CP Violation In Standard Model Research Articles

Primordial black holes and the origin of the matter-antimatter asymmetry.

We review here a new scenario of hot spot electroweak baryogenesis where the local energy released in the gravitational collapse to form primordial black holes (PBHs) at the quark-hadron (QCD) epoch drives over-the-barrier sphaleron transitions in a far from equilibrium environment with just the standard model CP violation. Baryons are efficiently produced in relativistic collisions around the black holes and soon redistribute to the rest of the universe, generating the observed matter-antimatter asymmetry well before primordial nucleosynthesis. Therefore, in this scenario there is a common origin of both the dark matter to baryon ratio and the photon to baryon ratio. Moreover, the sudden drop in radiation pressure of relativistic matter at H0/W±/Z0 decoupling, the QCD transition and e+e- annihilation enhances the probability of PBH formation, inducing a multi-modal broad mass distribution with characteristic peaks at 10-6, 1, 30 and 106 M⊙, rapidly falling at smaller and larger masses, which may explain the LIGO-Virgo black hole mergers as well as the OGLE-GAIA microlensing events, while constituting all of the cold dark matter today. We predict the future detection of binary black hole (BBH) mergers in LIGO with masses between 1 and 5 M⊙, as well as above 80 M⊙, with very large mass ratios. Next generation gravitational wave and microlensing experiments will be able to test this scenario thoroughly. This article is part of a discussion meeting issue 'Topological avatars of new physics'.

CP violation effects in the diphoton spectrum of heavy scalars

In a class of new physics models, an extended Higgs sector and new CP-violating sources are simultaneously present in order to explain the baryon asymmetry in the Universe. The aim of this work is to study the implications of beyond the Standard Model (SM) CP violation for the searches of heavy scalars at the LHC. In particular, we focus on the diphoton channel searches in the CP-violating two-Higgs-doublet model (CPV 2HDM). To have a sizable CPV in the scalar sector, the two heavy neutral scalars in 2HDM tend to be nearly degenerate. The theoretical constraints of unitarity, perturbativity and vacuum stability are considered, which requires that the heavy scalars $M_H \lesssim 1$ TeV in a large region of the parameter space. The experimental limits are also taken into account, including the direct searches of heavy neutral scalars in the final state of the SM $h$, $W$ and $Z$ bosons, the differential $t\bar{t}$ data, those from the charged scalar sector which is implied by the oblique $T$ parameter, as well as the precise measurements of the electric dipole moments of electron and mercury. The quantum interference effects between the resonances and the SM background are crucially important for the diphoton signals, and the CPV mixing of the quasi-degenerate heavy scalars could enhance significantly the resonance peak. With an integrated luminosity of 3000 fb$^{-1}$ at the LHC, almost the whole parameter space of CPV 2HDM could be probed in the diphoton channel, and the CPV could also be directly detected via the diphoton spectrum.

Predictive CP violating relations for charmless two-body decays of beauty baryons [formula omitted] and [formula omitted] with flavor [formula omitted] symmetry

Several baryons containing a heavy b-quark have been discovered. The decays of these states provide new platform for testing the standard model (SM). We study CP violation in SM for charmless two-body decays of the flavor SU(3) anti-triplet beauty baryon (b-baryon) B=(Ξb−,Ξb0,Λb0) in a model independent way. We found, in the flavor SU(3) symmetry limit, a set of new predictive relations among the branching ratio Br and CP asymmetry ACP for B decays, such as ACP(Ξb−→K0Ξ−)/ACP(Ξb−→K¯0Σ−)=−Br(Ξb−→K¯0Σ−)/Br(Ξb−→K0Σ−), ACP(Λb0→π−p)/ACP(Ξb0→K−Σ+)=−Br(Ξb0→K−Σ+)τΛb0/Br(Λb0→π−p)τΞb0, and ACP(Λb0→K−p)/ACP(Ξb0→π−Σ+)=−Br(Ξb0→π−Σ+)τΛb0/Br(Λb0→K−p)τΞb0. Future data from LHCb can test these relations and also other relations found.

