Search for Muon-Neutrino to Electron-Neutrino Transitions in MINOS

This Letter reports on a search for nu(mu)->nu(e) transitions by the MINOS experiment based on a 3.14x10(20) protons-on-target exposure in the Fermilab NuMI beam. We observe 35 events in the Far Detector with a background of 27 +/- 5(stat)+/- 2(syst) events predicted by the measurements in the Near Detector. If interpreted in terms of nu(mu)->nu(e) oscillations, this 1.5 sigma excess of events is consistent with sin(2)(2 theta(13)) comparable to the CHOOZ limit when |Delta m(2)|=2.43x10(-3) eV(2) and sin(2)(2 theta(23))=1.0 are assumed.

First Direct Observation of Muon Antineutrino Disappearance

This Letter reports the first direct observation of muon antineutrino disappearance. The MINOS experiment has taken data with an accelerator beam optimized for (nu) over bar (mu) production, accumulating an exposure of 1.71 x 10(20) protons on target. In the Far Detector, 97 charged current (nu) over bar (mu) events are observed. The no-oscillation hypothesis predicts 156 events and is excluded at 6.3 sigma. The best fit to oscillation yields vertical bar Delta(m) over bar (2)vertical bar = [3.36(-0.40)(+0.46)(stat) +/- 0.06(sys)] x 10(-3) eV(2), sin(2)(2 (theta) over bar) = 0.86(-0.12)(+0.11)(stat) +/- 0.01(syst). The MINOS nu(mu) and (nu) over bar (mu) measurements are consistent at the 2.0% confidence level, assuming identical underlying oscillation parameters.

Search for Active Neutrino Disappearance Using Neutral-Current Interactions in the MINOS Long-Baseline Experiment

We report the first detailed comparisons of the rates and spectra of neutral-current neutrino interactions at two widely separated locations. A depletion in the rate at the far site would indicate mixing between nu(mu) and a sterile particle. No anomalous depletion in the reconstructed energy spectrum is observed. Assuming oscillations occur at a single mass-squared splitting, a fit to the neutral- and charged-current energy spectra limits the fraction of nu(mu) oscillating to a sterile neutrino to be below 0.68 at 90% confidence level. A less stringent limit due to a possible contribution to the measured neutral-current event rate at the far site from nu(e) appearance at the current experimental limit is also presented.

Testing Lorentz Invariance and CPT Conservation with NuMI Neutrinos in the MINOS Near Detector

A search for a sidereal modulation in the MINOS near detector neutrino data was performed. If present, this signature could be a consequence of Lorentz and CPT violation as predicted by the effective field theory called the standard-model extension. No evidence for a sidereal signal in the data set was found, implying that there is no significant change in neutrino propagation that depends on the direction of the neutrino beam in a sun-centered inertial frame. Upper limits on the magnitudes of the Lorentz and CPT violating terms in the standard-model extension lie between 10(-4) and 10(-2) of the maximum expected, assuming a suppression of these signatures by a factor of 10(-17).

Measurement of neutrino oscillations with the MINOS detectors in the NuMI beam

This Letter reports new results from the MINOS experiment based on a two-year exposure to muon neutrinos from the Fermilab NuMI beam. Our data are consistent with quantum-mechanical oscillations of neutrino flavor with mass splitting vertical bar Delta m(2)vertical bar = (2.43 +/- 0.13) x 10(-3) eV(2) (68% C.L.) and mixing angle sin(2)(2 theta) > 0.90 (90% C.L.). Our data disfavor two alternative explanations for the disappearance of neutrinos in flight: namely, neutrino decays into lighter particles and quantum decoherence of neutrinos, at the 3.7 and 5.7 standard-deviation levels, respectively.

Active to Sterile Neutrino Mixing Limits from Neutral-Current Interactions in MINOS

Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of 7.07 x 10(20) protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of 754 +/- 28(stat) +/- 37(syst) for oscillations among three active flavors. The fraction f(s) of disappearing nu(mu) that may transition to nu(s) is found to be less than 22% at the 90% C.L.

Observation of the suppression of the flux of cosmic rays above 4x10(19) eV

The energy spectrum of cosmic rays above 2.5 x 10(18) eV, derived from 20 000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the particle flux, J proportional to E(-gamma), at energies between 4 x 10(18) eV and 4 x 10(19) eV is 2.69 +/- 0.02(stat) +/- 0.06(syst), steepening to 4.2 +/- 0.4(stat) +/- 0: 06 (syst) at higher energies. The hypothesis of a single power law is rejected with a significance greater than 6 standard deviations. The data are consistent with the prediction by Greisen and by Zatsepin and Kuz'min.

Upper limit on the diffuse flux of ultrahigh energy tau neutrinos from the Pierre Auger Observatory

The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and 31 August 2007 are used to place an upper limit on the diffuse flux of nu(tau) at EeV energies. Assuming an E(nu)(-2) differential energy spectrum the limit set at 90% C. L. is E(nu)(2)dN(nu tau)/dE(nu) < 1: 3 x 10(-7) GeV cm(-2) s(-1) sr(-1) in the energy range 2 x 10(17) eV< E(nu) < 2 x 10(19) eV.

