Charm System Research Articles

Enhancement of charm CP violation due to nearby resonances

Quantitative understanding of CP violation is extremely important as naturalness reasoning strongly suggests that new physics should be accompanied by beyond the Standard Model CP-odd phases. In 2019 LHCb made the first 5σ discovery of CP violation in the charm system, leading to the new world average ΔaCPdir=−0.00161±0.00028. While some calculations have found this observation as requiring new physics, we suggest that scalar resonances nearby to mD0, in particular, f0(1710) and/or f0(1790) cause enhancements for CP violation within the SM. Thereby, our calculations based on the Standard Model suggest compatibility with the LHCb observations for now. However, experimental information especially on f0(1790) is rather sparse limiting our accuracy and further data on these resonances is strongly advocated.

The charm of 331

We perform a detailed analysis of flavour changing neutral current processes in the charm sector in the context of 331 models. As pointed out recently, in the case of Z′ contributions in these models there are no new free parameters beyond those already present in the Bd,s and K meson systems analyzed in the past. As a result, definite ranges for new Physics (NP) effects in various charm observables could be obtained. While generally NP effects turn out to be small, in a number of observables they are much larger than the tiny effects predicted within the Standard Model. In particular we find that the branching ratio of the mode D0→ μ+μ−, despite remaining tiny, can be enhanced by 6 orders of magnitude with respect to the SM. We work out correlations between this mode and rare Bd,s and K decays. We also discuss neutral charm meson oscillations and CP violation in the charm system. In particular, we point out that 331 models provide new weak phases that are a necessary condition to have non-vanishing CP asymmetries. In the case of ∆ACP, the difference between the CP asymmetries in D0→ K+K− and D0→ π+π−, we find that agreement with experiment can be obtained provided that two conditions are verified: the phases in the ranges predicted in 331 models and large hadronic matrix elements.

Mixing and CP Violation in the Charm System

In recent years charm physics has undergone a renaissance, which has been catalyzed by an unexpected and impressive set of experimental results from the B factories, the Tevatron, and LHCb. The existence of [Formula: see text] oscillations is now well established, and the recent discovery of CP violation in D0 decays has further renewed interest in the charm sector. In this article, we review the current status of charm-mixing and CP-violation measurements and assess their agreement with theoretical predictions within the Standard Model and beyond. We look forward to the great improvements in experimental precision that can be expected over the coming two decades and to the prospects for corresponding advances in theoretical understanding.

CP violation in beauty and charm at LHCb

Precision measurements of CP violating observables in the decays of b and c hadrons are powerful probes to search for physics beyond the Standard Model. The most recent results on CP violation in the decay, mixing and interference of both b and c hadrons obtained by the LHCb Collaboration with Run I and years 2015-2016 of Run II are presented, including the first observation of CP violation in the charm system. In particular world best constraints and world first measurements are provided for CKM elements, unitarity angles and charm parameters. Prospects for future sensitivities are also discussed.

Charm physics

Charm physics is an active and productive field at hadron colliders. In these proceedings an overview of recent results in charm physics from the Tevatron and LHC experiments is given. Highlighted are the measurements of open charm production and production asymmetries, the recent precision measurements of the D masses, the confirmation of mixing in the D0 system, the searches for CP violation in the charm system and the searches for rare charm decays.

Mini-review of rare charmonium decays at BESIII

Recently, the LHCb experiment announced 3.5σ evidence for direct CP violation in D0 decay by looking at the difference between ACP(D0 → K+K−) and ACP(D0 → π+π−). This is the first evidence of CP violation in a charm system, which may indicate new physics beyond the Standard Model. Motivated by this measurement, we review rare processes in charmonium decay, especially, the weak decay, C or P violated decay, and lepton flavor violated decays. In case the new physics appears in charm sector, these rare decays of charmonium states will provide an opportunity to search for significant contributions from physics beyond the Standard Model. With huge J/ψ and ψ (2S) samples in BESIII experiment, the rare decays may be feasible.

CKM angle measurements and the search for CP violation in charm

This contribution reports on recent LHCb achievements in the pursuit of CKM triangle measure- ments and probes of CP violation in the charm system. These results are based on the 2010 dataset or, in some cases, preliminary results using the data collected by summer 2011.

