8001359
My recollections as a physicist
This presentation is a talk presented by the author at a Physics Symposium of the 50th anniversary of the Taiwan University, in December 1996. The author describes how he became a physicist, and then presents a brief outline of his professional career, most of which has centered at Stanford Linear Accelerator Center. He was involved in the discovery of the {tau} lepton, and in studies of CP violation through decay of the {tau}, in addition to studies of semileptonic decay of t, B, D, K, and {pi}.
121983457
Pair Production and Bremsstrahlung of Charged Leptons
Photo pair productions of electrons, muons, and heavy leptons and bremsstrahlung of electrons and muons are reviewed. Atomic and nuclear form factors necessary for these calculations are discussed. Straggling of electrons in matter and other sects due to 6nite target thickness are considered. Tables of radiation lengths of all materials and the energy dependence of photon absorption coefFicients of many materials are presented. Problems associated with production of particles by photon and electron beams are also discussed.
13561911
Addendum to the test of CP violation in Tau decay
We discuss the test of CP and CPT violation in τ decay without using the polarized electron beam by comparing partial fractions of τ− and τ+ decay into channels with strong final state interactions. For example, Γ(τ−→π−+π0+ν)≠Γ(τ+→π++π0+ν) signifies violation of CP. The optimum energy to investigate CP violation in τ decay is discussed. We conclude that this energy is a few MeV below ψ(2s) in order to avoid the charm contribution and over abundance of hadrons at the ψ(2s) peak.
16522997
RADIATIVE CORRECTIONS TO e+e- REACTIONS TO ALL ORDERS IN a USING THE RENORMALIZATION GROUP*
Renormalization group technique is used to improve the accuracy of the lowest order radiative corrections in QED. The exponentiation of infrared terms comes automatically. It also leads to exponentiation of the vertex functions. It predicts the -existence of conversion of photons into pairs and the result agrees with the Kroll-Wada relation. Kinoshita-Lee-Nauenberg cancellation of mass singularities occurs to all order in Q in leading log approximation in the final state if we sum over all the final states. Higher order corrections to the order o3 asymmetry is shown to be small. The results are used to derive useful formulas for the radiative corrections to processes such zas e+e+ p+p-, e+e--+ ~+~~~, e+e+ hadroqcontinuum, e+eT ---) very narrow ; -resonance such as $, and e+e+ not very narrow resonance such as ZO. .^ -_ . Submitted to Review of Modern Physics and Presented at the Asia Pacific Physics Conference Singapore, June 12-18, 1983 l Work supported by the Department of Energy, contract DEAC03-76SFOO515.
118138915
DEPOLARIZATION OF SPIN 1/2 PARTICLES BY ELECTROMAGNETIC SCATTERING
7044095
The investigation of CP violation through the decay of polarized tau leptons II
Under the assumption that CP violation is caused by exchange of anew boson, the authors propose to measure the magnitudes and CP-violating phases of the coupling constants of this boson to five different vertices in tau decay. This can be accomplished by studying the decay of polarized tau leptons produced at an e{sup +}e{sup {minus}} collider whose beams are polarized. These five coupling constants could be used to construct a future theory of CP violation. If CP is violated in any channel of tau decay, it will imply that there exists a new charged boson other than the W boson responsible for CP violation. It will also imply that CP violation is much more prevalent than the standard theory predicts and this may enable one to understand the preponderance of matter over antimatter in the present universe.
119232432
Sensitivities of the IceCube DeepCore detector to signatures of low-mass dark matter in the Galactic halo
We discuss the event rate in the DeepCore array due to neutrino flux produced by annihilations and decays of Galactic dark matter. This event rate is calculated with a 10 GeV threshold energy, which is smaller than the threshold energy taken in previous works. Taking into account the background event rate due to the atmospheric neutrino flux, we evaluate the sensitivity of the DeepCore array for probing the dark matter annihilation cross section and decay time. The sensitivity studies include the annihilation modes chi chi -> b (b) over bar, tau(+)tau(-), mu(+)mu(-), and nu(nu) over bar, and decay modes chi -> b (b) over bar, tau(+)tau(-), mu(+)mu(-), and nu(nu) over bar. We compare our results with corresponding constraints derived from observations of WMAP, ACT, and Fermi-LAT. DOI: 10.1103/PhysRevD.87.025003
118612935
The impact of propagation uncertainties on the potential Dark Matter contribution to the Fermi LAT mid-latitude gamma-ray data
We investigate the extent to which the uncertainties associated with the propagation of Galactic cosmic rays impact upon estimates for the {gamma}-ray flux from the mid-latitude region. We consider contributions from both standard astrophysical background (SAB) processes as well as resolved point sources. We have found that the uncertainties in the total {gamma}-ray flux from the mid-latitude region relating to propagation parameter values consistent with local B/C and {sup 10}Be/{sup 9}Be data dominate by 1-2 orders of magnitude. These uncertainties are reduced to less than an order of magnitude when the normalizations of the SAB spectral components are fitted to the corresponding Fermi LAT data. We have found that for many propagation parameter configurations (PPCs) our fits improve when an extragalactic background (EGB) component is simultaneously fitted to the data. We also investigate the improvement in our fits when a flux contribution from neutralino dark matter (DM), described by the minimal supersymmetric standard model, was simultaneously fitted to the data. We consider three representative cases of neutralino DM for both Burkert and Einasto DM density profiles, in each case simultaneously fitting a boost factor of the DM contribution together with the SAB and EGB components. We have found that formore » several PPCs there are significant improvements in our fits, yielding both substantial EGB and DM components, where for a few of these PPCs the best-fit EGB component is consistent with recent estimates by the Fermi Collaboration.« less
