In recent years charm physics has undergone a renaissance, one which has been catalysed by an unexpected and impressive set of experimental results from the $B$-factories, the Tevatron and LHCb. The existence of $D^0\bar{D}{}^0$ oscillations is now well established, and the recent discovery of $CP$ violation in $D^0$ 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 the prospects for corresponding advances in theoretical understanding.
We investigate the implications of direct CP violation (CPV) on the determination of the unitarity triangle angle γ from B -> DK decays. We show that γ can still be extracted even with the inclusion of direct CPV in charm if (i) at least one of the D decays has negligible CP violation; and (ii) data from charm factory at threshold are used. If approximate expressions without including direct CP violation in charm are used, this can result in a shift in γ that is O(r_D/r_B). It is modest for B -> DK but can be O(1) for B -> Dπ. We illustrate the size of the shift on an example of Gronau-London-…
Search For Non-Standard Model CP/T violation At Tau-Charm Factory
我们系统地调查发现CP/T违反的可能性，在$τ$部门在陶魅力工厂。CP/T破坏可能发生在$τ$对产生过程中，表示为电偶极矩，并在$tau$衰减过程中。假设在Tau Charm工厂可以观测到$10^{-19}$ e cm的电偶极矩和$10^{-3}$的CP/T破坏效应，我们研究了与产生$τ$扇区CP/T破坏有关的SM的所有可能扩展。并指出有几种模型有望产生这种CP/T破坏。对于这些模型，我们考虑了所有的理论和目前的实验约束，并发现存在一些参数空间，这将导致一个可测量的CP/T破坏。因此，我们认为Tau Charm工厂是发现$τ$扇区CP/T违反的一个有希望的地方。
A new interpretation of intrinsic charm phenomenon based on the assumption of pentaquark $\left| u u d c\bar{c} \right>$ mixing with a proton is offered. The structure function of the $c$-quark in the pentaquark is constructed. Mixing different states is considered theoretically and using experiment data on $D$-meson production and inclusive production of the hidden charm particles.
We derive a strong bound on the chromo-electric dipole moment of the charm quark, and we quantify its impact on models that allow for a sizeable flavour violation in the up quark sector. In particular we show how the constraints coming from the charm and up CEDMs limit the size of new physics contributions to direct flavour violation in D meson decays. We also specialize our analysis to the cases of split-families Supersymmetry and composite Higgs models. The results we expose motivate an increase in experimental sensitivity to fundamental hadronic dipoles, and a further exploration of the SM …
The recent measurement of $ΔA_{CP}$ by the LHCb collaboration requires an ${\cal O}(10)$ enhancement coming from hadronic physics in order to be explained within the SM. We examine to what extent can NP models explain $ΔA_{CP}$ without such enhancements. We discuss the implications in terms of a low energy effective theory as well as in the context of several explicit NP models.
I review the implications of recent measurements of CP violation in D meson decays in the context of standard model extensions. Using effective theory methods, one can derive significant constraints on the possible non-standard contributions from measurements of neutral D meson mixing and direct CP violation in kaon decays. Due to an approximate universality of CP violation in new physics scenarios which only break the SU(3)_Q flavor symmetry of the standard model kinetic Lagrangian, such contributions are particularly constrained by epsilon'/epsilon. Explanations of the observed effect within…
We study the $K^0_S-K^0_L$ asymmetries and $CP$ violations in charm-baryon decays with neutral kaons in the final state. The $K^0_S-K^0_L$ asymmetry can be used to search for two-body doubly Cabibbo-suppressed amplitudes of charm-baryon decays, with the one in $Λ^+_c\to pK^0_{S,L}$ as a promising observable. Besides, it is studied for a new $CP$-violation effect in these processes, induced by the interference between the Cabibbo-favored and doubly Cabibbo-suppressed amplitudes with the neutral kaon mixing. Once the new CP-violation effect is determined by experiments, the direct $CP$ asymmetry…
The talk reviews the status of Standard Model predictions for lifetimes and mixing rates of charmed mesons. I discuss sources of SU(3) breaking in the hadron state affecting the Delta C = 2 Hamiltonian and argue that they are the dominant effect generating a D0 decay width splitting.
