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M. Graham

Publications and source records attributed to M. Graham.

42 records · Page 3Linked to original sources

Search for a new gauge boson in the $A'$ Experiment (APEX)

We present a search at Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling $α'$ to electrons. Such a particle $A'$ can be produced in electron-nucleus fixed-target scattering and then decay to an $e^+e^-$ pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175--250 MeV, found no evidence for an $A'\to e^+e^-$ reaction, and set an upper limit of $α'/α\simeq 10^{-6}$. Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.

hep-ex

Towards Real-time Classification of Astronomical Transients

Exploration of time domain is now a vibrant area of research in astronomy, driven by the advent of digital synoptic sky surveys. While panoramic surveys can detect variable or transient events, typically some follow-up observations are needed; for short-lived phenomena, a rapid response is essential. Ability to automatically classify and prioritize transient events for follow-up studies becomes critical as the data rates increase. We have been developing such methods using the data streams from the Palomar-Quest survey, the Catalina Sky Survey and others, using the VOEventNet framework. The goal is to automatically classify transient events, using the new measurements, combined with archival data (previous and multi-wavelength measurements), and contextual information (e.g., Galactic or ecliptic latitude, presence of a possible host galaxy nearby, etc.); and to iterate them dynamically as the follow-up data come in (e.g., light curves or colors). We have been investigating Bayesian methodologies for classification, as well as discriminated follow-up to optimize the use of available resources, including Naive Bayesian approach, and the non-parametric Gaussian process regression. We will also be deploying variants of the traditional machine learning techniques such as Neural Nets and Support Vector Machines on datasets of reliably classified transients as they build up.

astro-ph

Precision measurements of the total and partial widths of the psi(2S) charmonium meson with a new complementary-scan technique in antiproton-proton annihilations

We present new precision measurements of the psi(2S) total and partial widths from excitation curves obtained in antiproton-proton annihilations by Fermilab experiment E835 at the Antiproton Accumulator in the year 2000. A new technique of complementary scans was developed to study narrow resonances with stochastically cooled antiproton beams. The technique relies on precise revolution-frequency and orbit-length measurements, while making the analysis of the excitation curve almost independent of machine lattice parameters. We study the psi(2S) meson through the processes pbar p -> e+ e- and pbar p -> J/psi + X -> e+ e- + X. We measure the width to be Gamma = 290 +- 25(sta) +- 4(sys) keV and the combination of partial widths Gamma_e+e- * Gamma_pbarp / Gamma = 579 +- 38(sta) +- 36(sys) meV, which represent the most precise measurements to date.

hep-ex

Some Pattern Recognition Challenges in Data-Intensive Astronomy

We review some of the recent developments and challenges posed by the data analysis in modern digital sky surveys, which are representative of the information-rich astronomy in the context of Virtual Observatory. Illustrative examples include the problems of an automated star-galaxy classification in complex and heterogeneous panoramic imaging data sets, and an automated, iterative, dynamical classification of transient events detected in synoptic sky surveys. These problems offer good opportunities for productive collaborations between astronomers and applied computer scientists and statisticians, and are representative of the kind of challenges now present in all data-intensive fields. We discuss briefly some emergent types of scalable scientific data analysis systems with a broad applicability.

astro-ph

Measurement of the branching ratios $ψ^\prime \to e^+ e^-$, $ψ^\prime \to J/ψππ$ and $ψ^\prime \to J/ψη$

We have measured several branching ratios for $ψ^\prime$ decay using the data collected by FNAL E835 experiment during year 2000, obtaining ${\cal B}(ψ^\prime \to e^+ e^-) = 0.0068\pm0.0001\pm0.0004$, ${\cal B}(ψ^\prime \to J/ψπ^+ π^-) = 0.292\pm0.005\pm0.018$, ${\cal B}(ψ^\prime \to J/ψπ^0 π^0) = 0.167\pm0.005\pm0.014$ and ${\cal B}(ψ^\prime \to J/ψη) = 0.028\pm0.002\pm0.002$. We also present a measurement of the dipion mass distribution in the decays $ψ^\prime \to J/ψππ$.

hep-ex

The European Large Area ISO Survey IV: the preliminary 90 micron luminosity function

We present the luminosity function of 90um selected galaxies from the European Large Area ISO Survey (ELAIS), extending to z=0.3. Their luminosities are in the range 10^9 < h_65^-2 L/Lsun < 10^12, i.e. non-ultraluminous. From our sample of 37 reliably detected galaxies in the ELAIS S1 region from the Efstathiou et al. (2000) S_90 >= 100mJy database, we found optical, 15um or 1.4GHz identifications for 24 (65%). We have obtained 2dF and UK Schmidt FLAIR spectroscopy of 89% of IDs to rigid multivariate flux limits. We construct a luminosity function assuming (a) our spectroscopic subset is an unbiased sparse sample, and (b) there are no galaxies which would not be represented in our spectroscopic sample at {\it any} redshift. We argue that we can be confident of both assumptions. We find the luminosity function is well-described by the local 100um luminosity function of Rowan-Robinson, Helou & Walker (1987). {\it Assuming} this local normalisation, we derive luminosity evolution of (1+z)^{2.45\pm0.85} (95% confidence). We argue that star formation dominates the bolometric luminosities of these galaxies and we derive comoving star formation rates in broad agreement with the Flores et al. (1999) and Rowan-Robinson et al. (1997) mid-IR-based estimates.

astro-ph