CP-odd State Research Articles

Probing CPV mixing in the Higgs sector in vector boson fusion at a 1 TeV ILC

With the current precision of measurements by the ATLAS and CMS experiments, it cannot be excluded that a standard model (SM)-like Higgs boson is a CP violating mixture of CP-even and CP-odd states. We explore this possibility here, assuming Higgs boson production in ZZ-fusion, at 1 TeV ILC, with unpolarized beams. The full simulation of SM background and fast simulation of the signal is performed, simulating 8 ab−1 of data collected with the ILD detector. We demonstrate that the CP mixing angle ΨCP between scalar and pseudoscalar states can be measured with the statistical uncertainty of 3.8 mrad at 68% CL, corresponding to 1.44×10−5 for the CP parameter fCP, for the pure scalar state. This is the first result on sensitivity of an e+e− collider to measure fCP in the Higgs production vertex in vector boson fusion. Published by the American Physical Society 2024

Full NLO QCD predictions for Higgs-pair production in the 2-Higgs-doublet model

After the discovery of the Higgs boson in 2012 at the CERN Large Hadron Collider (LHC), the study of its properties still leaves room for an extended Higgs sector with more than one Higgs boson. 2-Higgs doublet models (2HDMs) are well-motivated extensions of the Standard Model (SM) with five physical Higgs bosons: two CP-even states h and H, one CP-odd state A, and two charged states H^pm _{}. In this letter, we present the calculation of the full next-to-leading order (NLO) QCD corrections to hH and AA production at the LHC in the 2HDM at small values of the ratio of the vacuum expectation values, tan beta , including the exact top-mass dependence everywhere in the calculation. Using techniques applied in the NLO QCD SM Higgs pair production calculation, we present results for the total cross section as well as for the Higgs-pair-mass distribution at the LHC. We also provide the top-quark scale and scheme uncertainties which are found to be sizeable.

Testing CP properties of extra Higgs states at the HL-LHC

Extra Higgs states appear in various scenarios beyond the current Standard Model of elementary particles. If discovered at the LHC or future colliders, the question will arise whether CP is violated or conserved in the extended scalar sector. An unambiguous probe of (indirect) CP violation would be the observation that one of the extra Higgs particles is an admixture of a CP-even and a CP-odd state. We discuss the possibility to discover scalar CP violation in this way at the high-luminosity (HL) phase of the LHC. We focus on the Two-Higgs Doublet Model of type I, where we investigate its currently allowed parameter region. Considering a benchmark point that is compatible with the current constraints but within reach of the HL-LHC, we study the prospects of determining the CP property of an extra neutral Higgs state H via the angular distribution of final states in the decay H→ tau overline{tau} . The analysis is performed at the reconstructed level, making use of a Boosted Decision Tree for efficient signal-background separation and a shape analysis for rejecting a purely CP-even or odd nature of H.

Maximum value of the spin-independent cross section in the 2HDM+a

We investigate the maximum value of the spin-independent cross section (σSI) in a dark matter (DM) model called the two-Higgs doublet model + a (2HDM+a). This model can explain the measured value of the DM energy density by the freeze-out mechanism. Also, σSI is suppressed by the momentum transfer at the tree level, and loop diagrams give the leading contribution to it. The model prediction of σSI highly depends on values of c1 and c2 that are the quartic couplings between the gauge singlet CP-odd state (a0) and Higgs doublet fields (H1 and H2), {c}_1{a}_0^2{H}_1^{dagger }{H}_1kern0.33em andkern0.33em {c}_2{a}_0^2{H}_2^{dagger }{H}_2 . We discuss the upper and lower bounds on c1 and c2 by studying the stability of the electroweak vacuum, the condition for the potential bounded from the below, and the perturbative unitarity. We find that the condition for the stability of the electroweak vacuum gives upper bounds on c1 and c2. The condition for the potential to be bounded from below gives lower bounds on c1 and c2. It also constrains the mixing angle between the two CP-odd states. The perturbative unitarity bound gives the upper bound on the Yukawa coupling between the dark matter and a0 and the quartic coupling of a0. Under these theoretical constraints, we find that the maximum value of the σSI is ∼ 5 × 10−47 cm2 for mA = 600 GeV, and the LZ and XENONnT experiments can see the DM signal predicted in this model near future.

