arXiv subjects

J. Becker

Publications and source records attributed to J. Becker.

At least 217 records · Page 12Linked to original sources

arXiv2012

Spectral analysis and interpretation of the γ-ray emission from the Starburst galaxy NGC 253

Very-high-energy (VHE; E >100 GeV) and high-energy (HE; 100 MeV < E < 100 GeV) data from γ-ray observations performed with the H.E.S.S. telescope array and the Fermi-LAT instrument, respectively, are analysed in order to investigate the non-thermal processes in the starburst galaxy NGC 253. The VHE γ-ray data can be described by a power law in energy with differential photon index Γ=2.14 \pm 0.18_stat \pm 0.30_sys and differential flux normalisation at 1 TeV of F_0 = (9.6 \pm 1.5_stat (+5.7,-2.9)_sys) x 10^{-14} TeV^{-1} cm^{-2} s^{-1}. A power-law fit to the differential HE γ-ray spectrum reveals a photon index of Γ=2.24 \pm 0.14_stat \pm 0.03_sys and an integral flux between 200 MeV and 200 GeV of F(0.2-200 GeV) = (4.9 \pm 1.0_stat \pm 0.3_sys) x 10^{-9} cm^{-2} s^{-1}. No evidence for a spectral break or turnover is found over the dynamic range of both the LAT instrument and the H.E.S.S. experiment: a combined fit of a power law to the HE and VHE γ-ray data results in a differential photon index Γ=2.34 \pm 0.03 with a p-value of 30%. The γ-ray observations indicate that at least about 20% of the energy of the cosmic rays capable of producing hadronic interactions is channeled into pion production. The smooth alignment between the spectra in the HE and VHE γ-ray domain suggests that the same transport processes dominate in the entire energy range. Advection is most likely responsible for charged particle removal from the starburst nucleus from GeV to multiple TeV energies. In a hadronic scenario for the γ-ray production, the single overall power-law spectrum observed would therefore correspond to the mean energy spectrum produced by the ensemble of cosmic-ray sources in the starburst region.

astro-ph.HE↗

arXiv2012

First observation of the isospin violating decay $J/ψ\rightarrow Λ\barΣ^{0}+c.c.$

Using a sample of $(225.2\pm 2.8)\times 10^6$ $J/ψ$ events collected with the BESIII detector, we present results of a study of $J/ψ\rightarrow γΛ\barΛ$ and report the first observation of the isospin violating decay $J/ψ\rightarrowΛ\barΣ^{0}+c.c.$, in which $\barΣ^{0}$ decays to $γ\barΛ$. The measured branching fractions are $\mathcal{B}(J/ψ\rightarrow\barΛΣ^{0}$) = $(1.46\pm0.11\pm0.12) \times10^{-5}$ and $\mathcal{B}(J/ψ\rightarrowΛ\bar{Σ^{0}}$) = $(1.37\pm0.12\pm0.11) \times10^{-5}$. We search for $Λ(1520) \rightarrow γΛ$ decay, and find no evident signal, and an upper limit for the product branching fraction $\mathcal{B}(J/ψ\rightarrowΛ\barΛ(1520)+c.c.)\times \mathcal{B}(Λ(1520)\rightarrowγΛ)<4.1 \times10^{-6}$ is set at the 90% confidence level. We also report the observation of $η_{c}\rightarrowΛ\barΛ$ in $J/ψ\rightarrow γη_{c}$, $η_{c}\rightarrowΛ\barΛ$ and measure the branching fraction $\mathcal{B}(η_{c}\rightarrowΛ\barΛ) =(1.16\pm0.12 (stat)\pm0.19(syst)\pm0.28(PDG))\times10^{-3}$.

hep-ex↗

arXiv2012

Technical Design Report for the: PANDA Micro Vertex Detector

This document illustrates the technical layout and the expected performance of the Micro Vertex Detector (MVD) of the PANDA experiment. The MVD will detect charged particles as close as possible to the interaction zone. Design criteria and the optimisation process as well as the technical solutions chosen are discussed and the results of this process are subjected to extensive Monte Carlo physics studies. The route towards realisation of the detector is outlined.

