arXiv subjects

T. Adams

Publications and source records attributed to T. Adams.

At least 127 records · Page 7Linked to original sources

arXiv2009

Skyrmion Lattice in a Doped Semiconductor

We report a comprehensive small angle neutron scattering study (SANS) of the magnetic phase diagram of the doped semiconductor Fe_{1-x}Co_{x}Si for x=0.2 and 0.25. For magnetic field parallel to the neutron beam we observe a six-fold intensity pattern under field-cooling, which identifies the A-phase of Fe_{1-x}Co_{x}Si as a skyrmion lattice. The regime of the skyrmion lattice is highly hysteretic and extents over a wide temperature range, consistent with the site disorder of the Fe and Co atoms. Our study identifies Fe_{1-x}Co_{x}Si is a second material after MnSi in which a skyrmion lattice forms and establishes that skyrmion lattices may also occur in strongly doped semiconductors.

cond-mat.str-el↗

arXiv2008

SUSY Searches at the Tevatron

Numerous searches for evidence of supersymmetry at the Tevatron have been performed by the CDF and D0 collaborations. Recent results are presented here including squarks and gluinos in jets and missing transverse energy, stop in several different decay modes, charginos and neutralinos in trileptons, neutralinos in di-photons, R-parity violating sneutrinos in e+mu events, and long-lived particles. These explore many variations of SUSY such as MSSM, mSUGRA, and GMSB. While no evidence of SUSY production is observed, 95% CL limits on cross sections and SUSY parameter space are set. Most of these limits are the world's best.

hep-ex↗

arXiv2008

Searches for Long-lived Particles at the Tevatron Collider

Several searches for long-lived particles have been performed using data from p-pbar collisions from Run II at the Tevatron. In most cases, new analysis techniques have been developed to carry out each search and/or estimate the backgrounds. These searches expand the discovery potential of the CDF and D0 experiments to new physics that may have been missed by traditional search techniques. This review discusses searches for (1) neutral, long-lived particles decaying to muons, (2) massive, neutral, long-lived particles decaying to a photon and missing energy, (3) stopped gluinos, and (4) charged massive stable particles. It summarizes some of the theoretical and experimental motivations for such searches.

hep-ex↗

arXiv2007

Confirmation of a pi_1^0 Exotic Meson in the ηπ^0 System

The exclusive reaction $π^- p \to ηπ^0 n$, $η\to π^+ π^- π^0$ at 18 GeV$/c$ has been studied with a partial wave analysis on a sample of 23~492 $ηπ^0 n$ events from BNL experiment E852. A mass-dependent fit is consistent with a resonant hypothesis for the $P_+$ wave, thus providing evidence for a neutral exotic meson with $J^{PC} = 1^{-+}$, a mass of $1257 \pm 20 \pm 25$ MeV$/c^2$, and a width of $354 \pm 64 \pm 60$ MeV$/c^2$. New interpretations of the meson exotics in neutral $ηπ^0$ system observed in E852 and Crystal Barrel experiments are discussed.

hep-ex↗

arXiv2007

Searches for New Phenomena with Lepton Final States at the Tevatron

Numerous searches for new phenomena have been carried out using data from proton-antiproton collisions at Fermilab's Tevatron. Final states with leptons give signatures which are relatively unique and generally have small backgrounds. We present many of the latest results from the CDF and D0 collaborations from 0.4-1.2 fb^-1 of data. Topics include supersymmetry, extra gauge bosons, Randall-Sundrum gravitons, excited electrons and neutral, long-lived particles.

hep-ex↗

arXiv2007

The D0 Run II Impact Parameter Trigger

Many physics topics to be studied by the D0 experiment during Run II of the Fermilab Tevatron ppbar collider give rise to final states containing b--flavored particles. Examples include Higgs searches, top quark production and decay studies, and full reconstruction of B decays. The sensitivity to such modes has been significantly enhanced by the installation of a silicon based vertex detector as part of the DO detector upgrade for Run II. Interesting events must be identified initially in 100-200 microseconds to be available for later study. This paper describes custom electronics used in the DO trigger system to provide the real--time identification of events having tracks consistent with the decay of b--flavored particles.

