arXiv subjects

Isard Dunietz

Publications and source records attributed to Isard Dunietz.

26 records · Page 2Linked to original sources

arXiv1995

Angular distributions and lifetime differences in $B_s \to J/ψϕ$ decays

The strange $B$ meson $B_s \equiv \bar b s$ and its charge-conjugate $\bar B_s \equiv b \bar s$ are expected to mix with one another in such a way that the mass eigenstates $B_s^H$ (``heavy'') and $B_s^L$ (``light'') may have a perceptible lifetime difference of up to 40\%, with the CP-even eigenstate being shorter-lived. A simple transversity analysis permits one to separate the CP-even and CP-odd components of $B_s \to J/ψϕ$, and thus to determine the lifetime difference. The utility of a similar analysis for $B^0 \to J/ψK^{*0}$ is noted.

hep-ph↗

arXiv1995

Hadronization of $b\to c\bar cs$

The b -> c cbar s transition is usually believed to hadronize predominantly in Bbar -> X_c Ds(*)- with the Ds(*)- originating from the virtual W. We demonstrate in a variety of independent ways that other hadronization processes cannot be neglected. The invariant mass of cbar s has sizable phase-space beyond m_D+m_K. The rate for Bbar -> D Dbar Kbar X could be significant and should not be ignored as was done in previous experimental analyses. We estimate the number of charmed hadrons per B-decay, n_c, to be about 1.3 to higher accuracy than obtained in previous investigations. Even though n_c is currently measured to be about 1.1, observing a significant Bbar -> D Dbar Kbar X would support n_c of about 1.3. Many testable consequences result, some of which we discuss.

hep-ph↗

arXiv1995

Bs-Bs.bar 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 $Δmt$. 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 $ρ^0 K_S, \; D_s^{(*)\pm}K^{(*)\mp}$, can be used to extract the notoriously difficult CKM unitarity triangle angle $γ$. Sizable CP violating effects may be seen with such untagged $B_s$ data samples. Listing $ΔΓ$ as an observable allows for additional important standard model constraints. Within the CKM model, the ratio $ΔΓ/ Δm$ involves no CKM parameters, only a QCD uncertainty. Thus a measurement of $ΔΓ\;(Δm)$ would predict $Δm \;(ΔΓ)$, 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 $(| ΔΓ| / Γ)_{B_s} <~ 0.3$. 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.

hep-ph↗

arXiv1994

Isospin Considerations in Correlations of Pions and $B$ mesons

The correlations between a $B$ meson and a pion produced nearby in phase space should respect isospin reflection symmetry $I_3 \to -I_3$. Thus, one generally expects similar $π^+ B^0$ and $π^- B^+$ correlations (non-exotic channels), and similar $π^- B^0$ and $π^+ B^+$ correlations (exotic channels). Exceptions include (a) fragmentation processes involving exchange of quarks with the producing system, (b) misidentification of charged kaons as charged pions, and (c) effects of decay products of the associated $\overline{B}$. All of these can affect the apparent signal for correlations of charged $B$ mesons with charged hadrons. The identification of the flavor of neutral $B$ mesons through the decay $B^0 \to K^{*0} J/ψ$ requires good particle identification in order that the decay $K^{*0} \to K^+ π^-$ not be mistaken for $\overline{K}^{*0} \to K^- π^+$, in which case the correlations of neutral $B$ mesons with hadrons can be underestimated.

hep-ph↗

arXiv1994

Distinguishing $B$ and $\overline B$ Hadrons

Distinguishing the flavor of $B$ and $\overline B$ hadrons is critical in studies of CP-violation, $B^0 -\overline{B^0}$ mixing, and the underlying $b$-decay mechanisms. Methods of $b$ ``flavor tagging" are broadly divided into ``opposite $b$" tagging and self-tagging of the signal $b$ hadron. The former, while understood, has the perceived drawback of low efficiency. The latter, while having the potential for an order of magnitude higher efficiency, has yet to be demonstrated for neutral $B$ hadrons. In this article we review opposite $b$ tagging in light of methods whose efficacy has only recently been demonstrated or suggested. In addition, we recommend a number of tagging methods for the opposite $b$ including: $K^{*0}$ and $K^{*\pm}$ with large inclusive yields of 15\% and 18\%; $\overline Λ$ and $\overline Λp $; partially reconstructed charmed hadrons; sophisticated jet charge techniques, etc. We also recommend the use of self-tagging for the $opposite$ $b$ hadron. Such an inversion of self-tagging could conceivably increase the efficiency of opposite $b$ tagging and even mitigate the effects of neutral $B$ mixing. Self-tagging of the signal hadron, when possible, could be used either by itself or to confirm the result from the opposite $b$ tag. We suggest that all methods be weighted by their dilutions and combined to yield efficient tagging. For a given detector, this requires that the dilution of each tag be well measured. We therefore review the determination of the dilution $D_T$ for a general tag $T$ in some detail. Finally, we briefly consider $B$ sector and suggest a number of exclusive modes which can be combined for higher statistics probes of the unitarity angles. While ambitious from an experimental perspective, the program of flavor identification outlined here has the potential to yield important fundamental results in the near future.

hep-ph↗

arXiv1994

Inconclusive Inclusive Nonleptonic $B$ Decays

We reconsider the conflict between recent calculations of the semileptonic branching ratio of the $B$ meson and the experimentally measured rate. Such calculations depend crucially on the application of ``local duality'' in nonleptonic decays, and we discuss the relation of this assumption to the weaker assumptions required to compute the semileptonic decay rate. We suggest that the discrepancy between theory and experiment might be due to the channel with two charm quarks in the final state, either because of a small value for $m_c$ or because of a failure of local duality. We examine the experimental consequences of such solutions for the charm multiplicity in $B$ decays.

hep-ph↗

arXiv1994

Another Source of Baryons in $B$ Meson Decays

It is usually assumed that the production of baryons in $B$ meson decays is induced primarily by the quark level process $b\to c\bar ud$, where the charm quark hadronizes into a charmed baryon. With this assumption, the $Λ_c$ momentum spectrum would indicate that the transition $B\toΛ_c X$ is dominated by multi-body $B$ decays. However, a closer examination of the momentum spectrum reveals that the mass $m_X$ against which the $Λ_c$ is recoiling almost always satisfies $m_X\agt m_{Ξ_c}$. This fact leads us to examine the hypothesis that the production of charmed baryons in $B$ decays is in fact dominated by the underlying transition $b\to c\bar cs$, and is seen primarily in modes with two charmed baryons in the final state. We propose a number of tests of this hypothesis. If this mechanism is indeed important in baryon production, then there are interesting consequences and applications, including potentially important implications for the ``charm deficit'' in $B$ decays.

hep-ph↗

arXiv1993

Direct CP violation in b -> d J/ψdecays

We investigate the possibility of observing direct CP violation in self-tagging B-meson decays of the type b -> d J/ψ. The CP asymmetry can be generated due to strong or electromagnetic scattering in the final state, or due to long distance effects. The first two contributions give asymmetries of a few 10^(-3), in the standard model. The long distance effects are hard to estimate, but it cannot be excluded that they yield asymmetries of about 1%.

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