Ensemble fermions for electroweak dynamics and the fermion preheating temperature

We refine the implementation of ensemble fermions for the electroweak sector of the Standard Model, introduced previously. We consider the behavior of different observables as the size of the ensemble is increased and show that the dynamics converges for ensemble sizes small enough that simulations of the entire electroweak sector become numerically tractable. We apply the method to the computation of the effective preheating temperature during a fast electroweak transition, relevant for Cold Electroweak Baryogenesis. We find that this temperature is never below 20 GeV, and this in combination with the early results convincingly rules out Standard Model CP-violation as the origin of the baryon asymmetry of the Universe.

Recent results on CP violation in charm and τ decays from BABAR

In the Standard Model CP violation in charm decays is expected to be very small, at the level of 0.1% or below, while CP violation in τ decays is predicted to be negligible. A significant excess of CP violation with respect to the Standard Model predictions would be a signature of new physics. We report on recent searches for CP violation in charm meson decays and in τ lepton decays at BABAR, using a data sample corresponding to an integrated luminosity of about 470 fb−1. In particular, we report on searches for CPV in the decay modes with a K0S in the final state, such as D+ → K0SK+, D+s → K0SK+, D+s → K)Sπ+ and τ+ → π+K0Sv̄τ, and in the 3-body D+ → K+K−π+ decay. A lifetime ratio analysis of D0 → K+K−, π+π− with respect to D0 → K−π+ decays, which is sensitive to D0-D̄0 mixing and CP violation, is also presented here.

Testing for new physics in singly Cabibbo suppressedDdecays

We devise tests for a new physics origin of the recently measured direct CP violation in singly Cabibbo suppressed D decays. The tests take the form of sum rules for the CP asymmetries in various D decays. They are based on the fact that within the standard model CP violation arises from interference of the dominant tree amplitudes with the Delta I=1/2 penguin amplitudes. The sum rules would be violated if the observed CP violation is due to new physics contributions to the effective weak Hamiltonian that change isospin by Delta I=3/2.

Standard modelCPviolation and cold electroweak baryogenesis

Using large scale real-time lattice simulations, we calculate the baryon asymmetry generated at a fast, cold electroweak symmetry breaking transition. CP-violation is provided by the leading effective bosonic term resulting from integrating out the fermions in the Minimal Standard Model at zero temperature, and performing a covariant gradient expansion [1]. This is an extension of the work presented in [2]. The numerical implementation is described in detail, and we address issues specifically related to using this CP-violating term in the context of Cold Electroweak Baryogenesis. The results support the conclusion of [2], that Standard Model CP-violation may be able to reproduce the observed baryon asymmetry in the Universe in the context of Cold Electroweak Baryogenesis.

Implications of CP violating 2HDM in B physics

The charged fermion mass matrices are invariant under U(1)3 symmetry linked to the fermion number transformation. Under the condition that the definition of this symmetry in arbitrary weak basis does not depend upon Higgs parameters such as ratio of vacuum expectation values, a class of two Higgs doublet models (2HDM) can be identified in which tree level flavor changing neutral currents normally present in 2HDM are absent. However unlike the type I or type II Higgs doublet models, the charged Higgs couplings in these models contain additional flavor dependent CP violating phases. These phases can account for the recent hints of the beyond standard model CP violation in the Bd and Bs mixing. In particular, there is a range of parameters in which new phases do not contribute to the K meson CP violation but give identical new physics phases in the Bd and Bs meson mixing.

Exploring the di-photon decay of a light Higgs boson in the MSSM with explicit CP violation

The di-photon decay channel of the lightest Higgs boson is considered as a probe to explore CP violation in the minimal supersymmetric standard model (MSSM). The scalar/pseudo-scalar mixing is considered along with CP violation entering through the Higgs–sfermion–sfermion couplings, with and without light sparticles. The impact of a light stop on the decay width and branching ratio (BR) is established through a detailed study of the amplitude of the process H1→γγ. The other sparticles have little influence even when they are light. With a suitable combination of other MSSM parameters, a light stop can change the BR by more than 50% with a CP-violating phase φμ∼90°, while the change is almost nil with a heavy stop.

