121781142
Development of a scintillating-fibre detector for fast topological triggers in high-luminosity particle physics experiments
Abstract In the framework of the RD-17 project at CERN an extensive work is in progress on the development of scintillating-fibre detectors using position-sensitive photomultipliers. With 0.5 mm diameter fibres a spatial resolution of about 125 μm was obtained with a detection efficiency higher than 95%. The time resolution of the detector is about 600 ps, and the track position is properly digitised in real time in less than 10 ns by a peak sensing circuit. A simulation, based on experimental data, has also been performed to compare different types of front-end electronics.
118218838
Search for large extra dimensions in the diphoton final state at the Large Hadron Collider
A search for large extra spatial dimensions via virtual-graviton exchange in the diphoton channel has been carried out with the CMS detector at the LHC. No excess of events above the standard model expectations is found using a data sample collected in proton-proton collisions at $ \sqrt {s} = 7 $ TeV and corresponding to an integrated luminosity of 36 pb−1. New lower limits on the effective Planck scale in the range of 1.6–2.3TeV at the 95% confidence level are set, providing the most restrictive bounds to date on models with more than two large extra dimensions.
119204233
Search for new physics in events with same-sign dileptons and b-tagged jets in pp collisions at $ \sqrt {s} = 7 $ TeV
A bstractA search for new physics is performed using isolated same-sign dileptons with at least two b-quark jets in the final state. Results are based on a 4.98 fb−1 sample of proton-proton collisions at a centre-of-mass energy of 7 TeV collected by the CMS detector. No excess above the standard model background is observed. Upper limits at 95% confidence level are set on the number of events from non-standard-model sources. These limits are used to set constraints on a number of new physics models. Information on acceptance and efficiencies are also provided so that the results can be used to confront additional models in an approximate way.
119163191
Search for a fermiophobic Higgs boson in pp collisions at $ \sqrt {s} = 7 $ TeV
A bstractCombined results are reported from searches for a fermiophobic Higgs boson in the γγ, WW, and ZZ decay modes in proton-proton collisions at $ \sqrt {s} = 7 $ TeV. The explored Higgs boson mass range is 110–300 GeV. The data sample corresponds to an integrated luminosity of 4.9–5.1 fb−1. A fermiophobic Higgs boson is excluded at 95% confidence level in the mass range 110–194 GeV, and at 99% confidence level in the mass ranges 110–124.5 GeV, 127–147.5 GeV, and 155–180 GeV.
24410937
Measurement of the polarization of W bosons with large transverse momenta in W + jets events at the LHC.
A first measurement of the polarization of W bosons with large transverse momenta in pp collisions is presented. The measurement is based on 36 pb⁻¹ of data recorded at √s = 7 TeV by the CMS detector at the LHC. The left-handed, right-handed, and longitudinal polarization fractions (f(L), f(R), and f₀, respectively) of W bosons with transverse momenta larger than 50 GeV are determined by using decays to both electrons and muons. The muon final state yields the most precise measurement: (f(L) - f(R))⁻ = 0.240 ± 0.036(stat) ± 0.031(syst) and f₀⁻ = 0.183 ± 0.087(stat) ± 0.123(syst) for negatively charged W bosons and (f(L) - f(R))⁺ = 0.310 ± 0.036(stat) ± 0.017(syst) and f₀⁺ = 0.171 ± 0.085(stat) ± 0.099(syst) for positively charged W bosons. This establishes, for the first time, that W bosons produced in pp collisions with large transverse momenta are predominantly left-handed, as expected in the standard model.
209048432
Search for supersymmetry in hadronic final states with missing transverse energy using the variables alphaT and b-quark multiplicity in pp collisions at sqrt(s) = 8 TeV
118663105
Extended tails from SGR 1806-20 bursts
In 2004, SGR 1806-20 underwent a period of intense and long-lasting burst activity that included the giant flare of 2004 December 27—the most intense extra-solar transient event ever detected at Earth. During this active episode, we routinely monitored the source with Rossi X-ray Timing Explorer and occasionally with Chandra. During the course of these observations, we identified two relatively bright bursts observed with Konus-Wind in hard X-rays that were followed by extended X-ray tails or afterglows lasting hundreds to thousands of seconds. Here, we present detailed spectral and temporal analysis of these events observed about 6 and 1.5 months prior to the 2004 December 27 giant flare. We find that both X-ray tails are consistent with a cooling blackbody of constant radius. These spectral results are qualitatively similar to those of the burst afterglows recorded from SGR 1900+14 and recently from SGR 1550–5418. However, the latter two sources exhibit significant increase in their pulsed X-ray intensity following the burst, while we did not detect any significant changes in the rms pulsed amplitude during the SGR 1806-20 events. Moreover, we find that the fraction of energy partitioned to the burst (prompt energy release) and the tail (afterglow) differs by an order of magnitude between SGR 1900+14 and SGR 1806-20. We suggest that such differences can be attributed to differences in the crustal heating mechanism of these neutron stars combined with the geometry of the emitting areas.