physics.ins-det↗

arXiv2012

Study of $J/ψ\to p\bar{p}$ and $J/ψ\to n\bar{n}$

The decays $J/ψ\to p\bar{p}$ and $J/ψ\to n\bar{n}$ have been investigated with a sample of 225.2 million $J/ψ$ events collected with the BESIII detector at the BEPCII $e^+e^-$ collider. The branching fractions are determined to be $\mathcal{B}(J/ψ\to p\bar{p})=(2.112\pm0.004\pm0.031)\times10^{-3}$ and $\mathcal{B}(J/ψ\to n\bar{n})=(2.07\pm0.01\pm0.17)\times10^{-3}$. Distributions of the angle $θ$ between the proton or anti-neutron and the beam direction are well described by the form $1+α\cos^2θ$, and we find $α=0.595\pm0.012\pm0.015$ for $J/ψ\to p\bar{p}$ and $α=0.50\pm0.04\pm0.21$ for $J/ψ\to n\bar{n}$. Our branching-fraction results suggest a large phase angle between the strong and electromagnetic amplitudes describing the $J/ψ\to N\bar{N}$ decay.

hep-ex↗

arXiv2012

Constraints on the gamma-ray emission from the cluster-scale AGN outburst in the Hydra A galaxy cluster

In some galaxy clusters powerful AGN have blown bubbles with cluster scale extent into the ambient medium. The main pressure support of these bubbles is not known to date, but cosmic rays are a viable possibility. For such a scenario copious gamma-ray emission is expected as a tracer of cosmic rays from these systems. Hydra A, the closest galaxy cluster hosting a cluster scale AGN outburst, located at a redshift of 0.0538, is investigated for being a gamma-ray emitter with the High Energy Stereoscopic System (H.E.S.S.) array and the Fermi Large Area Telescope (Fermi-LAT). Data obtained in 20.2 hours of dedicated H.E.S.S. observations and 38 months of Fermi-LAT data, gathered by its usual all-sky scanning mode, have been analyzed to search for a gamma-ray signal. No signal has been found in either data set. Upper limits on the gamma-ray flux are derived and are compared to models. These are the first limits on gamma-ray emission ever presented for galaxy clusters hosting cluster scale AGN outbursts. The non-detection of Hydra A in gamma-rays has important implications on the particle populations and physical conditions inside the bubbles in this system. For the case of bubbles mainly supported by hadronic cosmic rays, the most favorable scenario, that involves full mixing between cosmic rays and embedding medium, can be excluded. However, hadronic cosmic rays still remain a viable pressure support agent to sustain the bubbles against the thermal pressure of the ambient medium. The largest population of highly-energetic electrons which are relevant for inverse-Compton gamma-ray production is found in the youngest inner lobes of Hydra A. The limit on the inverse-Compton gamma-ray flux excludes a magnetic field below half of the equipartition value of 16 muG in the inner lobes.

astro-ph.CO↗

arXiv2012

Technical Design Report for the: PANDA Straw Tube Tracker

This document describes the technical layout and the expected performance of the Straw Tube Tracker (STT), the main tracking detector of the PANDA target spectrometer. The STT encloses a Micro-Vertex-Detector (MVD) for the inner tracking and is followed in beam direction by a set of GEM-stations. The tasks of the STT are the measurement of the particle momentum from the reconstructed trajectory and the measurement of the specific energy-loss for a particle identification. Dedicated simulations with full analysis studies of certain proton-antiproton reactions, identified as being benchmark tests for the whole PANDA scientific program, have been performed to test the STT layout and performance. The results are presented, and the time lines to construct the STT are described.

physics.ins-det↗

arXiv2012

Measurements of the mass and width of the eta_c using psi' -> gamma eta_c

The mass and width of the lowest lying S-wave spin singlet charmonium state, the eta_c, are measured using a data sample of 1.06x10^8 psi' decays collected with the BESIII detector at the BEPCII storage ring. We use a model that incorporates interference between the signal reaction, psi' -> gamma eta_c, and a non-resonant radiative background to successfully describe the line shape of the eta_c. We measure the eta_c mass to be 2984.3 +- 0.6 +- 0.6 MeV/c^2 and the total width to be 32.0 +- 1.2 +- 1.0 MeV, where the first errors are statistical and the second are systematic.

