Time-integrated CP Asymmetries Research Articles

Measurement of the Time-Integrated CP Asymmetry in D^{0}→K^{-}K^{+} Decays.

The time-integrated CP asymmetry in the Cabibbo-suppressed decay D^{0}→K^{-}K^{+} is measured using proton-proton collision data, corresponding to an integrated luminosity of 5.7 fb^{-1} collected at a center-of-mass energy of 13TeV with the LHCb detector. The D^{0} mesons are required to originate from promptly produced D^{*+}→D^{0}π^{+} decays, and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time-integrated CP asymmetry is measured to be A_{CP}(K^{-}K^{+})=[6.8±5.4±1.6]×10^{-4} where the first uncertainty is statistical and the second systematic. The direct CP asymmetries in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays, a_{K^{-}K^{+}}^{d} and a_{π^{-}π^{+}}^{d}, are derived by combining A_{CP}(K^{-}K^{+}) with the time-integrated CP asymmetry difference, ΔA_{CP}=A_{CP}(K^{-}K^{+})-A_{CP}(π^{-}π^{+}), and other inputs, giving a_{K^{-}K^{+}}^{d}=(7.7±5.7)×10^{-4},a_{π^{-}π^{+}}^{d}=(23.2±6.1)×10^{-4},with a correlation coefficient corresponding to ρ=0.88. The compatibility of these results with CP symmetry is 1.4 and 3.8 standard deviations for D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays, respectively. This is the first evidence for direct CP violation in a specific D^{0} decay.

Observation of CP violation in two-body {B}_{(s)}^0 -meson decays to charged pions and kaons

The time-dependent CP asymmetries of B0→ π+π− and {B}_s^0 → K+K− decays are measured using a data sample of pp collisions corresponding to an integrated luminosity of 1.9 fb−1, collected with the LHCb detector at a centre-of-mass energy of 13 TeV. The results areCππ=−0.311±0.045±0.015,Sππ=−0.706±0.042±0.013,CKK=0.123±0.034±0.015,SKK=0.164±0.034±0.014,AKKΔΓ=−0.83±0.05±0.09,\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ {\\displaystyle \\begin{array}{c}{C}_{\\pi \\pi}=-0.311\\pm 0.045\\pm 0.015,\\\\ {}{S}_{\\pi \\pi}=-0.706\\pm 0.042\\pm 0.013,\\\\ {}{C}_{KK}=0.123\\pm 0.034\\pm 0.015,\\\\ {}{S}_{KK}=0.164\\pm 0.034\\pm 0.014,\\\\ {}{\\mathcal{A}}_{KK}^{\\Delta \\varGamma }=-0.83\\pm 0.05\\pm 0.09,\\end{array}} $$\\end{document}where the first uncertainties are statistical and the second systematic. The same data sample is used to measure the time-integrated CP asymmetries of B0→ K + π− and {B}_s^0 →K−π+ decays and the results areACPB0=−0.0824±0.0033±0.0033,ACPBs0=0.236±0.013±0.011.\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ {\\displaystyle \\begin{array}{c}{A}_{CP}^{B^0}=-0.0824\\pm 0.0033\\pm 0.0033,\\\\ {}{A}_{CP}^{B_s^0}=0.236\\pm 0.013\\pm 0.011.\\end{array}} $$\\end{document}All results are consistent with earlier measurements. A combination of LHCb measurements provides the first observation of time-dependent CP violation in {B}_s^0 decays.

Measurement of the time-integrated CP asymmetry in D0\u2009\u2192\u2009KS0KS0 decays

A measurement of the time-integrated CP asymmetry in D0 → KS0KS0 decays is reported. The data correspond to an integrated luminosity of about 2 fb−1 collected in 2015–2016 by the LHCb collaboration in pp collisions at a centre-of-mass energy of 13 TeV. The D0 candidate is required to originate from a D*+ → D0π+ decay, allowing the determination of the flavour of the D0 meson using the pion charge. The D0 → K+K− decay, which has a well measured CP asymmetry, is used as a calibration channel. The CP asymmetryfor D0 → KS0KS0 is measured to beACPD0→KS0KS0=4.3±3.4±1.0%,\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ {\\mathcal{A}}^{CP}\\left({D}^0\\to {K}_S^0{K}_S^0\\right)=\\left(4.3\\pm 3.4\\pm 1.0\\right)\\%, $$\\end{document}where the first uncertainty is statistical and the second is systematic. This result is combined with the previous LHCb measurement at lower centre-of-mass energies to obtainACPD0→KS0KS0=2.3±2.8±0.9%.\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ {\\mathcal{A}}^{CP}\\left({D}^0\\to {K}_S^0{K}_S^0\\right)=\\left(2.3\\pm 2.8\\pm 0.9\\right)\\%. $$\\end{document}

