The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while ...discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV/c2 WIMP mass and, at >75% C.L., the entire 3sigma allowed region for the WIMP signal reported by the DAMA experiment.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
We present new results on the Hubble diagram of distant type Ia supernovae (SNe Ia) segregated according to the type of host galaxy. This makes it possible to check earlier evidence for a ...cosmological constant by explicitly comparing SNe residing in galaxies likely to contain negligible dust with the larger sample. The cosmological parameters derived from these SNe Ia hosted by presumed dust-free early-type galaxies support earlier claims for a cosmological constant, which we demonstrate at ≃5σ significance, and the internal extinction implied is small even for late-type systems (AB < 0.2). Thus, our data demonstrate that host galaxy extinction is unlikely to systematically dim distant SNe Ia in a manner that would produce a spurious cosmological constant. Our analysis is based on new Hubble Space Telescope STIS ‘snapshot’ images and Keck-II echellette spectroscopy at the locations of the SNe, spanning the redshift range 0 < z < 0.8. Selecting from the sample discovered by the Supernova Cosmology Project (SCP), we classify the host galaxies of 39 distant SNe using the combination of STIS imaging, Keck spectroscopy and ground-based broad-band photometry. The distant data are analysed in comparison with a low-redshift sample of 25 SNe Ia re-calibrated according to the precepts of the SCP. The scatter observed in the SNe Ia Hubble diagrams correlates closely with host galaxy morphology. We find this scatter is smallest for SNe Ia occurring in early-type hosts and largest for those occurring in late-type galaxies. Moreover, SNe residing in late-type hosts appear ≃ 0.14 ± 0.09 mag fainter in their light-curve-width-corrected luminosity than those in early-type hosts, as expected if a modest amount of dust extinction is a contributing factor. As in previous studies, these results are broadly independent of whether corrections based upon SN light-curve shapes are performed. We also use our high-redshift data set to search for morphological dependences in the SNe light curves, as are sometimes seen in low-redshift samples. No significant trends are found, possibly because the range of light-curve widths is too limited.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
We present spectra for 14 high-redshift (0.17 < z < 0.83) supernovae, which were discovered by the Supernova Cosmology Project as part of a campaign to measure cosmological parameters. The spectra ...are used to determine the redshift and classify the supernova type, essential information if the supernovae are to be used for cosmological studies. Redshifts were derived either from the spectrum of the host galaxy or from the spectrum of the supernova itself. We present evidence that these supernovae are of Type Ia (SNe Ia) by matching to spectra of nearby supernovae. We find that the dates of the spectra relative to maximum light determined from this fitting process are consistent with the dates determined from the photometric light curves, and, moreover, the spectral time sequences for SNe Ia at low and high redshift are indistinguishable. We also show that the expansion velocities measured from blueshifted Ca H and K are consistent with those measured for low-redshift SNe Ia. From these first-level quantitative comparisons we find no evidence for evolution in SN Ia properties between these low- and high-redshift samples. Thus, even though our samples may not be complete, we conclude that there is a population of SNe Ia at high redshift whose spectral properties match those at low redshift.
We present VLT FORS1 and FORS2 spectra of 39 candidate high-redshift supernovae that were discovered as part of a cosmological study using type Ia supernovae (SNe Ia) over a wide range of redshifts. ...From the spectra alone, 20 candidates are spectrally classified as SNe Ia with redshifts ranging from z = 0.212 to z = 1.181. Of the remaining 19 candidates, 1 might be a type II supernova and 11 exhibit broad supernova-like spectral features and/or have supernova-like light curves. The candidates were discovered in 8 separate ground-based searches. In those searches in which SNe Ia at z similar to 0.5 were targeted, over 80% of the observed candidates were spectrally classified as SNe Ia. In those searches in which SNe Ia with z > 1 were targeted, 4 candidates with z > 1 were spectrally classified as SNe Ia and later followed with ground and space based observatories. We present the spectra of all candidates, including those that could not be spectrally classified as supernova.
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We present a novel technique for fitting restframe I-band light curves on a data set of 42 type Ia supernovae (SNe Ia). Using the result of the fit, we construct a Hubble diagram with 26 SNe from the ...subset at 0.01 < z < 0.1. Adding two SNe at z similar to 0.5 yields results consistent with a flat A-dominated "concordance universe" ( Omega sub(M), Omega sub( Lambda )) = (0.25, 0.75). For one of these, SN 2000fr, new near infrared data are presented. The high redshift supernova NIR data are also used to test for systematic effects in the use of SNe Ia as distance estimators. A flat, Lambda = 0, universe where the faintness of supernovae at z similar to 0.5 is due to grey dust homogeneously distributed in the intergalactic medium is disfavoured based on the high-z Hubble diagram using this small data-set. However, the uncertainties are large and no firm conclusion may be drawn. We explore the possibility of setting limits on intergalactic dust based on B - I and B - V colour measurements, and conclude that about 20 well measured SNe are needed to give statistically significant results. We also show that the high redshift restframe I-band data points are better fit by light curve templates that show a prominent second peak, suggesting that they are not intrinsically underluminous.
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The Cryogenic Dark Matter Search (CDMS) employs massive ionization- and phonon-mediated detectors to search for WIMPs via their elastic scattering interactions with nuclei while discriminating ...against interactions by other background particles. Limits on the WIMP-nucleon scattering cross-section, based on 3.1
kg
d of exposure, exclude new parameter space in the 10–30
GeV WIMP mass region and also a portion of the region allowed by the DAMA annual modulation search (Bernabei, Phys. Lett. 450 (1999) 448).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The Cryogenic Dark Matter Search experiment uses cooled germanium and silicon detectors for a direct search for weakly interacting massive particles in our Galaxy. The novel detectors allow a high ...degree of background rejection by discriminating between electron and nuclear recoils through the simultaneous measurement of the energy deposited in phonons and ionization. Exposures on the order of one kilogram-day from initial runs of our experiment yield (preliminary) upper limits on the WIMP-nucleon cross section that are comparable to much longer runs of other experiments. Current and future runs promise significant improvement, primarily due to improved detectors and reduced surface-electron backgrounds.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The CDMS experiment utilizes Ge and Si detectors operating at
20
mK
to search for the Dark Matter of the Universe hypothesized to exist in the form of weakly interacting massive particles (WIMPs). In ...early 2000, CDMS set the most competitive exclusion limit for scalar-interaction WIMPs in the Stanford Underground Facility (SUF). A new search (CDMS II) is now commencing with several improvements: a deep-site facility in the Soudan mine, Minnesota; and the detector technology has been further improved to aid in the rejection of surface-electron (
β) events. A new generation of detectors, sensitive to the initial athermal phonon flux from a particle event, have been in operation for the past year at Stanford's shallow site and are ready for installation at the deep site.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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