hep-ex↗

arXiv2012

First observation of the M1 transition $ψ(3686)\to γη_c(2S)$

Using a sample of 106 million ψ(3686) events collected with the BESIII detector at the BEPCII storage ring, we have made the first measurement of the M1 transition between the radially excited charmonium S-wave spin-triplet and the radially excited S-wave spin-singlet states: ψ(3686)\toγη_c(2S). Analyses of the processes ψ(2S)\to γη_c(2S) with η_c(2S)\to \K_S^0 Kπand K^+K^-π^0 gave an η_c(2S) signal with a statistical significance of greater than 10 standard deviations under a wide range of assumptions about the signal and background properties. The data are used to obtain measurements of the η_c(2S) mass (M(η_c(2S))=3637.6\pm 2.9_\mathrm{stat}\pm 1.6_\mathrm{sys} MeV/c^2), width (Γ(η_c(2S))=16.9\pm 6.4_\mathrm{stat}\pm 4.8_\mathrm{sys} MeV), and the product branching fraction (\BR(ψ(3686)\to γη_c(2S))\times \BR(η_c(2S)\to K\bar Kπ) = (1.30\pm 0.20_\mathrm{stat}\pm 0.30_\mathrm{sys})\times 10^{-5}). Combining our result with a BaBar measurement of \BR(η_c(2S)\to K\bar K π), we find the branching fraction of the M1 transition to be \BR(ψ(3686)\toγη_c(2S)) = (6.8\pm 1.1_\mathrm{stat}\pm 4.5_\mathrm{sys})\times 10^{-4}.

hep-ex↗

arXiv2012

Two-photon widths of the $χ_{c0, 2}$ states and helicity analysis for $χ_{c2}\arγγ$}

Based on a data sample of 106 M $ψ^{\prime}$ events collected with the BESIII detector, the decays $ψ^{\prime}\arγχ_{c0, 2}$,$χ_{c0, 2}\arγγ$ are studied to determine the two-photon widths of the $χ_{c0, 2}$ states. The two-photon decay branching fractions are determined to be ${\cal B}(χ_{c0}\arγγ) = (2.24\pm 0.19\pm 0.12\pm 0.08)\times 10^{-4}$ and ${\cal B}(χ_{c2}\arγγ) = (3.21\pm 0.18\pm 0.17\pm 0.13)\times 10^{-4}$. From these, the two-photon widths are determined to be $Γ_{γγ}(χ_{c0}) = (2.33\pm0.20\pm0.13\pm0.17)$ keV, $Γ_{γγ}(χ_{c2}) = (0.63\pm0.04\pm0.04\pm0.04)$ keV, and $\cal R$ $=Γ_{γγ}(χ_{c2})/Γ_{γγ}(χ_{c0})=0.271\pm 0.029\pm 0.013\pm 0.027$, where the uncertainties are statistical, systematic, and those from the PDG ${\cal B}(ψ^{\prime}\arγχ_{c0,2})$ and $Γ(χ_{c0,2})$ errors, respectively. The ratio of the two-photon widths for helicity $λ=0$ and helicity $λ=2$ components in the decay $χ_{c2}\arγγ$ is measured for the first time to be $f_{0/2} =Γ^{λ=0}_{γγ}(χ_{c2})/Γ^{λ=2}_{γγ}(χ_{c2}) = 0.00\pm0.02\pm0.02$.

hep-ex↗

arXiv2012

H.E.S.S. observations of the Carina nebula and its enigmatic colliding wind binary Eta Carinae