The impact of a 4th generation on mixing and CP violation in the charm system

We study \( {D^0} - {\overline D^0} \) mixing in the presence of a fourth generation of quarks. In particular, we calculate the size of the allowed CP violation which is found at the observable level well beyond anything possible with CKM dynamics. We calculate the semileptonic asymmetry a SL(D) and the mixing induced CP asymmetry η f S f (D) which are correlated with each other. We also investigate the correlation of η f S f (D) with a number of prominent observables in other mesonic systems like ε′/ε, Br(K L → π0 \( \nu \overline \nu \)), Br(K + → π+ \( \nu \overline \nu \)), Br(B s → μ+μ-), Br(B d → μ+μ-) and finally S ψϕ(B s ) in the Bs system. We identify a clear pattern of flavour and CP violation predicted by the SM4 model: While simultaneous large 4G effects in the K and D systems are possible, accompanying large NP effects in the B d system are disfavoured. However this behaviour is not as pronounced as found for the LHT and RSc models. In contrast to this, sizeable CP violating effects in the B s system are possible unless extreme effects in η f S f (D) are found, and Br(B s → μ+μ-) can be strongly enhanced regardless of the situation in the D system. We find that, on the other hand, S ψϕ(B s ) > 0.2 combined with the measured ε′/ε significantly diminishes 4G effects within the D system.

Flavour physics and CP violation

It is well known that the study of flavour physics and CP violation is very important to critically test the Standard Model and to look for possible signature of new physics beyond it. The observation of CP violation in kaon system in 1964 has ignited a lot of experimental and theoretical efforts to understand its origin and to look for CP violation effects in other systems besides the neutral kaons. The two B-factories BABAR and BELLE, along with other experiments, in the last decade or so made studies in flavour physics and CP violation a very interesting one. In this article we discuss the status and prospectives of the flavour physics associated with the strange, charm and bottom sectors of the Standard Model. The important results in kaon sector will be briefly discussed. Recently, mixing in the charm system has been observed, which was being pursued for quite some time without any success. The smallness of the mixing parameters in the charm system is due to the hierarchical structure of the CKM matrix. Interestingly, so far we have not found CP violation in the charm system but in the future, with more dedicated experiments at charm threshold, the situation could change. Many interesting observations have been made in the case of bottom mesons and some of them show some kind of deviations from that of the Standard Model expectations which are mainly associated with the b → s flavour changing neutral current transitions. It is long believed that the B s system could be the harbinger of new physics since it is a system in which both bottom and strange quarks are the constituents. Recently, D0 and CDF announced their result for the B s mixing which is claimed to be the first possible new physics signature in the flavour sector. We plan to touch upon all important issues pointing out both theoretical and experimental developments and future prospects in this review article.

D0−D¯0mixing inΥ(1S)→D0D¯0decay at a super-Bfactory

${D}^{0}\mathrm{\text{\ensuremath{-}}}{\overline{D}}^{0}$ mixing and significant $CP$ violation in the charm system may indicate the signature of new physics. In this study, we suggest that the coherent ${D}^{0}{\overline{D}}^{0}$ events from the decay of $\ensuremath{\Upsilon}(1S)\ensuremath{\rightarrow}{D}^{0}{\overline{D}}^{0}$ can be used to measure both mixing parameters and $CP$ violation in charm decays. The neutral $D$ mesons from $\ensuremath{\Upsilon}(1S)$ decay are strongly boosted, so that it will offer the possibility to measure the proper-time interval $\ensuremath{\Delta}t$ between the fully reconstructed ${D}^{0}$ and ${\overline{D}}^{0}$. Both coherent and time-dependent information can be used to extract ${D}^{0}\mathrm{\text{\ensuremath{-}}}{\overline{D}}^{0}$ mixing parameters. The sensitivity of the measurement should be improved at $B$ factories or at super-$B$.

CHARM MIXING IN THE STANDARD MODEL AND BEYOND

The motivation most often cited in searches for [Formula: see text] mixing and CP-violation in charm system lies with the possibility of observing a signal from New Physics which dominates that from the Standard Model. We review recent theoretical predictions and experimental constraints on [Formula: see text] mixing parameters, concentrating on possible effects of New Physics.

Mixing and CP-violation in charm

The motivation most often cited in searches for D0-anti-D0 mixing and CP-violation in charm system lies with the possibility of observing a signal from new physics which dominates that from the Standard Model. We review recent theoretical predictions and experimental constraints on D0-anti-D0 mixing parameters. We also discuss the current status of searches for CP-violation in charmed meson transitions, as well as some recent theoretical ideas.

Charm system tests of CPT and Lorentz invariance with FOCUS

We have performed a search for CPT violation in neutral charm meson oscillations. While flavor mixing in the charm sector is predicted to be small by the Standard Model, it is still possible to investigate CPT violation through a study of the proper time dependence of a CPT asymmetry in right-sign decay rates for D0→K−π+ and D0→K+π−. This asymmetry is related to the CPT violating complex parameter ξ and the mixing parameters x and y: ACPT∝(Reξ)y−(Imξ)x. Our 95% confidence level limit is −0.0068<(Reξ)y−(Imξ)x<0.0234. Within the framework of the Standard Model Extension incorporating general CPT violation, we also find 95% confidence level limits for the expressions involving coefficients of Lorentz violation of (−2.8<N(x,y,δ)(Δa0+0.6ΔaZ)<4.8)×10−16 GeV, (−7.0<N(x,y,δ)ΔaX<3.8)×10−16 GeV, and (−7.0<N(x,y,δ)ΔaY<3.8)×10−16 GeV, where N(x,y,δ) is the factor which incorporates mixing parameters x, y and the doubly Cabibbo-suppressed to Cabibbo-favored relative strong phase δ.