We present the summary of the Working Group on lifetimes, mixing and weak mixing phases in charm and beauty mesons at the CKM 2010 workshop. In the past year or so good progress was achieved on both experimental and theoretical sides. While this yields improvement in our understanding of neutral meson mixing, further work is necessary to achieve the highest possible precision in order to investigate current hints for deviations between experiment and standard model predictions. With the recent LHC startup we see bright prospects for the near term future for huge improvements.
The coherence factor and average strong phase difference of D0 and D0bar decay amplitudes to the same final state play an important role in the precision determination of the CKM parameter gamma using B- -> DK- and related decay modes. So far, this important input from the charm sector could only be obtained from measurements based on quantum-correlated DDbar pairs produced at the charm threshold. We propose to constrain these parameters using charm mixing, using the large charm samples available at the B factories and LHCb. We demonstrate for the example of D0->Kpipipi that a substantial impr…
The reported CP asymmetry in D->K^+K^- / pi^+pi^- is argued to be too large to naturally fit the SM. If so, a new source of CP violation is implied in the Delta C=1 sector with a milliweak strength. CP-odd interactions in the flavor-diagonal sector are strongly constrained by the EDMs placing severe limitations on the underlying theory. While the largest effects usually come from the New Physics energy scale, they are strongly model-dependent. Yet the interference of the CP-odd forces manifested in D decays with the conventional CP-even Delta C=1 weak interaction generates at the charm scale a…
I review recent results in theoretical and experimental analyses of CP-violation in charmed transitions, paying particular attention to constraints on parameters of beyond the Standard Model interactions.
We present a minimal extension of the Standard Model that can simultaneously account for the anomalies in semi-leptonic B meson decays and the muon g-2, give large CP violation in charm decays (up to the value recently measured by LHCb), and provide thermal-relic dark matter, while evading all constraints set by other flavour observables, LHC searches, and dark matter experiments. This is achieved by introducing only four new fields: a vectorlike quark, a vectorlike lepton, and two scalar fields (a singlet and a doublet) that mix due to the electroweak symmetry breaking and provide the dark ma…
We study the decay of the lightest neutral Higgs boson to a charm quark pair at full one-loop level in the MSSM with non-minimal quark flavour violation (QFV). In the numerical analysis we consider mixing between the second and the third squark generation and all relevant constraints from B meson data are taken into account. It is shown that the full one-loop corrected decay width can be quite sensitive to the MSSM QFV parameters due to large $\tilde c - \tilde t$ mixing and large trilinear couplings. After summarising the theoretical and experimental errors, we conclude that an observation of…
There exist experimental hints from the B sector for CP violation beyond the Standard Model (SM) CKM paradigm. An anomalous dimuon asymmetry was reported by the D0 collaboration, while tension exists between $B \to τν$ and $S_{ψK}$. These measurements, disfavoring the SM at the ~3$σ$ level, can be explained by new physics in both $B_d$-$\bar{B}_d$ and $B_s$- $\bar{B}_s$ mixing, arising from (1) new bosonic degrees of freedom at or near the electroweak scale, and (2) new, large CP-violating phases. These two new physics ingredients are precisely what is required for electroweak baryogenesis to …
Mixing and CP violation in charm meson decays provide a unique probe of possible physics beyond the standard model. In this paper, we give a brief review of the current measurements from the BABAR experiment.
We re-analyze the results of the searches for Heavy Neutral Leptons (HNLs) by the CHARM experiment. We study HNL decay channel $N\to e^{+}e^{-}ν/μ^{+}μ^{-}ν$ and show that, in addition to the constraints on the HNL's mixings with $ν_e$ or $ν_μ$, the same data also implies limits on the HNLs that mix only with $ν_τ$ and have masses in the range $380 \text{ MeV}<m_{N}\lesssim 1.6\text{ GeV}$ - the region in the parameter space that was considered in the literature as a target for HNLs searches.
It is suggested that the Higgs boson may have a branching ratio into the $c \bar{c}$ mode suppressed by several orders of magnitude compared with conventional predictions and in addition some small but detectable flavour-violating modes such as $b \bar{s}$ and $τ\barμ$. The suggestion is based on a scheme proposed and tested earlier for explaining the mixing pattern and mass hierarchy of fermions in terms of a rotating mass matrix. If confirmed, the effects would cast new light on the geometric origin of fermion generations and of the Higgs field itself.
