arXiv subjects

A. Hafner

Publications and source records attributed to A. Hafner.

100 records · Page 6Linked to original sources

arXiv2015

Observation of $e^+e^-\to π^0π^0 h_c$ and a neutral charmoniumlike structure $Z_c(4020)^0$

Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider at center-of-mass energies of $\sqrt{s}=4.23$, 4.26, and 4.36~GeV, we observe $\EE\to \pphc$ for the first time. The Born cross sections are measured and found to be about half of those of $\EE\to π^+π^-h_c$ within less than 2$σ$. In the $π^0h_c$ mass spectrum, a structure at 4.02~GeV/$c^2$ is found. It is most likely to be the neutral isospin partner of the $\zcp^{\pm}$ observed in the process of $\EE\to π^+π^-h_c$ is found. A fit to the $π^0 h_c$ invariant mass spectrum, with the width of the $\zcpn$ fixed to that of its charged isospin partner and possible interferences with non-$\zcpn$ amplitudes neglected, gives a mass of ($4023.9\pm 2.2 \pm 3.8$)~MeV/$c^2$ for the $\zcpn$, where the first error is statistical and the second systematic.

hep-ex↗

arXiv2015

Search for the $Y(4140)$ via $e^{+} e^{-} \to γϕJ/ψ$ at $\sqrt{s}=$ 4.23, 4.26 and 4.36 GeV

Using data samples collected at center-of-mass energies $\sqrt{s} = 4.23$, 4.26, and 4.36 GeV with the BESIII detector operating at the BEPCII storage ring, we search for the production of the charmoniumlike state $Y(4140)$ through a radiative transition followed by its decay to $ϕJ/ψ$. No significant signal is observed and upper limits on $σ[e^{+} e^{-} \rightarrow γY(4140)] \cdot \mathcal{B}(Y(4140)\rightarrow ϕJ/ψ)$ at the $90\%$ confidence level are estimated as 0.35, 0.28, and 0.33 pb at $\sqrt{s} = 4.23$, 4.26, and 4.36 GeV, respectively.

hep-ex↗

arXiv2015

Precision measurement of the $D^{*0}$ decay branching fractions

Using 482 pb$^{-1}$ of data taken at $\sqrt{s}=4.009$ GeV, we measure the branching fractions of the decays of $D^{*0}$ into $D^0π^0$ and $D^0γ$ to be $\BR(D^{*0} \to D^0π^0)=(65.5\pm 0.8\pm 0.5)%$ and $\BR(D^{*0} \to D^0γ)=(34.5\pm 0.8\pm 0.5)%$ respectively, by assuming that the $D^{*0}$ decays only into these two modes. The ratio of the two branching fractions is $\BR(D^{*0} \to D^0π^0)/\BR(D^{*0} \to D^0γ) =1.90\pm 0.07\pm 0.05$, which is independent of the assumption made above. The first uncertainties are statistical and the second ones systematic. The precision is improved by a factor of three compared to the present world average values.

hep-ex↗

arXiv2015

Study of $e^+e^-\toωχ_{cJ}$ at center-of-mass energies from 4.21 to 4.42 GeV

Based on data samples collected with the BESIII detector at the BEPCII collider at 9 center-of-mass energies from 4.21 to 4.42 GeV, we search for the production of $e^+e^-\to ωχ_{cJ}$ ($J$=0, 1, 2). The process $e^+e^-\to ωχ_{c0}$ is observed for the first time, and the Born cross sections at $\sqrt{s}$=4.23 and 4.26 GeV are measured to be $(55.4\pm 6.0\pm 5.9)$ and $(23.7\pm 5.3\pm 3.5)$ pb, respectively, where the first uncertainties are statistical and the second are systematic. The $ωχ_{c0}$ signals at the other 7 energies and $e^+e^-\to ωχ_{c1}$ and $ωχ_{c2}$ signals are not significant, and the upper limits on the cross sections are determined. By examining the $ωχ_{c0}$ cross section as a function of center-of-mass energy, we find that it is inconsistent with the line shape of the $Y(4260)$ observed in $e^+ e^-\toπ^+π^-J/ψ$. Assuming the $ωχ_{c0}$ signals come from a single resonance, we extract mass and width of the resonance to be $(4230\pm8\pm6)$ MeV/$c^2$ and $(38\pm12\pm2)$ MeV, respectively, and the statistical significance is more than $9σ$.

hep-ex↗

arXiv2015

Search for the weak decays $J/ψ\to D^{(*)}_{s}eν_{e}$

Using a sample of $2.25\times 10^8$ $J/ψ$ events collected with the BESIII detector at the BEPCII collider, we search for the $J/ψ$ semi-leptonic weak decay $J/ψ\to D^{-}_{s} e^{+}ν_{e}+c.c.$ with a much higher sensitivity than previous searches. We also perform the first search for $J/ψ\to D^{*-}_{s} e^{+}ν_{e}+c.c.$ No significant excess of a signal above background is observed in either channel. At the $90\%$ confidence level, the upper limits are determined to be $\mathcal{B}(J/ψ\to D^{-}_{s}e^{+}ν_{e}+c.c.)<1.3\times10^{-6}$ and $\mathcal{B}(J/ψ\to {D^{*}_{s}}^{-}e^{+}ν_{e}+c.c.)<1.8\times10^{-6}$, respectively. Both are consistent with Standard Model predictions.

