Showing papers by "Subir Sarkar published in 2003"
TL;DR: In this paper, the authors report on measurements of differential cross sections dsigma/dp(T) for prompt charm meson production in ppmacr; collisions at sqrt[s]=1.96 TeV using 5.8+/-0.3 pb(-1) of data from the CDF II detector at the Fermilab Tevatron.
Abstract: We report on measurements of differential cross sections dsigma/dp(T) for prompt charm meson production in ppmacr; collisions at sqrt[s]=1.96 TeV using 5.8+/-0.3 pb(-1) of data from the CDF II detector at the Fermilab Tevatron. The data are collected with a new trigger that is sensitive to the long lifetime of hadrons containing heavy flavor. The charm meson cross sections are measured in the central rapidity region |y| K-pi(+), D(*+)-->D0pi(+), D+-->K-pi(+)pi(+), D(+)(s)-->phipi(+), and their charge conjugates. The measured cross sections are compared to theoretical calculations.
193 citations
TL;DR: In this article, it was shown that an Einstein-de Sitter universe with zero cosmological constant can fit the data as well as the best concordance model, and unlike a Λ-dominated universe, such an universe has no strong integrated Sachs-Wolfe effect.
Abstract: Precision measurements of the cosmic microwave background by WMAP are believed to have established a flat Λ-dominated universe, seeded by nearly scale-invariant adiabatic primordial fluctuations. However by relaxing the hypothesis that the fluctuation spectrum can be described by a single power law, we demonstrate that an Einstein-de Sitter universe with zero cosmological constant can fit the data as well as the best concordance model. Moreover unlike a Λ-dominated universe, such an universe has no strong integrated Sachs-Wolfe effect, so is in better agreement with the low quadrupole seen by WMAP. The main concern is that the Hubble constant is required to be rather low: H0 � 46 km s −1 Mpc −1 ; we discuss whether this can be consistent with observations. Furthermore for universes consisting only of baryons and cold dark matter, the amplitude of matter fluctuations on cluster scales is too high, a problem which seems generic. However, an additional small contribution (ΩX ∼ 0.1) of matter which does not cluster on small scales, e.g. relic neutrinos with mass of order eV or a "quintessence" with w ∼ 0, can alleviate this problem. Such models provide a satisfying description of the power spectrum derived from the 2dF galaxy redshift survey and from observations of the Ly-α forest. We conclude that Einstein-de Sitter models can indeed accommodate all data on the large scale structure of the Universe, hence the Hubble diagram of distant type Ia supernovae remains the only direct evidence for a non-zero cosmological constant.
161 citations
TL;DR: In this article, the authors relax the hypothesis that the fluctuation spectrum can be described by a single power law, and demonstrate that an Einstein-de Sitter universe with zero cosmological constant can fit the data as well as the best concordance model.
Abstract: Precision measurements of the cosmic microwave background by WMAP are believed to have established a flat $\Lambda$-dominated universe, seeded by nearly scale-invariant adiabatic primordial fluctuations. However by relaxing the hypothesis that the fluctuation spectrum can be described by a single power law, we demonstrate that an Einstein-de Sitter universe with {\em zero} cosmological constant can fit the data as well as the best concordance model. Moreover unlike a $\Lambda$-dominated universe, such an universe has no strong integrated Sachs-Wolfe effect, so is in better agreement with the low quadrupole seen by WMAP. The main problem is that the Hubble constant is required to be rather low: $H_0 \simeq 46$ km/s/Mpc; we discuss whether this can be consistent with observations. Furthermore for universes consisting only of baryons and cold dark matter, the amplitude of matter fluctuations on cluster scales is too high, a problem which seems generic. However, an additional small contribution ($\Omega_X \sim 0.1$) of matter which does not cluster on small scales, e.g. relic neutrinos with mass of order eV or a `quintessence' with $w \sim 0$, can alleviate this problem. Such models provide a satisfying description of the power spectrum derived from the 2dF galaxy redshift survey and from observations of the Ly-$\alpha$ forest. We conclude that Einstein-de Sitter models can indeed accommodate all data on the large scale structure of the Universe, hence the Hubble diagram of distant Type Ia supernovae remains the only {\em direct} evidence for a non-zero cosmological constant.
144 citations
TL;DR: The sky distribution of cosmic rays with energies above the ''GZK cutoff'' holds important clues to their origin, and it has been argued that such clusters are aligned with BL Lacertae objects, implicating these as the sources as discussed by the authors.
Abstract: The sky distribution of cosmic rays with energies above the ``GZK cutoff'' holds important clues to their origin. The AGASA data, although consistent with isotropy overall, shows evidence for small-angle clustering, and it has been argued that such clusters are aligned with BL Lacertae objects, implicating these as the sources. It has also been suggested that such clusters can arise if the cosmic rays come from the decays of very massive relic particles in the galactic halo, due to the expected clumping of cold dark matter. We examine these claims and show that both are, in fact, unjustified.