The massive binary system Eta Carinae and the surrounding HII complex, the Carina Nebula, are potential particle acceleration sites from which very-high-energy (VHE; E > 100 GeV) γ-ray emission could be expected. This paper presents data collected during VHE γ-ray observations with the H.E.S.S. telescope array from 2004 to 2010, which cover a full orbit of Eta Carinae. In the 33.1-hour data set no hint of significant γ-ray emission from Eta Carinae has been found and an upper limit on the γ-ray flux of 7.7 x 10-13 ph cm-2 s-1 (99% confidence level) is derived above the energy threshold of 470 GeV. Together with the detection of high-energy (HE; 0.1 GeV > E > 100 GeV) γ-ray emission by the Fermi-LAT up to 100 GeV, and assuming a continuation of the average HE spectral index into the VHE domain, these results imply a cut-off in the γ-ray spectrum between the HE and VHE γ-ray range. This could be caused either by a cut-off in the accelerated particle distribution or by severe γ-γ absorption losses in the wind collision region. Furthermore, the search for extended γ-ray emission from the Carina Nebula resulted in an upper limit on the γ-ray flux of 4.2 x 10-12 ph cm-2 s-1 (99% confidence level). The derived upper limit of ~23 on the cosmic-ray enhancement factor is compared with results found for the old-age mixed-morphology supernova remnant W 28.

astro-ph.HE↗

arXiv2012

Discovery of VHE γ-ray emission and multi-wavelength observations of the BL Lac object 1RXS J101015.9-311909

1RXS J101015.9-311909 is a galaxy located at a redshift of z=0.14 hosting an active nucleus belonging to the class of bright BL Lac objects. Observations at high (HE, E > 100 MeV) and very high (VHE, E > 100 GeV) energies provide insights into the origin of very energetic particles present in such sources and the radiation processes at work. We report on results from VHE observations performed between 2006-10 with H.E.S.S. H.E.S.S. data have been analysed with enhanced analysis methods, making the detection of faint sources more significant. VHE emission at a position coincident with 1RXS J101015.9-311909 is detected with H.E.S.S. for the first time. In a total good-quality livetime of about 49 h, we measure 263 excess counts, corresponding to a significance of 7.1σ. The photon spectrum above 0.2 TeV can be described by a power-law with a photon index of Γ = 3.08\pm0.42_{stat}\pm0.20_{sys}. The integral flux above 0.2 TeV is about 0.8% of the flux of the Crab nebula and shows no significant variability over the time reported. In addition, public Fermi/LAT data are analysed to search for high energy emission from the source. The Fermi/LAT HE emission is significant at 8.3σ in the chosen 25-month dataset. UV and X-ray contemporaneous observations with the Swift satellite in May 2007 are also reported, together with optical observations performed with the ATOM telescope located at the H.E.S.S. site. Swift observations reveal an absorbed X-ray flux of F_{0.3-7 keV} = 1.04^{+0.04}_{-0.05} \times 10^{-11} erg.cm^{-2}.s^{-1} in the 0.3-7 keV range. Finally, all the available data are used to study the source's multi-wavelength properties. The SED can be reproduced using a simple one-zone SSC model with emission from a region with a Doppler factor of 30 and a magnetic field between 0.025 and 0.16 G. These parameters are similar to those obtained for other sources of this type.

astro-ph.HE↗

arXiv2012

Discovery of VHE emission towards the Carina arm region with the H.E.S.S. telescope array: HESS J1018-589

The observational coverage with HESS of the Carina region in VHE gamma-rays benefits from deep exposure (40 h) of the neighboring open cluster Westerlund 2. The observations have revealed a new extended region of VHE gamma-ray emission. The new VHE source HESS J1018-589 shows a bright, point-like emission region positionally coincident with SNR G284.3-1.8 and 1FGL J1018.6 - 5856 and a diffuse extension towards the direction of PSR J1016-5857. A soft Gamma=2.7+-0.5 photon index, with a differential flux at 1TeV of N0=(4.2+-1.1)10^-13 TeV^-1 cm^-2 s^-1 is found for the point-like source, whereas the total emission region including the diffuse emission region is well fit by a power-law function with spectral index Gamma=2.9+-0.4 and differential flux at 1TeV of N0=(6.8+-1.6) 10^-13 TeV^-1 cm^-2 s^-1. This H.E.S.S. detection motivated follow-up X-ray observations with the XMM-Newton satellite to investigate the origin of the VHE emission. The analysis of the XMM-Newton data resulted in the discovery of a bright, non-thermal point-like source (XMMU J101855.4-58564) with a photon index of Gamma=1.65+-0.08 in the center of SNRG284.3-1.8, and a thermal, extended emission region coincident with its bright northern filament. The characteristics of this thermal emission are used to estimate the plasma density in the region as n~0.5 cm^-3(2.9kpc/d)^2. The position of XMMUJ101855.4-58564 is compatible with the position reported by the Fermi-LAT collaboration for the binary system 1FGL J1018.6-5856 and the variable Swift XRT source identified with it. The new X-ray data are used alongside archival multi-wavelength data to investigate the relationship between the VHE gamma-ray emission from HESSJ1018-589 and the various potential counterparts in the Carina arm region.

