arXiv subjects

David Atwood

Publications and source records attributed to David Atwood.

At least 55 records · Page 3Linked to original sources

arXiv1998

Extracting information on CKM phases, electro-weak penguins and new physics from B --> VV decays

We derive constraints for $B\to VV$ modes ($V= vector meson) that allow aquantitative assessment of the contributions from electroweak penguins (EWP) and/or new physics. Interplay of direct CP with oscillation studies then leads to the extraction of the angles alpha and gamma, using B--> K* omega rho and B--> rho omega (phi) respectively, if by using our constraint equations it can be experimentally demonstrated that color-suppressed EWP are small.

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arXiv1998

Two body decays of the $b$-quark: Applications to direct CP violation, searches for electro-weak penguins and new physics

A systematic experimental search for two-body hadronic decays of the b-quark of the type b to quark + meson is proposed. These reactions have a well defined experimental signature and they should be theoretically cleaner compared to exclusive decays. Many modes have appreciable branching ratios and partial rate asymmetries may also be quite large (about 8-50%) in several of them. In a few cases electroweak penguins appear to be dominant and may be measurable. CP violating triple correlation asymmetries provide a clean test of the Standard Model.

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arXiv1997

The Possibility of Large Direct CP Violation in B to K pi-Like Modes Due to Long Distance Rescattering Effects and Implications for the Angle gamma

We consider the strong rescattering effects that can occur in the decays such as B -> K pi, K* pi, K rho... and their impact on direct CP violation in these modes. First we discuss, in general, how the CPT theorem constrains the resulting pattern of partial rate asymmetries leading to different brands of direct CP. Traditional discussions have centered around the absorptive part of the penguin graph which has Delta I=0 in b -> s transitions and as a result causes ``simple'' CP violation; long-distance final state rescattering effects, in general, will lead to a different pattern of CP: ``compound'' CP violation. Predictions of simple CP are quite distinct from that of compound CP. Final states rescattering phases in B decays are unlikely to be small possibly causing large compound CP violating partial rate asymmetries in these modes. CPT theorem requires a cancellation of PRA due to compound CP amongst the $Kπ$ states themselves; thus there can be no net cancellation with other states such as K*π, Kρetc. Therefore, each class of such modes, namely K pi, K rho, K^*pi, K a_1 etc. can have large direct CP emanating from rescattering effects. Various repercussions for the angle $γ$ are also discussed.

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arXiv1997

$t \to cWW$ and $WW \to \bar{t}c + t\bar{c}$ in Extended Models

Jenkins has pointed out that the process $t\to cW^+W^-$ is GIM suppressed in the standard model. In this note, we calculate the branching ratio for a wide range of models, in which the decay occurs at tree level through exchange of a scalar, fermion or vector. In the case of scalar exchange, a scalar mass between $2m_W$ and 200 GeV leads to a resonant enhancement, giving a branching ratio as high as a few tenths of a percent. We then note that all of these models will also allow $W^+W^-\to \bar{t}c+t\bar{c}$, and we calculate the single-top/single-charm production rate at the LHC. The rates aren't negligibly small, but the background from single-top/single-bottom production will probably swamp the signal.

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arXiv1997

New Methods for Extracting the CKM Angle $γ$ using $B^\pm\to D^0 K^-$; $\bar D^0 K^-$

In this talk I will discuss the extraction of the CKM angle $γ$ at B-factories through the interference of the subprocesses $B^-\to K^- D^0$ and $B^- \to K^-\bar D^0$. This seemingly impossible interference may be accomplished by allowing both $D^0$ and $\bar D^0$ to decay to a common final state. If only CP eigenstate decay modes of the $D$ are considered, the branching ratio for $B^- \to \bar D^0 K^-$ must be experimentally I describe why this determination is likely to be experimentally impossible. On the other hand, if more general $D$ decays are considered, the angle $γ$ may then be determined. In fact, it is possible that a reasonable determination of $γ$ may be made with O(10^8) B's.

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arXiv1997

Desperately Seeking Non-Standard Phases via Direct CP Violation in $b\to sg^\ast$ Process

Attributing the recent CLEO discovery of $B \to η' + X_s$ to originate (primarily) from the fragmentation of an off-shell gluon ($g^*$) via $b \to s + g^*$, $g^* \to g + η'$, we emphasize that many such states ($X_g$) should materialize. Indeed the hadronic fragments ($X_g$) of $g^*$ states are closely related to those seen in $ψ\to γ(ϕ, ω) + X_g$. A particular final state of considerable interest is $X_g=K^+K^-$. Signals from such states in $B$ decays can be combined to provide a very sensitive search for CP violating phase(s) from non-standard physics. The method should work even if the contribution of these source(s) to the rates is rather small ($\sim10%$) to the point that a comparison between theory and experiment may find it extremely difficult to reveal the presence of such a new physics.

