9516390
Supernova Acceleration Probe: Studying Dark Energy with Type Ia Supernovae
The Supernova Acceleration Probe (SNAP) will use Type Ia supernovae (SNe Ia) as distance indicators to measure the effect of dark energy on the expansion history of the Universe. (SNAP's weak-lensing program is described in a companion White Paper.) The experiment exploits supernova distance measurements up to their fundamental systematic limit; strict requirements on the monitoring of each supernova's properties lead to the need for a space-based mission. Results from pre-SNAP experiments, which characterize fundamental SN Ia properties, will be used to optimize the SNAP observing strategy to yield data, which minimize both systematic and statistical uncertainties. SNAP has achieved technological readiness and the collaboration is poised to begin construction.
37710923
Discovery of TeV Gamma-ray Emission from Tycho's Supernova Remnant
We report the discovery of TeV gamma-ray emission from the Type Ia supernova remnant (SNR) G120.1+1.4, known as Tycho's SNR. Observations performed in the period 2008-2010 with the VERITAS ground-based gamma-ray observatory reveal weak emission coming from the direction of the remnant, compatible with a point source located at 00h25m270, + 64°10'50'' (J2000). The TeV photon spectrum measured by VERITAS can be described with a power law dN/dE = C(E/3.42 TeV)–Γ with Γ = 1.95 ± 0.51stat ± 0.30sys and C = (1.55 ± 0.43stat ± 0.47sys) × 10–14 cm–2 s–1 TeV–1. The integral flux above 1 TeV corresponds to ~0.9% of the steady Crab Nebula emission above the same energy, making it one of the weakest sources yet detected in TeV gamma rays. We present both leptonic and hadronic models that can describe the data. The lowest magnetic field allowed in these models is ~80 μG, which may be interpreted as evidence for magnetic field amplification.
124867075
An amplitude analysis of the decay $B^\pm \to \pi^\pm \pi^\pm \pi^\mp$
We present a Dalitz-plot analysis of charmless B+- decays to the final state pi+- pi+- pi-+ using 210 fb^-1 of data recorded by the BABAR experiment at sqrt(s) = 10.58 GeV. We measure the branching fractions B(B+- -> pi+- pi+- pi-+) = (16.2 +- 1.2 +- 0.9) x 10^-6 and B(B+- -> rho^0(770) pi+-) = (8.8 +- 1.0 +- 0.6 +0.1-0.7) x 10^-6. Measurements of branching fractions for the quasi-two-body decays B+- -> rho^0(1450) pi+-, B+- -> f_0(980) pi+- and B+- -> f_2(1270) pi+- are also presented. We observe no charge asymmetries for the above modes, and there is no evidence for the decays B+- -> chic0 pi+-, B+- -> f_0(1370) pi+- and B+- -> sigma pi+-.
118937544
VERITAS: Status and Highlights
The VERITAS telescope array has been operating smoothly since 2007, and has detected gamma-ray emission above 100 GeV from 40 astrophysical sources. These include blazars, pulsar wind nebulae, supernova remnants, gamma- ray binary systems, a starburst galaxy, a radio galaxy, the Crab pulsar, and gamma-ray sources whose origin remains unidentified. In 2009, the array was reconfigured, greatly im proving the sensitivity. We summarize the current status of the observatory, describe some of the scientific highlights since 2009, and outline plans for the future.
18988438
VERITAS Discovery of >200 GeV Gamma-Ray Emission from the Intermediate-Frequency-Peaked BL Lacertae Object W Comae
We report the detection of very high-energy -ray emission from the intermediate-frequencypeaked BLLacertae object WComae (z = 0.102) by VERITAS, an array of four imaging atmospheric-Cherenkov telescopes. The source was observed between January and April 2008. A strong outburst of -ray emission was measured in the middle of March, lasting for only four days. The energy spectrum measured during the two highest flare nights is fit by a power-law and is found to be very steep, with a differential photon spectral index of = 3 .81±0.35stat±0.34syst. The integral photon flux above 200GeV during those two nights corresponds to roughly 9% of the flux from the Crab Nebula. Quasi-simultaneous Swift observations at X-ray energies were triggered by the VERITAS observations. The spectral energy distribution of the flare data can be described by synchrotron-self-Compton (SSC) or external-Compton (EC) leptonic jet models, with the latter offering a more natural set of parameters to fit the data.
29318124
Discovery of Variability in the Very High Energy γ-Ray Emission of 1ES 1218+304 with VERITAS
We present results from an intensive VERITAS monitoring campaign of the high-frequency peaked BL Lac object 1ES 1218+304 in 2008/2009. Although 1ES 1218+304 was detected previously by MAGIC and VERITAS at a persistent level of ~6% of the Crab Nebula flux, the new VERITAS data reveal a prominent flare reaching ~20% of the Crab. While very high energy (VHE) flares are quite common in many nearby blazars, the case of 1ES 1218+304 (redshift z = 0.182) is particularly interesting since it belongs to a group of blazars that exhibit unusually hard VHE spectra considering their redshifts. When correcting the measured spectra for absorption by the extragalactic background light, 1ES 1218+304 and a number of other blazars are found to have differential photon indices Γ≤ 1.5. The difficulty in modeling these hard spectral energy distributions in blazar jets has led to a range of theoretical γ-ray emission scenarios, one of which is strongly constrained by these new VERITAS observations. We consider the implications of the observed light curve of 1ES 1218+304, which shows day scale flux variations, for shock acceleration scenarios in relativistic jets, and in particular for the viability of kiloparsec-scale jet emission scenarios.
