-
K. Barbary,
G. Aldering,
R. Amanullah,
M. Brodwin,
N. Connolly,
K. S. Dawson,
M Doi,
P. Eisenhardt,
L. Faccioli,
V. Fadeyev, [......],
D. Rubin,
D. J. Schlegel,
A. L. Spadafora,
S. A. Stanford, M Strovink,
N Suzuki,
N. Takanashi,
K. Tokita,
N Yasuda,
for the Supernova Cosmology Project
[show abstract]
[hide abstract]
ABSTRACT: We present a measurement of the volumetric Type Ia supernova (SN Ia) rate out
to z ~ 1.6 from the Hubble Space Telescope Cluster Supernova Survey. In
observations spanning 189 orbits with the Advanced Camera for Surveys we
discovered 29 SNe, of which approximately 20 are SNe Ia. Twelve of these SNe Ia
are located in the foregrounds and backgrounds of the clusters targeted in the
survey. Using these new data, we derive the volumetric SN Ia rate in four broad
redshift bins, finding results consistent with previous measurements at z > 1
and strengthening the case for a SN Ia rate that is equal to or greater than
~0.6 x 10^-4/yr/Mpc^3 at z ~ 1 and flattening out at higher redshift. We
provide SN candidates and efficiency calculations in a form that makes it easy
to rebin and combine these results with other measurements for increased
statistics. Finally, we compare the assumptions about host-galaxy dust
extinction used in different high-redshift rate measurements, finding that
different assumptions may induce significant systematic differences between
measurements.
10/2011;
-
N. Suzuki,
D. Rubin,
C. Lidman,
G. Aldering,
R. Amanullah,
K. Barbary,
L. F. Barrientos,
J. Botyanszki,
M. Brodwin,
N. Connolly, [......],
S. A. Stanford,
V. Stanishev,
D. Stern, M. Strovink,
N. Takanashi,
K. Tokita,
M. Wagner,
L. Wang,
N. Yasuda,
H. K. C. Yee
[show abstract]
[hide abstract]
ABSTRACT: We present ACS, NICMOS, and Keck AO-assisted photometry of 20 Type Ia
supernovae SNe Ia from the HST Cluster Supernova Survey. The SNe Ia were
discovered over the redshift interval 0.623 < z < 1.415. Fourteen of these SNe
Ia pass our strict selection cuts and are used in combination with the world's
sample of SNe Ia to derive the best current constraints on dark energy. Ten of
our new SNe Ia are beyond redshift $z=1$, thereby nearly doubling the
statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed
analysis corrects for the recently identified correlation between SN Ia
luminosity and host galaxy mass and corrects the NICMOS zeropoint at the count
rates appropriate for very distant SNe Ia. Adding these supernovae improves the
best combined constraint on the dark energy density \rho_{DE}(z) at redshifts
1.0 < z < 1.6 by 18% (including systematic errors). For a LambdaCDM universe,
we find \Omega_\Lambda = 0.724 +0.015/-0.016 (68% CL including systematic
errors). For a flat wCDM model, we measure a constant dark energy
equation-of-state parameter w = -0.985 +0.071/-0.077 (68% CL). Curvature is
constrained to ~0.7% in the owCDM model and to ~2% in a model in which dark
energy is allowed to vary with parameters w_0 and w_a. Tightening further the
constraints on the time evolution of dark energy will require several
improvements, including high-quality multi-passband photometry of a sample of
several dozen z>1 SNe Ia. We describe how such a sample could be efficiently
obtained by targeting cluster fields with WFC3 on HST.
