Measurement Of CP Asymmetry Research Articles

Measurement of time-dependent CP asymmetries and the CP-odd fraction in the decay B0-->D(*+)D(*-).

We present a measurement of time-dependent CP asymmetries and an updated determination of the CP-odd fraction in the decay B0-->D(*+)D(*-) using a data sample of 88x10(6)BB pairs collected by the BABAR detector at the PEP-II B Factory at SLAC. We determine the CP-odd fraction to be 0.063+/-0.055(stat)+/-0.009(syst). The time-dependent CP asymmetry parameters Im(lambda(+)) and /lambda(+)/ are determined to be 0.05+/-0.29(stat)+/-0.10(syst) and 0.75+/-0.19(stat)+/-0.02(syst), respectively. The standard model predicts these parameters to be -sin(2beta and 1, respectively, in the absence of penguin diagram contributions.

Improved measurement of the partial-rateCPasymmetry inB+→K0π+andB−→K0π−decays

We report an improved measurement of the partial-rate CP asymmetry in B±→K0π± decays. The analysis is based on a data sample of 85×106 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB e+e− storage ring. We measure ACP(K0π±)=0.07−0.08+0.09−0.03+0.01, where the first and second errors are statistical and systematic, respectively; the corresponding 90% confidence-level interval is −0.10<ACP(K0π±)<0.22. Received 24 April 2003DOI:https://doi.org/10.1103/PhysRevD.68.011103©2003 American Physical Society

New physics contributions to theB→φKSdecay

Recent measurements of the time-dependent CP asymmetry of the $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\varphi}{K}_{S}$ decay give results whose central values differ from standard model expectations. It is shown how such data can be used to identify new physics contributions in a model-independent manner. In general, a sizable new amplitude with nontrivial weak and strong phases would be required to explain current data. An improvement in the quality of data will allow one to form a more definite conclusion.

Measurements of time dependent CP asymmetry in B → VV decays with BELLE

A study of CP violation in B → J/ψK ∗(K 0 Sπ 0 ) decays by time dependent angular analysis is discussed. Status of time independent analyses for other B → VV decays is also reported. The data used for the analyses are taken with the Belle detector at KEK.

Study of CP asymmetries in charmless hadronic B decays: Toward a measurement of α

We present preliminary measurements of time-dependent CP asymmetries in neutral B meson decays to π + π − and π + π − π 0 final states, where the latter is measured in the region of the Dalitz plane dominated by the ϱ resonance. We also present preliminary measurements of the branching fraction for the decay B + → π + π 0 and an improved upper limit for B 0 → π 0 π 0, both of which are needed to extract the CP parameter α from the time-dependent dependent CP asymmetry in the π + π − channel. These results are obtained from a data sample of approximately 88 million γ(4 S) → B B decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC.

Improving bounds on γ in B±→DK± and B±,0→DXs±,0

In view of recent experimental progress in rate and CP asymmetry measurements in B±→DK±, we reconsider information on the weak phase γ which can be obtained from these processes. Model-independent inequalities are proven for sin2γ in terms of two ratios of partial rates for B±,0→DXs±,0, where Xs is any multiparticle charmless state carrying strangeness ±1. Good prospects are shown to exist for using these inequalities and CP asymmetry measurements in two body and multibody decays in order to improve present bounds on γ.

Measurements of sin 2α from the B factories

In this report, I review the experimental determination of the CKM angle α through the measurements of the time-dependent CP asymmetry of the decay B 0 → π + π − by the B aB ar and Belle experiments.

CP asymmetry in B-->phiK(S) decays in left-right models and its implications for Bs decays.

In left-right models the gluonic penguin contribution to b-->ss;s transition is enhanced by m(t)/m(b) due to the presence of (V+A) currents and by large values of loop functions. Together those effects may overcome the suppression due to the small left-right mixing angle xi less, similar 0.013. Two independent new phases in the B-->phiK(S) decay amplitude appearing in a large class of left-right models can modify the time-dependent CP asymmetry in this decay mode by O(1) and explain the recent BABAR and Belle CP asymmetry measurements in this channel. This scenario implies observable deviations from the standard model also in B(s) decays which could be measured at Tevatron and LHC.

Direct CP asymmetry of B→Xd,sγ in a model with vector quarks

We investigate the effect of vector quarks on the inclusive decays B -> X_d,s \gamma. We show that the branching ratio of B -> X_d \gamma can differ sizably from the SM and MSSM predictions, being enhanced to present experimental observability or suppressed such that present runs of the B factories would not observe it. Current measurements of the direct CP asymmetry (A_CP) for B -> X_s \gamma are sensitive to the contribution from B -> X_d \gamma. For a sufficiently enhanced BR(B -> X_d \gamma) we show that the dominant contribution to the combined asymmetry may be from B -> X_d \gamma. Thus any large value for A_CP should not immediately be attributed to B -> X_s \gamma, which stresses the importance of good K/pi separation.

