arXiv subjects

A. Hafner

Publications and source records attributed to A. Hafner.

At least 19 recordsLinked to original sources

arXiv2026

Murriyang cryogenic phased array feed: spectral-line results and noise-reduction methods

Spectral-line results from a new cryogenic phased array feed (cryoPAF) on the Murriyang telescope at Parkes are presented. This array offers a significant improvement in field of view, aperture efficiency, bandwidth, chromaticity and survey speed compared with conventional horn-fed receivers. We demonstrate this with measurements of sky calibrators and observations of 21-cm neutral hydrogen (HI) in the LMC and the nearby galaxy NGC 6744. Within 0.3 deg of the optical axis, the ratio of system temperature to dish aperture efficiency is 25 K and the ratio with beam efficiency is 21 K (at 1.4 GHz). For the previously measured $T_{sys} = 17$ K, respective efficiency values 0.7 and 0.8 are derived. Our HI observational results are in good agreement with previous results, although detailed comparison with multibeam observations of the LMC suggests that the earlier observations may have missed an extended component of low-column-density gas ($8\times 10^{18}$ cm$^{-2}$). We use the cryoPAF zoom-band and wideband data to make a preliminary investigation of whether the large number of simultaneous beams (72) permits the use of novel data reduction methods to reduce the effects of foreground/background continuum contamination and RFI. We also investigate if these methods can better protect against signal loss for the detection of faint, extended cosmological signals such as HI intensity maps. Using robust higher-order singular value decomposition (SVD) techniques, we find encouraging results for the detection of both compact and extended sources, including challenging conditions with high RFI occupancy and significant sky continuum structure. Examples are shown that demonstrate that 3D SVD techniques offer a significant improvement in noise reduction and signal capture compared with more traditional layered 2D techniques.

astro-ph.IM↗

arXiv2025

Faint absorption of the ground state hyperfine-splitting transitions of hydroxyl at 18 cm in the Galactic Disk

The interstellar hydride hydroxyl (OH) is a potential tracer of CO-dark molecular gas. We present new absorption line observations of OH at 18-cm wavelength towards four continuum sources. We compare these to the [CII] line at 1.9 THz obtained with SOFIA, observations of the neutral atomic hydrogen 21 cm line with the VLA, and CO lines obtained with APEX. We trace OH over a large range of molecular hydrogen column densities, and derive OH abundances with respect to molecular and total hydrogen column densities. Increased sensitivity and spectral resolution allowed us to detect weak and narrow features. We identify only one OH absorption component out of 23 without CO counterpart, yet several with intermediate molecular gas fractions. A potential association of [CII] 158 mu m emission with an OH absorption component is seen toward one sightline. Our results confirm that OH absorption traces molecular gas across diffuse and dense environments of the interstellar medium. At the sensitivity limits of the present observations our detection of only one CO-dark molecular gas feature appears in agreement with previous studies. We conclude that if OH absorption was to be used as a CO-dark molecular gas tracer, deeper observations or stronger background targets are necessary to unveil its full potential as a CO-dark molecular gas tracer, and yet it will never be an exclusive tracer of CO-dark molecular gas. For OH hyperfine-splitting transitions in the vicinity of photodissociation regions in W43-South, we detect a spectral and spatial offset between the peak of the inversion of the OH 1612 MHz line and the absorption of the OH 1720 MHz line on the one hand, and the absorption of the OH main lines on the other hand, which provides additional constraints on the interpretation of the OH 18 cm line signatures typical of HII regions.

astro-ph.GA↗

arXiv2024

SDHDF: A new file format for spectral-domain radio astronomy data

Radio astronomy file formats are now required to store wide frequency bandwidths and multiple simultaneous receiver beams and must be able to account for versatile observing modes and numerous calibration strategies. The need to capture and archive high-time and high frequency-resolution data, along with the comprehensive metadata that fully describe the data, implies that a new data format and new processing software are required. This requirement is suited to a well-defined, hierarchically-structured and flexible file format. In this paper we present the Spectral-Domain Hierarchical Data Format (`SDHDF') -- a new file format for radio astronomy data, in particular for single dish or beam-formed data streams. Since 2018, SDHDF has been the primary format for data products from the spectral-line and continuum observing modes at Murriyang, the CSIRO Parkes 64-m radio telescope, and we demonstrate that this data format can also be used to store observations of pulsars and fast radio bursts.