Measurement of the Neutrino Mass Splitting and Flavor Mixing by MINOS

Measurements of neutrino oscillations using the disappearance of muon neutrinos from the Fermilab NuMI neutrino beam as observed by the two MINOS detectors are reported. New analysis methods have been applied to an enlarged data sample from an exposure of 7.25 x 10(20) protons on target. A fit to neutrino oscillations yields values of vertical bar Delta m(2)vertical bar = (2.32(-0.08)(+0.12) x 10(-3) eV(2) for the atmospheric mass splitting and sin(2)(2 theta) > 0.90 (90% C.L.) for the mixing angle. Pure neutrino decay and quantum decoherence hypotheses are excluded at 7 and 9 standard deviations, respectively.

Magnetoelectric effects in an organometallic quantum magnet

Metal-organic materials constitute a new field in which to search for ferroelectricity and coupling between electricity and magnetism. We observe a magnetic field-induced change in the electric polarization, Delta P(H), that reaches 50 mu C/m(2) in single crystals of NiCl(2)-4SC(NH(2))(2) (DTN). DTN forms a tetragonal structure that breaks inversion symmetry with the electrically polar thiourea molecules [SC(NH(2))] all tilted in the same direction along the c axis. The field H induces canted antiferromagnetism of the Ni S = 1 spins between 2 and 12 T and our measurements show that the electric polarization increases monotonically in this range, saturating above 12 T. By modeling the microscopic origin of this magnetoelectric effect, we find that the leading contribution to Delta P comes from the change in the crystal electric field, with a smaller contribution from magnetic exchange striction. The finite value of Delta P induced by magnetostriction results from the polar nature of the thiourea molecules bonded to the Ni atoms, and it is amplified by the softness of these organic molecules.

Thermal Transport and Strong Mass Renormalization in NiCl(2)-4SC(NH(2))(2)

Several quantum paramagnets exhibit magnetic-field-induced quantum phase transitions to an anti-ferromagnetic state that exists for H(c1) <= H <= H(c2). For some of these compounds, there is a significant asymmetry between the low-and high-field transitions. We present specific heat and thermal conductivity measurements in NiCl(2)-4SC(NH(2))(2), together with calculations which show that the asymmetry is caused by a strong mass renormalization due to quantum fluctuations for H <= H(c1) that are absent for H >= H(c2). We argue that the enigmatic lack of asymmetry in thermal conductivity is due to a concomitant renormalization of the impurity scattering.

Direct measurement of spin correlations using magnetostriction

We demonstrate that the short-range spin correlator < S(i)center dot S(j)>, a fundamental measure of the interaction between adjacent spins, can be directly measured in certain insulating magnets. We present magnetostriction data for the insulating organic compound NiCl(2)-4SC(NH(2))(2), and show that the magnetostriction as a function of field is proportional to the dominant short-range spin correlator. Furthermore, the constant of proportionality between the magnetostriction and the spin correlator gives information about the spin-lattice interaction. Combining these results with the measured Young's modulus, we are able to extract dJ/dz, the dependence of the superexchange constant J on the Ni interionic distance z.

Experimental studies of di-jet survival and surface emission bias in Au plus Au collisions via angular correlations with respect to back-to-back leading hadrons

We report first results from an analysis based on a new multi-hadron correlation technique, exploring jet-medium interactions and di-jet surface emission bias at the BNL Relativistic Heavy Ion Collider (RHIC). Pairs of back-to-back high-transverse-momentum hadrons are used for triggers to study associated hadron distributions. In contrast with two-and three-particle correlations with a single trigger with similar kinematic selections, the associated hadron distribution of both trigger sides reveals no modification in either relative pseudorapidity Delta eta or relative azimuthal angle Delta phi from d + Au to central Au + Au collisions. We determine associated hadron yields and spectra as well as production rates for such correlated back-to-back triggers to gain additional insights on medium properties.

Scaling properties at freeze-out in relativistic heavy-ion collisions

Identified charged pion, kaon, and proton spectra are used to explore the system size dependence of bulk freeze-out properties in Cu + Cu collisions at root s(NN) = 200 and 62.4 GeV. The data are studied with hydrodynamically motivated blast-wave and statistical model frameworks in order to characterize the freeze-out properties of the system. The dependence of freeze-out parameters on beam energy and collision centrality is discussed. Using the existing results from Au + Au and pp collisions, the dependence of freeze-out parameters on the system size is also explored. This multidimensional systematic study furthers our understanding of the QCD phase diagram revealing the importance of the initial geometrical overlap of the colliding ions. The analysis of Cu + Cu collisions expands the system size dependence studies from Au + Au data with detailed measurements in the smaller system. The systematic trends of the bulk freeze-out properties of charged particles is studied with respect to the total charged particle multiplicity at midrapidity, exploring the influence of initial state effects.

High p(T) nonphotonic electron production in p plus p collisions at root s=200 GeV

We present the measurement of nonphotonic electron production at high transverse momentum (p(T) > 2.5 GeV/c) in p + p collisions at root s = 200 GeV using data recorded during 2005 and 2008 by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The measured cross sections from the two runs are consistent with each other despite a large difference in photonic background levels due to different detector configurations. We compare the measured nonphotonic electron cross sections with previously published RHIC data and perturbative quantum chromodynamics calculations. Using the relative contributions of B and D mesons to nonphotonic electrons, we determine the integrated cross sections of electrons (e++e-2/2) at 3 GeV/c < p(T) < 10 GeV/c from bottom and charm meson decays to be [(d sigma((B -> e)+(B -> D -> e))/(dy(e))](ye=0) 4.0 +/- 0.5(stat) +/- 1.1(syst) nb and [(d sigma(D -> e))/(dy(e))](ye=0) = 6.2 +/- 0.7(stat) +/- 1.5(syst) nb, respectively.