The NMSSM is within reach of the LHC: mass correlations & decay signatures

The Next-to-Minimal Supersymmetric Standard Model (NMSSM), the singlet extension of the MSSM which fixes many of the MSSM’s shortcomings, is shown to be within reach of the upcoming runs of the Large Hadron Collider (LHC). A systematic treatment of the various Higgs decay channels and their interplay has been lacking due to the seemingly large number of free parameters in the NMSSM’s Higgs sector. We demonstrate that due to the SM-like nature of the observed Higgs boson, the NMSSM’s Higgs and neutralino sectors have highly correlated masses and couplings and can effectively be described by four physically intuitive parameters: the physical masses of the two CP-odd states and their mixing angle, and tan β, which plays a minor role. The heavy Higgs bosons in the NMSSM have large branching ratios into pairs of lighter Higgs bosons or a light Higgs and a Z boson. Search channels arising via these Higgs cascades are unique to models like the NMSSM with a Higgs sector larger than that of the MSSM. In order to cover as much of the NMSSM parameter space as possible, one must combine conventional search strategies employing decays of the additional Higgs bosons into pairs of SM particles with Higgs cascade channels. We demonstrate that such a combination would allow a significant fraction of the viable NMSSM parameter space containing additional Higgs bosons with masses below 1 TeV to be probed at future runs of the LHC.

On the pair correlations of neutral K, D, B and Bs mesons with close momenta produced in inclusive multiparticle processes

The phenomenological structure of inclusive cross-sections of the production of two neutral K mesons in hadron–hadron, hadron–nucleus and nucleus–nucleus collisions is theoretically investigated taking into account the strangeness conservation in strong and electromagnetic interactions. Relations describing the dependence of the correlations of two short-lived and two long-lived neutral kaons $K_S^0K_S^0,K_L^0K_L^0$ and the correlations of “mixed” pairs $K_S^0K_L^0$ at small relative momenta upon the space-time parameters of the generation region of K0 and K̅0 mesons have been obtained. These relations involve the contributions of Bose-statistics and S -wave strong final-state interaction of two K0 (K̅0) mesons as well as of the K0 and K̅0 mesons, and also the additional contribution of transitions K+K– → K0 K̅0, and they depend upon the relative fractions of generated pairs K0K0, K̅0 K̅0 and K0 K̅0. It is shown that under the strangeness conservation the correlation functions of the pairs $K_S^0K_S^0$ and $K_L^0K_L^0$, produced in the same inclusive process, coincide, and the difference between the correlation functions of the pairs $K_S^0K_S^0$ and $K_S^0K_L^0$ is conditioned exclusively by the production of the pairs of non-identical neutral kaons K0 K̅0. For comparison, analogous correlations for the pairs of neutral heavy mesons D0, B0 and $B_s^0$, generated in multiple inclusive processes with charm (beauty) conservation, are also theoretically analyzed. These correlations are described by quite similar expressions: in particular, just as for K0 mesons, the correlation functions for the pairs of states with the same CP parity (RS S = RLL) and with different CP parity (RS L) do not coincide, and the difference between them is conditioned exclusively by the production of pairs D0 D̅0, B0B̅0 and $B_s^0\bar B_s^0$. However, contrary to the case of K0 mesons, here the distinction of CP-even and CP-odd states encounters difficulties – due to the insignificant differences of their lifetimes and the relatively small probability of purely CP-even and CP-odd decay channels. Nevertheless, one may hope that it will become possible at future colliders.

Some hadronic parameters of charmonia in varvec{N_{text {f}}=2} lattice QCD

The phenomenology of leptonic decays of quarkonia holds many interesting features: for instance, it can establish constraints on scenarios beyond the Standard Model with the Higgs sector enriched by a light CP-odd state. In the following paper, we report on a two-flavor lattice QCD study of the eta _c and J/psi decay constants, f_{eta _c}=387(3)(3), {mathrm{MeV}} and f_{J/psi }=399(4)(2), {mathrm{MeV}}. We also examine some properties of the first radial excitation eta _c(2S) and psi (2S).

