Measurement of CP Observables in B - D 0 K - Decays at CDF

MEASUREMENT OF CP OBSERVABLES IN B-D0K- DECAYS AT CDFKaren GibsonUniversity of PittsburghICHEP 200808/01/08

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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

= arg((-VudV*ub)/(VcdV*cb))Note: Charge conjugates of B- and D0 decays are implied unless both are specifically discussed!

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CURRENT STATUS OF As of FPCP 2007, B-

D0K- asymmetries have been measured by Belle and BaBaR Measurement is still

quite statistically limited

All additional measurements help significantly CDF’s large sample of B-

decays gives opportunity to contribute significantly!

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GLW METHOD

Measure CP asymmetry between B+ DCP0K+ and B- DCP

0K-

Ambiguities in remain Measure sin two possible solutions

Relative phase between f.s. final states sinsin)()(2

)()(00

2020

----

--

-

KDBAKDBA

KDBAKDBA CPCP

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B-D0K- DECAYS

Consider flavor-specific and CP-even D0 decays CP-even: D0K+K-, D0 p+p-

Flavor-specific: D0K-p Don’t consider CP-odd decays

D0Ks0p0, D0Ks

0r0, D0Ks0w, D0Ks

0j Can’t easily reconstruct p0, r0, w & statistics too low in Ks

0j

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CP OBSERVABLES IN GLW METHOD Start with experimentally accessible

observables:

Construct CP observables:

,)()()()(

00

00

--

--

pp DBBRDBBRKDBBRKDBBRR

)()()()(

00

00

-

-

-

-

pp CPCP

CPCP

DBBRDBBRKDBBRKDBBRR

-

-

-

-

-

CP

CPCP

CPCPCP

RrKDBBRKDBBRKDBBRKDBBRA

/sinsin2)()()()(

00

00

,coscos21 2 rrRRRCP

)(

)(where

0

0

--

--

KDBA

KDBAr

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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 fit Invariant mass, particle momenta, dE/dx First measurement at a hadron collider!

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SELECTION TO REDUCE BACKGROUNDS

Optimize sensitivity to ACP+ Fit in mass window m(D0p) [5.17, 5.60] GeV/c2

Reduce backgrounds from decays other than B-D0(*)p-

Veto event in ±2s around B-J/K- to eliminate contamination in B-D0[ pp-]K- sample Must include background

events from B- K- K K- in likelihood fit

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RECONSTRUCTED B- AFTER SELECTION

N(B-D0[ K-p]p-) ~ 7,500

N(B-D0[ K+K-]p-) ~ 1,000

N(B-D0[ pp-]p-) ~ 250

D0 K-p

D0 K+K- D0 p+p-

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INPUTS TO LIKELIHOOD FIT Variables input to fit

m(D0p) ptot = pp/K + pD0

a = 1 - pp/K/pD0, pp/K pD0

-(1 - pD0/pp/K), pp/K pD0

k = (dE/dxmeas – dE/dxexp(p))/ (dE/dxexp(K) – dE/dxexp(p))

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MAXIMUM LIKELIHOOD FIT Total 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 PDFs Use mass sidebands for background Fbg PDF

)),(,,())),(,,()),(,,(

)),(,,()1(()1((

0

0**

0

0*

kpakpakpa

kpa

pppp

pp

DmpFfDmpFfDmpFf

DmpFfffL

totbgbg

totDDtotDD

Nevents

ktotDKDDbg

---

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RAW ASYMMETRIES

Correct raw numbers Use Monte Carlo to correct for relative efficiencies

between decay modes Also correct for small biases observed in pseudo-

experiments

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SYSTEMATIC UNCERTAINTIESSource R RCP+ ACP+

dE/dx 0.0028 0.056 0.030Input B- mass 0.0002 0.004 0.002D0*p- mass model 0.0028 0.025 0.006Combinatoric mass model 0.0002 0.020 0.001(a, ptot) model of combinatoric bg.

0.0002 0.100 0.020

(a, ptot) model of D0p- 0.0001 0.002 0.001(a, ptot) model of D0*p- 0.0007 0.004 0.002(a, ptot) model of D0K- 0.0006 0.002 0.004Bias error 0.0001 0.005 0.003MC statistics 0.002 - -

Total 0.0045 0.12 0.04

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RESULTS

First measurement of CP observables at a hadron collider will soon be submitted to PRD!

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)

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BACK-UP

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DATA SELECTION Optimize 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 Valuec3D

2 13pT(B)/(pT(B)+DR=1.0pT(trk))

> 0.65

Lxy(B)/sLxy(B) > 12

Lxy(D) > 0.04 cmLxy(BD) > 0.01 cm|d0(B)| 0.007 cmpT(p/K ) > 2 GeV/cDR(p,D0) 2

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SIGNAL PDFS Signal probabilities FDK and FDp include correlations

between a and ptot

Shapes of m(a, ptot) and P(a, ptot) are determined from CDF Monte Carlo that includes realistic detector simulation

)(),()),()(()),(,,( 00 kaapkpa PpPpmDmGDmpF tottotitoti -

---

--

--

22

22

222222

))2/()1((

))2/()1((

))2/((2),( 0

aa

aa

aa

p

p

totK

tot

totDKBtot

pm

pm

pmmmmpmwhere

2222

22222

))2/(())2/((

))2/()1((2 0

aa

aa

p

p

---

---

totKtot

totDKB

pmpm

pmmmm

for a > 0

for a 0

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BACKGROUND PDFS Background probabilities FD*p and Fbg 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

)(),())(()),(,,( 00 kapkpa PpPDmBGDmpF tottoti

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RAW YIELDS FROM FITDecay Raw Fraction Raw YieldB+ D0p+ 0.902 ± 0.006 3769 ± 68B- D0p- 0.902 ± 0.006 3763 ± 68B+ D0K+ 0.060 ± 0.005 250 ± 26B- D0K- 0.064 ± 0.005 266 ± 27B+ DCP

0p+ [K+K-]p+ 0.902 ± 0.017 498 ± 29B- DCP

0p- [K+K-]p+ 0.849 ± 0.017 509 ± 29B+ DCP

0K+ [K+K-]K+ 0.060 ± 0.017 33 ± 11B- DCP

0K- [K+K-]K+ 0.116 ± 0.017 70 ± 13B+ DCP

0p+ [p+p-]p+ 0.902 ± 0.017 109 ± 14B- DCP

0p- [p+p-]p+ 0.849 ± 0.017 139 ± 15B+ DCP

0K+ [p+p-]K+ 0.060 ± 0.017 7 ± 3B- DCP

0K- [p+p-]K+ 0.116 ± 0.017 19 ± 5

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EXTRACTING ASYMMETRY RATES Use 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-fDp-fD*p

Correct for relative efficiencies between decay modes using realistic MC

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CHECKS OF FIT Check goodness of

fit with relative likelihood

)()()(

backgroundpdfDKBpdfDKBpdfRL