New parametrization of the neutrino mixing matrix for neutrino oscillations

In this paper we study three active neutrino oscillations, favored by recent data from SuperK and SNO, using a new parametrization of the lepton mixing matrix $V$ constructed from a linear combination of the unit matrix $I$, and a hermitian unitary matrix $U$, that is, $V = \cos\theta I + i\sin \theta U$. There are only three real parameters in $V$ including the parameter $\theta$. It is interesting to find that experimental data on atmospheric neutrino dictates the angle $\theta$ to be $\pi/4$ such that the $\nu_\mu$ and $\nu_\tau$ mixing is maximal. The solar neutrino problem is solved via the MSW effect with a small mixing angle, with $U$ depending on one small parameter $\epsilon$. The resulting mixing matrix with just two parameters ($\theta$ and $\epsilon$) predicts that the oscillating probabilities for $\nu_e\to \nu_\mu$ and $\nu_e \to \nu_\tau$ to be equal and of the order $2\epsilon^2 = (0.25\sim 2.5)\times 10^{-3}$. The measurement of CP asymmetries at the proposed Neutrino Factories would also provide a test of our parametrization.

First-year experience with the BaBar silicon vertex tracker

Within its first year of operation, the BaBar Silicon Vertex Tracker (SVT) has accomplished its primary design goal, measuring the z vertex coordinate with sufficient accuracy as to allow the measurement of the time-dependent CP asymmetry in the neutral B-meson system. The SVT consists of five layers of double-sided, AC-coupled silicon-strip detectors of 300 μm thickness with a readout strip pitch of 50–210 μm and a stereo angle of 90° between the strips on the two sides. Detector alignment and performance with respect to spatial resolution and efficiency in the reconstruction of single hits are discussed. In the day-to-day operation of the SVT, radiation damage and protection issues were of primary concern. The SVT is equipped with a dedicated system (SVTRAD) for radiation monitoring and protection, using reverse-biased photodiodes. The evolution of the SVTRAD thresholds on the tolerated radiation level is described. Results on the first-year radiation exposure as measured with the SVTRAD system and on the so far accumulated damage are presented. The implications of test-irradiation results and possible future PEP-II luminosity upgrades on the radiation limited lifetime of the SVT are discussed.

$D^0 - \overline{D^0}$ Mixing and D0→K-π+π0 Resonant Substructure Results from CLEO

The CLEO Collaboration has an active charm physics effort underway using 14fb-1 of CLEO II and CLEO II.V data. A recent analysis of the time dependence of the 'wrong-sign' decay D0→K+ π- has placed limits on x′ and y′, the amplitudes that describe mixing in the D0 system. The 95% CL limits, with no assumptions about CP violation, are (1/2)x′2 &lt; 0.041% and -5.8% &lt; y′ &lt; 1.0%. Measurements of D0 decay rates to CP eigenstates, D0→K- K+ and D0→π-π+, provide preliminary CP asymmetry measurements [Formula: see text] and [Formula: see text]. A third analysis provides the first preliminary evidence for the decay D0→K+π- π0. Finally, a new Dalitz analysis of the decay D0→K-π+ π0 gives preliminary evidence for several new resonance contributions in this decay and also requires the presence of a significant non-resonant component.

Can R-parity violation lower sin2β?

Recent time-dependent CP asymmetry measurements in the B d → J / ψK S channel by the BaBar and Belle Collaborations yield somewhat lower values of sin2 β compared to the one obtained from the standard model fit. If the inconsistency between these numbers persists with more statistics, this will signal new physics contaminating the B d → J / ψK S channel, thus disturbing the extraction of β . We show that the R -parity-violating interactions in supersymmetric theories can provide extra new phases which play a role in significantly reducing the above CP asymmetry, thus explaining why BaBar and Belle report lower values of sin2 β . The same couplings also affect the B d → φK S decay rate and asymmetry, explain the B → η ′ K anomaly, and predict nonzero CP asymmetry in dominant B s decays. The scenario will be tested in the ongoing and upcoming B factories.

Mixing and CP violation in the charm sector

The results on D0-D0 mixing and CP asymmetrymeasurements in the charm sector are reviewed. There are intriguingrecent results from CLEO and FOCUS on the D0-D0 mixing.No CP violation has been reported in the charm meson decays. In anycase the role of charm remains unique to exploring new physics beyond thestandard model.