astro-ph.IM↗

arXiv2023

Model-independent extraction of form factors and $|V_{cb}|$ in $\overline{B} \rightarrow D \ell^- \overline{\nu}_\ell$ with hadronic tagging at BaBar

Using the entire BaBar $\Upsilon(4S)$ data set, the first two-dimensional unbinned angular analysis of the semileptonic decay $\overline{B} \rightarrow D \ell^- \overline{\nu}_\ell$ is performed, employing hadronic reconstruction of the tag-side $B$ meson from $\Upsilon(4S)\to B\overline{B}$. Here, $\ell$ denotes the light charged leptons $e$ and $\mu$. A novel data-driven signal-background separation procedure with minimal dependence on simulation is developed. This procedure preserves all multi-dimensional correlations present in the data. The expected $\sin^2\theta_\ell$ dependence of the differential decay rate in the Standard Model is demonstrated, where $\theta_\ell$ is the lepton helicity angle. Including input from the latest lattice QCD calculations and previously available experimental data, the underlying form factors are extracted using both model-independent (BGL) and dependent (CLN) methods. Comparisons with lattice calculations show flavor SU(3) symmetry to be a good approximation in the $B_{(s)}\to D_{(s)}$ sector. Using the BGL results, the CKM matrix element $|V_{cb}|=(41.09\pm 1.16)\times 10^{-3}$ and the Standard Model prediction of the lepton-flavor universality violation variable $\mathcal{R}(D)=0.300\pm 0.004$, are extracted. The value of $|V_{cb}|$ from $\overline{B} \rightarrow D \ell^- \overline{\nu}_\ell$ tends to be higher than that extracted using $\overline{B} \rightarrow D \ell^- \overline{\nu}_\ell$. The Standard Model $\mathcal{R}(D)$ calculation is at a $1.97\sigma$ tension with the latest HFLAV experimental average.

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arXiv2020

Observation of a cross-section enhancement near mass threshold in $e^{+}e^{-}\rightarrowΛ\barΛ$

The process $e^{+}e^{-}\rightarrowΛ\barΛ$ is studied using data samples at $\sqrt{s}=2.2324$, 2.400, 2.800 and 3.080 GeV collected with the BESIII detector operating at the BEPCII collider. The Born cross section is measured at $\sqrt{s}$=2.2324 GeV, which is 1.0 MeV above the $Λ\barΛ$ mass threshold, to be $305\pm45^{+66}_{-36}$ pb, where the first uncertainty is statistical and the second systematic. The substantial cross section near threshold is significantly larger than that expected from theory, which predicts the cross section to vanish at threshold. The Born cross sections at $\sqrt{s}$=2.400, 2.800 and 3.080 GeV are measured and found to be consistent with previous experimental results, but with improved precision. Finally, the corresponding effective electromagnetic form factors of $Λ$ are deduced.

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arXiv2019

Measurement of $e^{+}e^{-}\rightarrow π^{+}π^{-}ψ(3686)$ from 4.008 to 4.600$\sim$GeV and observation of a charged structure in the $π^{\pm}ψ(3686)$ mass spectrum

We study the process $e^{+}e^{-} \rightarrow π^{+}π^{-}ψ(3686)$ using 5.1 $fb^{-1}$ of data collected at 16 center-of-mass energy ($\sqrt{s}$) points from 4.008 to 4.600$\sim$GeV by the BESIII detector operating at the BEPCII collider. The measured Born cross sections for $e^{+}e^{-}\rightarrow π^{+}π^{-}ψ(3686)$ are consistent with previous results, but with much improved precision. A fit to the cross section shows contributions from two structures: the first has $M=4209.5\pm7.4\pm1.4$$\sim$MeV/$c^{2}$ and $Γ=80.1\pm24.6\pm2.9$$\sim$MeV, and the second has $M=4383.8\pm4.2\pm0.8$$\sim$MeV/c$^{2}$ and $Γ=84.2\pm12.5\pm2.1$$\sim$MeV, where the first errors are statistical and the second systematic. The lower-mass resonance is observed in the process $e^{+}e^{-}\rightarrow π^{+}π^{-}ψ(3686)$ for the first time with a statistical significance of $5.8σ$. A charged charmonium-like structure is observed in the $π^{\pm}ψ(3686)$ invariant mass spectrum for data at $\sqrt{s} = 4.416~$GeV. A fit with an $S$-wave Breit-Wigner function yields a mass $M=4032.1\pm2.4$~$MeV$^{2}$, where the errors are statistical only. However, there are still unresolved discrepancies between the fit model and data. The width of the intermediate state varies in a wide range for different kinematic regions within the data set. Therefore no simple interpretation of the data has been found, and a future data sample with larger statistics and more theoretical input will be required to better understand this issue.

