arXiv subjects

David Atwood

Publications and source records attributed to David Atwood.

At least 37 records · Page 2Linked to original sources

arXiv2003

Role of Charm Factory in Extracting CKM-Phase Information via B --> DK

In this paper we study the impact of data that can be obtained from a Charm Factory on the determination of the CKM parameter gamma from decays of the form B -> D0 K where the D0 decays to specific inclusive and exclusive final states. In particular, for each exclusive final state $f$, the charm factory can determine the strong phase difference between D0-> f and D0-bar -> f by exploiting correlations in psi(3770)-> D0 D0-bar. This provides crucial input to the determination of gamma via the interference of B+- -> K+- D0 -> f with B+- -> K+- D0-bar -> f. We discuss how the method may be generalized to inclusive final states and illustrate with a toy model how such methods may offer one of the best means to determine gamma with 10^8-10^9 B-mesons.

hep-ph↗

arXiv2003

Measurement of gamma at B Factories Using Inclusive D Decays

We discuss the determination of the CKM phase gamma through the decay B- -> K- D0 and related processes. In particular, we consider the use of this methods when the D0 subsequently decays to an inclusive state. We emphasize that strong phase information obtained at a psi(3770) charm factory can provide additional information which will be helpful in determining gamma.

hep-ph↗

arXiv2002

Pristine Determination of the Unitarity Triangle Using B -> K D0 Processes

There is no good reason to think that BSM-CP-odd phases(s) will necessarily cause large deviations in B-physics from predictions of the SM. Therefore, residual theory error in extraction of the unitarity triangle can undermine experimental efforts to search for BSM phase(s). We stress that final states containing D0 or D0-bar in decays of charged and neutral B's can yield all the angles of the unitarity triangle with negligble theory error (i.e. O(0.1%)).

hep-ph↗

arXiv2002

Getting beta-alpha without penguins

Oscillation effects in B0 -> Ks D0 and related processes are considered to determine delta=beta-alpha+pi. We suggest that D0 decays to CP eigenstates used in concert with inclusive D0 decays provide a powerful method for determining delta cleanly i.e. without any complication from penguin processes. The CP asymmetry is expected to be <=40% for D0 decays to non-CP eigenstates and <=80% for decays to CP eigenstates. This method can lead to a fairly accurate determination of delta with O(10^8-10^9) B-mesons.

hep-ph↗

arXiv2002

Lifetime Differences in Heavy Mesons With Time Independent Measurements

Heavy meson pairs produced in the decays of heavy quarkonium resonances at e+ e- machines (beauty and tau-charm factories) have the useful property that the two mesons are in the CP-correlated states. By tagging one of the mesons as a CP eigenstate, a lifetime difference of heavy neutral meson mass eigenstates width difference may be determined by measuring the leptonic branching ratio of the other meson. We discuss the use of this and related methods both in the case where time dependent mixing is small and when it is significant. We consider the impact of possible CP-violating effects and present the complete results for CP-entangled decay rates with CP-violation taken into account.

hep-ph↗

arXiv2002

Flavor changing Z-decays from scalar interactions at a Giga-Z Linear Collider

The flavor changing decay Z -> d_I \bar{d}_J is investigated with special emphasis on the b \bar{s} final state. Various models for flavor violation are considered: two Higgs doublet models (2HDM's), supersymmetry (SUSY) with flavor violation in the up and down-type squark mass matrices and SUSY with flavor violation mediated by R-parity-violating interaction. We find that, within the SUSY scenarios for flavor violation, the branching ratio for the decay Z -> b \bar{s} can reach 10^{-6} for large \tanβvalues, while the typical size for this branching ratio in the 2HDM's considered is about two orders of magnitudes smaller at best. Thus, flavor changing SUSY signatures in radiative Z decays such as Z -> b \bar{s} may be accessible to future ``Z factories'' such as a Giga-Z version of the TESLA design.

hep-ph↗

arXiv2001

Using Imprecise Tags of CP Eigenstates in B(s) and the Determination of the CKM Phase gamma

We consider the possibility of studying the CP properties of various B(s) decays at an electro-positron machine tuned to the Upsilon(5s). Since decay modes of the B(s) with definite CP are relatively rare, we suggest that the use of more common modes which are not pure CP eigenstates may allow the determination of the CKM phase gamma. By studying the degree of correlation between different decay modes at a Upsilon(5s) it is possible to determine the degree of affinity of each decay mode to a CP eigenstate. Once this is known, the correlation between a decay mode with a greater affinity to a particular CP eigenstate with a mode such as D(s) + K- gives a determination of the phase gamma.