The Astrophysical Journal 05/2011; 746(1). · 6.02 Impact Factor
-
K. Barbary,
G. Aldering,
R. Amanullah,
M. Brodwin,
N. Connolly,
K. S. Dawson,
M Doi,
P. Eisenhardt,
L. Faccioli,
V. Fadeyev, [......],
D. Rubin,
D. J. Schlegel,
A. L. Spadafora,
S. A. Stanford, M Strovink,
N Suzuki,
N. Takanashi,
K. Tokita,
N Yasuda,
for the Supernova Cosmology Project
[show abstract]
[hide abstract]
ABSTRACT: We report a measurement of the Type Ia supernova (SN Ia) rate in galaxy
clusters at 0.9 < z < 1.45 from the Hubble Space Telescope (HST) Cluster
Supernova Survey. This is the first cluster SN Ia rate measurement with
detected z > 0.9 SNe. Finding 8 +/- 1 cluster SNe Ia, we determine a SN Ia rate
of 0.50 +0.23-0.19 (stat) +0.10-0.09 (sys) SNuB (SNuB = 10^-12 SNe L_{sun,B}^-1
yr^-1). In units of stellar mass, this translates to 0.36 +0.16-0.13 (stat)
+0.07-0.06 (sys) SNuM (SNuM = 10^-12 SNe M_sun^-1 yr^-1). This represents a
factor of approximately 5 +/- 2 increase over measurements of the cluster rate
at z < 0.2. We parameterize the late-time SN Ia delay time distribution with a
power law (proportional to t^s). Under the assumption of a cluster formation
redshift of z_f = 3, our rate measurement in combination with lower-redshift
cluster SN Ia rates constrains s = -1.41 +0.47/-0.40, consistent with
measurements of the delay time distribution in the field. This measurement is
generally consistent with expectations for the "double degenerate" scenario and
inconsistent with some models for the "single degenerate" scenario predicting a
steeper delay time distribution at large delay times. We check for
environmental dependence and the influence of younger stellar populations by
calculating the rate specifically in cluster red-sequence galaxies and in
morphologically early-type galaxies, finding results similar to the full
cluster rate. Finally, the upper limit of one host-less cluster SN Ia detected
in the survey implies that the fraction of stars in the intra-cluster medium is
less than 0.47 (95% confidence), consistent with measurements at lower
redshifts.
The Astrophysical Journal 10/2010; 745(1). · 6.02 Impact Factor
-
R. Amanullah,
C. Lidman,
D. Rubin,
G. Aldering,
P. Astier,
K. Barbary,
M. S. Burns,
A. Conley,
K. S. Dawson,
S. E. Deustua, [......],
N. Panagia,
S. Perlmutter,
J. Raux,
P. Ruiz-Lapuente,
A. L. Spadafora, M. Strovink,
N. Suzuki,
L. Wang,
W. M. Wood-Vasey,
N. Yasuda
[show abstract]
[hide abstract]
ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise Hubble Space Telescope data, and spectra of six SNe Ia that were discovered during 2001, are presented. Additionally, for the two SNe with z > 1, we present ground-based J-band photometry from Gemini and the Very Large Telescope. These are among the most distant SNe Ia for which ground-based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation. We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 SNe, the Union2 compilation. The flat concordance ΛCDM model remains an excellent fit to the Union2 data with the best-fit constant equation-of-state parameter w = –0.997+0.050 –0.054(stat)+0.077 –0.082(stat + sys together) for a flat universe, or w = –1.038+0.056 –0.059(stat)+0.093 –0.097(stat + sys together) with curvature. We also present improved constraints on w(z). While no significant change in w with redshift is detected, there is still considerable room for evolution in w. The strength of the constraints depends strongly on redshift. In particular, at z 1, the existence and nature of dark energy are only weakly constrained by the data.
The Astrophysical Journal 05/2010; 716(1):712. · 6.02 Impact Factor
-
R. Amanullah,
C. Lidman,
D. Rubin,
G. Aldering,
P. Astier,
K. Barbary,
M. S. Burns,
A. Conley,
K. S. Dawson,
S. E. Deustua, [......],
N. Panagia,
S. Perlmutter,
J. Raux,
P. Ruiz-Lapuente,
A. L. Spadafora, M Strovink,
N Suzuki,
L Wang,
W. M. Wood-Vasey,
N Yasuda
[show abstract]
[hide abstract]
ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae
(SNe Ia) at high redshifts. Light curves, including high signal-to-noise HST
data, and spectra of six SNe Ia that were discovered during 2001 are presented.