48 citations
TL;DR: In this paper, a search for the production of long-lived charged massive particles in a data sample of 90 pb(-1) of roots = 1.8 TeV p (p) over bar collisions recorded by the Collider Detector at Fermilab is reported.
Abstract: We report a search for the production of long-lived charged massive particles in a data sample of 90 pb(-1) of roots = 1.8 TeV p (p) over bar collisions recorded by the Collider Detector at Fermilab. The search uses the muonlike penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data are found to agree with background expectations, and cross section limits of O(1) pb are derived using two reference models, a stable quark and a stable scalar lepton.
42 citations
TL;DR: In this article, a search for colour reconnection effects in hadronic decays of W pairs is performed with the L3 detector at centre-of-mass energies between 189 and 209 ǫGeV.
23 citations
TL;DR: In this article, the authors measured single particle inclusive differential cross sections as a function of the particle transverse momentum, and pseudo-rapidity, and showed that the data are well described by an exponential, typical of soft hadronic processes.
16 citations
TL;DR: In this paper, events stemming from the pair-production of Z bosons in e+e collisions are studied using 217.4 pb-1 of data collected with the L3 detector at centre-of-mass energies from 200 GeV up to 209 GeV.
15 citations
TL;DR: In this paper, the mass difference m(D-s(+))-m(D+), where both the D-s and D+ are reconstructed in the phipi(+) decay channel, was measured using 11.6 pb(-1) of data collected by CDF II using the new displaced-track trigger.
Abstract: We present a measurement of the mass difference m(D-s(+))-m(D+), where both the D-s(+) and D+ are reconstructed in the phipi(+) decay channel. This measurement uses 11.6 pb(-1) of data collected by CDF II using the new displaced-track trigger. The mass difference is found to be m(D-s(+))-m(D+)=99.41+/-0.38(stat)+/-0.21(syst) MeV/c(2).
13 citations
TL;DR: The results from a similar measurement performed in a subsample of pp events containing a leading (high longitudinal momentum) antiproton were reported in this paper, and large pseudorapidity gaps are presumed to be due to Pomeron exchanges and are the signature for diffraction.
Abstract: The results from a similar measurement performed in a subsample of pp events containing a leading (high longitudinal momentum) antiproton. As such, large pseudorapidity gaps are presumed to be due to Pomeron exchanges and are the signature for diffraction. The process with a leading beam particle in the final state, which is kinematically associated with an adjacent pseudorapidity gap, is known as single diffraction dissociation (SD), while that with a central gap as double diffraction dissociation (DD).
12 citations
TL;DR: In this paper, a study was performed to search for the production of a new heavy vector gauge boson in 1.8 TeV pp collisions and decaying into the tb final state.
Abstract: A study was performed to search for the production of a new heavy vector gauge boson in 1.8 TeV pp collisions and decaying into the tb final state. No evidence was obtained for a signal above the expected background contributions. A fit of the final state invariant mass distribution was used to exclude a W′ boson with 225
TL;DR: In this paper, a search for the flavor-changing neutral current decay D/sup 0/ to mu/sup +/ mu /sup -/ in pp collisions at square root s=1.96 TeV using 65 pb/sup -1/ of data collected by the CDF II experiment at the Fermilab Tevatron Collider.
Abstract: We report on a search for the flavor-changing neutral current decay D/sup 0/ to mu /sup +/ mu /sup -/ in pp collisions at square root s=1.96 TeV using 65 pb/sup -1/ of data collected by the CDF II experiment at the Fermilab Tevatron Collider. A displaced-track trigger selects long-lived D/sup 0/ candidates in the D/sup 0/ to mu /sup +/ mu /sup -/ search channel, the kinematically similar D/sup 0/ to pi /sup +/ pi /sup -/ channel used for normalization, the Cabibbo-favored D/sup 0/ to K/sup -/ pi /sup +/ channel used to optimize the selection criteria in an unbiased manner, and their charge conjugates. Finding no signal events in the D/sup 0/ to mu /sup +/ mu /sup -/ search window, we set an upper limit on the branching fraction B(D/sup 0/ to mu /sup +/ mu /sup -/) lt or=2.5*10/sup -6/ (3.3*10/sup -6/) at the 90% (95%) confidence level.
01 Jan 2003
TL;DR: In this paper, it was shown that neutrino mixing angles are large, which excludes the possibility of a large asymmetry and disfavours new neutrinos beyond those now known.
