D0 Mixing Research Articles

On the role of LHC and HL-LHC in constraining flavor changing neutral currents

The Standard Model has no Flavor-Changing Neutral Current (FCNC) processes at the tree level. Therefore, processes featuring FCNC in new physics are tightly constrained by data. Typically, the lower bounds on the scale of new physics obtained from K−K¯ or B−B¯ mixing lie well above 10 TeV, surpassing the reach of current and future colliders. In this paper, we demonstrate, using a specific Z′ model that features flavor-changing interactions, that such limits can be severely weakened by specific choices of the quark mixing matrices with no prejudice while maintaining the CKM matrix in agreement with the data. We highlight the valuable role of the often-overlooked D0 mixing in deriving robust FCNC limits and show that the LHC and HL-LHC are promising probes for flavor-changing interactions mediated by a Z′ boson.

Social status and previous experience in the group as predictors of welfare of sows housed in large semi-static groups.

Mixing gestating sows implies hierarchy formation and has detrimental consequences on welfare. The effects of social stress on the most vulnerable individuals may be underestimated and it is therefore important to evaluate welfare between individuals within groups. This study aimed at investigating the impact of social status and previous experience in the group on well-being of sows housed in large semi-static groups. We assessed aggression (d0 (mixing), d2, d27, d29), body lesions (d1, d26, d84) and feeding order on 20 groups of 46–91 animals. Social status was based on the proportion of fights won during a 6-hr observation period between d0 and d2. Dominants (29%) were those who won more fights than they lost, Subdominants (25%) won fewer fights than they lost, Losers (23%) never won any fight in which they were involved while Avoiders (23%) were never involved in fights. Resident sows (70%) were already present in the group in the previous gestation while New sows (30%) were newly introduced at mixing. Subdominants and Dominants were highly involved in fights around mixing but this was more detrimental for Subdominants than Dominants, Losers and Avoiders since they had the highest body lesion scores at mixing. Avoiders received less non-reciprocal agonistic acts than Losers on d2 (P = 0.0001) and had the lowest body lesion scores after mixing. However, Avoiders and Losers were more at risk in the long-term since they had the highest body lesions scores at d26 and d84. They were followed by Subdominants and then Dominants. New sows fought more (P<0.0001), tended to be involved in longer fights (P = 0.075) around mixing and had more body lesions throughout gestation than Resident sows. Feeding order from one-month post-mixing was influenced both by the previous experience in the group and social status (P<0.0001). New sows, especially with a low social status, are more vulnerable throughout gestation and could serve as indicators of non-optimal conditions.

Overview of recent LHCb results

A selection of the most recent and relevant measurements by the LHCb experiment is presented. It includes the determination of the CKM angle γ, obtained from a combination of a number of measurements of B meson decays, the measurement of the D0 - D0 mixing parameters and the results of several tests of the lepton-flavour universality of the electroweak couplings.

Charm mixing and CP violation at LHCb

The LHCb experiment has collected the world's largest sample of charmed hadrons. Using data corresponding to an integrated luminosity of 3.0 fb−1 recorded in 2011 and 2012, measurements of direct and indirect CP violation in the charm sector and of D0 mixing parameters were performed. Results from several decay modes are presented with complementary time-dependent and time-integrated analyses.

Charm mixing and CP violation at LHCb

In pp collisions at the LHC the LHCb experiment has collected the world's largest sample of charmed hadrons. Using data of an integrated luminosity of 1.0 fb−1 recorded in 2011 a measurement of direct and indirect CP violation in the charm sector and of D0 mixing parameters was performed. Results from several decay modes are presented with complementary time-dependent and time-integrated analyses.

Measurement ofCP-violating asymmetries inD0→π+π−andD0→K+K−decays at CDF

We report on a measurement of CP-violating asymmetries (Acp) in the Cabibbo-suppressed D0 --> pi+ pi- and D0 --> K+K- decays reconstructed in a data sample corresponding to 5.9 fb-1 of integrated luminosity collected by the upgraded Collider Detector at Fermilab. We use the strong decay D*+ --> D0 pi+ to identify the flavor of the charmed meson at production and exploit CP-conserving strong c-cbar pair-production in p-pbar collisions. High-statistics samples of Cabibbo-favored D0 --> K- p+ decays with and without a D* tag are used to correct for instrumental effects and significantly reduce systematic uncertainties. We measure Acp(D0 --> pi+ pi-) = (+0.22 +- 0.24 (stat) +- 0.11 (syst))% and Acp(D 0 --> K+ K-) = (-0.24 +- 0.22 (stat) +- 0.09 (syst))%, in agreement with CP conservation. These are the most precise determinations from a single experiment to date. Under the assumption of negligible direct CP violation in D0 --> pi+ pi- and D0 --> K+K- decays, the results provide an upper limit to the CP-violating asymmetry in D0 mixing, |Acp^{ind}(D0)|< 0.13% at the 90% confidence level.

D0-D̄0 mixing and other charm decays at Belle

The D0-D̄0 mixing at Belle in different modes with corresponding methods is reported in this paper, there is a clear evidence for non-zero y D0 mixing parameter, and the measurement of D0 mixing parameter x is still a challenge. CP violation in the decays is not observed. Branching fractions of other charm decays are presented.

