=∆ σ
- Established by extensive test with Monte Carlo (MC) events- Final parameters obtained from B flavor data in simultaneous fit with CP data
σ(∆t) (ps)
J/ψKs φKs
10Mahalaxmi Krishnamurthy Beauty 2003
• Fix parameters (yields) that depend exclusively on CP sample• Float parameters that depend on B flavor sample• Total 40 parameters:
• Use 86200 B-flavor, 2138 φKs(π+π-)• Maximum likelihood fit:
L = L(MES) x L(∆E) x L(F ) x L(cosθH) x L(∆t)
4FractionsTag
Bkg. dilution asym.
Bkg. Dilution
Sig. dilution asym.
Sig. Dilution
Bkg. time evolution.
Bkg. Resolution
Sig. Resolution
S and C
40TOTAL
4
4
4
4
6
3
9∆t
2CP
Tested with J/ψ Ks data, MC data mockfit and Toy MC.
CP Fit Strategy
11Mahalaxmi Krishnamurthy Beauty 2003
charmonium modes world average
Zoom into the signal region (mES>5.27GeV, |∆E| < 0.06 GeV)
Time Dependent CP Fit for φφφφKs
Raw asymmetry:
WAS = 0.736 http://www.slac.stanford.edu/xorg/hfag
S = 0.45 ±±±± 0.43C = -0.38 ±±±± 0.37
statistical error only
12Mahalaxmi Krishnamurthy Beauty 2003
• Standard Model: expect S=0 and C=0
S = 0.23 ±±±± 0.24C = - 0.14 ±±±± 0.18
Time Dependent CP Fit for φφφφK+
signal events : 252 purity : 76 ±±±±0.1%
Use φK+ as control sample
MES (GeV/c2)
13Mahalaxmi Krishnamurthy Beauty 2003
Systematic Uncertainties
14Mahalaxmi Krishnamurthy Beauty 2003
Old result: Fit to φKs, Ks →π+π- and Ks → π0π0 sample combined(80 fb-1) S = -0.18 ± 0.51 C = -0.80 ± 0.38
Old Ks →π+π– only: S = -0.12 ± 0.52 C = -0.77 ± 0.41
Overlap between reprocessed (new) Run1+2 and old Ks →π+π– (80% overlap)
Old Ks →π+π– : S = 0.02 ± 0.55 C = -0.57 ± 0.44
New Ks →π+π– : S = 0.05 ± 0.51 C = -0.25 ± 0.48
New+Run3 Ks →π+π– : S = 0.45 ± 0.43(110 fb-1) C = -0.38 ± 0.37
The move ……..
∆∆∆∆S ~ 0.0∆∆∆∆C ~ 0.3
15Mahalaxmi Krishnamurthy Beauty 2003
The Understanding
% change in tag due to reprocessing : ~ 8%
~ 3 events flip tag around ∆t = 0
Low statistics channels are prone to fluctuations !Low statistics channels are prone to fluctuations !
old sample : F+ - F- = 5 eventsnew sample : if all 3 flip events are B0 or B0 tags (F+ - F- = 2 or 8 ) ∆C ~ ±±±±0.3 ∆S ~ 0.0- swap of the samples confirms the effect
=> change of result covered by statistical error.
-> F± integrated rate of B0/B0
tagged events-> average dilution <D>=0.61±0.04
-
cp
16Mahalaxmi Krishnamurthy Beauty 2003
More results
•B (B0→ φφφφK0) = (8.4 +1.5 ± 0.3) x 10-6
•B (B+ → φφφφK+) = (10.0 +0.9 ± 0.5) x 10-6
•B (B+ → φπφπφπφπ+) < 0.41 x 10-6
•Acp(B+ → φφφφK+) = 0.04 ± 0.09 ± 0.01
-1.3
-0.8
C (B+ → φφφφK+) = -0.14 ± 0.18 Acp = 0.05 ± 0.07
C (B0 → φφφφKs) = -0.38 ± 0.37 Acp = 0.14 ± 0.14
⇒ the two independent methods give the same result of Acp in φK+
in 80 fb-1
hep-ex/0309025
in 110 fb-1
time dependent:
17Mahalaxmi Krishnamurthy Beauty 2003
- Measured time dependent asymmetry in B0 -> φφφφKs(ππππ+π π π π -). - More CP events are needed by increase of luminosity and by including other channels e.g. φφφφKl, φφφφKs(ππππ 0π π π π 0).
- Expectation for the error in 300 fb-1 : σ σ σ σ (S) = 0.26 σ σ σ σ (C ) = 0.17
Summary / Outlook
18Mahalaxmi Krishnamurthy Beauty 2003
19Mahalaxmi Krishnamurthy Beauty 2003
Current status of S
average
20Mahalaxmi Krishnamurthy Beauty 2003
S = 0.45 ±±±± 0.43
• 15% correlation
Time Dependent CP Fit for φφφφKs
S
C = -0.38 ±±±± 0.37
C