physics.ins-det↗

arXiv2005

Precise Measurement of Neutrino and Anti-neutrino Differential Cross Sections

The NuTeV experiment at Fermilab has obtained a unique high statistics sample of neutrino and anti-neutrino interactions using its high-energy sign-selected beam. We present a measurement of the differential cross section for charged-current neutrino and anti-neutrino scattering from iron. Structure functions, F_2(x,Q^2) and xF_3(x,Q^2), are determined by fitting the inelasticity, y, dependence of the cross sections. This measurement has significantly improved systematic precision as a consequence of more precise understanding of hadron and muon energy scales.

hep-ex↗

arXiv2003

A Departure from Prediction: Electroweak Physics at Nutev

The NuTeV experiment has performed precision measurements of the ratio of neutral-current to charged-current cross-sections in high rate, high energy neutrino and anti-neutrino beams on a dense, primarily steel, target. The separate neutrino and anti-neutrino beams, high statistics, and improved control of other experimental systematics, allow the determination of electroweak parameters with significantly greater precision than past neutrino-nucleon scattering experiments. Our null hypothesis test of the standard model prediction measures sin2thetaW=0.2277+/-0.0013(stat)+/-0.0009(syst), a value which is 3.0 standard deviations above the prediction. We discuss possible explanations for and implications of this discrepancy.

hep-ex↗

arXiv2003

A Precise Determination of Electroweak Parameters in Neutrino-Nucleon Scattering

The NuTeV collaboration has extracted sin^2theta_W from the ratios of neutral current to charged current neutrino and anti-neutrino cross-sections. Our value, sin^2theta_W(on-shell)=0.2277+/-0.0013(stat)+/-0.0009(syst), is three standard deviations above the standard model prediction. We also present a model independent analysis of the same data.

hep-ex↗

arXiv2002

Off the Mass Shell: Electroweak Physics at NuTeV

The NuTeV collaboration has performed precision measurements of the ratio of neutral current to charged current cross-sections in high rate, high energy neutrino and anti-neutrino beams on a dense, primarily steel, target. The separate neutrino and anti-neutrino beams, high statistics, and improved control of other experimental systematics, allow the determination of electroweak parameters with significantly greater precision than past neutrino-nucleon scattering experiments. Our null hypothesis test of the standard model prediction measures sin2thetaW=0.2277+/-0.0013(stat)+/-0.0009(syst), a value which is 3 sigma above the prediction. We discuss possible explanations for and implications of this discrepancy.

hep-ex↗

arXiv2002

A Search for Muon-neutrino to Electron-neutrino and Muon-antineutrino to Electron-antineutrino Oscillations at NuTeV

Limits on $ν_μ\to ν_e$ and $\barν_μ\to \barν_e$ oscillations are extracted using the NuTeV detector with sign-selected $ν_μ$ and $\nub_μ$ beams. In $\nub_μ$ mode, for the case of $\sin^2 2α= 1$, $Δm^2 > 2.6$ ${\rm eV^2}$ is excluded, and for $Δm^2 \gg 1000$ ${\rm eV^2}$, $\sin^2 2α> 1.1 \times 10^{-3}$. The NuTeV data exclude the high $Δm^2$ end of $\barν_μ\to \barν_e$ oscillations parameters favored by the LSND experiment without the need to assume that the oscillation parameters for $ν$ and $\nub$ are the same. We present the most stringent experimental limits for $ν_μ(\barν_μ) \to ν_e (\barν_e)$ oscillations in the large $Δm^2$ region.

hep-ex↗

arXiv2001

Young Physicists' Forum

The Young Physicists' Forum was an opportunity for the younger members of the particle-physics community to gather at Snowmass 2001 and to study and debate major issues that face the field over the next twenty years. Discussions were organized around three major topics: outreach and education, the impact of globalization, and building a robust and balanced field. We report on the results of these discussions, as presented on July 17, 2001.