Abstract: The standard Big Bang cosmology predicts the existence of an, as yet undetected, relic neutrino background, similar to the photons observed in the cosmic microwave background. If neutrinos have mass, then such relic neutrinos are a natural candidate for the dark matter of the universe, and indeed were the first particles to be proposed for this role. This possibility has however been increasingly constrained by cosmological considerations, particularly of large-scale structure formation, thus yielding stringent bounds on neutrino masses, which have yet to be matched by laboratory experiments. Another probe of relic neutrinos is primordial nucleosynthesis which is sensitive to the number of neutrino types (including possible sterile species) as well as to any lepton asymmetry. Combining such arguments with the experimental finding that neutrino mixing angles are large, excludes the possibility of a large asymmetry and disfavours new neutrinos beyond those now known.
TL;DR: In this paper, lepton flavor violating decays of a heavy neutral particle in pp collisions at √s = 18 TeV were studied and the position of PP collisions along the beam line was measured in the vertex time projection chamber (VTX).
Abstract: Lepton flavor violating decays of a heavy neutral particle in pp collisions at √s = 18 TeV were studied The position of PP collisions along the beam line was measured in the vertex time projection chamber (VTX) The results show no evidence for new particles with lepton flavor violating decays The limits on the cross section for production and decay of single sneutrino with R-parity violating interactions were also set
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TL;DR: In this paper, it was shown that the spectrum of cosmic rays with energies above 4 x 10−10−10 GeV exhibits the expected ''GZK cutoff'' at this energy, and if there is indeed a cutoff then the sources are cosmologically distant and rather exotic in nature.
Abstract: Observations of cosmic rays with energies above ~ 4 x 10^{10} GeV have inspired several speculative suggestions concerning their origin. The crucial question is whether or not the spectrum exhibits the expected `GZK cutoff' at this energy -- concerning which there are presently contradictory results. If there is indeed a cutoff, then the sources are cosmologically distant and rather exotic in nature. If there is no cutoff then new physics is required.
TL;DR: In this paper, the authors used the complete set of non-linear dust fluid equations coupled with the dust charging equation and Poisson equation to study the propagation of large-amplitude dust acoustic stationary shock wave.
Abstract: In a dusty plasma, the non-adiabaticity of the charge variation on a dust grain surface results in an anomalous dissipation. Analytical investigation shows that this results in a small but finite amplitude dust acoustic (DA) wave propagation which is described by the Korteweg-de Vries-Burger equation. Results of the numerical investigation of the propagation of large-amplitude dust acoustic stationary shock wave are presented here using the complete set of non-linear dust fluid equations coupled with the dust charging equation and Poisson equation. The DA waves are of compressional type showing considerable increase of dust density, which is of significant importance in astrophysical context as it leads to enhanced gravitational attraction considered as a viable process for star formation. The DA shock transition to its far downstream amplitude is oscillatory in nature due to dust charge fluctuations, the oscillation amplitude and shock width depending on the ratioω
pd/Vch and other plasma parameters
21 Mar 2003-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The SVT architecture and design is briefly covered and reports on the SVT building/commissioning experience (hardware and software) and on the first results from the initial running are reported.
Abstract: The Collider Detector at Fermilab (CDF) Silicon Vertex Tracker (SVT) is a device that works inside the CDF Level 2 trigger to find and fit tracks in real time using the central silicon vertex detector information. SVT starts from tracks found by the Level 1 central chamber fast trigger and adds the silicon information to compute transverse track parameters with offline quality in about . The CDF SVT is fully installed and functional and has been exercised with real data during the spring and summer 2001. It is a complex digital device of more than 100 VME boards that performs a dramatic data reduction (only about one event in a thousand is accepted by the trigger). Diagnosing rare failures poses a special challenge and SVT internal data flow is monitored by dedicated hardware and software. This paper briefly covers the SVT architecture and design and reports on the SVT building/commissioning experience (hardware and software) and on the first results from the initial running.
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TL;DR: In this paper, it was shown that neutrino mixing angles are large, which excludes the possibility of a large asymmetry and disfavours new neutrinos beyond those now known.
Abstract: The standard Big Bang cosmology predicts the existence of an, as yet undetected, relic neutrino background, similar to the photons observed in the cosmic microwave background. If neutrinos have mass, then such relic neutrinos are a natural candidate for the dark matter of the universe, and indeed were the first particles to be proposed for this role. This possibility has however been increasingly constrained by cosmological considerations, particularly of large-scale structure formation, thus yielding stringent bounds on neutrino masses, which have yet to be matched by laboratory experiments. Another probe of relic neutrinos is primordial nucleosynthesis which is sensitive to the number of neutrino types (including possible sterile species) as well to any lepton asymmetry. Combining such arguments with the experimental finding that neutrino mixing angles are large, excludes the possibility of a large asymmetry and disfavours new neutrinos beyond those now known.
TL;DR: In this paper, the cross section of the process e+e- → Ze+e − e −e −e- is measured with 0.7 fb-1 of data collected with the L3 detector at LEP.