hep-ex↗

arXiv2018

Precision Study of $η^\prime\rightarrowγπ^+π^-$ Decay Dynamics

Using a low background data sample of $9.7\times10^{5}$ $Jψ\rightarrowγη^\prime$, $η^\prime\rightarrowγπ^+π^-$ events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of $η^\prime\rightarrowγπ^+π^-$ are studied with both model-dependent and model-independent approaches. The contributions of $ω$ and the $ρ(770)-ω$ interference are observed for the first time in the decays $η^\prime\rightarrowγπ^+π^-$ in both approaches. Additionally, a contribution from the box anomaly or the $ρ(1450)$ resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.

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arXiv2018

Measurements of the Branching Fractions of the Singly-Cabibbo-Suppressed Decays $D^0\toωη$, $η^{(\prime)}π^0$ and $η^{(\prime)}η$

By analyzing a data sample of 2.93 fb$^{-1}$ collected at $\sqrt s=$ 3.773 GeV with the BESIII detector operated at the BEPCII storage rings, we measure the branching fractions ${\mathcal B}(D^0\toωη)=(2.15\pm0.17_{\rm stat.}\pm0.15_{\rm sys.})\times 10^{-3}$, ${\mathcal B}(D^0\toηπ^0)=(0.58\pm0.05_{\rm stat.}\pm0.05_{\rm sys.})\times 10^{-3}$, ${\mathcal B}(D^0\toη^\primeπ^0)=(0.93\pm0.11_{\rm stat.}\pm0.09_{\rm sys.})\times 10^{-3}$, ${\mathcal B}(D^0\toηη)=(2.20\pm0.07_{\rm stat.}\pm0.06_{\rm sys.})\times 10^{-3}$ and ${\mathcal B}(D^0\toη^\primeη)=(0.94\pm0.25_{\rm stat.}\pm0.11_{\rm sys.})\times 10^{-3}$. We note that ${\mathcal B}(D^0\to ωη)$ is measured for the first time and that ${\mathcal B}(D^0\to ηη)$ is measured with much improved precision.

hep-ex↗

arXiv2018

Study of $η(1475)$ and $X(1835)$ in radiative $J/ψ$ decays to $γϕ$

The decay $J/ψ\rightarrow γγϕ$ is studied using a sample of $1.31 \times10^{9}$ $J/ψ$ events collected with the BESIII detector. Two structures around 1475 MeV/c$^2$ and 1835 MeV/c$^2$ are observed in the $γϕ$ invariant mass spectrum for the first time. With a fit on the $γϕ$ invariant mass, which takes into account the interference between the two structures, and a simple analysis of the angular distribution, the structure around 1475 MeV/c$^2$ is found to favor an assignment as the $η(1475)$ and the mass and width for the structure around 1835 MeV/c$^2$ are consistent with the $X(1835)$. The statistical significances of the two structures are $13.5 σ$ and $6.3 σ$, respectively. The results indicate that both $η(1475)$ and $X(1835)$ contain a sizeable $s\bar{s}$ component.

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arXiv2018

Search for $ψ(3686)\to γη_c(η(1405))\to γπ^{+}π^{-}π^{0}$

Using a sample of $448.1\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector, a search for the isospin violating decay $η_{c}\toπ^{+}π^{-}π^{0}$ via $ψ(3686)\toγη_{c}$ is presented. No signal is observed, and the upper limit on $\mathcal{B}(ψ(3686)\to γη_{c}\to γπ^{+}π^{-}π^{0} )$ is determined to be $1.6\times10^{-6}$ at the $90\%$ confidence level. In addition, a search for $η(1405)\to f_{0}(980)π^{0}$ in $ψ(3686)$ radiative decays is performed. No signal is observed, and the branching fraction $\mathcal{B}(ψ(3686)\toγη(1405)\to γf_{0}(980)π^{0}\toγπ^+π^-π^0 )$ is calculated to be less than $ 5.0\times10^{-7}$ at the $90\%$ confidence level.