Publisher’s Note: Improved measurement ofCP-violation parameterssin2ϕ1and|λ|,Bmeson lifetimes, andB0−B¯0mixing parameterΔmd[Phys. Rev. D71, 072003 (2005)

We present a precise measurement of the standard model CP-violation parameter sin(2phi1), the direct CP violation parameter |lambda|, the lifetimes of charged and neutral B mesons and their ratio, and the B0-B0bar mixing parameter Delta m_d based on a sample of 152 x 10^6 BB-bar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. One of two B mesons is fully reconstructed in a CP-eigenstate or a flavor-eigenstate decay channel. The flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time interval between the two B meson decay points, we obtain sin(2phi1) = 0.728 +/- 0.056(stat) +/- 0.023(syst), |lambda| = 1.007 +/- 0.041(stat) +/- 0.033(syst), tau_B0 = 1.534 +/- 0.008(stat) +/- 0.010(syst) ps, tau_B+ = 1.635 +/- 0.011(stat) +/- 0.011(syst) ps, tau_B+/tau_B0 = 1.066 +/- 0.008(stat) +/- 0.008(syst) and Delta m_d = 0.511 +/- 0.005(stat) +/- 0.006(syst) ps-1. The results for sin(2phi1) and |lambda| are the most precise measurements performed so far, and are consistent with the standard model expectations. The significance of the observed deviation from unity in the lifetime ratio exceeds five standard deviations.

Improved measurement ofCP-violation parameterssin2ϕ1and|λ|,Bmeson lifetimes, andB0-B¯0mixing parameterΔmd

We present a precise measurement of the standard model CP-violation parameter sin2 phi(1), the direct CP violation parameter vertical bar lambda vertical bar, the lifetimes of charged and neutral B mesons and their ratio, and the B-0-(B) over bar (0) mixing parameter Delta m(d) based on a sample of 152x10(6) B(B) over bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. One of two B mesons is fully reconstructed in a CP-eigenstate or a flavor-eigenstate decay channel. The flavor of the accompanying B meson is identified from its decay products. From the distributions of the time interval between the two B meson decay points, we obtain sin2 phi(1)=0.728 +/- 0.056(stat)+/- 0.023(syst), vertical bar lambda vertical bar=1.007 +/- 0.041(stat)+/- 0.033(syst), tau(B)(0)=[1.534 +/- 0.008(stat)+/- 0.010(syst)] ps, tau(B)(+)=[1.635 +/- 0.011(stat)+/- 0.011(syst)] ps, tau(B)(+)/tau(B)(0)=1.066 +/- 0.008(stat)+/- 0.008(syst) and Delta m(d)=[0.511 +/- 0.005(stat)+/- 0.006(syst)] ps(-1). The results for sin2 phi(1) and vertical bar lambda vertical bar are consistent with the standard model expectations. The significance of the observed deviation from unity in the lifetime ratio exceeds 5 standard deviations.

Sin(2 φ1) results from Belle

We present an improved measurement of the Standard Model CP violation parameter sin(2 φ 1) based on a 41.8 fb −1 data sample collected at the ϒ(4 S) resonance with the Belle detector at the KEKB asymmetric e + e − collider. One neutral B meson is reconstructed in six (c c)K( ∗) 0 CP-eigenstate decay channels and the flavor of the accompanying B meson is identified from its charged particle decay products. From the asymmetry in the distribution of the time interval between the two B-meson decay points, we determine sin(2 φ 1) = 0.82 ± 0.12( stat) ± 0.05( syst). We also show a result of the charmless hadronic B d 0 → η′ K S 0 analysis. The extracted CP violation parameter is sin(2( φ 1 + δ)) = 2.39 −0.40 +0.53( stat) ± 0.07( syst).

Measurement of sin 2ø 1 at Belle and BaBar

Recent measurements by Belle and BaBar of the Standard Model CP violation parameter sin 2ø 1 are presented. Indirect CP violation is discussed, and the analysis techniques employed by the two experiments are described.

Supersymmetric Higgs boson decays in the MSSM with explicit CP violation

Decays into neutralinos and charginos are among the most accessible supersymmetric decay modes of Higgs particles in most supersymmetric extensions of the Standard Model. In the presence of explicitly CP--violating phases in the soft breaking sector of the theory, the couplings of Higgs bosons to charginos and neutralinos are in general complex. Based on a specific benchmark scenario of CP violation, we analyze the phenomenological impact of explicit CP violation in the Minimal Supersymmetric Standard Model on these Higgs boson decays. The presence of CP--violating phases could be confirmed either directly through the measurement of a CP--odd polarization asymmetry of the produced charginos and neutralinos, or through the dependence of CP--even quantities (branching ratios and masses) on these phases.

