D 0 K Decays at CDF Karen Gibson University of Pittsburgh ICHEP 2008 080108 CP Asymmetries in B D 0 K Decays CP asymmetries in B D 0 K decays can be used to gain information about CKM angle ID: 493447
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Slide1
Measurement of CP Observables in B-D0K- Decays at CDF
Karen Gibson
University of Pittsburgh
ICHEP 2008
08/01/08Slide2
CP Asymmetries in B-D0K- Decays
CP asymmetries in B
-
D0K- decays can be used to gain information about CKM angle Use method devised by Gronau-London-Wyler (GLW) to construct CP asymmetries based on decay rates
g
= arg((-VudV*ub)/(VcdV*cb))
Note: Charge conjugates of B- and D0 decays are implied unless both are specifically discussed!
2Slide3
Current status of
As of FPCP 2007, B
-
D0K- asymmetries have been measured by Belle and BaBaRMeasurement is still quite statistically limitedAll additional measurements help significantlyCDF’s large sample of B
- decays gives opportunity to contribute significantly!
3Slide4
GLW MethodMeasure CP asymmetry between B+
D
CP
0K+ and B- DCP0K- Ambiguities
in g remainMeasure sin
g two possible solutionsRelative phase between f.s. final states
4Slide5
B-D0K- Decays
Consider flavor-specific and CP-even D
0
decaysCP-even: D0K+K-, D0 p
+p
-Flavor-specific: D0K-p+ Don’t consider CP-odd decays D0Ks0p0, D0Ks
0r0, D0Ks0w, D
0
K
s
0
j
Can’t easily reconstruct
p
0
,
r
0
,
w &
statistics too low in K
s
0j
5Slide6
CP Observables in GLW MethodStart with experimentally accessible observables:Construct CP observables:
6Slide7
Measurement of B-D0K- at CDF
Use data collected with
with
CDF’s displaced track trigger detector between February 2002 and February 2006 Measure relative BR using kinematic information and particle-flavor identification in simultaneous maximum likelihood fitInvariant mass, particle momenta, dE/
dxFirst measurement at a
hadron collider!7Slide8
Selection to Reduce BackgroundsOptimize sensitivity to ACP+Fit
in mass window m(D
0
p) [5.17, 5.60] GeV/c2Reduce backgrounds from decays other than B-D0(*)p
-Veto event in ±2
s around B-J/K- to eliminate contamination in B-D0[ p+p-]K- sampleMust include background events from
B- K- K+ K- in likelihood fit
8Slide9
Reconstructed B- after Selection
N(B
-
D0
[ K-
p+]p-) ~ 7,500N(B-
D0[ K+K-]
p
-
) ~ 1,000
N(B
-
D
0
[
p
+
p
-
]
p
-
) ~ 250
D
0
K
-
p
+
D
0
K
+
K
-
D
0
p
+
p
-
9Slide10
Inputs to Likelihood FitVariables input to fitm(D0p
)
p
tot = pp/K + pD0a = 1 - pp/K/pD
0, pp/K
pD0 -(1 - pD0/pp/K), pp/K pD0k = (dE/dxmeas
– dE/dxexp(p))/ (dE/dxexp(K) – dE/dxexp(
p
))
10Slide11
Maximum Likelihood FitTotal likelihood written for each channel and charge
Simultaneously minimize all six likelihoods
Use MC to model correlations between
a and ptot in FDK, FDp, and FD*p PDFsUse mass sidebands for background Fbg PDF
11Slide12
Raw AsymmetriesCorrect raw numbersUse Monte Carlo to correct for relative efficiencies between decay modes
Also correct for small biases observed in pseudo-experiments
12Slide13
Systematic Uncertainties
Source
R
RCP+ACP+dE/dx0.00280.056
0.030Input B-
mass0.00020.0040.002D0*p- mass model0.00280.0250.006Combinatoric mass model0.0002
0.0200.001(a, ptot) model of combinatoric bg.
0.0002
0.100
0.020
(
a
, p
tot
) model of
D
0
p
-
0.0001
0.002
0.001
(
a
, p
tot
) model of
D
0
*
p
-
0.0007
0.004
0.002
(
a
, p
tot
) model of
D
0
K
-
0.0006
0.002
0.004
Bias
error
0.0001
0.005
0.003
MC statistics
0.002
-
-Total0.00450.120.04
13Slide14
ResultsFirst measurement of CP observables at a hadron
collider
will soon be submitted to PRD!14
R = 0.0745 ± 0.0043 (stat) ± 0.0045 (
syst)RCP+ = 1.30 ± 0.24 (stat) ± 0.12 (syst)ACP+ = 0.39 ± 0.17 (stat) ± 0.04 (syst)Slide15
Back-up15Slide16
Data SelectionOptimize selection for sensitivity to ACP+Use pseudo-experiments to choose value of cuts based on smallest expected error on ACP+
Table of selection requirements
Parameter
Valuec
3D2 13
pT(B)/(pT(B)+DR=1.0pT(trk))> 0.65Lxy(B)/sLxy(B)>
12Lxy(D)> 0.04 cmLxy(BD)>
0.01 cm
|d
0
(B)|
<
0.007 cm
p
T
(
p
/K )
>
2
GeV
/
c
DR(p,D
0)
< 2
16Slide17
Signal PDFsSignal probabilities FDK and
F
D
p include correlations between a and ptot Shapes of m(a, p
tot) and P(a
, ptot) are determined from CDF Monte Carlo that includes realistic detector simulationwhere
for a > 0
for
a
0
17Slide18
Background PDFsBackground probabilities FD*p
and
F
bg also include correlations between a and ptot PD*p (a, ptot) determined from CDF Monte Carlo that includes realistic detector simulation
Pbg
(a, ptot) determined from mass sidebands 18Slide19
Raw Yields from FitDecay
Raw Fraction
Raw Yield
B+ D0p+0.902 ± 0.006
3769 ± 68B
- D0p-0.902 ± 0.0063763 ± 68B+ D0K+
0.060 ± 0.005250 ± 26B- D0
K
-
0.064 ± 0.005
266 ± 27
B
+
D
CP
0
p
+
[K
+
K-
]
p
+
0.902 ± 0.017
498 ± 29
B
-
D
CP
0
p
-
[K
+
K
-
]
p
+
0.849 ± 0.017
509 ± 29
B
+
DCP0K+ [K+K-]K+0.060 ± 0.017
33 ± 11
B
-
D
CP
0
K
-
[K
+
K
-
]
K
+
0.116 ± 0.017
70
± 13
B
+
D
CP
0
p
+
[
p
+
p
-
]
p
+
0.902 ± 0.017
109 ± 14
B
-
D
CP
0
p
- [p+p-]p+0.849 ± 0.017139 ± 15B+ DCP0K+ [p+p-]K+0.060 ± 0.0177 ± 3B- DCP0K- [p+p-]K+0.116 ± 0.01719 ± 5
19Slide20
Extracting Asymmetry RatesUse fractions measured in fit times total number of B - events measured in each sample to determine number of events in individual components
e.g. N(B
-
D0 K- [K+K-]K-) = NKKK(1-fbg)(1-fD
p-fD*
p)Correct for relative efficiencies between decay modes using realistic MC20Slide21
Checks of FitCheck goodness of fit with relative likelihood
21