hep-ph↗

arXiv2001

Determining the phases alpha and gamma from time-dependent CP violation in B0 decays to rho(omega) + pseudoscalar

A method is proposed for the determination of the unitarity angle alpha through tree penguin interference. The modes needed would be of the form B0/B0-bar -> rho0 M and B0/B0-bar -> omega M where M is spin-0 uu-bar/dd-bar meson, for instance M=pi0, eta, eta',a0 or f0. An analogous method can also determine gamma using M=KS or K_L. The validity of the theoretical approximations used may be tested by over determining alpha with several modes. If two or more modes are used, the determination has a four-fold ambiguity but additional information from pure penguin decays or theoretical estimates may be used to reduce the ambiguity to alpha, alpha+pi. The method as applied to determining gamma is probably less promising.

hep-ph↗

arXiv2001

Determining the Phases alpha and gamma from Direct CP Violation in B_u, B_d and B_s Decays to Two Vectors

A method for clean determination of the unitarity angles alpha and gamma is proposed that uses only direct CP violation and does not require any time dependent measurements. The method takes advantage of helicity amplitudes for B_u, B_d and B_s decay to two vector mesons and can be used, at any B-facility, in conjunction with a large number of modes. It also allows for experimental tests of theoretical approximations involved.

hep-ph↗

arXiv2001

CP Asymmetry Measurements in psi K0 and the CKM Paradigm

Recent experimental observations of CP asymmetry in B0 -> psi K0 constitute the first significant signal of CP violation outside the neutral kaon system; thus they represent an important milestone to test the CKM paradigm. We, therefore, undertake a critical appraisal of the existing experimental and theoretical inputs used to deduce constraints on sin(2 beta) and other important parameters and thus find, in particular, sin(2 beta) > 0.50 at 95% CL which is completely compatible with the combined experimental result: sin(2 beta) = 0.46 +- 0.17, representing an important success of the CKM model of CP violation. Searches for new physics in B decays to psi+K0 like final states will require improved precision; we make some suggestions to facilitate these. We also present a global fit including the new CP asymmetry measurements in B->psi+K0 as an additional input yielding e.g. gamma =29-56 degrees, eta-bar = >.19-.36, rho-bar=.15-.37, Jcp=(1.8 - 3.0) X 10^(-5), $Br(K+ -> pi+ nu nu-bar)=(0.51 - 0.90) X 10^(-10) and Br(KL -> pi0 nu nu-bar) = (0.11 - 0.31) X 10^(-10) at 95% CL.

hep-ph↗

arXiv2001

Strategies for The Determination of phi3 in B- -> D0 K-

Direct CP violation in decays such as B- -> D0 K- is sensitive to the CKM angle phi_3 because these decays allow the interference of b-quark to c-quark with b-quark to u-quark transitions. Indeed, phi_3 may be determined if one can infer the strong phase of the B and subsequent D0 decays from experimental data. In this talk, I will discuss how this can be carried out using either a single decay mode of the D0 by combining data from a number of D0 decay modes as well as the use of other, analogous decays and the prospects of implementing such methods at various B-factories. Since the properties of the D0 decays are crucial to these methods, it is possible that D0-D0-bar mixing at the 1% level will contaminate the results. I will therefore discuss various methods to remove such confounding effects so that phi-3 may be determined even if such mixing is present.

hep-ph↗

arXiv2000

Improved Methods for Observing CP Violation in B+/- --> K+/- D0 and Measuring the CKM Phase gamma

Various methods are discussed for obtaining the CKM angle gamma through the interference of the charged B-meson decay channels B- -> K- D0 and B- -> K- D0-bar where the D0 and D0-bar decay to common final states. It is found that choosing final states which are not CP eigenstates can lead to large direct CP violation which can give significant bounds on gamma without any theoretical assumptions. If two or more modes are studied, gamma may be extracted with a precision on the order of +/-15 degrees given about 10^8 B-mesons. We also discuss the case of three body decays of the D0 where additional information may be obtained from the distribution of the D0 decay products and consider the impact of D-D-bar oscillations.