hep-ex↗

arXiv2001

Extraction of R = sigma_L/sigma_T from CCFR nu_mu-Fe and nubar_mu-Fe differential cross sections

We report on the extraction of R=sigma_L/sigma_T from CCFR nu_mu-Fe and nubar_mu-Fe differential cross sections. The CCFR differential cross sections do not show the deviations from the QCD expectations that are seen in the CDHSW data at very low and very high x. R as measured in nu_mu scattering is in agreement with R as measured in muon and electron scattering. All data on R for Q^2 > 1 GeV^2 are in agreement with a NNLO QCD calculation which includes target mass effects. We report on the first measurements of R in the low x and Q^2 < 1 GeV^2 region (where an anomalous large rise in R for nuclear targets has been observed by the HERMES collaboration).

hep-ex↗

arXiv2001

Extraction of R=sigma_L/sigma_T from CCFR Neutrino and Antinetrino Differential Cross Sections

We report on the extraction of R=sigam_L/sigma_T from CCFR neutrino and antineutrino-Iron differential cross sections. R as measured in neutrno scattering is in agreement with $R$ as measured in muon and electron scattering. All data on R for Q2 > 1 GeV2 are in agreement with a NNLO QCD calculation which uses NNLO PDFs and includes target mass effects. We report on the first measurements of R in the low x and Q2 < 1 GeV2 region (where an anomalous large rise in R for nuclear targets has been observed by the HERMES collaboration).

hep-ex↗

arXiv2001

Observation of an Anomalous Number of Dimuon Events in a High Energy Neutrino Beam

A search for long-lived neutral particles (N^0's) with masses above 2.2 GeV/c^2 that decay into at least one muon has been performed using an instrumented decay channel at the NuTeV experiment at Fermilab. Data were examined for particles decaying into the final states mu mu, mu e, and mu pi. Three mu mu events were observed over an expected Standard Model background of 0.069 +/- 0.010 events; no events were observed in the other modes.

hep-ex↗

arXiv2000

Recent structure function results from neutrino scattering at Fermilab

We report on the extraction of the structure functions F_2 and Delta xF_3 = xF_3(nu)-xF_3(nubar) from CCFR nu_mu-Fe and nubar_mu-Fe different ial cross sections. The extraction is performed in a physics model independent (PMI) way. This first measurement of Delta xF_3, which is useful in testing models of heavy charm production, is higher than current theoretical predictios. The ratio of the F_2 (PMI) values measured in nu_mu and mu scattering is in agreement (within 5%) with the NLO predictions using massive charm production schemes, thus resolving the long-standing discrepancy between the two sets of data. In addition, measurements of F_L (or, equivalently, R) and 2xF_1 are reported in the kinematic region where anomalous nuclear effects in R are observed at HERMES.

hep-ex↗

arXiv2000

New Measurements of Nucleon Structure Functions from CCFR/NuTeV

We report on the extraction of the structure functions F_2 and Delta xF_3 = xF_3nu-xF_3nub from CCFR neutrino-Fe and antineutrino-Fe differential cross sections. The extraction is performed in a physics model independent (PMI) way. This first measurement for Delta xF_3, which is useful in testing models of heavy charm production, is higher than current theoretical predictions. Within 5% the F_2 (PMI) values measured in neutrino and muon scattering are in agreement with the predictions of Next-to-Leading-Order PDFs (using massive charm production schemes), thus resolving the long-standing discrepancy between the two measurements.

hep-ex↗

arXiv2000

New Measurements of Nucleon Structure Functions from the CCFR/NuTeV Collaboration

We report on the extraction of the structure functions F_2 and Delta xF_3 = xF_3nu-xF_3nubar from CCFR neutrino-Fe and antineutrino-Fe differential cross sections. The extraction is performed in a physics model independent (PMI) way. This first measurement for Delta xF_3, which is useful in testing models of heavy charm production, is higher than current theoretical predictions. The F_2 (PMI) values measured in neutrino and muon scattering are in good agreement with the predictions of Next to Leading Order PDFs (using massive charm production schemes), thus resolving the long-standing discrepancy between the two sets of data.

hep-ex↗