Additionally, for the two SNe with z>1, we present ground-based J-band
photometry from Gemini and the VLT. These are among the most distant SNe Ia for
which ground based near-IR observations have been obtained. We add these six
SNe Ia together with other data sets that have recently become available in the
literature to the Union compilation (Kowalski et al. 2008). We have made a
number of refinements to the Union analysis chain, the most important ones
being the refitting of all light curves with the SALT2 fitter and an improved
handling of systematic errors. We call this new compilation, consisting of 557
supernovae, the Union2 compilation. The flat concordance LambdaCDM model
remains an excellent fit to the Union2 data with the best fit constant equation
of state parameter w=-0.997^{+0.050}_{-0.054} (stat) ^{+0.077}_{-0.082}
(stat+sys\ together) for a flat universe, or w=-1.035^{+0.055}_{-0.059}
(stat)^{+0.093}_{-0.097} (stat+sys together) with curvature. We also present
improved constraints on w(z). While no significant change in w with redshift is
detected, there is still considerable room for evolution in w. The strength of
the constraints depend strongly on redshift. In particular, at z > 1, the
existence and nature of dark energy are only weakly constrained by the data.
04/2010;
-
K. S. Dawson,
G. Aldering,
R. Amanullah,
K. Barbary,
L. F. Barrientos,
M. Brodwin,
N. Connolly,
A. Dey,
M Doi,
M. Donahue, [......],
V. Stanishev,
D. Stern, M Strovink,
N Suzuki,
N. Takanashi,
K. Tokita,
M Wagner,
L Wang,
N Yasuda,
H. K. C. Yee
[show abstract]
[hide abstract]
ABSTRACT: We present a new survey strategy to discover and study high redshift Type Ia supernovae (SNe Ia) using the Hubble Space Telescope (HST). By targeting massive galaxy clusters at 0.9<z<1.5, we obtain a twofold improvement in the efficiency of finding SNe compared to an HST field survey and a factor of three improvement in the total yield of SN detections in relatively dust-free red-sequence galaxies. In total, sixteen SNe were discovered at z>0.95, nine of which were in galaxy clusters. This strategy provides a SN sample that can be used to decouple the effects of host galaxy extinction and intrinsic color in high redshift SNe, thereby reducing one of the largest systematic uncertainties in SN cosmology. Comment: 15 pages, 8 figures, accepted by AJ, see http://www.supernova.lbl.gov for additional information pertaining to the HST Cluster SN Survey
08/2009;
-
S. Nobili,
V. Fadeyev,
G. Aldering,
R. Amanullah,
K. Barbary,
M. S. Burns,
K. S. Dawson,
S. E. Deustua,
L. Faccioli,
A. S. Fruchter, [......],
C. Lidman,
J. Meyers,
P. E. Nugent,
R. Pain,
N. Panagia,
S. Perlmutter,
D. Rubin,
A. L. Spadafora, M. Strovink,
N. Suzuki
[show abstract]
[hide abstract]
ABSTRACT: We present data from the Supernova Cosmology Project for five high redshift Type Ia supernovae (SNe Ia) that were obtained using the NICMOS infrared camera on the Hubble Space Telescope. We add two SNe from this sample to a rest-frame I-band Hubble diagram, doubling the number of high redshift supernovae on this diagram. This I-band Hubble diagram is consistent with a flat universe (ΩM, ΩΛ) = (0.29, 0.71). A homogeneous distribution of large grain dust in the intergalactic medium (replenishing dust) is incompatible with the data and is excluded at the 5σ confidence level, if the SN host galaxy reddening is corrected assuming RV = 1.75. We use both optical and infrared observations to compare photometric properties of distant SNe Ia with those of nearby objects. We find generally good agreement with the expected color evolution for all SNe except the highest redshift SN in our sample (SN 1997ek at z = 0.863) which shows a peculiar color behavior. We also present spectra obtained from ground-based telescopes for type identification and determination of redshift.