hep-ex↗

arXiv2014

Study of J/psi->eta phi pi+pi- at BESIII

Based on a sample of $2.25\times 10^{8} J/ψ$ events taken with the BESIII detector at the BEPCII collider, we present the results of a study of the decay $J/ψ\to ηϕπ^{+}π^{-}$. The $Y(2175)$ resonance is observed in the invariant mass spectrum of $ϕf_{0}(980)$ with a statistical significance of greater than $10σ$. The corresponding mass and width are determined to be $M=2200\pm 6 \mathrm{(stat.)} \pm 5\mathrm{(syst.)} \mathrm{MeV}/c^{2}$ and $Γ=104\pm 15\mathrm{(stat.)}\pm 15\mathrm{(syst.)}$ MeV, respectively, and the product branching fraction is measured to be $\mathcal{B}(J/ψ\toηY(2175)$, $Y(2175)\to ϕf_{0}(980)$, $f_{0}(980)\to π^{+}π^{-})= (1.20\pm 0.14\mathrm{(stat.)}\pm 0.37 \mathrm{(syst.)})\times 10^{-4}$. The results are consistent within errors with those of previous experiments. We also measure the branching fraction of $J/ψ\to ϕf_1(1285)$ with $f_1(1285)\to ηπ^{+}π^{-}$ and set upper limits on the branching fractions for $J/ψ\to ϕη(1405)$/$ϕX(1835)$/$ϕX(1870)$ with $η(1405)$/$X(1835)$/$X(1870)\to ηπ^{+}π^{-}$ at the 90\% confidence level.

hep-ex↗

arXiv2014

Evidence for $e^+e^-\toγχ_{c1, 2}$ at center-of-mass energies from 4.009 to 4.360 GeV

Using data samples collected at center-of-mass energies of $\sqrt{s}$ = 4.009, 4.230, 4.260, and 4.360 GeV with the BESIII detector operating at the BEPCII collider, we perform a search for the process $e^+e^-\toγχ_{cJ}$ $(J = 0, 1, 2)$ and find evidence for $e^+e^-\toγχ_{c1}$ and $e^+e^-\toγχ_{c2}$ with statistical significances of 3.0$σ$ and 3.4$σ$, respectively. The Born cross sections $σ^{B}(e^+e^-\toγχ_{cJ})$, as well as their upper limits at the 90% confidence level are determined at each center-of-mass energy.

hep-ex↗

arXiv2014

Updated Measurement of the Single Top Quark Production Cross Section and $V{tb}$ in the Missing Transverse Energy Plus Jets Topology in $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV

An updated measurement of the single top quark production cross section is presented using the full data set collected by the Collider Detector at Fermilab (CDF) and corresponding to 9.5 fb${}^{-1}$ of integrated luminosity from proton-antiproton collisions at 1.96 TeV center-of-mass energy. The events selected contain an imbalance in the total transverse energy, jets identified as originating from $b$ quarks, and no identified leptons. The sum of the $s$- and $t$-channel single top quark cross sections is measured to be $3.53_{-1.16}^{+1.25}$ pb and a lower limit on $V_{tb}$ of 0.63 is obtained at the 95% credibility level. These measurements are combined with previously reported CDF results obtained from events with an imbalance in total transverse energy, jets identified as originating from $b$ quarks, and exactly one identified lepton. The combined cross section is measured to be $3.02_{-0.48}^{+0.49}$ pb and a lower limit on $V{tb}$ of 0.84 is obtained at the 95% credibility level.

hep-ex↗

arXiv2012

Track Finding Efficiency in BaBar

We describe several studies to measure the charged track reconstruction efficiency and asymmetry of the BaBar detector. The first two studies measure the tracking efficiency of a charged particle using $τ$ and initial state radiation decays. The third uses the $τ$ decays to study the asymmetry in tracking, the fourth measures the tracking efficiency for low momentum tracks, and the last measures the reconstruction efficiency of $K_S^0$ particles. The first section also examines the stability of the measurements vs BaBar running periods.

hep-ex↗

arXiv2009

Quest for precision in hadronic cross sections at low energy: Monte Carlo tools vs. experimental data

We present the achievements of the last years of the experimental and theoretical groups working on hadronic cross section measurements at the low energy e+e- colliders in Beijing, Frascati, Ithaca, Novosibirsk, Stanford and Tsukuba and on tau decays. We sketch the prospects in these fields for the years to come. We emphasise the status and the precision of the Monte Carlo generators used to analyse the hadronic cross section measurements obtained as well with energy scans as with radiative return, to determine luminosities and tau decays. The radiative corrections fully or approximately implemented in the various codes and the contribution of the vacuum polarisation are discussed.

hep-ph↗