17747494
Observation of the production of a W boson in association with a single charm quark.
The first observation of the production of a W boson with a single charm quark (c) jet in pp[over ¯] collisions at √s=1.96  TeV is reported. The analysis uses data corresponding to 4.3  fb(-1), recorded with the CDF II detector at the Fermilab Tevatron. Charm quark candidates are selected through the identification of an electron or muon from charm-hadron semileptonic decay within a hadronic jet, and a Wc signal is observed with a significance of 5.7 standard deviations. The production cross section σ(Wc)(p(Tc)>20  GeV/c,|η(c)|<1.5)×B(W→ℓν) is measured to be 13.6(-3.1)(+3.4)  pb and is in agreement with theoretical expectations. From this result the magnitude of the quark-mixing matrix element V(cs) is derived, |V(cs)|=1.08±0.16 along with a lower limit of |V(cs)|>0.71 at the 95% confidence level, assuming that the Wc production through c to s quark coupling is dominant.
122950163
The performance of the CDF luminosity monitor
Abstract We describe the initial performance of the detector used for the luminosity measurement in the CDF experiment in Run II at the Tevatron. The detector consists of low-mass gaseous Cherenkov counters with high light yield (∼100 photoelectrons) and monitors the process of inelastic p p scattering. It allows for several methods of precise luminosity measurements at peak instantaneous luminosities of 2×10 32 cm −2 s −1 , corresponding to an average of six p p interactions per bunch crossing.
118414507
Measurement of branching ratio and $B_s^0$ lifetime in the decay $B_s^0 \rightarrow J/\psi f_0(980)$ at CDF
We present a study of Bs0 decays to the CP-odd final state J/ψ f0(980) with J/ψ → µ+µ- and f0(980) → π+π-. Using pp collision data with an integrated luminosity of 3.8 fb-1 collected by the CDF II detector at the Tevatron we measure a Bs0 lifetime of τ(B0s → J/ψ f0(980)) = 1.70-0.11+0.12(stat) ± 0.03(syst) ps. This is the first measurement of the Bs0} lifetime in a decay to a CP eigenstate and corresponds in the standard model to the lifetime of the heavy Bs0 eigenstate. We also measure the product of branching fractions of B0s → J/ψ f0(980) and f0(980) → π+π- relative to the product of branching fractions of B0s → J/ψφ and φ→K+K- to be Rf0/ψ = 0.257 ± 0.020(stat) ± 0.014(syst), which is the most precise determination of this quantity to date.
12148304
Updated search for the standard model Higgs boson in events with jets and missing transverse energy using the full CDF data set
We present an updated search for the Higgs boson produced in association with a vector boson in the final state with missing transverse energy and two jets. We use the full CDF data set corresponding to an integrated luminosity of 9.45 fb−1 at a proton-antiproton center-of-mass energy of s√=1.96 TeV. New to this analysis is the inclusion of a b-jet identification algorithm specifically optimized for H→bb¯ searches. Across the Higgs boson mass range 90≤mH≤150 GeV/c2, the expected 95% credibility level upper limits on the VH production cross section times the H→bb¯ branching fraction are improved by an average of 14% relative to the previous analysis. At a Higgs boson mass of 125 GeV/c2, the observed (expected) limit is 3.06 (3.33) times the standard model prediction, corresponding to one of the most sensitive searches to date in this final state.
123114924
ATLAS measurements of the properties of jets for boosted particle searches
Measurements are presented of the properties of high transverse momentum jets, produced in proton-proton collisions at a center-of-mass energy of root s = 7 TeV. The data correspond to an integrated luminosity of 35 pb(-1) and were collected with the ATLAS detector in 2010. Jet mass, width, eccentricity, planar flow and angularity are measured for jets reconstructed using the anti-k(t) algorithm with distance parameters R 0: 6 and 1.0, with transverse momentum p(T) > 300 GeV and pseudorapidity vertical bar eta vertical bar < 2. The measurements are compared to the expectations of Monte Carlo generators that match leading-logarithmic parton showers to leading-order, or next-to-leading-order, matrix elements. The generators describe the general features of the jets, although discrepancies are observed in some distributions.
10189692
Combination of the top-quark mass measurements from the Tevatron collider
We thank the Fermilab staff and technical staffs of the 
participating institutions for their vital contributions and 
acknowledge support from the DOE and NSF (USA), ARC 
(Australia), CNPq, FAPERJ, FAPESP, and FUNDUNESP 
(Brazil), NSERC (Canada), NSC, CAS, and CNSF 
(China), Colciencias (Colombia), MSMT and GACR 
(Czech Republic), the Academy of Finland, CEA, and 
CNRS/IN2P3 (France), BMBF and DFG (Germany), 
DAE and DST (India), SFI (Ireland), INFN (Italy), 
MEXT (Japan), the Korean World Class University 
Program and NRF (Korea), CONACyT (Mexico), FOM 
(Netherlands), MON, NRC KI, and RFBR (Russia), the 
Slovak R&D Agency, the Ministerio de Ciencia e 
Innovacio´n, and Programa Consolider-Ingenio 2010 
(Spain), The Swedish Research Council (Sweden), SNSF 
(Switzerland), STFC and the Royal Society (United 
Kingdom), and the A. P. Sloan Foundation (USA).