hep-ex↗

arXiv2017

Dark Photon Search in the Mass Range Between 1.5 and 3.4 GeV/$c^2$

Using a data set of 2.93 fb$^{-1}$ taken at a center-of-mass energy $\sqrt{s}$ = 3.773 GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, also denoted as a dark photon. We examine the initial state radiation reactions $e^+e^-\rightarrow e^+e^-γ_{\rm ISR}$ and $e^+e^-\rightarrow μ^+μ^-γ_{\rm ISR}$ for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs. We observe no obvious enhancement in the mass range between 1.5 and 3.4 GeV/$c^{2}$ and set a 90% confidence level upper limit on the mixing strength of the dark photon and the Standard Model photon. We obtain a competitive limit in the tested mass range.

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arXiv2017

Measurement of Singly Cabibbo Suppressed Decays $Λ_c^{+}\to pπ^{+}π^{-}$ and $Λ_c^{+}\to pK^{+}K^{-}$

Using 567 $pb^{-1}$ of data collected with the BESIII detector at a center-of-mass energy of $\sqrt{s}=$ 4.599 $GeV$, near the $Λ_{c}^{+}Λ_{c}^{-}$ threshold, we study the singly Cabibbo-suppressed decays $Λ_c^{+}\to pπ^{+}π^{-}$ and $Λ_c^{+}\to pK^{+}K^{-}$. By normalizing with respect to the Cabibbo-favored decay $Λ_c^{+}\to pK^{-}π^{+}$, we obtain ratios of branching fractions: $\frac{\mathcal{B}(Λ_c^{+}\to pπ^{+}π^{-})}{\mathcal{B}(Λ_c^{+}\to pK^{-}π^{+})}$ = $(6.70 \pm 0.48 \pm 0.25)\%$, $\frac{\mathcal{B}(Λ_c^{+}\to pϕ)}{\mathcal{B}(Λ_c^{+}\to pK^{-}π^{+})}$ = $(1.81 \pm 0.33 \pm 0.13)\%$, and $\frac{\mathcal{B}(Λ_c^{+}\to pK^{+}K^{-}_{\text{non-}ϕ})}{\mathcal{B}(Λ_c^{+}\to pK^{-}π^{+})}$ = $(9.36 \pm 2.22 \pm 0.71)\times10^{-3}$, where the uncertainties are statistical and systematic, respectively. The absolute branching fractions are also presented. Among these measurements, the decay $Λ_c^{+}\to pπ^{+}π^{-}$ is observed for the first time, and the precision of the branching fraction for $Λ_c^{+}\to pK^{+}K^{-}_{\text{non-}ϕ}$ and $Λ_c^{+}\to pϕ$ is significantly improved.

hep-ex↗

arXiv2017

Measurement of $e^{+}e^{-} \to π^{0}π^{0}ψ(3686)$ at $\sqrt{s}$ from 4.009 to 4.600 GeV and observation of a neutral charmoniumlike structure

Using $e^{+}e^{-}$ collision data collected with the BESIII detector at the BEPCII collider corresponding to an integrated luminosity of 5.2 $fb^{-1}$ at center-of-mass energies ($\sqrt{s}$) from 4.009 to 4.600 GeV, the process $e^{+}e^{-} \to π^{0} π^{0}ψ(3686)$ is studied for the first time. The corresponding Born cross sections are measured and found to be half of those of the reaction $e^{+}e^{-} \to π^{+}π^{-}ψ(3686)$. This is consistent with the expectation from isospin symmetry. Furthermore, the Dalitz plots for $π^{0}π^{0}ψ(3686)$ are accordant with those of $π^{+}π^{-}ψ(3686)$ at all energy points, and a neutral analogue to the structure in $π^\pm ψ(3686)$ around 4040 MeV/$c^{2}$ first observed at $\sqrt{s}$=4.416 GeV is observed in the isospin neutral mode at the same energy.

hep-ex↗

arXiv2017

Search for the rare decays $J/ψ\to D^{0} e^{+}e^{-} +c.c.$ and $ψ(3686) \to D^{0} e^{+}e^{-} +c.c.$