The Astrophysical Journal 07/2009; 700(2):1415. · 6.02 Impact Factor
-
D. Rubin,
E. V. Linder,
M. Kowalski,
G. Aldering,
R. Amanullah,
K. Barbary,
N. V. Connolly,
K. S. Dawson,
L. Faccioli,
V. Fadeyev, [......],
J. Meyers,
S. Nobili,
P. E. Nugent,
R. Pain,
S. Perlmutter,
P. Ruiz-Lapuente,
A. L. Spadafora, M. Strovink,
N. Suzuki,
and H. Swift
[show abstract]
[hide abstract]
ABSTRACT: The recent robust and homogeneous analysis of the world's supernova distance-redshift data, together with cosmic microwave background and baryon acoustic oscillation data—provides a powerful tool for constraining cosmological models. Here we examine particular classes of scalar field, modified gravity, and phenomenological models to assess whether they are consistent with observations even when their behavior deviates from the cosmological constant Λ. Some models have tension with the data, while others survive only by approaching the cosmological constant, and a couple are statistically favored over Λ cold dark matter. Dark energy described by two equation-of-state parameters has considerable phase space to avoid Λ and next-generation data will be required to constrain such physics, with the level of complementarity between probes varying with cosmology.
The Astrophysical Journal 03/2009; 695(1):391. · 6.02 Impact Factor
-
M. Kowalski,
D. Rubin,
G. Aldering,
R. J. Agostinho,
A. Amadon,
R. Amanullah,
C. Balland,
K. Barbary,
G. Blanc,
P. J. Challis, [......],
A. L. Spadafora,
L.-G. Strolger, M. Strovink,
N. B. Suntzeff,
N. Suzuki,
R. C. Thomas,
N. A. Walton,
L. Wang,
W. M. Wood-Vasey,
and J. L. Yun
[show abstract]
[hide abstract]
ABSTRACT: We present a new compilation of Type Ia supernovae (SNe Ia), a new data set of low-redshift nearby-Hubble-flow SNe, and new analysis procedures to work with these heterogeneous compilations. This "Union" compilation of 414 SNe Ia, which reduces to 307 SNe after selection cuts, includes the recent large samples of SNe Ia from the Supernova Legacy Survey and ESSENCE Survey, the older data sets, as well as the recently extended data set of distant supernovae observed with the Hubble Space Telescope (HST). A single, consistent, and blind analysis procedure is used for all the various SN Ia subsamples, and a new procedure is implemented that consistently weights the heterogeneous data sets and rejects outliers. We present the latest results from this Union compilation and discuss the cosmological constraints from this new compilation and its combination with other cosmological measurements (CMB and BAO). The constraint we obtain from supernovae on the dark energy density is ΩΛ = 0.713+ 0.027−0.029(stat)+ 0.036−0.039(sys) , for a flat, ΛCDM universe. Assuming a constant equation of state parameter, w, the combined constraints from SNe, BAO, and CMB give w = − 0.969+ 0.059−0.063(stat)+ 0.063−0.066(sys) . While our results are consistent with a cosmological constant, we obtain only relatively weak constraints on a w that varies with redshift. In particular, the current SN data do not yet significantly constrain w at z > 1. With the addition of our new nearby Hubble-flow SNe Ia, these resulting cosmological constraints are currently the tightest available.
The Astrophysical Journal 12/2008; 686(2):749. · 6.02 Impact Factor
-
A. Conley,
G. Goldhaber,
L. Wang,
G. Aldering,
R. Amanullah,
E. D. Commins,
V. Fadeyev,
G. Folatelli,
G. Garavini,
R. Gibbons, [......],
P. E. Nugent,
R. Pain,
S. Perlmutter,
E. Smith,
A. L. Spadafora,
V. Stanishev, M. Strovink,
R. C. Thomas,
W. M. Wood-Vasey,
and (The Supernova Cosmology Project
[show abstract]
[hide abstract]
ABSTRACT: We present measurements of Ωm and ΩΛ from a blind analysis of 21 high-redshift supernovae using a new technique (CMAGIC) for fitting the multicolor light curves of Type Ia supernovae, first introduced by Wang and coworkers. CMAGIC takes advantage of the remarkably simple behavior of Type Ia supernovae on color-magnitude diagrams and has several advantages over current techniques based on maximum magnitudes. Among these are a reduced sensitivity to host galaxy dust extinction, a shallower luminosity-width relation, and the relative simplicity of the fitting procedure. This allows us to provide a cross-check of previous supernova cosmology results, despite the fact that current data sets were not observed in a manner optimized for CMAGIC. We describe the details of our novel blindness procedure, which is designed to prevent experimenter bias. The data are broadly consistent with the picture of an accelerating universe and agree with a flat universe within 1.7 σ, including systematics. We also compare the CMAGIC results directly with those of a maximum magnitude fit to the same supernovae, finding that CMAGIC favors more acceleration at the 1.6 σ level, including systematics and the correlation between the two measurements. A fit for w assuming a flat universe yields a value that is consistent with a cosmological constant within 1.2 σ.
