Fermilab Research Articles

New results on searches for new physics beyond the standard model in the D0 experiment

The latest results obtained from searches for particles and phenomena beyond the Standard Model (new physics) in the D0 experiment at the Tevatron [Fermi National Accelerator Laboratory (FNAL), USA] on the basis of a statistical sample corresponding to an accumulated luminosity of 1 to 3 fb−1 in 2008 are considered.

Measurement of the top quark mass andpp¯→tt¯cross section in the all-hadronic mode with the CDF II detector

We present a measurement of the top quark mass and of the top-antitop pair production cross section using p-pbar data collected with the CDFII detector at the Tevatron Collider at the Fermi National Accelerator Laboratory and corresponding to an integrated luminosity of 2.9 fb-1. We select events with six or more jets satisfying a number of kinematical requirements imposed by means of a neural network algorithm. At least one of these jets must originate from a b quark, as identified by the reconstruction of a secondary vertex inside the jet. The mass measurement is based on a likelihood fit incorporating reconstructed mass distributions representative of signal and background, where the absolute jet energy scale (JES) is measured simultaneously with the top quark mass. The measurement yields a value of 174.8 +- 2.4(stat+JES) ^{+1.2}_{-1.0}(syst) GeV/c^2, where the uncertainty from the absolute jet energy scale is evaluated together with the statistical uncertainty. The procedure measures also the amount of signal from which we derive a cross section, sigma_{ttbar} = 7.2 +- 0.5(stat) +- 1.0 (syst) +- 0.4 (lum) pb, for the measured values of top quark mass and JES.

Studying ofBs→K(*)−π+,K(*)−ρ+decays within supersymmetry

Recent results from CDF Collaboration favor a large CP asymmetry in $B_s\rightarrow K^-\pi^+$ decay, while the Standard Model prediction is very small. Moreover, the measurement of its branching ratio is lower than the Standard Model prediction based on the QCD factorization. We compute the gluino-mediated supersymmetry contributions to $B_{s}\to K^{(*)-}\pi^{+}$,$K^{(*)-}\rho^{+}$ decays in the frame of the mass insertion method, and find that for $\frac{m^2_{\tilde{g}}}{m^2_{\tilde{q}}}\leq2$, the theoretical predictions including the LR and RL mass insertion contributions are compatible with the measurements of $B_s\to K^-\pi^+$ decay and $B^0-\bar{B}^0$ mixing within $2\sigma$ ranges. Using the constrained LR and RL mass insertion parameter spaces, we explore the supersymmetry mass insertion effects on the branching ratios, the direct CP asymmetries and the polarization fractions in $B_{s}\to K^{*-}\pi^+, K^{-}\rho^+, K^{*-}\rho^+$ decays. We find the constrained LR and RL insertions can provide sizable contributions to the branching ratios of $B_{s}\to K^{*-}\pi^{+}$,$K^{(*)-}\rho^{+}$ as well as the direct CP asymmetry and the longitudinal polarization of $B_{s}\to K^{*-}\rho^{+}$ decay without conflict with all related data within $2\sigma$ ranges. Near future experiments at Fermi Lab and CERN LHC-b can test our predictions and shrink/reveal the mass insertion parameter spaces.

A generic readout environment for prototype pixel detectors

Pixel detectors for experimental particle physics research have been implemented with a variety of readout formats and potentially generate massive amounts of data. Examples include the PSI46 device for the Compact Muon Solenoid (CMS) experiment which implements an analog readout, the Fermilab FPIX2.1 device with a digital readout, and the Fermilab Vertically Integrated Pixel device. The Electronic Systems Engineering Department of the Computing Division at the Fermi National Accelerator Laboratory has developed a data acquisition system flexible and powerful enough to meet the various needs of these devices to support laboratory test bench as well as test beam applications. The system is called CAPTAN (Compact And Programmable daTa Acquisition Node) and is characterized by its flexibility, versatility and scalability by virtue of several key architectural features. These include a vertical bus that permits the user to stack multiple boards, a gigabit Ethernet link that permits high speed communications to the system and a core group of boards that provide specific processing and readout capabilities for the system. System software based on distributed computing techniques supports an expandable network of CAPTANs. In this paper, we describe the system architecture and give an overview of its capabilities.