Search for TeV scale physics in heavy flavor decays

The subject of heavy flavor decays as probes for physics at and beyond the TeV scale is covered from the experimental perspective. Emphasis is placed on the more traditional beyond the standard model topics that have potential for impact in the early LHC era, and that are in anticipation of the B factory upgrade(s). The aim is to explain the physics, without getting too involved in the details, whether experimental or theoretical, to give the interested non-expert a perspective on the flavor/TeV link. We cover the forefront topics of CP violation in b→s transitions involving penguin and box diagrams, and probes of charged Higgs, right-handed and scalar interactions. We touch briefly on ϒ decay, D 0 mixing, rare K decays, and lepton flavor violating probes in τ decay. Our own phenomenological work is often used for illustration.

D0 mixing, lifetime differences, and hadronic decays of charmed hadrons

Presented are preliminary results from the BABAR Collaboration on charm physics, including limits on D 0 mixing from the ratio of lifetimes from K − π +, K + K −, and π + π − final states (using 47.8 fb −1 of data) and branching ratio, and Dalitz amplitude analyses of the decays D 0 → K 0K −π +, K 0 K +π − , and K 0 K +K − (using 22 fb −1 of data). The status of direct measurements of D 0 mixing using wrong-sign D 0 → K + π − decays is also discussed.

Study of the decay D0 --> K+pi-.

Using a large sample of photoproduced charm mesons from the FOCUS experiment at Fermilab (FNAL-E831), we observe the decay D0-->K+pi- with a signal yield of 149+/-31 events compared to a similarly cut sample consisting of 36 760+/-195 D0-->K-pi+ events. We use the observed ratio of D0-->K+pi- to D0-->K-pi+ (0.404+/-0.085+/-0.025)% to obtain a relationship between the D0 mixing and doubly Cabibbo suppressed decay parameters.

$$D\bar D$$ and$$B\bar B$$ mixingmixing

The results on D0 and B0 mixing are reviewed. The status of searches for D0 mixing is given and the role of the interference with doubly-Cabibbosuppressed decays is discussed. Both integrated and time-dependent measurements on Bd0 decays are presented: a very good precision on Δmd determination is reached. Limits on Δms are given.

On testing unitarity of the quark mixing matrix

Unitarity triangles and characteristic measurables of the 3 × 3 Cabibbo-Kobayashi-Maskawa (CKM) matrix are discussed. Beyond the 3 × 3 CKM scheme we make a rephasing-invariant generalization of the Gronau-WylerDunietz approach to determine the weak phase shift in Bu± → DK± or in Bd → DK*, which is only sensitive to the underlying new physics in D0−D0 mixing. We also show that the weak angle γ ≡ arg(−Vub*VudVcbVcd*) is possible to be determined from the CP asymmetries of some Bd decays, even in a non-standard model with an extended quark sector. Brief comments are given on tests of unitarity of the 3 × 3 CKM matrix.

Upper limit on B d0 − [formula omitted]d0 mixing as evidence for the existence of the top quark

We consider the mixing between the neutral B d 0 mesons in an SU(2) L×U(1) model without a top quark, in which b L is an SU(2) L singlet. The mixing parameter x d = δm B d 0 / Γ b, arising from the resulting flavour changing neutra currents is found to be one to two orders of magnitude larger than the value measured experimentally. This is a very strong evidence for the existence of the top quark, comparable to that coming from the b→ μ + μ −X branching ratio.

Static cavity calculation of heavy meson neutral mixing with QCD corrections

The neutral mixing matrix elements describing D0 and B0 mixing are calculated in a static cavity model previously fitted to the ΔI=12 rule of kaon decay. Since the model is based on O(g) wavefunctions, computation of hadronic matrix elements includes O(g2) corrections. Specifically, we compute the quantities ƒDBDand ƒBBB for basis sizes NB=1, 2, 3 and 6. At NB=6 we find the values ƒDBB=90 MeV and ƒBBB=62 MeV. The ratio of these quantities agrees well with non-relativistic expectations.

Study of D0-D-bar0 mixing.

We present a study of D0 mixing using events of the type D*+→π+D0, with D0→K+π− and D0→K+π−π+π−. The decay time is used to separate mixing from doubly Cabibbo-suppressed decays. We observe no evidence for mixing in either mode. Combining the results from the two decay modes, we find rM=0.0005 ±0.0020 or rM<0.0037 at the 90% confidence level, where rM is the ratio of wrong-sign decays from mixing to right-sign decays. We also present limits on doubly Cabibbo-suppressed decays and consider the effect of possible interference.Received 18 December 1987DOI:https://doi.org/10.1103/PhysRevLett.60.1239©1988 American Physical Society

The effect of B d0 [formula omitted]d0 mixing on searches for CP violation

We use recently reported B d 0 B d 0 mixing to remove almost all dependence on the top quark mass from analyses of CP violation. We obtain a bound on the KM angles S 3 S δ⩽1.4×10 −2, with a preferred value near 8×10 −3. The combination S 1 S 2 S 3 S δ relevant for CP violation is bounded by 2.7×10 −4. Consequences for experiments with kaons, hyperons and B-mesons are discussed.