hep-ph↗

arXiv2000

CP Violation in Top Physics

CP violation in top physics is reviewed. The Standard Model has negligible effects, consequently CP violation searches involving the top quark may constitute the best way to look for physics beyond the Standard Model. Non-standard sources of CP violation due to an extended Higgs sector with and without natural flavor conservation and supersymmetric theories are discussed. Experimental feasibility of detecting CP violation effects in top quark production and decays in high energy e+ e-, gamma-gamma, mu+ mu-, pp and p-bar p colliders are surveyed. Searches for the electric, electro-weak and the chromo-electric dipole moments of the top quark in e+ e- -> t-bar t and in p p -> t-bar t X are descibed. In addition, other mechanisms that appear promising for experiments, e.g., tree-level CP violation in e+ e- -> t-bar t h, t-bar t Z, t-bar t nu_e-bar nu_e and in the top decay t -> b tau nu_tau and CP violation driven by s-channel Higgs exchanges in p p, gamma gamma, mu+ mu- -> t-bar t etc., are also discussed.

hep-ph↗

arXiv2000

Gauge Boson - Gauge Boson Scattering in Theories with Large Extra Dimensions

We consider the scattering amplitudes of the form V_1 V_2 -> V_3 V_4, where V_i=γ, Z, W or g(=gluon) are the Standard Model gauge bosons, due to graviton exchange in Kaluza-Klein theories with large extra dimensions. This leads to a number of experimentally viable signatures at high energy leptonic and hadronic colliders. We discuss the observability or future limits on the scale of the gravitational interactions (m_D), that may be obtained at an e+e- Next Linear Collider (NLC) and at the LHC, by studying some of these type of gauge boson scattering processes. We find that the attainable limits through these type of processes are: m_D > 3 TeV at the NLC and m_D > 6 TeV at the LHC.

hep-ph↗

arXiv1999

Dijet Production at Hadron Colliders in Theories with Large Extra Dimensions

We consider the production of high invariant mass jet pairs at hadron colliders as a test for TeV scale gravitational effects. We find that this signal can probe effective Planck masses of about 10 TeV at the LHC with center of mass energy of 14 TeV and 1.5 TeV at the Tevatron with center of mass energy of 2 TeV. These results are compared to analogous scattering processes at leptonic colliders.

hep-ph↗

arXiv1999

Graviton Production By Two Photon and Electron-Photon Processes In Kaluza-Klein Theories With Large Extra Dimensions

We consider the production of gravitons via two photon and electron-photon fusion in Kaluza-Klein theories which allow TeV scale gravitational interactions. We show that at electron-positron colliders, the processes l+l- -> l+ l- graviton, with l=e, mu, can lead to a new signal of low energy gravity of the form l+l- -> l+l- + missing energy which is well above the Standard Model background. For example, with two extra dimensions at the Next Linear Collider with a center of mass energy of 500 or 1000 GeV, hundreds to thousands such l+ l- graviton events may be produced if the scale of the gravitational interactions, M_D, is around a few TeV. At a gamma-electron collider, more stringent bounds may be placed on M_D via the related reaction e^-γ-> e^- graviton. For instance, if a 1TeV electron positron collider is converted to an electron-photon collider, a bound of ~10TeV may be placed on the scale M_D if the number of extra dimensions delta=2 while a bound of ~4TeV may be placed if delta=4.

hep-ph↗

arXiv1999

General analysis of B decays to two pseudoscalars for EWP, rescattering and color suppression effects

A general analysis for B decays to two pseudoscalars, involving ten modes, is presented. A simple model for final state interactions and rescattering effects is proposed. We show how the data can be used to deduce important information on electroweak penguins (EWP), rescattering and color suppression effects and on the CKM parameters in a largely model independent way by using chisquared-minimization. We find that the current data suggests the presence of color-suppressed tree at levels somewhat larger than simple theoretical estimates. Once the data improves the extraction of alpha and/or gamma may become feasible with this method as we illustrate with the existing data.

hep-ph↗

arXiv1999

Graviton Production By Two Photon Processes In Kaluza-Klein Theories With Large Extra Dimensions

We consider the production of gravitons via two photon fusion in Kaluza-Klein theories which allow TeV scale gravitational interactions. We find that the processes l+ l- to l+ l- + graviton, with l=electron or muon can put quite stringent bounds on such theories. For example, with two extra dimensions at the Next Linear Collider with a center of mass energy of 500 (1000) GeV attainable bounds on the scale of the gravitational interactions can reach about 6 (9) TeV.

hep-ph↗