Using the data samples of $(1310.6\pm7.2 )\times 10^{6}$ $J/ψ$ events and $(448.1\pm2.9)\times 10^{6}$ $ψ(3686)$ events collected with the BESIII detector, we search for the rare decays $J/ψ\to D^{0} e^{+}e^{-} +c.c.$ and $ψ(3686) \to D^{0} e^{+}e^{-} +c.c.$. No significant signals are observed and the corresponding upper limits on the branching fractions at the $90\%$ confidence level are determined to be $Br(J/ψ\to D^{0} e^{+}e^{-} +c.c.)< 8.5\times 10^{-8}$ and $Br (ψ(3686) \to D^{0} e^{+}e^{-} +c.c.)<1.4\times 10^{-7}$, respectively. Our limit on $Br(J/ψ\to D^{0} e^{+}e^{-} +c.c.)$ is more stringent by two orders of magnitude than the previous results, and the $Br(ψ(3686) \to D^{0} e^{+}e^{-} +c.c.)$ is measured for the first time.

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arXiv2017

Measurement of the integrated luminosity and the center-of-mass energy of the data taken by BESIII at $\sqrt{s} = 2.125$ GeV

To study the nature of the state $Y(2175)$, a dedicated data set of $e^+e^-$ collision data was collected at the center-of-mass energy of 2.125 GeV with the BESIII detector at the BEPCII collider. By analyzing large-angle Bhabha scattering events, the integrated luminosity of this data set is determined to be $108.49\pm0.02\pm0.85$ pb$^{-1}$, where the first uncertainty is statistical and the second one is systematic. In addition, the center-of-mass energy of the data set is determined with radiative dimuon events to be $2126.55\pm0.03\pm0.85$ MeV, where the first uncertainty is statistical and the second one is systematic.

hep-ex↗

arXiv2017

Observation of $e^+ e^- \to ηY(2175)$ at center-of-mass energies above 3.7$\sim$GeV

The state $Y(2175)$ is observed in the process $e^+ e^- \to ηY(2175)$ at center-of-mass energies between 3.7 and 4.6$\sim$GeV with a statistical significance larger than $10σ$ using data collected with the BESIII detector operating at the BEPCII storage ring. This is the first observation of the $Y(2175)$ in this process. The mass and width of the $Y(2175)$ are determined to be ($2135\pm 8\pm 9$)~MeV/$c^2$ and ($104\pm 24\pm 12$)~MeV, respectively, and the production cross section of $e^+ e^- \to ηY(2175)\to ηϕf_{0}(980)\to ηϕπ^+ π^-$ is at a several hundred femtobarn level. No significant signal for the process $e^+ e^- \to η' Y(2175)$ is observed and the upper limit on $σ(e^+ e^- \to η' Y(2175))/σ(e^+ e^- \to ηY(2175))$ is estimated to be 0.43 at the 90\% confidence level. We also search for $ψ(3686) \to ηY(2175)$. No significant signal is observed, indicating a strong suppression relative to the corresponding $J/ψ$ decay, in violation of the "12\% rule."

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arXiv2017

Determination of the number of $ψ(3686)$ events at BESIII

The numbers of $ψ(3686)$ events accumulated by the BESIII detector for the two rounds of data taking during 2009 and 2012 are determined to be $(107.0\pm0.8)\times 10^6$ and $(341.1\pm 2.1)\times 10^6$, respectively, by counting inclusive hadronic events, where the uncertainty is dominated by systematics and the statistical uncertainty is negligible. The number of events for the sample taken in 2009 is consistent with that of the previous measurement. The total number of $ψ(3686)$ events for the two data-taking periods is $(448.1\pm2.9)\times10^6$.

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arXiv2017

Measurement of cross sections of the interactions $e^+e^-\rightarrow ϕϕω$ and $e^+e^-\rightarrow ϕϕϕ$ at center-of-mass energies from 4.008 to 4.600 GeV

Using data samples collected with the BESIII detector at the BEPCII collider at six center-of-mass energies between 4.008 and 4.600 GeV, we observe the processes $e^+e^-\rightarrow ϕϕω$ and $e^+e^-\rightarrow ϕϕϕ$. The Born cross sections are measured and the ratio of the cross sections $σ(e^+e^-\rightarrow ϕϕω)/σ(e^+e^-\rightarrow ϕϕϕ)$ is estimated to be $1.75\pm0.22\pm0.19$ averaged over six energy points, where the first uncertainty is statistical and the second is systematic. The results represent first measurements of these interactions.

hep-ex↗