LHC signatures of neutral pseudo-Goldstone boson in the E6CHM

The breakdown of the SU(6) global symmetry to its SU(5) subgroup, that contains the standard model (SM) gauge group, in the E6 inspired composite Higgs model (E6CHM) results in a set of pseudo-Nambu–Goldstone bosons (pNGBs). This set, in particular, involves the SM-like Higgs doublet and a SM singlet boson. In the limit when CP is conserved the SM singlet scalar A is a CP-odd state that does not mix with the SM-like Higgs. The interactions of A with exotic matter beyond the SM, which ensures anomaly cancellation and approximate gauge coupling unification, can induce couplings of this pseudoscalar to the SM gauge bosons. We specify the interactions of the SM singlet pNGB state with the exotic vector-like fermions, top quark and SM gauge bosons. Also we explore the dependence of the branching ratios of the pseudoscalar A and its LHC production cross section on the parameters of the E6CHM.

Bs lifetime measurement in the CP-odd channel B0s → J/Ψ f0 (980) by the DO experiment

The lifetime measurement of the B0s meson in the decay channel B0s → J/Ψ f0 (980) is reported, which is a CP-odd state. Using 10.4 fb-1 of data collected with the D0 detector in Run II of the Tevatron, the lifetime of the CP-odd component of the B0s meson is measured to be τ(B0s) = 1.70 ± 0.14 (stat) ± 0.05 (syst) ps.

Phenomenology of SU(5) low-energy realizations: The diphoton excess and Higgs flavor violation

We discuss different SU(5) low-energy realizations and illustrate their use with the diphoton excess and Higgs flavor violation, which require new physics at the TeV scale. In particular, we study two scenarios for a 750 GeV resonance: in the first one the resonance belongs to the adjoint of SU(5), being either an SU(2)L singlet or a triplet, while in the second case the signal is due to the CP-even and CP-odd states of a new SU(2)L Higgs doublet belonging to a 45H or a 70H representations, giving rise to a two-Higgs doublet model at low energies. We study the fine-tuning needed for the desired members of the multiplets to be light enough, while having the rest at the GUT scale. In these scenarios, the production and decay into photons of the new resonance are mediated by the leptoquarks (LQ) present in these large SU(5) representations. We analyze the phenomenology of such scenarios, focusing on the most relevant predictions that can help to disentangle the different models, like decays into gauge bosons, Standard Model (SM) fermions and LQs pair production. In the case of the 45H (the Georgi–Jarlskog model), we also study the possibility to have Higgs flavor violation. We find that Bs mixing limits (in addition to τ→μγ) always imply that Br(h→τμ,bs)≲10−5.

Bs0lifetime measurement in theCP-odd decay channelBs0→J/ψ f0(980)

The lifetime of the $B^{0}_{s}$ meson is measured in the decay channel $B^{0}_{s} \to J/\psi\mbox{ }\pi^+ \pi^-$ with $880 \leq M_{\pi^+\pi^-} \leq 1080$ MeV/$c^2$, which is mainly a CP-odd state and dominated by the $f_{0}(980)$ resonance. In 10.4 fb$^{-1}$ of data collected with the D0 detector in Run II of the Tevatron, the lifetime of the $B^{0}_{s}$ meson is measured to be $\tau(B^{0}_{s}) = 1.70\pm 0.14 \mbox{ (stat)} \pm 0.05 \mbox{ (syst) ps}$. Neglecting CP violation in $B_s^0/\bar{B}_s^0$ mixing, the measurement can be translated into the width of the heavy mass eigenstate of the $B^0_s$, $\Gamma_H = 0.59 \pm 0.05 \mbox{ (stat)} \pm 0.02 \mbox{ (syst)} \mbox{ ps$^{-1}$}$.

Diphoton signatures from heavy axion decays at the CERN Large Hadron Collider

Recently, the LHC collaborations, ATLAS and CMS, have announced an excess in the diphoton channel with local significance of about $3\,\sigma$ around an invariant mass distribution of $\sim 750$ GeV, after analyzing new data collected at centre-of-mass energies of $\sqrt{s} = 13~{\rm TeV}$. We present a possible physical interpretation of such a signature, within the framework of a minimal UV-complete model with a massive singlet pseudo-scalar state $a$ that couples to a new TeV-scale coloured vector-like fermion $F$, whose hypercharge quantum number is a non-zero integer. The pseudo-scalar state $a$ might be a heavy pseudo-Goldstone boson, such as a heavy axion, which decays into two photons and whose mass lies around the excess region. The mass of the CP-odd state $a$ and its coupling to $F$ may be due to non-perturbative effects, which can break the original Goldstone shift symmetry dynamically. The possible role that the heavy axion $a$ can play in the radiative generation of a seesaw Majorana scale and in the solution to the so-called strong CP problem is briefly discussed.