The Astrophysical Journal 12/2008; 644(1):1. · 6.02 Impact Factor
-
M. Kowalski,
D. Rubin,
G. Aldering,
R. J. Agostinho,
A. Amadon,
R. Amanullah,
C. Balland,
K. Barbary,
G. Blanc,
P. J. Challis, [......],
A. L. Spadafora,
L. -G. Strolger, M Strovink,
N. B. Suntzeff,
N Suzuki,
R. C. Thomas,
N. A. Walton,
L Wang,
W. M. Wood-Vasey,
J. L. Yun
[show abstract]
[hide abstract]
ABSTRACT: We present a new compilation of Type Ia supernovae (SNe Ia), a new dataset of low-redshift nearby-Hubble-flow SNe and new analysis procedures to work with these heterogeneous compilations. This ``Union'' compilation of 414 SN Ia, which reduces to 307 SNe after selection cuts, includes the recent large samples of SNe Ia from the Supernova Legacy Survey and ESSENCE Survey, the older datasets, as well as the recently extended dataset of distant supernovae observed with HST. A single, consistent and blind analysis procedure is used for all the various SN Ia subsamples, and a new procedure is implemented that consistently weights the heterogeneous data sets and rejects outliers. We present the latest results from this Union compilation and discuss the cosmological constraints from this new compilation and its combination with other cosmological measurements (CMB and BAO). The constraint we obtain from supernovae on the dark energy density is $\Omega_\Lambda= 0.713^{+0.027}_{-0.029} (stat)}^{+0.036}_{-0.039} (sys)}$, for a flat, LCDM Universe. Assuming a constant equation of state parameter, $w$, the combined constraints from SNe, BAO and CMB give $w=-0.969^{+0.059}_{-0.063}(stat)^{+0.063}_{-0.066} (sys)$. While our results are consistent with a cosmological constant, we obtain only relatively weak constraints on a $w$ that varies with redshift. In particular, the current SN data do not yet significantly constrain $w$ at $z>1$. With the addition of our new nearby Hubble-flow SNe Ia, these resulting cosmological constraints are currently the tightest available.
05/2008;
-
V. M. Abazov,
B. Abbott,
M. Abolins,
B. S. Acharya,
M. Adams,
T. Adams,
M. Agelou,
J.-L. Agram,
S. H. Ahn,
M. Ahsan, [......],
Z. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
A. Zieminski,
R. Zitoun,
V. Zutshi,
E. G. Zverev,
A. Zylberstejn
Phys. Rev. D. 02/2008; 77(3).
-
V. M. Abazov,
B. Abbott,
M. Abolins,
B. S. Acharya,
M. Adams,
T. Adams,
M. Agelou,
J.-L. Agram,
S. H. Ahn,
M. Ahsan, [......],
Z. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
A. Zieminski,
R. Zitoun,
V. Zutshi,
E. G. Zverev,
A. Zylberstejn
Physical review D: Particles and fields 01/2008; 77(3):39901.
