arXiv subjects

F. Herrmann

Publications and source records attributed to F. Herrmann.

61 records · Page 4Linked to original sources

arXiv2012

Leading order determination of the gluon polarisation from DIS events with high-p_T hadron pairs

We present a determination of the gluon polarisation Delta g/g in the nucleon, based on the longitudinal double-spin asymmetry of DIS events with a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam scattering off a polarised ^6LiD target. The gluon polarisation is evaluated by a Neural Network approach for three intervals of the gluon momentum fraction x_g covering the range 0.04 < x_g < 0.27. The values obtained at leading order in QCD do not show any significant dependence on x_g. Their average is Delta g/g = 0.125 +/- 0.060 (stat.) +/- 0.063 (syst.) at x_g=0.09 and a scale of mu^2 = 3 (GeV/c)^2.

hep-ex↗

arXiv2012

Implementation of mean-timing and subsequent logic functions on an FPGA

This article describes the implementation of a mean-timer and coincidence logic on a Virtex-5 FPGA for trigger purposes in a particle physics experiment. The novel feature is that the mean-timing and the coincidence logic are not synchronized with a clock which allows for a higher resolution of approximately 400 ps, not limited by a clock frequency.

physics.ins-det↗

arXiv2012

First Measurement of Chiral Dynamics in π^- γ-> π^- π^- π^+

The COMPASS collaboration at CERN has investigated the π^- γ-> π^- π^- π^+ reaction at center-of-momentum energy below five pion masses, sqrt(s) < 5 m(π), embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, t' < 0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the 3π-invariant mass m(3π) = sqrt(s) were extracted. The absolute cross section was determined in seven bins of $\sqrt{s}$ with an overall precision of 20%. At leading order, the result is found to be in good agreement with the prediction of chiral perturbation theory over the whole energy range investigated.

hep-ex↗

arXiv2008

Binary Black Hole Encounters, Gravitational Bursts and Maximum Final Spin

The spin of the final black hole in the coalescence of nonspinning black holes is determined by the ``residual'' orbital angular momentum of the binary. This residual momentum consists of the orbital angular momentum that the binary is not able to shed in the process of merging. We study the angular momentum radiated, the spin of the final black hole and the gravitational bursts in a series of orbits ranging from almost direct infall to numerous orbits before infall that exhibit multiple bursts of radiation in the merger process. We show that the final black hole gets a maximum spin parameter $a/M_h \le 0.78$, and this maximum occurs for initial orbital angular momentum $L \approx M^2_h$.

gr-qc↗

arXiv2007

Unequal Mass Binary Black Hole Plunges and Gravitational Recoil

We present results from fully nonlinear simulations of unequal mass binary black holes plunging from close separations well inside the innermost stable circular orbit with mass ratios q = M_1/M_2 = {1,0.85,0.78,0.55,0.32}, or equivalently, with reduced mass parameters $η=M_1M_2/(M_1+M_2)^2 = {0.25, 0.248, 0.246, 0.229, 0.183}$. For each case, the initial binary orbital parameters are chosen from the Cook-Baumgarte equal-mass ISCO configuration. We show waveforms of the dominant l=2,3 modes and compute estimates of energy and angular momentum radiated. For the plunges from the close separations considered, we measure kick velocities from gravitational radiation recoil in the range 25-82 km/s. Due to the initial close separations our kick velocity estimates should be understood as a lower bound. The close configurations considered are also likely to contain significant eccentricities influencing the recoil velocity.

gr-qc↗

arXiv2001

Star Formation in M51 Triggered by Galaxy Interaction

We have mapped the inner 360'' regions of M51 in the 158micron [CII] line at 55'' spatial resolution using the Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO). The emission is peaked at the nucleus, but is detectable over the entire region mapped, which covers much of the optical disk of the galaxy. There are also two strong secondary peaks at ~43% to 70% of the nuclear value located roughly 120'' to the north-east, and south-west of the nucleus. These secondary peaks are at the same distance from the nucleus as the corotation radius of the density wave pattern. The density wave also terminates at this location, and the outlying spiral structure is attributed to material clumping due to the interaction between M51 and NGC5195. This orbit crowding results in cloud-cloud collisions, stimulating star formation, that we see as enhanced [CII] line emission. The [CII] emission at the peaks originates mainly from photodissociation regions (PDRs) formed on the surfaces of molecular clouds that are exposed to OB starlight, so that these [CII] peaks trace star formation peaks in M51. The total mass of [CII] emitting photodissociated gas is ~2.6x10^{8} M_{sun}, or about 2% of the molecular gas as estimated from its CO(1-0) line emission. At the peak [CII] positions, the PDR gas mass to total gas mass fraction is somewhat higher, 3-17%, and at the secondary peaks the mass fraction of the [CII] emitting photodissociated gas can be as high as 72% of the molecular mass.... (continued)

astro-ph↗

arXiv1998

CII Emission From NGC 4038/39 (The Antennae)

We present observations of NGC 4038/39 in the [CII] 158 micron fine structure line taken with the MPE/UCB Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the KAO with 55" resolution. The total [CII] luminosity of the Antennae is 3.7x10^8 L(sun), which is about 1% of the FIR luminosity. The main part of the [CII] emission probably arises from photodissociation regions (PDRs). Up to 1/3 of the observed [CII] emission may originate from the CNM for higher temperatures and densities. From PDR models we derive densities and FUV intensities for the nuclei and the interaction zone. The minimum masses in the [CII] emitting regions in the interaction zone and the nuclei are a few x 10^(7) M(sun). We find that the [CII] to CO intensity ratio at the interaction zone is a factor of 2.6 lower than usually observed in starburst galaxies, but still a factor of about 1.3 to 1.4 higher than at the nuclei of NGC 4038/39, indicating no global starburst is taking place in the Antennae. [CII] emission arising partly from confined starburst regions and partly from surrounding quiescent clouds could explain the observed [CII] radiation at the interaction zone and the nuclei. There are small confined regions with high star formation activity in the interaction zone and with a lower star formation activity in the nuclei. This supports the high density and high FUV intensity for the PDRs in the interaction zone and the nuclei.

astro-ph↗