A Simple Method for the Comparison of Commercially Available ATP Hygiene-Monitoring Systems

The purpose of this study was to evaluate a methodology which could easily be used in any test laboratory in a uniform and consistent way for determining the sensitivity and reproducibility of results obtained with three ATP hygiene-monitoring systems. The test protocol discussed here allows such comparisons to be made, thereby establishing a method of benchmarking both new systems and developments of existing systems. The sensitivity of the LUMINOMETER K, PocketSwab (Charm Sciences) was found to be between 0.4 and 4.0 nmol of ATP with poor reproducibility at the 40.0 nmol level (CV, 35%). The sensitivity of the IDEXX LIGHTNING system and the Biotrace UNILITE Xcel were both between 0.04 and 0.4 nmol with coefficients of variation (CVs) of between 9% at 0.04 nmol and 10% at 0.4 nmol for the IDEXX system and 17% at 0.04 nmol and 21% at 0.4 nmol for the Biotrace system. The three systems were tested with a range of dilutions of different food residues: orange juice, raw milk, and ground beef slurry. All three test systems allowed detection of orange juice and raw milk at dilutions of 1:1,000, although the CV of results from the Charm system (54 and 74% respectively) was poor at this dilution for both residues. The sensitivity of the test systems was poorer for ground beef slurry than it was for orange juice and raw milk. Both the Biotrace and IDEXX systems were able to detect a 1:100 dilution of beef slurry (with CVs of 17 and 10% respectively), whilst at this dilution results from the Charm system had a CV of 55%. It was possible by using the method described in this paper to rank in order of sensitivity and reproducibility the three single-shot ATP hygiene-monitoring systems investigated, with the IDEXX LIGHTNING being the best, followed by the Biotrace UNILITE Xcel, and then the Charm LUMINOMETER K, PocketSwab.

D0-D¯0mixing andCPviolation in neutralD-meson decays

D^0-\bar{D}^0 mixing at the detectable level or significant CP violation in the charm system may strongly signify the existence of new physics. In view of the large discovery potential associated with the fixed target experiments, the B-meson factories and the \tau-charm factories, we make a further study of the phenomenology of D^0-\bar{D}^0 mixing and CP violation in neutral $D$-meson decays. The generic formulas for the time-dependent and time-integrated decay rates of both coherent and incoherent D^0\bar{D}^0 events are derived, and their approximate expressions up to the second order of the mixing parameters x_D and y_D are presented. Explicitly we discuss D^0-\bar{D}^0 mixing and various CP-violating signals in neutral D decays to the semileptonic final states, the hadronic CP eigenstates, the hadronic non-CP eigenstates and the CP-forbidden states. A few non-trivial approaches to the separate determination of x_D and y_D and to the demonstration of direct and indirect CP asymmetries in the charm sector are suggested.

Search for CP violation in D0 decay.

Using 2.7 fb−1 of data taken with the CLEO II detector, we have searched for CP violation in the charm system. We looked for asymmetries in the number of decays of D0’s and D¯0’s to the CP eigenstates K+K−, KS0φ, and KS0π0. Confidence intervals (90%) on these asymmetries were found to be -0.020<AKK<0.180, -0.182<AKS0φ<0.126, and -0.067<AKS0π0<0.031, respectively.Received 22 May 1995DOI:https://doi.org/10.1103/PhysRevD.52.4860©1995 American Physical Society

E2 strength in the radiative charmed baryon decay [formula omitted

The radiative decay ∑ Q ∗ → Λ Qγ can have both magnetic dipole (M1) and electric quadrupole (E2) components. In the heavy quark limit M Q → ∞ the transition arises from the spin of the light degrees of freedom changing from s l = 1 to s l = 0 and hence the E2 contribution vanishes. We compute the leading contribution to the E2 strength in chiral perturbation theory and find that the amplitude is enhanced by a small energy denominator in the chiral limit. This enhancement essentially compensates for the 1 M c suppression that is present in the charm system. We find a mixing ratio of order a few percent dependent upon the ∑ c-∑ c ∗ spin symmetry breaking mass difference. The analogous quantity in the b-baryon sector is smaller by a factor of ∼ M c M b .