Measurement of CP asymmetries in two-body B(s)0 -meson decays to charged pions and kaons

The time-dependent $C\!P$ asymmetries in $B^0\to\pi^+\pi^-$ and $B_s^0\to K^+\!K^-$ decays are measured using a data sample of $pp$ collisions corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The same data sample is used to measure the time-integrated $C\!P$ asymmetries in $B^0\to K^+\pi^-$ and $B_s^0\to\pi^+ K^-$ decays. The results are $C_{\pi^+\pi^-} = -0.34 \pm 0.06 \pm 0.01$, $S_{\pi^+\pi^-} = -0.63 \pm 0.05 \pm 0.01$, $C_{K^+\!K^-} = 0.20 \pm 0.06 \pm 0.02$, $S_{K^+\!K^-} = 0.18 \pm 0.06 \pm 0.02$, $C_{K^+\!K^-}^{\Delta\Gamma} = -0.79 \pm 0.07 \pm 0.10$, $A_{C\!P}^{B^0} = -0.084 \pm 0.004 \pm 0.003$, and $A_{C\!P}^{B_s^0} = 0.213 \pm 0.015 \pm 0.007$, where the first uncertainties are statistical and the second systematic. Evidence for $C\!P$ violation is found in the $B_s^0\to K^+\!K^-$ decay for the first time.

On the difference of time-integrated CP asymmetries in D0 → K+K− and D0 → π+π− decays: Unparticle physics contribution

The LHCb Collaboration has recently measured the difference of time-integrated CP asymmetry in D0→K+K− and D0→π+π− decays, more precisely. The reported value is ΔACP=−0.10±0.08(stat)±0.03(syst)% which indicates no evidence for CP violation. We consider the possible unparticle physics contribution in this quantity and by using the LCHb data try to constrain the parameter space of unparticle stuff.

Measurement of the Difference of Time-Integrated CP Asymmetries in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} Decays.

A search for CP violation in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays is performed using pp collision data, corresponding to an integrated luminosity of 3 fb^{-1}, collected using the LHCb detector at center-of-mass energies of 7 and 8TeV. The flavor of the charm meson is inferred from the charge of the pion in D^{*+}→D^{0}π^{+} and D^{*-}→D[over ¯]^{0}π^{-} decays. The difference between the CP asymmetries in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays, ΔA_{CP}≡A_{CP}(K^{-}K^{+})-A_{CP}(π^{-}π^{+}), is measured to be [-0.10±0.08(stat)±0.03(syst)]%. This is the most precise measurement of a time-integrated CP asymmetry in the charm sector from a single experiment.

Formula omitted] mixing and CP violation results from Belle

We report the results on D0−D‾0 mixing in the decays of D0→K+π− and D0→KS0π+π−, and CP violation in D0→π0π0 using a data sample with an integrated luminosity of about 1 ab−1 recorded with the Belle detector, at different center of mass energies. The mixing is observed in D0→K+π− with the mixing parameters x′2=(0.09±0.22)×10−3, y′=(4.6±3.4)×10−3 and the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates RD=(3.53±0.13)×10−3, where the quoted uncertainties combine both statistical and systematic contributions. For the D0→KS0π+π− decay, assuming CP conservation we measure mixing parameters x=(0.56±0.19−0.09−0.09+0.03+0.06)% and y=(0.30±0.15−0.05−0.06+0.04+0.03)%, where the uncertainties are statistical, experimental systematics, and that due to amplitude model. We measure the mixing parameters allowing CP violation for this decay mode, and obtain |q/p|=0.90−0.15−0.04−0.05+0.16+0.05+0.06 and arg(q/p)=(−6±11±3−4+3)° that are consistent with no CP violation. The time-integrated CP asymmetry in the decay D0→π0π0 is measured to be, [−0.03±0.64(stat)±0.10(syst)]%, consistent with CP conservation. We also present an updated measurement of CP asymmetry in D0→KS0π0.

Measurement of the time-integrated CP asymmetry in D 0 → K S 0 K S 0 decays

The time-integrated $CP$ asymmetry in the decay $D^0 \to K^0_S K^0_S$ is measured using $3 fb^{-1}$ of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The flavour of the $D^0$ meson is determined by use of the decay $D^{*+} \to D^0 \pi^+$ and its charge conjugate mode. The result is \[ {\cal A}_{CP} = -0.029 \pm 0.052 \pm 0.022, \] where the first uncertainty is statistical and the second systematic. The result is consistent with Standard Model expectations and improves the uncertainty with respect to the only previous measurement of this quantity by more than a factor of three.