Scenarii for interpretations of the LHC diphoton excess: Two Higgs doublets and vector-like quarks and leptons

An evidence for a diphoton resonance at a mass of 750 GeV has been observed in the data collected at the LHC run at a center of mass energy of 13 TeV. We explore several interpretations of this signal in terms of Higgs-like resonances in a two-Higgs doublet model and its supersymmetric incarnation, in which the heavier CP-even and CP-odd states present in the model are produced in gluon fusion and decay into two photons through top quark loops. We show that one cannot accommodate the observed signal in the minimal versions of these models and that an additional particle content is necessary. We then consider the possibility that vector-like quarks or leptons strongly enhance the heavy Higgs couplings to photons and eventually gluons, without altering those of the already observed 125 GeV state.

Diboson excesses demystified in effective field theory approach

We study the collider implication of a neutral resonance which decays to several diboson final states such as W + W −, ZZ, and Zγ via a minimal set of effective operators. We consider both CP-even and CP-odd bosonic states with spin 0, 1, or 2. The production cross sections for the bosonic resonance states are obtained with the effective operators involving gluons (and quarks), and the branching fractions are obtained with the operators responsible for the interactions with electroweak gauge bosons. We demonstrate that each scenario allows for a broad parameter space which could accommodate the recently-reported intriguing excesses in the ATLAS diboson final states, and discuss how the CP states and spin information of the resonance can be extracted at the LHC run II.

Towards a supersymmetric description of the Fermi Galactic center excess

We attempt to build a model that describes the {\it Fermi} galactic gamma-ray excess (FGCE) within a UV-complete Supersymmetric framework; we find this to be highly non-trivial. At the very least a successful Supersymmetric explanation must have several important ingredients in order to fit the data and satisfy other theoretical and experimental constraints. Under the assumption that a {\it single} annihilation mediator is responsible for both the observed relic density as well as the FGCE, we show that the requirements are not easily satisfied in many TeV-scale SUSY models, but can be met with some model building effort in the general NMSSM with $\sim 10$ parameters beyond the MSSM. We find that the data selects a particular region of the parameter space with a mostly singlino lightest Supersymmetric particle and a relatively light CP-odd Higgs boson that acts as the mediator for dark matter annihilation. We study the predictions for various observables within this parameter space, and find that searches for this light CP-odd state at the LHC, as well as searches for the direct detection of dark matter, are likely to be quite challenging. It is possible that a signature could be observed in the flavor sector; however, indirect detection remains the best probe of this scenario.

CP mixed property of the Higgs-like particle in the decay channel h→Z Z*→4l

Current experiments do not support, as ATLAS and CMS Collaborations at the Large Hadron Collider reported, that the Higgs-like resonance discovered in July 2012 is a pure CP-odd state. We examine a general hZZ vertex which contains CP-even and CP-odd couplings, by studying the process [Formula: see text] with l1, l2 = e or μ, to explore the CP mixed property of the Higgs-like particle. One momentum asymmetry and two angular asymmetries have been analyzed in order to reveal the difference from different CP-couplings. Our study shows that these asymmetries could be interesting observables in the future precise experiments.

Low-mass Higgs bosons in the NMSSM and their LHC implications

We study the Higgs sector of the Next to Minimal Supersymmetric Standard Model (NMSSM) in light of the discovery of the SM-like Higgs boson at the LHC. We perform a broad scan over the NMSSM parameter space and identify the regions that are consistent with current Higgs search results at colliders. In contrast to the commonly studied "decoupling" scenario in the literature where the Minimal Supersymmetric Standard Model CP-odd Higgs boson mass is large mA >> mZ, we pay particular attention to the light Higgs states in the case when mA <~ 2mZ . The Higgs bosons in the NMSSM, namely three CP-even states, two CP-odd states, and two charged Higgs states, could all be rather light, near or below the electroweak scale, although the singlet-like states can be heavier. The SM-like Higgs boson could be either the lightest CP-even scalar or the second lightest CP-even scalar, but is unlikely to be the heaviest scalar. These NMSSM parameter regions have unique properties and offer rich phenomenology. The decay branching fractions for the SM-like Higgs boson may be modified appreciably. The correlations of gamma gamma/V V and V V/b b can be substantially altered. The new Higgs bosons may be readily produced at the LHC and may decay to non-standard distinctive final states, most notably a pair of Higgs bosons when kinematically accessible. We evaluate the production and decay of the Higgs bosons and comment on further searches at the LHC to probe the Higgs sector of the NMSSM.