Observation of large CP violation in the neutral B meson system.

We present a measurement of the standard model CP violation parameter sin2 phi(1) based on a 29.1 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. One neutral B meson is fully reconstructed as a J/psi K(S), psi(2S)K(S), chi(c1)K(S), eta(c)K(S), J/psi K(L), or J/psi K(*0) decay and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we determine sin2 phi(1) = 0.99+/-0.14(stat)+/-0.06(syst). We conclude that we have observed CP violation in the neutral B meson system.

Measurement of the CP violation parameter sin2 phi(1) in B(0)(d) meson decays.

We present a measurement of the standard model CP violation parameter sin2 phi(1) (also known as sin2beta) based on a 10.5 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e(+)e(-) collider. One neutral B meson is reconstructed in the J/psiK(S), psi(2S)K(S), chi(c1)K(S), eta(c)K(S), J/psiK(L), or J/psipi(0) CP-eigenstate decay channel and the flavor of the accompanying B meson is identified from its charged particle decay products. From the asymmetry in the distribution of the time interval between the two B-meson decay points, we determine sin2 phi(1) = 0.58(+0.32)(-0.34)(stat)+0.09-0.10(syst).

Zee neutrino mass matrix in the gauge mediated supersymmetry breaking scenario

It is well known that Zee type neutrino mass matrix can provide bi-maximal neutrino mixing for three neutrinos. We study the reconciliation of this model with the gauge mediated supersymmetry breaking scenario, which naturally suppresses the large flavor changing neutral current and CP violation in the supersymmetric standard model. When the messenger fields have suitable B– L charges, the radiative correction naturally induces the Zee neutrino mass matrix, which provides tiny neutrino masses and large lepton flavor mixings. Our numerical results are consistent with the neutrino oscillation experiments in both three and four neutrino models.

Seesaw-constrained minimal supersymmetric standard model, solution to the supersymmetricCPproblem, and a supersymmetric explanation ofε′/ε

We analyze CP violation in the supersymmetric standard model (MSSM) embedded minimally into a left-right symmetric gauge structure with the seesaw mechanism for neutrino masses. With the plausible assumption of universal scalar masses it is shown that CP violation in the hadron sector of the MSSM is described by a single phase residing in the supersymmetry breaking Lagrangian. This improves the CP properties of the MSSM by providing a natural solution to the SUSY CP problem. Furthermore, $\epsilon'/\epsilon$ vanishes in this model above the seesaw scale; extrapolation to the weak scale then leads to a prediction in agreement with the NA31 and the recent KTeV observations. The electric dipole moment of the neutron is naturally suppressed, we estimate its magnitude to be about $4 \times 10^{-29}$ ecm. Additional predictions include a tightly constrained super particle spectrum and vanishingly small CP asymmetries in the $B$ meson system.

Measurement ofsin2βfromB→J/ψKS0with the CDF detector

This paper reports an updated measurement of the Standard Model CP violation parameter $\sin2\beta$ using the CDF Detector at Fermilab. The entire Run I data sample of 110 pb$^{-1}$ of proton antiproton collisions at $\sqrt{s}=1.8 TeV$ is used to identify a signal sample of $\sim 400$ $B \to J/\psi K^0_S$ events, where $J/\psi \to \mu^+\mu^-$ and $K_S^0 \to \pi^+\pi^-$. The flavor of the neutral B meson is identified at the time of production by combining information from three tagging algorithms: a same-side tag, a jet-charge tag, and a soft-lepton tag. A maximum likelihood fitting method is used to determine $\sin2\beta = 0.79 {+0.41\atop-0.44}$(stat+syst). This value of $\sin 2 \beta$ is consistent with the Standard Model prediction, based upon existing measurements, of a large positive CP violating asymmetry in this decay mode.

Additional phases induced by the supersymmetricCPphases

Explicit CP violation in the minimal supersymmetric standard model (MSSM) radiatively induces a finite unremovable alignment between the Higgs doublets. This additional phase can be as large as the original CP phases in certain portions of the MSSM parameter space. Considering the specific case of the charginos, this additional phase is shown to induce a conceivable amount of CP violation near the would-be CP conserving points. Moreover, CP violation in the absence of this phase is smaller than that in the presence of it, and the former can never compete with the latter, however large $\mathrm{tan}\ensuremath{\beta}$ is.