Jet Physics at the Tevatron

Jets have been used to verify the theory of quantum chromodynamics (QCD), measure the structure of the proton, and search for physics beyond the Standard Model. In this article, we review the current status of jet physics at the Tevatron, a [Formula: see text] TeV [Formula: see text] collider at the Fermi National Accelerator Laboratory. We report on recent measurements of the inclusive jet production cross section, dijet production measurements, and the results of searches for physics beyond the Standard Model using jets.

Exclusivepp→ppπ+π−reaction: From the threshold to LHC

We evaluate differential distributions for the four-body $pp\ensuremath{\rightarrow}pp{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ (and $p\overline{p}\ensuremath{\rightarrow}p\overline{p}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$) reaction which constitutes an irreducible background to three-body processes $pp\ensuremath{\rightarrow}ppM$, where $M$ are a broad resonances in the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ channel, e.g., $M=\ensuremath{\sigma}$, ${\ensuremath{\rho}}^{0}$, ${f}_{0}(980)$, ${f}_{2}(1275)$, ${f}_{0}(1500)$. We include both double-diffractive contribution (both Pomeron and Reggeon exchanges) as well as pion-pion rescattering contribution. The first process dominates at higher energies and small pion-pion invariant masses while the second becomes important at lower energies and higher pion-pion invariant masses. The amplitude(s) is(are) calculated in the Regge approach. We compare our results with measured cross sections for the Intersecting Storage Ring and Fermi National Accelerator Laboratory experiments. We make predictions for future experiments at the anti-Proton ANnihilation at DArmstadt (PANDA), Relativistic Heavy Ion Collider, Tevatron, and LHC energies. Differential distributions in invariant two-pion mass, pion rapidities and transverse momenta of pions are presented. The two-dimensional distribution in $({y}_{{\ensuremath{\pi}}^{+}},{y}_{{\ensuremath{\pi}}^{\ensuremath{-}}})$ is particularly interesting. The higher the incident energy, the higher preference for the same-hemisphere emission of pions. The processes considered constitute a sizeable contribution to the total nucleon-nucleon cross section as well as to pion inclusive cross section.

Charged kaon mass measurement using the Cherenkov effect

The two most recent and precise measurements of the charged kaon mass use X-rays from kaonic atoms and report uncertainties of 14 and 22 ppm yet differ from each other by 122 ppm. We describe the possibility of an independent mass measurement using the measurement of Cherenkov light from a narrow-band beam of kaons, pions, and protons. This technique was demonstrated using data taken opportunistically by the Main Injector Particle Production experiment at Fermi National Accelerator Laboratory which recorded beams of protons, kaons, and pions ranging in momentum from + 37 to + 63 GeV / c . The measured value is 491.3 ± 1.7 MeV / c 2 , which is within 1.4 σ of the world average. An improvement of two orders of magnitude in precision would make this technique useful for resolving the ambiguity in the X-ray data and may be achievable in a dedicated experiment.

MINOS experiment at Fermilab

MINOS is a two-detector experiment to study neutrino oscillations in the NuMI high-intensity neutrino beam at the Fermi National Accelerator Laboratory. Results on ν μ disappearance, ν e appearance, sterile neutrino mixing ( ν neutral current ‘disappearance’), and ν ̄ μ disappearance are summarized for an exposure of ≈ 3 × 10 20 protons on target. Data from a 7×10 20 POT exposure already in hand are being analyzed.