117587456
Is light neutralino as dark matter still viable
Motivated by the recent re-confirmation by CoGENT of the low-energy excess of events observed last year, and the recent improved limits from the XENON-100 experiment that are in contention with the CoGENT data, we re-examine the low mass neutralino region of the Minimal Supersymmetric Standard Model and of the Next-to-Minimal Supersymmetric Standard Model, both without assuming gaugino mass unification. We make several focused scans for each model, determining conservative constraints on input parameters. We then determine how these constraints are made increasingly stringent as we re-invoke our experimental constraints involving the dark matter relic abundance, collider constraints from LEP and the Tevatron, and then from flavour physics, as a series of successive 2 sigma hard cuts. We find that for both models, when all relevant constraints are applied in this fashion, we do not generate neutralino LSPs that possess a spin-independent scattering cross section in excess of 10^-5 pb and a mass ~7 GeV < m_chi < ~9 GeV that is necessary in order to explain the CoGENT observations.
119110843
Bayesian implications of current LHC supersymmetry and dark matter detection searches for the constrained MSSM
We investigate the impact of recent limits from LHC searches for supersymmetry and from direct and indirect searches for dark matter on global Bayesian inferences of the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM). In particular we apply recent exclusion limits from the CMS \alpha_T analysis of 1.1/fb of integrated luminosity, the current direct detection dark matter limit from XENON100, as well as recent experimental constraints on \gamma-ray fluxes from dwarf spheroidal satellite galaxies of the Milky Way from the FermiLAT telescope, in addition to updating values for other non-LHC experimental constraints. We extend the range of scanned parameters to include a significant fraction of the focus point/hyperbolic branch region. While we confirm earlier conclusions that at present LHC limits provide the strongest constraints on the model's parameters, we also find that when the uncertainties are not treated in an excessively conservative way, the new bounds from dwarf spheroidal have the power to significantly constrain the focus point/hyperbolic branch region. Their effect is then comparable, if not stronger, to that from XENON100. We further analyze the effects of one-year projected sensitivities on the neutrino flux from the Sun in the 86-string IceCube+DeepCore configuration at the South Pole. We show that data on neutrinos from the Sun, expected for the next few months at IceCube and DeepCore, have the potential to further constrain the same region of parameter space independently of the LHC and can yield additional investigating power for the model.
122803295
Constrained next-to-minimal supersymmetric standard model with a 126 GeV Higgs boson: A global analysis
We present the first global analysis of the constrained next-to-minimal supersymmetric standard model that investigates the impact of the recent discovery of a 126 GeV Higgs-like boson, of the observation of a signal for branching ratio $\mathrm{BR}({\mathrm{B}}_{\mathrm{s}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$, and of constraints on supersymmetry from $\ensuremath{\sim}5/\mathrm{fb}$ of data accumulated at the LHC, as well as of other relevant constraints from colliders, flavor physics and dark matter. We consider three possible cases, assuming in turn that the discovered Higgs boson is (i) the lightest Higgs boson of the model; (ii) the next-to-lightest Higgs boson; and (iii) a combination of both roughly degenerate in mass. The likelihood function for the Higgs signal uses signal rates in the $\ensuremath{\gamma}\ensuremath{\gamma}$ and $ZZ\ensuremath{\rightarrow}4l$ channels, while that for the Higgs exclusion limits assumes decay through the $\ensuremath{\gamma}\ensuremath{\gamma}$, $\ensuremath{\tau}\ensuremath{\tau}$, $ZZ$ and ${W}^{+}{W}^{\ensuremath{-}}$ channels. In all cases considered we identify the 68% and 95% credible posterior probability regions in a Bayesian approach. We find that, when the constraints are applied with their respective uncertainties, the first case shows strong CMSSM-like behavior, with the stau coannihilation region featuring highest posterior probability, the best-fit point, a correct mass of the lightest Higgs boson and the lighter top squark mass in the ballpark of 1 TeV. We also expose in this region a linear relationship between the trilinear couplings of the stau and the top squark, with both of them being strongly negative as enforced by the Higgs mass and the relic density, which outside of the stau coannihilation region show some tension. The second and the third case, on the other hand, while allowed are disfavored by the constraints from direct detection of dark matter and from $\mathrm{BR}({\mathrm{B}}_{\mathrm{s}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$. Without the anomalous magnetic moment of the muon the fit improves considerably, especially for negative effective $\ensuremath{\mu}$ parameter. We discuss how the considered scenarios could be tested further at the LHC and in dark matter searches.