Charm mixing and CP violation observables are examined in the light of the recently reported evidence from LHCb for CP violation in the charm sector. If the result is confirmed as being due to direct CP violation at the 1% level, its effect will need to be taken into account in the interpretation of CP violation observables. The contributions of direct and indirect CP violation to the decay rate asymmetry difference DeltaACP and the ratios of effective lifetimes AGamma and yCP are considered here. Terms relevant to the interpretation of future high precision measurements which have been neglec…
我回顾了几个涉及重强子CP破坏的问题。特别地，我讨论了（i）超子：衰变$Λ^0 \to p π^-$中的CP破坏，（ii）魅力：在SM之内和之外的D^0系统中的间接CP破坏，和（iii）美：在SM之外的中性B介子系统中的间接CP破坏。1996年8月在加拿大蒙特利尔举行的第二届超子、魅力和美强子国际会议上发表的演讲。
费米实验室的BTeV实验可以重建>10^9的粲衰变，比现存最大的样本高出三个数量级。该实验可能在Tevatron Run II期间运行。它将在魅力CP破坏、变味中性流和轻子数破坏衰变以及D0反D0混合等领域具有重要的新物理学意义，并且如果发生在标准模型预测的水平上，它可以在Cabibbo抑制的D衰变中观察到直接的CP破坏。
We investigate the impact of charm mixing on the model-independent gamma measurement using Dalitz plot analysis of the three-body D decay from B+->DK+ process, and show that ignoring the mixing at all stages of the analysis is safe up to a sub-degree level of precision. We also find that in the coherent production of D0-D0* system in e+e- collisions, the effect of charm mixing is enhanced, and propose a model-independent method to measure charm mixing parameters in the time-integrated Dalitz analysis at charm factories.
A method for measuring the average longitudinal polarization of the electron beam at an electron-positron collider operating near the $J/ψ$ resonance is proposed. The method utilizes the differential cross-section of $J/ψ\to [Λ\to pπ^-][\barΛ\to\bar{p}π^+]$ decay. It can be used to measure the average longitudinal polarization of electrons with the statistical precision better than $10^{-3}$ at a Super Charm-Tau factory operating at the luminosity of $10^{35}~\mathrm{cm}{}^{-2}\mathrm{s}{}^{-1}$. The method is discussed in the context of the weak mixing angle measurement in the same experiment…
We point out that the CP asymmetries in the decays $D^0\rightarrow K_{S} K^{*0}$ and $D^0\rightarrow K_{S} \overline{K}{}^{*0}$ are potential discovery channels for charm CP violation in the Standard Model. We stress that no flavor tagging is necessary, the untagged CP asymmetry $a_{CP}^{\mathrm{dir}}(D \to K_S K^{*0})$ is essentially equal to the tagged one, so that the untagged measurement comes with a significant statistical gain. Depending on the relevant strong phase, $\vert a_{CP}^{\text{dir, untag}}\vert$ can be as large as $0.003$. The CP asymmetry is dominantly generated by exchange d…
Since the discovery of CP violation more than 5 decades ago, this phenomenon is still attracting a lot of interest. Among the many fascinating aspects of this subject, this review is dedicated to direct CP violation in non-leptonic decays. The advances within the last decade have been enormous, driven by the increasingly large samples of b- and c-hadron decays, and have led to very interesting results such as large CP asymmetries in charmless B decays and the observation of direct CP violation in the charm sector. We address the quest for understanding the origin of strong phases, the importan…
We point out that in the Standard Model (SM) there is no explanation why $|V_{23}|^2 + |V_{13}|^2$ is of order $10^{-3}$. A framework is described for explaining this small mixing, involving the introduction of vector-like quarks. A symmetry is introduced so that at a first stage $V_{CKM} = 1\>\!\!\!\mathrm{I}$ and only the third generation of quarks acquires a mass. It is shown that when interactions of vector-like quarks are taken into account a realistic quark mass spectrum is generated together with a correct $V_{CKM}$ matrix.