-
V M Abazov,
B Abbott,
M Abolins,
B S Acharya,
M Adams,
T Adams,
E Aguilo,
S H Ahn,
M Ahsan,
G D Alexeev, [......],
C Zeitnitz,
D Zhang,
T Zhao,
B Zhou,
J Zhu,
M Zielinski,
D Zieminska,
A Zieminski,
V Zutshi,
E G Zverev
[show abstract]
[hide abstract]
ABSTRACT: We report a study of the decay Bs(0)-->Ds(*)Ds(*) using a data sample corresponding to 1.3 fb(-1) of integrated luminosity collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron collider. One Ds(*) meson was partially reconstructed in the decay Ds-->phi mu nu, and the other Ds(*) meson was identified using the decay Ds-->phi pi where no attempt was made to distinguish Ds and Ds(*) states. For the branching fraction Br(Bs(0)-->Ds(*)Ds(*)) we obtain a 90% C.L. range [0.002,0.080] and central value 0.039(-0.017)(+0.019)(stat)(-0.015)(+0.016)(syst). This was subsequently used to make the most precise estimate of the width difference DeltaGamma(s)CP in the Bs(0)-Bs(0) system: DeltaGamma(s)CP/Gamma(s)=0.079(-0.035)(+0.038)(stat)(-0.030)(+0.031)(syst).
Physical Review Letters 01/2008; 99(24):241801. · 7.37 Impact Factor
-
V M Abazov,
B Abbott,
M Abolins,
B S Acharya,
M Adams,
T Adams,
E Aguilo,
S H Ahn,
M Ahsan,
G D Alexeev, [......],
C Zeitnitz,
D Zhang,
T Zhao,
B Zhou,
J Zhu,
M Zielinski,
D Zieminska,
A Zieminski,
V Zutshi,
E G Zverev
[show abstract]
[hide abstract]
ABSTRACT: We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb{-1} of lepton+jets data from pp[over] collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters kappa{g}{c}/Lambda and kappa{g}{u}/Lambda, where kappa{g} define the strength of tcg and tug couplings, and Lambda defines the scale of new physics. The limits at 95% C.L. are kappa{g}{c}/Lambda<0.15 TeV-1 and kappa{g}{u}/Lambda<0.037 TeV-1.
Physical Review Letters 12/2007; 99(19):191802. · 7.37 Impact Factor
-
V M Abazov,
B Abbott,
M Abolins,
B S Acharya,
M Adams,
T Adams,
E Aguilo,
S H Ahn,
M Ahsan,
G D Alexeev, [......],
D Zhang,
T Zhao,
B Zhou,
J Zhu,
M Zielinski,
D Zieminska,
A Zieminski,
L Zivkovic,
V Zutshi,
E G Zverev
[show abstract]
[hide abstract]
ABSTRACT: We report a measurement of the Lambda(b)(0) lifetime using a sample corresponding to 1.3 fb(-1) of data collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron collider. The Lambda(b)(0) baryon is reconstructed via the decay Lambda(b)(0)-->micronuLambda(c)(+)X. Using 4437+/-329 signal candidates, we measure the Lambda(b)(0) lifetime to be tau(Lambda(b)(0))=1.290(-0.110)(+0.119)(stat)(-0.091)(+0.087)(syst) ps, which is among the most precise measurements in semileptonic Lambda(b)(0) decays. This result is in good agreement with the world average value.
Physical Review Letters 11/2007; 99(18):182001. · 7.37 Impact Factor
-
V M Abazov,
B Abbott,
M Abolins,
B S Acharya,
M Adams,
T Adams,
E Aguilo,
S H Ahn,
M Ahsan,
G D Alexeev, [......],
D Zhang,
T Zhao,
B Zhou,
J Zhu,
M Zielinski,
D Zieminska,
A Zieminski,
L Zivkovic,
V Zutshi,
E G Zverev
[show abstract]
[hide abstract]
ABSTRACT: This Letter presents the first strong evidence for the resolution of the excited B mesons B(1) and B(2)* as two separate states in fully reconstructed decays to B(+)(*)pi(-). The mass of B(1) is measured to be 5720.6+/-2.4+/-1.4 MeV/c(2) and the mass difference DeltaM between B(2)* and B(1) is 26.2+/-3.1+/-0.9 MeV/c;{2}, giving the mass of the B(2)* as 5746.8+/-2.4+/-1.7 MeV/c(2). The production rate for B(1) and B(2)* mesons is determined to be a fraction (13.9+/-1.9+/-3.2)% of the production rate of the B+ meson.