Prospects and status of the MINER [formula omitted]A experiment at FNAL

MINERνA is a detector designed to precisely study ν -nucleus interactions in the 1–10 GeV energy range in the NuMI high-intensity neutrino beam at the Fermi National Accelerator Laboratory. MINERνA will improve our knowledge of neutrino cross sections at low energy and low Q 2 , and of the A -dependence in ν interactions. These data will be interesting in their own right, and will be important to reduce systematic errors in ν oscillation experiments.

Experimental Studies of Shielding and Irradiation Effects at High-Energy Accelerator Facilities

Experimental studies of shielding and radiation effects are carried out at Fermi National Accelerator Laboratory (FNAL) under collaboration between FNAL and Japan, aiming at benchmarking simulation codes and studying irradiation effects for the upgrade and design of new high-energy accelerator facilities. The purposes of this collaboration are (a) acquisition of shielding data in a proton beam energy region above 100 GeV, (b) further evaluation of predictive accuracy of the PHITS and MARS codes, (c) modification of physics models and data in these codes if needed, (d) characterization of radiation fields for studies of radiation effects, and (e) development of a code module for an improved description of radiation effects.The first campaign of the experiment was carried out at the Pbar target station and NuMI experimental station at FNAL, which use irradiation of targets with 120-GeV protons for antiproton and neutrino production, respectively. The generated secondary particles passing through steel, concrete, and rock were measured by activation methods as well as by other detectors such as a scintillator with a veto counter, phoswich detector, and a Bonner ball counter on trial. Preliminary experimental and calculated results are presented.

The boundaries of the new frontier: rhetoric and communication at Fermi National Accelerator Laboratory

The boundaries of the new frontier: rhetoric and communication at Fermi National Accelerator Laboratory

Stefan Söldner-Rembold

A particle physicist at the University of Manchester, UK, Söldner-Rembold is the latest spokesperson elected to co-coordinate the D0 experiment, an exploration of the subatomic universe that started in 1992 at the Fermi National Accelerator Laboratory in Batavia, Illinois.

Relativistic light-on-heavy nuclear collisions and the implied rapidity asymmetry

We calculate pseudorapidity (\ensuremath{\eta}) asymmetry in $\mathit{pA}$ and $\mathit{dA}$ collisions in a pQCD-improved parton model. With the calculations tuned to describe existing spectra from $\mathit{pp}$ collisions and asymmetric systems at midrapidity and large rapidities at Fermi National Accelerator Laboratory and Relativistic Heavy Ion Collider energies, we investigate the roles of nuclear shadowing and multiple scattering on the observed asymmetry. Using this framework, we make predictions for pseudorapidity asymmetries at high ${p}_{T}$ and large \ensuremath{\eta} in a wide range of energies up to those of the Large Hadron Collider.

HINS Superconducting Lens and Cryostat Performance

Fermi National Accelerator Laboratory is involved in the development of a 60 MeV superconducting linac. This linac is part of the High Intensity Neutrino Source (HINS) R&D Program. The initial beam acceleration in the front end section of the linac is achieved using room temperature spoke cavities, each of which is combined with a superconducting focusing solenoid. These solenoid magnets are cooled with liquid helium at 4.5 K, operate at 250 A and have a maximum magnetic field strength of 7.5 T. A prototype solenoid cryostat was built and tested at the Fermilab Magnet Test Facility. This paper discusses the test results of the prototype and compares the measured and estimated performance of the cryostat. We also present the methods and results for measuring and fiducializing the axis of the solenoid lens.

Fermilab: physics, the frontier, and megascience

Fermi National Accelerator Laboratory, located in the western suburbs of Chicago, has stood at the frontier of high-energy physics for forty years. Fermilab is the first history of this laboratory and of its powerful accelerators told from the point of view of the people who built and used them for scientific discovery. Focusing on the first two decades of research at Fermilab, during the tenure of the laboratory's charismatic first two directors, Robert R. Wilson and Leon M. Lederman, the authors trace the rise of what they call megascience, the collaborative struggle to conduct large-scale international experiments in a climate of limited federal funding. In the midst of this new climate, Fermilab illuminates the growth of the modern research laboratory during the Cold War and captures the drama of human exploration at the cutting edge of science.