CP asymmetry measurements in J/ ψK0 and the CKM paradigm

Recent experimental observations of CP asymmetry in B→J/ψ +K 0 constitute the first significant signal of CP-violation outside the neutral kaon system; thus they represent an important milestone to test the CKM paradigm. We, therefore, undertake a critical appraisal of the existing experimental and theoretical inputs used to deduce constraints on sin2 β and other important parameters and thus find, in particular, sin2 β>0.47 at 95% CL which is completely compatible with the combined experimental result: sin2 β=0.48±0.16, representing an important success of the CKM model of CP-violation. Searches for new physics in B decays to J/ψ +K 0 like final states will require improved precision; we make some suggestions to facilitate these. We also present a global fit including the new CP asymmetry measurements in B→J/ψ +K 0 as an additional input yielding, e.g., γ=(29°→67°), η ̄ =(0.20→0.37) , ρ ̄ =(0.08→0.36) , J CP=(1.8→3.1)×10 −5, Br(K +→π +ν ν ̄ )=(0.52→0.92)×10 −10 , Br(K L→π 0ν ν ̄ )=(0.11→0.31)×10 −10 and Δm B s =(15.2–28.3) ps −1, all at 95% CL.

Nonleptonic charmlessBdecays: Factorization versus perturbative QCD

We compare the factorization approach, the perturbative QCD approach and the Beneke-Buchalla-Neubert-Sachrajda approach to nonleptonic charmless $B$ meson decays. We discuss their treatments of factorizable, nonfactorizable, and annihilation contributions, infrared-cutoff and scale dependences, and strong phases. It is proposed that measurement of CP asymmetries in two-body $B$ meson decays provides an appropriate test of the these approaches.

Study of exclusive two-bodyB0meson decays to charmonium

We present a study of three B0 decay modes useful for time-dependent CP asymmetry measurements. From a sample of 9.7×106 BB¯ meson pairs collected with the CLEO detector, we have reconstructed B0→J/ψKS0, B0→χc1KS0, and B0→J/ψπ0 decays. The latter two decay modes have been observed for the first time. We describe a KS0→π0π0 detection technique and its application to the reconstruction of the decay B0→J/ψKS0. Combining the results obtained using KS0→π+π− and KS0→π0π0 decays, we determine B(B0→J/ψK0)=(9.5±0.8±0.6)×10−4, where the first uncertainty is statistical and the second one is systematic. We also obtain B(B0→χc1K0)=(3.9−1.3+1.9±0.4)×10−4 and B(B0→J/ψπ0)=(2.5−0.9+1.1±0.2)×10−5. Received 28 April 2000DOI:https://doi.org/10.1103/PhysRevD.62.051101©2000 American Physical Society

CP-violating asymmetry in B decays to 3 pseudoscalar mesons

The measurement of CP asymmetries is charged B meson decays might provide the first demonstration of CP violation outside the K system. Among the usual three CP-odd phases α, β and γ, the phase γ seems to be the most difficult to explore experimentally. In this talk I would like to report on a recent analysis of the CP asymmetry in the partial widths for the non-leptonic decays B ± → M Mπ ± (M = π +, K +, π 0, η) , which results from the interference of the non-resonant decay amplitude with the resonant amplitude for B ± → χ c0 π ± followed by the decay χ c0 → M M . The CP violating phase γ can be extracted from the measured asymmetry. We find that the partial width asymmetry for B ± → π + π − π ± is about 0.33 sin γ, and about 0.45 sin γ for B ± → K + K − π ±, while it is somewhat smaller for B ± → π 0 π 0 π ± and B ± → ηηπ ±.

CPasymmetry forB→K*l+l−decay in the general two Higgs doublet model

We study CP asymmetry for the exclusive decay B --> K^* l^+ l^- in the two Higgs doublet model with three level flavor changing neutral currents (model III). We analyse the dependency of this quantity to the new phase coming from the complex Yukawa couplings in the theory and we find that there exist a considerable CP violation for the relevant process. Further, we see that the sign of the Wilson coefficient C_7^{eff} can be determined by fixing dilepton mass. Therefore, the future measurements of CP asymmetry for B --> K^* l^+ l^- decay will give a powerful information about the sign of Wilson coefficient C_{7}^{eff} and the new physics beyond the SM.

First Observation of the DecayB0→D*+D*−

We have observed four fully reconstructed B0 -> D*+D*- candidates in 5.8 million Upsilon(4S) -> BBbar decays recorded with the CLEO detector. The background is estimated to be 0.31 +- 0.10 events. The probability that the background could produce four or more signal candidates with the observed distribution among D*+ and D*- decay modes is 1.1 X 10^{-4}. The measured decay rate, Br(B0 -> D*+D*-) = [6.2 +4.0-2.9 (stat) +- 1.0(syst)] X 10^{-4}, is large enough for this decay mode to be of interest for the measurement of a time-dependent CP asymmetry.