Charm CP violation and mixing at Belle

We present charm CP violation and mixing measurements at Belle. They are the first observation of D0 − D̄0 mixing in e+e− collisions from D0 → K+π− decays, the most precise mixing and indirect CP violation parameters from D0 → K0Sπ+π− decays, and the timeintegrated CP asymmetries in D0 → π0π0 and D0 → K0Sπ0 decays. Our mixing measurement in D0 → K+π− decays excludes the no-mixing hypothesis at the 5.1 standard deviation level. The mixing parameters x = (0.56 ± 0.19+0.03+0.06−0.09−0.09)%, y = (0.30 ± 0.15+0.04+0.03−0.05−0.06)% and indirect CP violation parameters |q/p| = (0.90+0.16+0.05+0.06−0.15−0.04−0.05)%, arg(q/p) = (−6 ± 11 ± 3+3−4)° measured from D0 → K0Sπ+π− decays, and the time-integrated CP asymmetries AD0→π0π0CP = (−0.03 ± 0.64 ± 0.10)% and AD0→K0Sπ0CP = (−0.21 ± 0.16 ± 0.07)% are the most precisemeasurements to date. Our measurements here are consistent with predictions of the standard model.

Perturbative QCD study of [formula omitted] decays to a pseudoscalar meson and a tensor meson

We study two-body hadronic Bs→PT decays, with P(T) being a light pseudoscalar (tensor) meson, in the perturbative QCD approach. The CP-averaged branching ratios and the direct CP asymmetries of the ΔS=0 modes are predicted, where ΔS is the difference between the strange numbers of final and initial states. We also define and calculate experimental observables for the ΔS=1 modes under the Bs0–B¯s0 mixing, including CP averaged branching ratios, time-integrated CP asymmetries, and the CP observables Cf, Df and Sf. Results are compared to the Bs→PV ones in the literature, and to the B→PT ones, which indicate considerable U-spin symmetry breaking. Our work provides theoretical predictions for the Bs→PT decays for the first time, some of which will be potentially measurable at future experiments.

New physics models of direct CP violation in charm decays

Abstract In view of the recent LHCb measurement of ΔA CP, the difference between the time-integrated CP asymmetries in D → K + K − and D → π+π− decays, we perform a comparative study of the possible impact of New Physics degrees of freedom on the direct CP asymmetries in singly Cabibbo suppressed D meson decays. We systematically discuss scenarios with a minimal set of new degrees of freedom that have renormalizable couplings to the SM particles and that are heavy enough such that their effects on the D meson decays can be described by local operators. We take into account both constraints from low energy flavor observables, in particular D 0 − $ {\overline D^0} $ mixing, and from direct searches. While models that explain the large measured value for ΔA CP with chirally enhanced chromomagnetic penguins are least constrained, we identify a few viable models that contribute to the D meson decays at tree level or through loop induced QCD penguins. We emphasize that such models motivate direct searches at the LHC.

Angular analysis of B → V(→ P1P2) + decays

The angular analysis of exclusive rare B-meson decays via intermediate vector mesons V into 4-body final states of two pseudo-scalars P1, P2 and a pair of light leptons ℓ = e, μ offers a large set of observables. They can be used to test the electroweak short-distance couplings in the Standard Model and to search for New Physics. The two kinematic regions of low and high dilepton mass depend on short-distance physics in complementary ways and can be expanded in powers of ΛQCD/mb. These expansions guide towards suitable combinations of observables allowing to i) reduce the hadronic uncertainties in the extraction of the short-distance couplings or ii) test the lattice QCD B → V form factors in short-distance independent combinations. Several such possibilities of CP-averaged and CP-asymmetric (T-even and T-odd) quantities are presented for B̄0d → K̄*0(→ K−π+) + and time-integrated CP-asymmetries without tagging for B̄S, BS → ϕ(→ K−K+) + decays in view of the latest B-factory and CDF results and the forthcoming LHCb measurements.