123053703
PHASEFIX-correcting the tunes of the SLC arcs
The betatron phase advance tunes are crucial parameters in the SLC (Stanford Linear Collider) arc optics because of the strong cross coupling between the x and y phase spaces, which takes place at rolled achromat boundaries. Phase measurements have been performed with an accuracy of about 0.3 degrees /cell and, initially, substantial deviations from the design (108 degrees ) were observed. Corrections on an achromat-by-achromat basis have been performed to reduce the phase errors within less than 1 degrees /cell. They were done by adjusting a current balance between focusing (F) and defocusing (D) magnets and by changing the horizontal relative displacements of F and D magnets using the XMOV magnet movers or with realignment work.<<ETX>>
15066884
CLEO results on tau Michel parameters
We present measurements of the tau Michel Parameters made by the CLEO experiment. Three different analyses are performed: a spin-independent lepton spectrum analysis and a second spin-dependent analysis using l^± vs. π^‡π^0 events, and a third spin-dependent analysis using π^+ vs. π^− events. the results are used to derive limits on the general four-fermion couplings, the mass of the charged Higgs in the MSSM, and a right-handed W in left-right models. Many of these measurements are more precise than the PDG world averages.
120014189
Fat bundles and symplectic manifolds
A fat bundle is, roughly speaking, a bundle which has a lot of curvature, as opposed to a flat bundle, which has none. (The precise definition is given in Section 1.) For example, a bundle with structure group S’ is fat if it has a connection whose curvature is a symplectic structure on the base. The notion of fat bundle arises naturally from the study of riemannian fibre bundles with totally geodesic fibres. Positivity of certain sectional curvatures turns out to be equivalent to fatness of the connection determined by the orthogonal complements to the fibres. It was for this reason that fat bundles were introduced in a manuscript written at MIT in 1968 and circulated informally [20]. (The term unj7at used in that manuscript to mean fat is rather lacking in euphony; it is also slightly misleading, since a bundle which is not flat might not be unflat either-most bundles are somewhere in between.) Some of the results in this paper are taken from the 1968 manuscript, in particular Lemma 3.1, Theorem 4.1 and its corollaries, Theorem 6.1, and Theorem 7.2, but there are substantial additions as well. Using an idea of Sternberg, we show in Section 3 how to construct symplectic manifolds out of any fat bundle, using coadjoint orbits of the structure group; we then continue the discussion by using an idea of Thurston [ 181 to show that, whatever the connection, it is often possible to put a symplectic structure on the total space of a bundle whose tibres and base are symplectic. (In particular, it is sufficient that the bundle be compact and have simply connected fibres.) A problem which was posed and partially solved in [20] was to determine the fat 3-sphere bundles over S4. This problem has just been solved by Derdziriski and Rigas [7]-there is only the Hopf tibration S3 + S’ + S4. Their solution (see Section 7) uses ideas generated by the recent revival of interest in 4-dimensional riemarmian geometry [2] centered around the notion of self-duality. Several important contributions to the theory of fat bundles have been
122102571
dc readout experiment at the Caltech 40m prototype interferometer
The Laser Interferometer Gravitational Wave Observatory (LIGO) operates a 40m prototype interferometer on the Caltech campus. The primary mission of the prototype is to serve as an experimental testbed for upgrades to the LIGO interferometers and for gaining experience with advanced interferometric techniques, including detuned resonant sideband extraction (i.e. signal recycling) and dc readout (optical homodyne detection). The former technique will be employed in Advanced LIGO, and the latter in both Enhanced and Advanced LIGO. Using dc readout for gravitational wave signal extraction has several technical advantages, including reduced laser and oscillator noise couplings as well as reduced shot noise, when compared to the traditional rf readout technique (optical heterodyne detection) currently in use in large-scale ground-based interferometric gravitational wave detectors. The Caltech 40m laboratory is currently prototyping a dc readout system for a fully suspended interferometric gravitational wave detector. The system includes an optical filter cavity at the interferometer's output port, and the associated controls and optics to ensure that the filter cavity is optimally coupled to the interferometer. We present the results of measurements to characterize noise couplings in rf and dc readout using this system.
123600362
Advanced LIGO optical configuration and prototyping effort
The current plan for the Advanced LIGO dual-recycled optical configuration and control scheme is described, with emphasis on those elements which differ from Initial LIGO. Plans for prototyping this system are discussed, and the prototyping effort at the LIGO Caltech 40 Meter Interferometer Laboratory is described in some detail. Finally, some of the modelling efforts at Caltech are reviewed.