Large Width Difference Research Articles

SU(3) breaking effect in the Zc and Zcs states

Based on the hadronic resonance picture, we explore a unified framework to describe the observed Zcs and Zc states that are close to the thresholds of the D(*)D¯s(*) and D(*)D¯(*) systems, respectively. We assume that the Zcs(4000) and Zcs(3985) are two different states. Specifically, we assign the Zcs(4000) as the SU(3) partner of the Zc(3900) (JPC=1+−) due to its observation in the J/ΨK channel, the difficulty of this assignment is the large width difference between the Zcs(4000) and the Zc(3900) state. Then the Zcs(3985) should corresponds to the Zc state that is close to the threshold of DD¯* system with JPC=1++, the difficulty of this assignment is the absence of such a Zc state in experiment. We construct the effective potentials of the Zcs and Zc states by analogy with the effective potentials of the leading-order and next-to-leading-order N−N¯ interactions. Then we introduce an SU(3) breaking factor gx to identify the differences between the effective potentials in the Zcs and Zc states. We perform two calculations to discuss the differences and similarities of the Zcs and Zc states. In the first calculation, we show that the above two difficulties can be explained simultaneously by the inclusion of the SU(3) breaking effect. In the second calculation, we show that this framework is promising to simultaneously describe the interactions of the observed Zcs and Zc states that are close to the thresholds of the D(*)D¯s(*) and D(*)D¯(*) systems, respectively. Published by the American Physical Society 2024

Lessons from CLEO and FOCUS measurements of [formula omitted] mixing parameters

If the true values of the D 0 – D 0 mixing parameters lie within the one sigma ranges of recent measurements, then there is strong evidence for a large width difference, y≳0.01, and large SU(3) breaking effects in strong phases, δ≳ π/4. These constraints are model independent, and would become stronger if | M 12/ Γ 12|≪1 in the D 0 – D 0 system. The interesting fact that the FOCUS result cannot be explained by a large mass difference is not trivial and depends on the small D 0/ D 0 production asymmetry in FOCUS and the bounds on CP violating effects from CLEO. The large value of δ might help explain why y∼sin 2 θ c .

Strong phases and D0-anti-D0 mixing parameters

We argue that there could be large, SU(3) violating resonance contributions to D -> K pi decays which would affect the extraction of the D0-anti-D0 mixing parameters from experiment. Such contributions can induce a large strong phase in the interference between the doubly Cabibbo suppressed and the mixing induced Cabibbo favored contributions to the D0 -> K^+ pi^- and anti-D0 -> K^- pi^+ decays. Consequently, the interpretation of a large, CP conserving interference term can involve a large mass difference Delta M rather than a large width difference Delta Gamma.

Compositional and temperature dependence of free volume in segmented copolymer PET/PEO studied by positron annihilation lifetime measurement

Positron lifetime measurements were performed for segmented copolymer poly(ethylene oxide)–poly(ethylene terephthalate) (PEO/PET) as a function of the hard segment content (PET) and the temperature, which is used to study the free volume properties, structural transition and miscibility behaviour of segmented copolymer PEO/PET. From the variation of the ortho-positronium ( o-Ps) lifetimes with changes in the hard segment content, we find that the free volume decreases with increase of the hard segment, this fact means that the hard segment microdomains act as physical cross-links that suppress movement of the chains and that the interactions between the hard segment (PET) and soft segment (PEO) also plays an important role. On the other hand, the temperature dependence of positron lifetimes reveals the existence of two glass transition temperatures. This experimental results show that the hard segment PET is immiscibility with soft segment PEO in segmented copolymer PEO/PET (PEO molecular weight 4000, PET content 30 wt.%). The maximum entropy lifetime method (MELT) is used to detect the distributions of the free volume holes. Large differences in width of the free volume hole distributions as a function of temperature are observed.

Positron Lifetime Distributions and Free Volume Parameters of PEO/PMMA Blends Determined with the Maximum Entropy Method

The temperature dependence of the average free volume hole size and its distribution in blends of poly(methyl methacrylate) and poly(ethylene oxide) were studied by positron annihilation lifetime spectroscopy. Measurements at room temperature, 70 °C, and 110 °C all indicate that the average ortho-positronium lifetime (τ3), and thus the free volume hole size of the blends, shows a positive deviation from additivity of the values of the pure components. Mean ortho-positronium (o-Ps) lifetimes and intensities were calculated with the POSITRONFIT program, while o-Ps lifetime distributions were obtained from evaluations made with a recently introduced program based on Bayes' theorem and the maximum entropy principle. o-Ps lifetime distributions were successfully calculated for all measured spectra and offer valuable additional information about the structure of the studied blends. At 70 °C, the distributions seem to reflect the lifetimes in a blend of binodal composition. Large differences in width of the o-Ps lifetime distributions as a function of blend composition and temperature are observed.

The Bs width difference beyond the Standard Model

The Standard Model predicts a large width difference in the B s system. New physics can contribute significantly to the mass difference. If this contribution is CP violating, this will always result in a reduction of the width difference. The analyses of measurements of the width difference using B s decays into CP eigenstates have to be modified in the presence of new physics. We discuss how the width difference and the new CP violating phase in B s mixing can be measured.

Bs-B-bars mixing, CP violation, and extraction of CKM phases from untagged Bs data samples.

A width difference of the order of 20\% has previously been predicted for the two mass eigenstates of the $B_s$ meson. The dominant contributor to the width difference is the $b\rightarrow c\bar c s$ transition, with final states common to both $B_s$ and $\overline{B}_s$. All current experimental analyses fit the time-dependences of flavor-specific $B_s$-modes to a single exponential, which essentially determines the average $B_s$ lifetime. We stress that the same data sample allows even the measurement of the width difference. To see that, this note reviews the time-dependent formulae for tagged $B_s$ decays, which involve rapid oscillatory terms depending on $\Delta mt$. In untagged data samples the rapid oscillatory terms cancel. Their time-evolutions depend only on the much more slowly varying exponential falloffs. We discuss in detail the extraction of the two widths, and identify the large (small) CP-even (-odd) rate with that of the light (heavy) $B_s$ mass eigenstate. It is demonstrated that decay length distributions of some \underline{untagged} $B_s$ modes, such as $\rho^0 K_S, \; D_s^{(*)\pm}K^{(*)\mp}$, can be used to extract the notoriously difficult CKM unitarity triangle angle $\gamma$. Sizable CP violating effects may be seen with such untagged $B_s$ data samples. Listing $\Delta\Gamma$ as an observable allows for additional important standard model constraints. Within the CKM model, the ratio $\Delta\Gamma/ \Delta m$ involves no CKM parameters, only a QCD uncertainty. Thus a measurement of $\Delta\Gamma \;(\Delta m)$ would predict $\Delta m \;(\Delta\Gamma )$, up to the QCD uncertainty. A large width difference would automatically solve the puzzle of the number of charmed hadrons per $B$ decay in favor of theory. We also derive an upper limit of $(| \Delta\Gamma | / \Gamma)_{B_s} <~ 0.3$. Further, we must abandon the notion of branching fractions of $B_s\rightarrow f$, and instead consider $ B(B^0_{L(H)}\rightarrow f)$, in analogy to the neutral kaons.