More benefits of semileptonic rare B decays at low recoil: CP violation

We present a systematic analysis of the angular distribution of Bbar -> Kbar^\ast (-> Kbar pi) l^+ l^- decays with l = e, mu in the low recoil region (i.e. at high dilepton invariant masses of the order of the mass of the b-quark) to account model-independently for CP violation beyond the Standard Model, working to next-to-leading order QCD. From the employed heavy quark effective theory framework we identify the key CP observables with reduced hadronic uncertainties. Since some of the CP asymmetries are CP-odd they can be measured without B-flavour tagging. This is particularly beneficial for Bbar_s,B_s -> phi(-> K^+ K^-) l^+ l^- decays, which are not self-tagging, and we work out the corresponding time-integrated CP asymmetries. Presently available experimental constraints allow the proposed CP asymmetries to be sizeable, up to values of the order ~ 0.2, while the corresponding Standard Model values receive a strong parametric suppression at the level of O(10^-4). Furthermore, we work out the allowed ranges of the short-distance (Wilson) coefficients C_9,C_10 in the presence of CP violation beyond the Standard Model but no further Dirac structures. We find the Bbar_s -> mu^+ mu^- branching ratio to be below 9*10^-9 (at 95% CL). Possibilities to check the performance of the theoretical low recoil framework are pointed out.

Supersymmetric contributions to Bs → K−π+ decay

Recently, the CDF Collaboration has measured the branching fraction and time-integrated direct CP asymmetry of Bs → K−π+ decay. The branching ratio is lower than the previous predictions based on QCD factorization. The experimental results favor a large CP asymmetry in Bs → K−π+ decay while the standard model prediction is very small. We compute the supersymmetry contributions to Bs → K−π+ decay using the mass insertion method, and find that the LR and RL mass insertions could suppress this branching ratio and increase this direct CP asymmetry well in line with the experimental data.

CP and charge asymmetries at CDF

We present CDF results on the branching fractions and time-integrated direct CP asymmetries for B0 and Bs0 decay modes into pairs of charmless charged hadrons (pions or kaons). We report also the first observation of Bs0 → Ds±K± mode and the measurement of its branching fraction.

Measurement of the ratio [formula omitted] and the time-integrated CP asymmetry in [formula omitted

We report a high-statistics measurement of the relative branching fraction B(D0→π+π−π0)/B(D0→K−π+π0) using a 532 fb−1 data sample collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. The measured value of the relative branching fraction is B(D0→π+π−π0)/B(D0→K−π+π0)=(10.12±0.04(stat)±0.18(syst))×10−2, which has an accuracy comparable to the world average. We also present a measurement of the time-integrated CP asymmetry in D0→π+π−π0 decay. The result, ACP=(0.43±1.30)%, shows no significant CP violation.

Branching Fractions and Direct CP Asymmetries of Charmless B Decay Modes at the Tevatron

We present new CDF results on the branching fractions and time-integrated direct CP asymmetries for $B^{0}$ and $B^{0}_{s}$ decay modes into pairs of charmless charged hadrons (pion or kaon). The data set for this update amounts to 1 fb$^{-1}$ of $\bar{p}p$ collisions at $\sqrt{s}=1.96 \rm{TeV}$. We report the first observation of the $B^{0}_{s} \to K^{-}\pi^{+}$ mode and a measurement of its branching fraction and direct CP asymmetry. We also observe for the first time two charmless decays of $b$-baryon: $\Lambda^{0}_{b} \to p\pi^{-}$ and $\Lambda^{0}_{b} \to pK^{-}$.

Rare Hadronic B Decays

A review of recent results on branching fractions and time-integrated CP asymmetries of rare B_u and B_d decays to mesonic final states from BABAR, Belle and CLEO experiments is presented.

Probing New Physics from CP Violation in Radiative B Decays

When new CP-violating interactions are dominated by flavor changing neutral particle exchanges, which may occur in many extensions of the standard model, we examine a type-3 two-Higgs-doublet model and find that direct CP asymmetries can be as large as about 25%. Time-dependent and time-integrated mixing-induced CP asymmetries up to 85 and 40%, respectively, are possible without conflict with other constraints. It mainly requirs an enhanced chromo-magnetic dipole b → sg decay to be close to the present experimental bound.

On measuring CP violation in neutral B-meson decays at the Γ (4S) resonance

Within the standard model we carry out an analysis of CP-violating observables in neutral B-meson decays at the Γ (4S) resonance. Both time-dependent and time-integrated CP asymmetries are calculated, without special approximations, to meet various possible measurements at symmetric and asymmetric e + e − B factories. We show two ways to distinguish between direct and indirect CP-violating effects in the CP-eigenstate channels such as B d 0 B d 0 → π +π − and π 0 K S . Reliable knowledge of the Cabibbo-Kobayashi-Maskawa phase and angles can in principle be extracted from measurements of some non- CP-eigenstate channels, e.g. B d 0 B d 0 → D ±π ∓ and (−)D (∗)0 K S , even in the presence of significant final-state interactions.