astro-ph.HE↗

arXiv2012

First observation of $η(1405)$ decays into $f_{0}(980)π^0$

The decays $J/ψ\rightarrow γπ^+π^-π^0$ and $J/ψ\rightarrow γπ^0π^0π^0$ are analyzed using a sample of 225 million $\jpsi$ events collected with the BESIII detector. The decay of $η(1405)\ar f_{0}(980)π^0$ with a large isospin violation is observed for the first time. The width of the $f_{0}(980)$ observed in the dipion mass spectra is anomalously narrower than the world average. Decay rates for three-pion decays of the $η'$ are also measured precisely.

hep-ex↗

arXiv2012

The 2010 very high energy gamma-ray flare & 10 years of multi-wavelength observations of M 87

Abridged: The giant radio galaxy M 87 with its proximity, famous jet, and very massive black hole provides a unique opportunity to investigate the origin of very high energy (VHE; E>100 GeV) gamma-ray emission generated in relativistic outflows and the surroundings of super-massive black holes. M 87 has been established as a VHE gamma-ray emitter since 2006. The VHE gamma-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz VLBA). The excellent sampling of the VHE gamma-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (~day), peak fluxes (Phi(>0.35 TeV) ~= (1-3) x 10^-11 ph cm^-2 s^-1), and VHE spectra. 43 GHz VLBA radio observations of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken ~3 days after the peak of the VHE gamma-ray emission reveal an enhanced flux from the core. The long-term (2001-2010) multi-wavelength light curve of M 87, spanning from radio to VHE and including data from HST, LT, VLA and EVN, is used to further investigate the origin of the VHE gamma-ray emission. No unique, common MWL signature of the three VHE flares has been identified.

astro-ph.CO↗

arXiv2012

Precision measurement of the branching fractions of J/psi -> pi+pi-pi0 and psi' -> pi+pi-pi0

We study the decays of the J/psi and psi' mesons to pi+pi-pi0 using data samples at both resonances collected with the BES III detector in 2009. We measure the corresponding branching fractions with unprecedented precision and provide mass spectra and Dalitz plots. The branching fraction for J/psi -> pi+pi-pi0 is determined to be (2.137 +- 0.004 (stat.) +0.058-0.056 (syst.) +0.027-0.026 (norm.))*10-2, and the branching fraction for psi' -> pi+pi-pi0 is measured as (2.14 +- 0.03 (stat.) +0.08-0.07 (syst.) +0.09-0.08 (norm.))*10-4. The J/psi decay is found to be dominated by an intermediate rho(770) state, whereas the psi' decay is dominated by di-pion masses around 2.2 GeV/c2, leading to strikingly different Dalitz distributions.

