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تسجيل مستخدم جديدD0 Mixing and CP Violation in D Decays
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تأليف
Erica Polycarpo
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We present a brief review of CPV and mixing measurements in the charm sector, with emphasys in results published or presented since the previous edition of the Physics in Collision Symposia.
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Measurements of charm mixing parameters from the decay-time-dependent ratio of D0->K+pi- to D0->K-pi+ rates and the charge-conjugate ratio are reported. The analysis uses data, corresponding to 3 fb^{-1} of integrated luminosity, from proton-proton c
ollisions at 7 and 8 TeV center-of-mass energies recorded by the LHCb experiment. In the limit of charge-parity (CP) symmetry, the mixing parameters are determined to be x^2=(5.5 +- 4.9)x10^{-5}, y= (4.8 +- 1.0)x10^{-3}, and R_D=(3.568 +- 0.066)x10^{-3}. Allowing for CP violation, the mixing parameters are determined separately for D0 and D0bar mesons yielding A_D = (-0.7 +- 1.9)%, for the direct CP-violating asymmetry, and 0.75 < |q/p|< 1.24 at the 68.3% confidence level, where q and p are parameters that describe the mass eigenstates of the neutral charm mesons in terms of the flavor eigenstates. This is the most precise determination of these parameters from a single experiment and shows no evidence for CP violation.
In current searches for D0 anti-D0 mixing, the time evolution of ``wrong-sign decays is used to distinguish between a potential mixing signal and the dominant background from doubly-Cabibbo-suppressed decays. A term proportional to $Delta Mt$ in the
expression for the time evolution is often neglected in theoretical discussions and experimental analyses of these processes. We emphasize that, in general, this term does not vanish even in the case of CP invariance. Furthermore, CP invariance is likely to be violated if the rate of D0 anti-D0 mixing is close to the experimental bound. The consequence of either of these two facts is that the strongest existing measured bound is not applicable for constraining New Physics.
The phenomenon of mixing in neutral meson systems has now been observed in all flavours, but only in the past year in the D0 system. The standard model anticipated that, for the charm sector, the mixing rate would be small, and also that CP violation
, either in mixing or in direct decay, would be below the present levels of observability. It is hoped that further study of these phenomena might reveal signs of new physics. A review of recently available, experimental results is given.
The 10$^{rm th}$ International Workshop on the CKM Unitary Triangle took place at the University of Heidelberg on September 17$^{rm th}$-21$^{rm st}$, 2018. In this write-up, we summarize the material discussed at the workshop by the Working Group 7,
which focused on latest experimental results and theoretical developments in the study of mixing and $CP$ violation in the neutral $D$ system, and of $CP$ violation and decay properties of other charm mesons and baryons.
We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of $D^0to K^+pi^-$ to $D^0to K^-pi^+$ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of $5.0$ fb$^
{-1}$ recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be $x^2=(3.9 pm 2.7) times10^{-5}$, $y=(5.28 pm 0.52) times 10^{-3}$, and $R_D=(3.454 pm 0.031)times10^{-3}$. Without this assumption, the measurement is performed separately for $D^0$ and $overline{D}{}^0$ mesons, yielding a direct CP-violating asymmetry $A_D =(-0.1pm9.1)times10^{-3}$, and magnitude of the ratio of mixing parameters $1.00< |q/p| <1.35$ at the $68.3%$ confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed.
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