118566113
LOFT: the Large Observatory For X-ray Timing
The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated (<1 degree field of view) experiment operating in the energy range 2-50 keV, with a 10 m2 peak effective area and an energy resolution of 260 eV at 6 keV. The WFM will operate in the same energy range as the LAD, enabling simultaneous monitoring of a few-steradian wide field of view, with an angular resolution of <5 arcmin. The LAD and WFM experiments will allow us to investigate variability from submillisecond QPO’s to yearlong transient outbursts. In this paper we report the current status of the project.
119067824
X-Ray Bursts from the Transient Magnetar Candidate XTE J1810–197
We have discovered four X-ray bursts, recorded with the Rossi X-ray Timing Explorer Proportional Counter Array between 2003 September and 2004 April, that we show to originate from the transient magnetar candidate XTE J1810-197. The burst morphologies consist of a short spike or multiple spikes lasting ~1 s each, followed by extended tails of emission where the pulsed flux from XTE J1810-197 is significantly higher. The burst spikes are likely correlated with the pulse maxima, having a chance probability of a random phase distribution of 0.4%. The burst spectra are best fitted to a blackbody with temperatures 4-8 keV, considerably harder than the persistent X-ray emission. During the X-ray tails following these bursts, the temperature rapidly cools as the flux declines, maintaining a constant emitting radius after the initial burst peak. During the brightest X-ray tail, we detect a narrow emission line at 12.6 keV, with an equivalent width of 1.4 keV and a probability of chance occurrence of less than 4 × 10-6. The temporal and spectral characteristics of these bursts closely resemble the bursts seen from 1E 1048.1-5937 and a subset of the bursts detected from 1E 2259+586, thus establishing XTE J1810-197 as a magnetar candidate. The bursts detected from these three objects are sufficiently similar to one another, yet significantly different from those seen from soft gamma repeaters, that they likely represent a new class of bursts from magnetar candidates exclusive (thus far) to the anomalous X-ray pulsar-like sources.
15497000
Detailed analysis of the pulsations during and after burst from the bursting pulsar (GRO J1744-28)
The hard X-ray bursts observed during both major outbursts of the Bursting Pulsar (GRO J1744-28) show pulsations near the neutron star spin frequency with an enhanced amplitude relative to that of the persistent emission. Consistent with previous work, we find that the pulsations within bursts lag behind their expected arrival times based upon the persistent pulsar ephemeris. For an ensemble of 1293 bursts recorded with the Burst and Transient Source Experiment, the average burst pulse time delay (ΔtFWHM) is 61.0 ± 0.8 ms in the 25-50 keV energy range and 72 ± 5 ms in the 50-100 keV band. The residual time delay (Δtresid) from 10 to 240 s following the start of the burst is 18.1 ± 0.7 ms (25-50 keV). A significant correlation of the average burst time delay with burst peak flux is found. Our results are consistent with the model of the pulse time lags presented by Miller.
118728215
SIGNS OF MAGNETIC ACCRETION IN THE X-RAY PULSAR BINARY GX 301–2
Observations of the cyclotron resonance scattering feature in the X-ray spectrum of GX 301-2 suggest that the surface field of the neutron star is B CRSF ~ 4 × 1012 G. The same value has been derived in modeling the rapid spin-up episodes in terms of the Keplerian disk accretion scenario. However, the spin-down rate observed during the spin-down trends significantly exceeds the value expected in currently used spin-evolution scenarios. This indicates that either the surface field of the star exceeds 50 B CRSF or a currently used accretion scenario is incomplete. We show that the above discrepancy can be avoided if the accreting material is magnetized. The magnetic pressure in the accretion flow increases more rapidly than its ram pressure and, under certain conditions, significantly affects the accretion picture. The spin-down torque applied to the neutron star in this case is larger than that evaluated within a non-magnetized accretion scenario. We find that the observed spin evolution of the pulsar can be explained in terms of the magnetically controlled accretion flow scenario provided the surface field of the neutron star is ~B CRSF.