hep-ex↗

arXiv2012

A multiwavelength view of the flaring state of PKS 2155-304 in 2006

Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies (VHE, E>= 100 GeV) occurred, provide a detailed picture of the evolution of its emission. The complete data set from this campaign is presented, including observations in VHE gamma-rays (H.E.S.S.), X-rays (RXTE, CHANDRA, SWIFT XRT), optical (SWIFT UVOT, Bronberg, Watcher, ROTSE), and in the radio band (NRT, HartRAO, ATCA). Optical and radio light curves from 2004 to 2008 are compared to the available VHE data from this period, to put the 2006 campaign into the context of the long-term evolution of the source. The X-ray and VHE gamma-ray emission are correlated during the observed high state of the source, but show no direct connection with longer wavelengths. The long-term flux evolution in the optical and radio bands is found to be correlated and shows that the source reaches a high state at long wavelengths after the occurrence of the VHE flares. Spectral hardening is seen in the SWIFT XRT data. The nightly averaged high-energy spectra of the non-flaring nights can be reproduced by a stationary one-zone SSC model, with only small variations in the parameters. The spectral and flux evolution in the high-energy band during the night of the second VHE flare is modelled with multi-zone SSC models, which can provide relatively simple interpretations for the hour time-scale evolution of the high-energy emission, even for such a complex data set. For the first time in this type of source, a clear indication is found for a relation between high activity at high energies and a long-term increase in the low frequency fluxes.

astro-ph.HE↗

arXiv2012

Discovery of hard-spectrum γ-ray emission from the BL Lac object 1ES 0414+009

1ES 0414+009 (z = 0.287) is a distant high-frequency-peaked BL Lac object, and has long been considered a likely emitter of very-high energy (VHE, E>100 GeV) gamma-rays due to its high X-ray and radio flux. Observations in the VHE gamma-ray band and across the electromagnetic spectrum can provide insights into the origin of highly energetic particles present in the source and the radiation processes at work. Because of the distance of the source, the gamma-ray spectrum might provide further limits on the level of the Extragalactic Background Light (EBL). We report observations made between October 2005 and December 2009 with H.E.S.S., an array of four imaging atmospheric Cherenkov telescopes. Observations at high energies (HE, 100 MeV - 100 GeV) with the Fermi-LAT instrument in the first 20 months of its operation are also reported. To complete the multi-wavelength picture, archival UV and X-ray observations with the Swift satellite and optical observations with the ATOM telescope are also used. Based on the observations with H.E.S.S., 1ES 0414+009 is detected for the first time in the VHE band. An excess of 224 events is measured, corresponding to a significance of 7.8 sigma. The photon spectrum of the source is well described by a power law, with photon index of 3.45 \pm 0.25stat \pm 0.20syst. The integral flux above 200 GeV is (1.88 \pm 0.20stat \pm 0.38syst) \times10-12 cm-2 s-1. Observations with the Fermi-LAT in the first 20 months of operation show a flux between 200 MeV and 100 GeV of (2.3 \pm 0.2stat) \times 10-9 erg cm-2 s-1, and a spectrum well described by a power-law function with a photon index 1.85 \pm 0.18. Swift/XRT observations show an X-ray flux between 2 and 10 keV of (0.8 - 1) \times 10-11 erg cm-2 s-1, and a steep spectrum (2.2 - 2.3). Combining X-ray with optical-UV data, a fit with a log-parabolic function locates the synchrotron peak around 0.1 keV. ...

astro-ph.HE↗

arXiv2011

Simultaneous multi-wavelength campaign on PKS 2005-489 in a high state

The high-frequency peaked BL Lac object PKS 2005-489 was the target of a multi-wavelength campaign with simultaneous observations in the TeV gamma-ray (H.E.S.S.), GeV gamma-ray (Fermi/LAT), X-ray (RXTE, Swift), UV (Swift) and optical (ATOM, Swift) bands. This campaign was carried out during a high flux state in the synchrotron regime. The flux in the optical and X-ray bands reached the level of the historical maxima. The hard GeV spectrum observed with Fermi/LAT connects well to the very high energy (VHE, E>100GeV) spectrum measured with H.E.S.S. with a peak energy between ~5 and 500 GeV. Compared to observations with contemporaneous coverage in the VHE and X-ray bands in 2004, the X-ray flux was ~50 times higher during the 2009 campaign while the TeV gamma-ray flux shows marginal variation over the years. The spectral energy distribution during this multi-wavelength campaign was fit by a one zone synchrotron self-Compton model with a well determined cutoff in X-rays. The parameters of a one zone SSC model are inconsistent with variability time scales. The variability behaviour over years with the large changes in synchrotron emission and small changes in the inverse Compton emission does not warrant an interpretation within a one-zone SSC model despite an apparently satisfying fit to the broadband data in 2009.

astro-ph.HE↗