123869228
Minimization of Primary Electron Beam Radius at the Positron Production Target
To have a high positron yield, it is extremely important to minimize the primary electron beam radius at the positron production target. Various effects on electron beam blow-up have been analyzed. By comparing the measured beam radius with simulation, result at current BEPC positron source,some concrete effects on beam blow-up have been described. A design study on minimizing the electron beam radius at BEPC-II positron source is given, and the ways to reach this goal have been summarized.
118858199
SIGMOID-TO-FLUX-ROPE TRANSITION LEADING TO A LOOP-LIKE CORONAL MASS EJECTION
Sigmoids are one of the most important precursor structures for solar eruptions. In this Letter, we study a sigmoid eruption on 2010 August 1 with EUV data obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO). In AIA 94 A (Fe XVIII; 6 MK), topological reconfiguration due to tether-cutting reconnection is unambiguously observed for the first time, i.e., two opposite J-shaped loops reconnect to form a continuous S-shaped loop, whose central portion is dipped and aligned along the magnetic polarity inversion line (PIL), and a compact loop crossing the PIL. A causal relationship between photospheric flows and coronal tether-cutting reconnections is evidenced by the detection of persistent converging flows toward the PIL using line-of-sight magnetograms obtained by the Helioseismic and Magnetic Imager on board SDO. The S-shaped loop remains in quasi-equilibrium in the lower corona for about 50 minutes, with the central dipped portion rising slowly at ~10 km s–1. The speed then increases to ~60 km s–1 about 10 minutes prior to the onset of a GOES-class C3.2 flare, as the S-shaped loop speeds up its transformation into an arch-shaped loop, which eventually leads to a loop-like coronal mass ejection. The AIA observations combined with Hα filtergrams as well as hard X-ray imaging and spectroscopy are consistent with most flare loops being formed by reconnection of the stretched legs of less-sheared J-shaped loops that envelopes the rising flux rope, in agreement with the standard tether-cutting scenario.
119072516
Nonequilibrium pion dynamics near the critical point in a constituent quark model
Abstract We study static and dynamical critical phenomena of chiral symmetry breaking in a two-flavor Nambu–Jona-Lasinio constituent quark model. We obtain the low-energy effective action for scalar and pseudoscalar degrees of freedom to lowest order in quark loops and to quadratic order in the meson fluctuations around the mean field. The static limit of critical phenomena is shown to be described by a Ginzburg–Landau effective action including spatial gradients. Hence static critical phenomena is described by the universality class of the O(4) Heisenberg ferromagnet. Dynamical critical phenomena is studied by obtaining the equations of motion for pion fluctuations. We find that for T
119072239
Rapid Changes of Photospheric Magnetic Field after Tether-cutting Reconnection and Magnetic Implosion
The rapid, irreversible change of the photospheric magnetic field has been recognized as an important element of the solar flare process. This Letter reports such a rapid change of magnetic fields during the 2011 February 13 M6.6 flare in NOAA AR 11158 that we found from the vector magnetograms of the Helioseismic and Magnetic Imager (HMI) with 12 minute cadence. High-resolution magnetograms of Hinode that are available at ~–5.5, –1.5, 1.5, and 4 hr relative to the flare maximum are used to reconstruct a three-dimensional coronal magnetic field under the nonlinear force-free field (NLFFF) assumption. UV and hard X-ray images are also used to illuminate the magnetic field evolution and energy release. The rapid change is mainly detected by HMI in a compact region lying in the center of the magnetic sigmoid, where the mean horizontal field strength exhibited a significant increase of 28%. The region lies between the initial strong UV and hard X-ray sources in the chromosphere, which are cospatial with the central feet of the sigmoid according to the NLFFF model. The NLFFF model further shows that strong coronal currents are concentrated immediately above the region, and that, more intriguingly, the coronal current system underwent an apparent downward collapse after the sigmoid eruption. These results are discussed in favor of both the tether-cutting reconnection producing the flare and the ensuing implosion of the coronal field resulting from the energy release.
13535076
X-ray emission from betatron motion in a plasma wiggler.
The successful utilization of an ion channel in a plasma to wiggle a 28.5-GeV electron beam to obtain broadband x-ray radiation is reported. The ion channel is induced by the electron bunch as it propagates through an underdense 1.4-meter-long lithium plasma. The quadratic density dependence of the spontaneously emitted betatron x-ray radiation and the divergence angle of approximately (1-3)x10(-4) radian of the forward-emitted x-rays as a consequence of betatron motion in the ion channel are in good agreement with theory. The absolute photon yield and the peak spectral brightness at 14.2-keV photon energy are estimated.