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arXiv1997

B to eta' + X and The QCD Anomaly

Mechanisms for the observed large $Br(B \to η' +X_s)$ are examined. We propose that the dominant fraction of the $B \to η' +X_s$ rate is due mainly to $b \to s g^*$, where $g^*$ is an off-shell gluon, followed by $g^* \to gη'$ via the anomalous coupling of the $η'$ to two gluons. The calculated rate for $B \to η'+X_s$ is in rough accord with experiment using a fairly constant glue-glue-$η'$ form factor. This behavior of the form factor may be indicative of glueball dominance of the channel. Searches via the modes $η' h^+h^-$ ($h=π$ or $K$) may be worthwhile. Charmonia contributions [i.e $B \to η_c, ψ(\to η'+X) +X_s$] can only account for at most 20% of the central value of the signal. Implications for $B \to η' +X_d$ and for the corresponding $η$ modes are also given.

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arXiv1997

Mixing-induced CP Asymmetries in Radiative B Decays in and beyond the Standard Model

In the Standard Model (SM) the photon in radiative $\bar B^0$ and $\bar B_s$ decays is predominantly left-handed. Thus, mixing induced CP asymmetries in $b\to sγ$ and $b\to dγ$ are suppressed by $m_s/m_b$ and $m_d/m_b$, respectively, and are very small. In many extensions of the SM, such as the left-right symmetric model (LRSM), SU(2)xU(1) models with exotic fermions and SUSY, the amplitude of right-handed photons grows proportional to the virtual heavy fermion mass, which can lead to large asymmetries. As an example, in the LRSM, asymmetries larger than 50% are possible even when radiative decay rate measurements agree with SM predictions.

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arXiv1997

Parity Violation in Bottom Quark Pair Production at Polarized Hadron Colliders

Parity violation induced by the chromo-anapole form factor of the bottom quark, generated from weak corrections, is studied in polarized hadron collisions. The forward-backward asymmetry in the bottom quark pair production at polarized $pp$ and $p\bar{p}$ colliders is evaluated in the Standard Model and in a Two Higgs Doublet Model to examine the effects of parity violation. In the models studied, promising results are found for polarized $p\bar{p}$ colliders.

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arXiv1996

Enhanced CP Violation with $B\to K D^0 (\overline D^0)$ Modes and Extraction of the CKM Angle gamma

The Gronau-London-Wyler (GLW) method extracts the CKM angle $γ$ by measuring $B^\pm$ decay rates involving $D^0/\overline D^0$ mesons. Since that method necessitates the interference between two amplitudes that are significantly different in magnitude, the resulting asymmetries tend to be small. CP violation can be greatly enhanced for decays to final states that are common to both D^0 and $\overline D^0$ and that are not CP eigenstates. In particular, large asymmetries are possible for final states f such that $D^0\to f$ is doubly Cabibbo suppressed while $\overline D^0\to f$ is Cabibbo allowed. The measurement of interference effects in two such modes allows the extraction of $γ$ without prior knowledge of $Br(B^-\to K^- \overline D^0)$, which may be difficult to determine due to backgrounds.

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arXiv1996

Signals from Flavor Changing Scalar Currents at the Future Colliders

We present a general phenomenological analysis of a class of Two Higgs Doublet Models with Flavor Changing Neutral Currents arising at the tree level. The existing constraints mainly affect the couplings of the first two generations of quarks, leaving the possibility for non negligible Flavor Changing couplings of the top quark open. The next generation of lepton and hadron colliders will offer the right environment to study the physics of the top quark and to unravel the presence of new physics beyond the Standar Model. In this context we discuss some interesting signals from Flavor Changing Scalar Neutral Currents.

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arXiv1996

Phenomenology of Two Higgs Doublet Models with Flavor Changing Neutral Currents

A comprehensive phenomenological analysis of a two Higgs doublet model, with flavor changing scalar currents at the tree level, called model III, is presented. Constraints from existing experimental information especially on (Delta F)=2 processes are systematically incorporated. Constraints emerging from rare B-decays, Z-->b\bar b, and the ρparameter are also examined. Experimental implications for e^+e^- (μ^+μ^-)-->t\bar c+\bar t c, t-->cγ(Z,g), D^0-\bar D^0, and B^0_s-\bar B^0_s oscillations, and for e^+e^-(Z)-->b\bar s+s\bar b are investigated and experimental effort towards these is stressed. We also emphasize the importance of clarifying the experimental issues pertaining to Z-->b\bar b.