Analysis of Voltage Spikes in Superconducting ${\rm Nb}_{3}{\rm Sn}$ Magnets

Fermi National Accelerator Laboratory has been developing a new generation of superconducting accelerator magnets based on niobium tin (Nb3Sn). The performance of these magnets is influenced by thermo-magnetic instabilities, known as flux jumps, which can lead to premature trips of the quench detection system due to large voltage transients or quenches at low current. In an effort to better characterize and understand these instabilities, a system for capturing fast voltage transients was developed and used in recent tests of R&D model magnets. A new automated voltage spike analysis program was developed for the analysis of large amount of voltage-spike data. We report results from the analysis of large statistics data samples for short model magnets that were constructed using MJR and RRP strands having different sub-element size and structure. We then assess the implications for quench protection of Nb3Sn magnets.

Numerical simulations of stripping effects in high-intensity hydrogen ion linacs

Numerical simulations of ${\mathrm{H}}^{\ensuremath{-}}$ stripping losses from blackbody radiation, electromagnetic fields, and residual gas have been implemented into the beam dynamics code TRACK. Estimates of the stripping losses along two high-intensity ${\mathrm{H}}^{\ensuremath{-}}$ linacs are presented: the Spallation Neutron Source linac currently being operated at Oak Ridge National Laboratory and an 8 GeV superconducting linac currently being designed at Fermi National Accelerator Laboratory.

Neutrino flux prediction at MiniBooNE

The Booster Neutrino Experiment (MiniBooNE) searches for numu-to-nue oscillations using the O(1 GeV) neutrino beam produced by the Booster synchrotron at the Fermi National Accelerator Laboratory (FNAL). The Booster delivers protons with 8 GeV kinetic energy (8.89 GeV/c momentum) to a beryllium target, producing neutrinos from the decay of secondary particles in the beam line. We describe the Monte Carlo simulation methods used to estimate the flux of neutrinos from the beamline incident on the MiniBooNE detector for both polarities of the focussing horn. The simulation uses the Geant4 framework for propagating particles, accounting for electromagnetic processes and hadronic interactions in the beamline materials, as well as the decay of particles. The absolute double differential cross sections of pion and kaon production in the simulation have been tuned to match external measurements, as have the hadronic cross sections for nucleons and pions. The statistical precision of the flux predictions is enhanced through reweighting and resampling techniques. Systematic errors in the flux estimation have been determined by varying parameters within their uncertainties, accounting for correlations where appropriate.

Semi numerical solution of non-singlet Dokshitzer–Gribov–Lipatov–Altarelli–Parisi evolution equation up to next-to-next-to-leading order at small x

The non-singlet structure functions have been obtained by solving Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) evolution equations in next-next-to-leading order (NNLO) in the small-x limit. Here a Taylor series expansion has been used to solve the evolution equations and we obtain the semi numerical solution. Results are compared with the Fermi Lab experiment E665 data and New Muon Collaboration (NMC) data.

Proton Radiation Therapy in the Hospital Environment: Conception, Development, and Operation of the Initial Hospital-Based Facility

The world's first hospital-based proton treatment center opened at Loma Linda University Medical Center in 1990, following two decades of development. Patients' needs were the driving force behind its conception, development, and execution; the primary needs were delivery of effective conformal doses of ionizing radiation and avoidance of normal tissue to the maximum extent possible. The facility includes a proton synchrotron and delivery system developed in collaboration with physicists and engineers at Fermi National Accelerator Laboratory and from other high-energy-physics laboratories worldwide. The system, operated and maintained by Loma Linda personnel, was designed to be safe, reliable, flexible in utilization, efficient in use, and upgradeable to meet demands of changing patient needs and advances in technology. Since the facility opened, nearly 14,000 adults and children have been treated for a wide range of cancers and other diseases. Ongoing research is expanding the applications of proton therapy, while reducing costs.