The observables epsilon_K and Delta M_K play a prominent role in particle physics due to their sensitivity to new physics at short distances. To take advantage of this potential, a firm theoretical prediction of the standard-model background is essential. The charm-quark contribution is a major source of theoretical uncertainty. We address this issue by performing a next-to-next-to-leading-order (NNLO) QCD analysis of the charm-quark contribution eta_cc to the effective |Delta S|=2 Hamiltonian in the standard model. We find a large positive shift of 36%, leading to eta_cc = 1.87(76). This resu…
We study the charmonium spectrum including higher spin and gluonic excitations. We determine an upper limit on the mixing of the eta_c ground state with light pseudoscalar flavour-singlet mesons and investigate the mixing of charmonia near open charm thresholds with pairs of (excited) D and anti-D mesons. For charm and light valence quarks and nF=2 sea quarks, we employ the non-perturbatively improved Sheikholeslami-Wohlert (clover) action. Excited states are accessed using the variational technique, starting from a basis of suitably optimised operators. For some aspects of this study, the use…
LHCb is a dedicated heavy flavour physics precision experiment at the LHC searching for New Physics (NP) beyond the Standard Model (SM) through the study of very rare decays of beauty and charm-flavoured hadrons and precision measurements of CP-violating observables. In this review I will present a selection of recent precision measurements of CP-violating observables in the decays of beauty and charm-flavoured hadrons. These measurements are based on an integrated luminosity of up to $1.0 \rm{fb}^{-1}$ collected by LHCb in 2011.
CP violation (CPV) in the baryon sectors has not yet been established experimentally. In this work, we propose to search for the hyperon CPV through the Cabibbo-favored charm-baryon decaying processes involving a hyperon in the final states, such as $Λ_c^+\to Λ^0π^+, Λ^0\to pπ^-$. The CPV of the hyperon decays are purely revealed in these chain processes, since the CPV in the Cabibbo-favored charm decays are vanishing in the Standard Model (SM). The hyperons are polarized in the weak charm decays, so that we can measure the Lee-Yang asymmetric parameter $α$ by the angular distributions, and th…
There is growing evidence for deviation from the standard model predictions in the ratios between semi-tauonic and semi-leptonic $B$ decays, known as the $R(D^{(*)})$ puzzle. If the source of this non-universality is new physics, it is natural to assume that it also breaks CP symmetry. In this paper we study the possibility of measuring CP violation in semi-tauonic $B$ decays, exploiting interference between excited charm mesons. Given the current values of $R(D^{(*)})$, we find that our proposed CP-violation observable could be as large as about 10%. We discuss the experimental advantages of …
The LHCb collaboration recently announced preliminary evidence for CP violation in D meson decays. We discuss this result in the context of the standard model (SM), as well as its extensions. In the absence of reliable methods to evaluate the hadronic matrix elements involved, we can only estimate qualitatively the magnitude of the non-SM tree level operators required to generate the observed central value. In the context of an effective theory, we list the operators that can give rise to the measured CP violation and investigate constraints on them from other processes.
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 $5 σ$ discovery of CP violation in the charm system, leading to the new world average $Δa_{CP}^{\mathrm{dir}} = -0.00161 \pm 0.00028$. While some calculations have found this observation as requiring new physics, we suggest that scalar resonances nearby to $m_{D^0}$, in particular, $f_0(1710)$ and/or $f_0(1790)$ cause enhancements for CP violation within the SM. Thereby, our ca…
Time-dependent studies of inclusive charm decays to multibody self-conjugate final states can be used to determine the indirect $CP$-violating observable $A_Γ$ and the mixing observable $y_{CP}$, provided that the fractional $CP$-even content of the final state, $F_+$, is known. This approach can yield significantly improved sensitivity compared with the conventional method that relies on decays to $CP$ eigenstates. In particular, $D \to π^+π^-π^0$ appears to be an especially powerful channel, given its relatively large branching fraction and the high value of $F_+$ that has recently been meas…
After playing a pivotal role in the birth of the Standard Model in the 70's, the study of charm physics has undergone a revival during the last decade, triggered by a wealth of precision measurements from the charm and $B$ factories, and from the CDF and especially the LHCb experiments. In this article, we sum up how the unique phenomenology of charmed hadrons can be used to test the Standard Model and we review the latest measurements performed in this field by the LHCb experiment. These include the historic first observations of $CP$ violation and of a nonzero mass difference between the cha…