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arXiv1996

CP Conserving and CP Violating Asymmetries in $e^+e^-\to t\bar tν_e\barν_e$} at the NLC: Application to Determining the Higgs Width

The polarization asymmetries of $t$, $\bar t$ quarks can be used in the reaction $e^+e^-\to t\bar tν_e\barν_e$ to measure the Higgs width, in the Standard Model or in its extensions, and to search for non-standard CP violating phases. As an application of the CPT theorem the Higgs width is monitored through a CP-even, $T_N$-odd, polarization asymmetry, $B_y$. CP violation manifests through interference at tree graph level with the resonant Higgs amplitude. Consequently, the asymmetries are all quite sizable and can be in the range of 10--50\% for a wide choice of the Higgs mass.

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arXiv1996

CP Nonconservation in $p\bar p\to t\bar b X$ at the Tevatron

The reaction $p\bar p\to t\bar bX$ is found to be rather rich in exhibiting several different types of CP asymmetries. The spin of the top quark plays an important role. Asymmetries are related to form factors arising from radiative corrections of the $tbW$ production vertex due to non-standard physics. As illustrations, effects are studied in two Higgs Doublet Models and in Supersymmetric Models; asymmetries up to a few percent may be possible.

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arXiv1996

$R_b$ and $R_c$ in the Two Higgs Doublet Model with Flavor Changing Neutral Currents

A study of $R_b$ and $R_c$ is presented in the context of a Two Higgs Doublet Model (2HDM) with flavor changing scalar currents (FCSC). Implications of the model for the $ρ$-parameter and for $b\to sγ$ are also considered. The experimental data on $R_b$ places stringent constraints on the model parameters. The configuration of the model needed to account for $R_b$ is found to be irreconcilable with constraints from $b\to sγ$ and $ρ$. In particular, if $R^{\rm exp}_b>R^{\sss{\rm SM}}_b$ persists then this version of 2HDM will be ruled out or require significant modifications. Noting that aspects of the experimental analysis for $R_b$ and $R_c$ may be of some concern, we also disregard $R^{\rm exp}_b$ and $R^{\rm exp}_c$ and give predictions for these using constraints from $b\to sγ$ and $ρ$ parameter only. We emphasize the theoretical and experimental advantages of the observable $R_{b+c}\equiv Γ(Z\to b\bar b\mbox{ or } c\bar c)/Γ(Z\to\mbox{hadrons})$. We also stress the role of $R_\ell\equiv Γ(Z\to\mbox{hadrons})/Γ(Z\to \ell^+\ell^-)$ in testing the Standard Model (SM) despite its dependence on QCD corrections. Noting that in models with FCNC the amplitude for $Z\to c\bar c$ receives a contribution which grows with $m^2_t$, the importance and uniqueness of precision $Z\to c\bar c$ measurements for constraining flavor changing $t\bar c$ currents is underscored.

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arXiv1995

Flavor Changing Neutral Scalar Currents at $μ^+μ^-$ Colliders

The prospect of observing the flavor changing decay $\fH\to t\bar c$ of a neutral Higgs boson produced via $s$-channel and its subsequent decay into $t\bar c$ is considered at a $μ^+μ^-$ collider. Numerical estimates are given in the context of a two Higgs doublet model with flavor changing couplings. It is found that for many values of the model parameters such {\it tree-level} flavor changing decays will be produced at an observable level. In addition studies of the helicity of the top will allow the determination of the relative strengths of the flavor changing Higgs couplings and these may be measured with about $10^3$ events.

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arXiv1995

Probing flavor changing top-charm-scalar interactions in $e^+e^-$ collisions

Due to the very large mass of the top-quark, probing the flavor changing top-charm-scalar vertex is clearly very important. Fortunately the largeness of $m_t$ endows a unique signature to the resulting reaction i.e., $e^+e^-\to t\bar c (\bar t c)$ that should be helpful in identification of such events. A two Higgs doublet model, without natural flavor conservation, is used to give an illustrative estimate for the rate for these reactions.

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arXiv1995

Neutral Higgs CP Violation at $μ^+μ^-$ colliders

CP violating asymmetries in both the production and the decays of $s$-channel neutral Higgs bosons at $μ^+μ^-$ colliders can be large. If the CP violation occurs in the muon-Higgs coupling, one observes a production asymmetry with transversely polarized $μ^+μ^-$ beams. Likewise if the CP violation occurs in the top-Higgs or $τ$-Higgs coupling, one observes an azimuthal decay asymmetry in $μ^+μ-\to t\bar t$ (or $τ^+τ^-$). CP studies at such colliders allow a uniquely clean way of deducing the underlying CP phases; in turn these parameters would significantly improve our understanding of baryogenesis.

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