Gaseous detectors are used in high energy physics as trackers or, more generally, as devices for the measurement of the particle position. For this reason, they must provide high spatial resolution ...and they have to be able to operate in regions of intense radiation, i.e. around the interaction point of collider machines. Among these, Micro Pattern Gaseous Detectors (MPGD) are the latest frontier and allow to overcome many limitations of the pre-existing detectors, such as the radiation tolerance and the rate capability. The gas Electron Multiplier (GEM) is a MPGD that exploits an intense electric field in a reduced amplification region in order to prevent discharges. Several amplification stages, like in a triple-GEM, allow to increase the detector gain and to reduce the discharge probability. Reconstruction techniques such as charge centroid (CC) and micro-Time Projection Chamber (μTPC) are used to perform the position measurement. From literature triple-GEMs show a stable behaviour up to 108Hz/cm2. A testbeam with four planar triple-GEMs has been performed at the Mainz Microtron (MAMI) facility and their performance was evaluated in different beam conditions. In this article a focus on the time performance for the μTPC clusterization is given and a new measurement of the triple-GEM limits at high rate will be presented.
Future Physics Programme of BESIII Ahmed, S.; Amoroso, A.; Bennett, J. V. ...
Chinese physics C,
04/2020, Letnik:
44, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
There has recently been a dramatic renewal of interest in hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like
...XYZ
states at BESIII and
B
factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related
X
(1835) meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons.
We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII during the remaining operation period of BEPCII. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCII to higher luminosity.
The cross sections of e+e-→π+π-hc at center-of-mass energies from 3.896 to 4.600 GeV are measured using data samples collected with the BESIII detector operating at the Beijing Electron Positron ...Collider. The cross sections are found to be of the same order of magnitude as those of e+e-→π+π- J/ψ and e+e-→π+π-ψ (2S), but the line shape is inconsistent with the Y states observed in the latter two modes. Two structures are observed in the e+e- → π+π- hc cross sections around 4.22 and 4.39 GeV / c 2 , which we call Y ( 4220 ) and Y ( 4390 ) , respectively. A fit with a coherent sum of two Breit-Wigner functions results in a mass of (4218.4 $+5.5\atop{-4.5 ± 0.9) MeV/c2 and a width of 66.0$+12.3\atop-8.3$±0.4 MeV for the Y (4220), and a mass of (4391.5 $+6.3\atop-16.8$ ± 1.0) MeV/c2 and a width of (139.5$+16.2\atop-20.6 ± 0.6) MeV for the Y (4390), where the first uncertainties are statistical and the second ones systematic. The statistical significance of Y ( 4220 ) and Y(4390) is 10σ over one structure assumption.
In this paper, the spin and parity of the Zc(3900)± state are determined to be JP = 1+ with a statistical significance larger than 7σ over other quantum numbers in a partial wave analysis of the ...process e+e- → π+π-J/Ψ. We use a data sample of 1.92 fb-1 accumulated at $ \sqrt{s}=4.23 $ and 4.26 GeV with the BESIII experiment. When parametrizing the Zc(3900)± with a Flatté-like formula, we determine its pole mass Mpole = (3881.2±4.2stat ±52.7syst) MeV/c2 and pole width Γpole = (51.8± 4.6stat ± 36.0syst) MeV. Finally, we also measure cross sections for the process e+e- → Zc(3900)+π- + c.c. → J/Ψπ+π- and determine an upper limit at the 90% confidence level for the process e+e- → Zc(4020)+π- + c.c. → J/Ψ π+π-.
The cross section of the process e+e−→K+K− is measured at a number of center-of-mass energies s from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The ...results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of M=2239.2±7.1±11.3 MeV/c2 and a width of Γ=139.8±12.3±20.6 MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the timelike electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.
The process e+e- → Λ Λ ¯ is studied using data samples at √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 √s=2.2324 GeV, which is 1.0 MeV above the Λ Λ ¯ mass threshold, to be 305±$45_{-36}^{+66}$ 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 √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.
Using a data sample corresponding to an integrated luminosity of 2.93 fb−1 taken at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we perform an ...analysis of the semileptonic decays D0(+)→π−(0)μ+νμ. The branching fractions of D0→π−μ+νμ and D+→π0μ+νμ are measured to be (0.272±0.008stat±0.006syst)% and (0.350±0.011stat±0.010syst)%, respectively, where the former is of much improved precision compared to previous results and the latter is determined for the first time. Using these results along with previous BESIII measurements of D0(+)→π−(0)e+νe, we calculate the branching fraction ratios to be R0≡BD0→π−μ+νμ/BD0→π−e+νe=0.922±0.030stat±0.022syst and R+≡BD+→π0μ+νμ/BD+→π0e+νe=0.964±0.037stat±0.026syst, which are compatible with the theoretical expectation of lepton flavor universality within 1.7σ and 0.5σ, respectively. We also examine the branching fraction ratios in different four-momentum transfer square regions, and find no significant deviations from the standard model predictions.
Here, in an analysis of a 2.92 fb–1 data sample taken at 3.773 GeV with the BESIII detector operated at the BEPCII collider, we measure the absolute decay branching fractions to be B(D0 → K–e+νe) = ...(3.505 ± 0.014 ± 0.033)% and B(D0 → π–e+νe) = (0.295 ± 0.004 ± 0.003)%. From a study of the differential decay rates we obtain the products of hadronic form factor and the magnitude of the CKM matrix element $f$ $^{K}_{+}$(0)|Vcs| = 0.7172 ± 0.0025 ± 0.0035 and $f$ $^{π}_{+}$(0)|Vcd| = 0.1435 ± 0.0018 ± 0.0009.
Using a total of 9.0 fb−1 of e+e− collision data with center-of-mass energies between 4.15 and 4.30 GeV collected by the BESIII detector, we search for the processes e+e−→γX(3872) with X(3872)→π0χcJ ...for J=0, 1, 2. We report the first observation of X(3872)→π0χc1, a new decay mode of the X(3872), with a statistical significance of more than 5σ for all systematic fit variations. Normalizing to the previously established process e+e−→γX(3872) with X(3872)→π+π−J/ψ, we find B(X(3872)→π0χc1)/B(X(3872)→π+π−J/ψ)=0.88−0.27+0.33±0.10, where the first error is statistical and the second is systematic. We set 90% confidence level upper limits on the corresponding ratios for the decays to π0χc0 and π0χc2 of 19 and 1.1, respectively.
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