HiggsCPproperties from early LHC data

In this paper, we constrain CP violation in the Higgs sector using the measured signal strengths in the various Higgs search channels. To this end, we introduce a general parameterization for a resonance which is an admixture of a CP-even Higgs-like state and a CP-odd scalar. By performing a fit to the available data from the Tevatron and LHC experiments one obtains constraints on the mixing angle and the couplings of the resonance to Standard Model fields. Depending on the couplings, sizable mixing angles are still compatible with the data, but small mixing is in general preferred by the fit. In particular we find that a pure CP-odd state is disfavored by the current data at the 3 sigma level. Additionally we consider a mixed fermiophobic resonance and a model with two degenerate mixed resonances and find that both scenarios can successfully fit the data within current errors. Finally, we estimate that the mixing angle can be constrained to \alpha < 1.1 (0.7) in the full 8 TeV (14 TeV) run of the LHC.

Is the LHC observing the pseudoscalar state of a two-Higgs-doublet model?

The ATLAS and CMS collaborations have recently shown data suggesting the presence of a Higgs boson in the vicinity of 125 GeV. We show that a two-Higgs doublet model spectrum, with the pseudo-scalar state being the lightest, could be responsible for the diphoton signal events. In this model, the other scalars are considerably heavier and are not excluded by the current LHC data. If this assumption is correct, future LHC data should show a strengthening of the $\gamma\gamma$ signal, while the signals in the $ZZ^{(*)}\to 4\ell $ and $WW^{(*)}\to 2\ell 2\nu$ channels should diminish and eventually disappear, due to the absence of diboson tree-level couplings of the CP-odd state. The heavier CP-even neutral scalars can now decay into channels involving the CP-odd light scalar which, together with their larger masses, allow them to avoid the existing bounds on Higgs searches. We suggest additional signals to confirm this scenario at the LHC, in the decay channels of the heavier scalars into $AA$ and $AZ$. Finally, this inverted two-Higgs doublet spectrum is characteristic in models where fermion condensation leads to electroweak symmetry breaking. We show that in these theories it is possible to obtain the observed diphoton signal at or somewhat above of the prediction for the standard model Higgs for the typical values of the parameters predicted.

Triple-product asymmetries inK,D(s), andB(s)decays

One distinguishes between "true" CP violating triple product (TP) asymmetries which require no strong phases and "fake" asymmetries which are due to strong phases but require no CP violation. So far a single true TP asymmetry has been measured in $K_L\to \pi^+\pi^- e^+e^-$. A general discussion is presented for T-odd TP asymmetries in four-body decays. It is shown that TP asymmetries vanish for two identical and kinematically indistinguishable particles in the final state. Two examples are $D^0\to K^-\pi^+\pi^-\pi^+$ and $D^+\to K^-\pi^+\pi^+\pi^0$. A non-zero TP asymmetry can be expected when non-trivial kinematic correlations exist, as in the decay $K_L \to e^+ e^- e^+ e^-$. Triple product asymmetries measured in charmed particle decays indicate an interesting pattern of final-state interactions. We reiterate a discussion of TP asymmetries in $B$ meson decays to two vector mesons each decaying to a pseudoscalar pair, extending results to decays where one vector meson decays into a lepton pair. We derive expressions for time-dependent TP asymmetries for neutral B decays to flavorless states in terms of the neutral $B$ mass difference $\Delta m$ and the width-difference $\Delta\Gamma$. Time-integrated true CP violating asymmetries, measurable for untagged $B_s$ decays, are shown to be suppressed by neither $\Gamma_s/\Delta m_s$ nor $\Delta\Gamma_s/\Gamma_s$ if transversity amplitudes for CP-even and CP-odd states involve different weak phases. In contrast, fake asymmetries require flavor tagging and are suppressed by the former ratio when time-integrated. We apply our results to $B\to K^*\phi$ and $B_s\to\phi\phi$ data and suggest an application for $B_s\to J/\psi\phi$.