Physical Review Letters 11/2007; 99(17):172001. · 7.37 Impact Factor
-
V. M. Abazov,
B. Abbott,
M. Abolins,
B. S. Acharya,
M. Adams,
T. Adams,
E. Aguilo,
S. H. Ahn,
M. Ahsan,
G. D. Alexeev, [......],
C. Zeitnitz,
D. Zhang,
T. Zhao,
B. Zhou,
J. Zhu,
M. Zielinski,
D. Zieminska,
A. Zieminski,
V. Zutshi,
E. G. Zverev
[show abstract]
[hide abstract]
ABSTRACT: A measurement of the top quark pair production cross section in proton antiproton collisions at an interaction energy of √s=1.96 TeV is presented. This analysis uses 405±25 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. Fully hadronic tt̅ decays with final states of six or more jets are separated from the multijet background using secondary vertex tagging and a neural network. The tt̅ cross section is measured as σtt̅ =4.5-1.9+2.0(stat)-1.1+1.4(syst)±0.3(lumi) pb for a top quark mass of mt=175 GeV/c2.
Phys. Rev. D. 10/2007; 76(7).
-
N Kuznetsova,
K. Barbary,
B. Connolly,
A. G. Kim,
R Pain,
N A Roe,
G. Aldering,
R. Amanullah,
K. Dawson,
M Doi, [......],
J. Meyers,
S. Perlmutter,
D. Rubin,
D. J. Schlegel,
A. L. Spadafora,
V. Stanishev, M Strovink,
N Suzuki,
L Wang,
N Yasuda
[show abstract]
[hide abstract]
ABSTRACT: We present a new measurement of the volumetric rate of Type Ia supernova up to a redshift of 1.7, using the Hubble Space Telescope (HST) GOODS data combined with an additional HST dataset covering the North GOODS field collected in 2004. We employ a novel technique that does not require spectroscopic data for identifying Type Ia supernovae (although spectroscopic measurements of redshifts are used for over half the sample); instead we employ a Bayesian approach using only photometric data to calculate the probability that an object is a Type Ia supernova. This Bayesian technique can easily be modified to incorporate improved priors on supernova properties, and it is well-suited for future high-statistics supernovae searches in which spectroscopic follow up of all candidates will be impractical. Here, the method is validated on both ground- and space-based supernova data having some spectroscopic follow up. We combine our volumetric rate measurements with low redshift supernova data, and fit to a number of possible models for the evolution of the Type Ia supernova rate as a function of redshift. The data do not distinguish between a flat rate at redshift > 0.5 and a previously proposed model, in which the Type Ia rate peaks at redshift >1 due to a significant delay from star-formation to the supernova explosion. Except for the highest redshifts, where the signal to noise ratio is generally too low to apply this technique, this approach yields smaller or comparable uncertainties than previous work. Comment: Accepted for publication in ApJ
10/2007;
-
V M Abazov,
B Abbott,
M Abolins,
B S Acharya,
M Adams,
T Adams,
E Aguilo,
S H Ahn,
M Ahsan,
G D Alexeev, [......],
D Zhang,
T Zhao,
B Zhou,
J Zhu,
M Zielinski,
D Zieminska,
A Zieminski,
L Zivkovic,
V Zutshi,
E G Zverev
[show abstract]
[hide abstract]
ABSTRACT: We have measured the Lambda b lifetime using the exclusive decay Lambda b --> J/psi Lambda, based on 1.2 fb(-1) of data collected with the D0 detector during 2002-2006. From 171 reconstructed Lambda b decays, where the J/psi and Lambda are identified via the decays J/psi --> mu+ mu- and Lambda --> ppi, we measured the Lambda b lifetime to be tau(Lambda b)=1.218 (+0.130)/(-0.115) (stat) +/- 0.042(syst) ps. We also measured the B0 lifetime in the decay B0 --> J/psi(mu+ mu-)K(0)/(S)(pi+ pi-) to be tau(B0)=1.501 (+0.078)/(-0.074) (stat) +/- 0.050(syst) ps, yielding a lifetime ratio of tau(Lambda b)/tau(B0)=0.811 (+0.096)/(-0.087) (stat) +/- 0.034(syst).
Physical Review Letters 10/2007; 99(14):142001. · 7.37 Impact Factor
