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Based on e+e− collision data corresponding to an integrated luminosity of 4.5 fb−1 collected at the center-of-mass energies between 4.600 and 4.699 Gev with the BESIII detector at BEPCII, the absolute branching fraction of the inclusive decay Λ¯−c→n¯+X, where X refers to any possible final state particles, is measured. The absolute branching fraction is determined to be B(Λ¯−c→n¯+X)=(33.5±0.7±1.2)%, where the first uncertainty is statistical and the second systematic. Neglecting the effect of CP violation, the measurement indicates that about one-fourth of Λ+c decay modes with a neutron in the final state have not been observed.
Measurement of e⁺e⁻ → ΛΛ¯η from 3.5106 to 4.6988 GeV and study of ΛΛ¯ mass threshold enhancement
(2022)
Using data samples with a total integrated luminosity of approximately 18 fb−1 collected by the BESIII detector operating at the BEPCII, the process e+e−→ΛΛ¯η is studied at center-of-mass energies between 3.5106 and 4.6988 GeV. The Born cross section for the process e+e−→ΛΛ¯η is measured. No significant structure is observed in the Born cross section line shape. An enhancement near the ΛΛ¯ mass threshold is observed for the first time in the process. The structure can be described by an S-wave Breit-Wigner function. Neglecting contribution of excited Λ states and potential interferences, the mass and width are determined to be (2356±7±17) MeV/c2 and (304±28±54) MeV, respectively, where the first uncertainties are statistical and the second are systematic.
Measurement of e⁺e⁻ → ΛΛ¯η from 3.5106 to 4.6988 GeV and study of ΛΛ¯ mass threshold enhancement
(2022)
Using data samples with a total integrated luminosity of approximately 18 fb−1 collected by the BESIII detector operating at the BEPCII, the process e+e−→ΛΛ¯η is studied at center-of-mass energies between 3.5106 and 4.6988 GeV. The Born cross section for the process e+e−→ΛΛ¯η is measured. No significant structure is observed in the Born cross section line shape. An enhancement near the ΛΛ¯ mass threshold is observed for the first time in the process. The structure can be described by an S-wave Breit-Wigner function. Neglecting contribution of excited Λ states and potential interferences, the mass and width are determined to be (2356±7±17) MeV/c2 and (304±28±54) MeV, respectively, where the first uncertainties are statistical and the second are systematic.
Measurement of e⁺e⁻ → π⁺π⁻D⁺D⁻ cross sections at center-of-mass energies from 4.190 to 4.946 GeV
(2022)
Using data samples collected with the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the e+e−→π+π−D+D− process at center-of-mass energies from 4.190 to 4.946 GeV with a partial reconstruction method. Two resonance structures are seen and the resonance parameters are determined from a fit to the cross section line shape. The first resonance we observe has a mass of (4373.1 ± 4.0 ± 2.2) MeV/c2 and a width of (146.5 ± 7.4 ± 1.3) MeV, in agreement with those of the Y(4390) state; the other resonance has a mass of (4706 ± 11 ± 4) MeV/c2, a width of (45 ± 28 ± 9) MeV, and a statistical significance of 4.1 standard deviations (σ). This is the first evidence for a vector state at this mass value. The spin-3 D-wave charmonium state X(3842) is searched for through the e+e−→π+π−X(3842)→π+π−D+D− process, and evidence with a significance of 4.2σ is found in the data samples with center-of-mass energies from 4.600 to 4.700 GeV.
Cross sections for the process e+e−→K0SK0SJ/ψ at center-of-mass energies from 4.128 to 4.950 GeV are measured using data samples with a total integrated luminosity of 21.2 fb−1 collected by the BESIII detector operating at the BEPCII storage ring. The Y(4230) state is observed in the energy dependence of the e+e−→K0SK0SJ/ψ cross section for the first time with a statistical significance of 26.0σ. In addition, an enhancement around 4.710~GeV, called the Y(4710), is seen with a statistical significance of 4.2σ. There is no clear structure around 4.484 GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the Y(4230) state to be 4226.9±6.6±21.9 MeV/c2 and 71.7±16.2±31.4 MeV, respectively, and the mass and width of the Y(4710) state to be 4704.0±52.3±69.5 MeV/c2 and 183.2±114.0±90.8 MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of e+e−→K0SK0SJ/ψ to e+e−→K+K−J/ψ is measured to be 0.415+0.032−0.026±0.017, or 0.449+0.034−0.028±0.019 if three-body phase space is considered.
he decay D→K−π+ is studied in a sample of quantum-correlated DD¯ pairs, based on a data set corresponding to an integrated luminosity of 2.93\,fb−1 collected at the ψ(3770) resonance by the BESIII experiment. The asymmetry between CP-odd and CP-even eigenstate decays into K−π+ is determined to be AKπ=0.132±0.011±0.007, where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a K0L meson. The branching fractions of the K0L modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly CP-even tag D→π+π−π0 and the ensemble of CP-odd eigenstate tags, the observable Aπππ0Kπ is measured to be 0.130±0.012±0.008. The two asymmetries are sensitive to rKπDcosδKπD, where rKπD and δKπD are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing D→K−π+ tagged by D→K0S,Lπ+π− are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both rKπDcosδKπD and rKπDsinδKπD. A fit to AKπ, Aπππ0Kπ and the phase-space distribution of the D→K0S,Lπ+π− tags yields δKπD=(187.5+8.9−9.7+5.4−6.4) degrees, where external constraints are applied for rKπD and other relevant parameters. This is the most precise measurement of δKπD in quantum-correlated DD¯ decays.
The decay D→K−π+ is studied in a sample of quantum-correlated DD¯ pairs, based on a data set corresponding to an integrated luminosity of 2.93\,fb−1 collected at the ψ(3770) resonance by the BESIII experiment. The asymmetry between CP-odd and CP-even eigenstate decays into K−π+ is determined to be AKπ=0.132±0.011±0.007, where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a K0L meson. The branching fractions of the K0L modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly CP-even tag D→π+π−π0 and the ensemble of CP-odd eigenstate tags, the observable Aπππ0Kπ is measured to be 0.130±0.012±0.008. The two asymmetries are sensitive to rKπDcosδKπD, where rKπD and δKπD are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing D→K−π+ tagged by D→K0S,Lπ+π− are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both rKπDcosδKπD and rKπDsinδKπD. A fit to AKπ, Aπππ0Kπ and the phase-space distribution of the D→K0S,Lπ+π− tags yields δKπD=(187.6+8.9−9.7+5.4−6.4) degrees, where external constraints are applied for rKπD and other relevant parameters. This is the most precise measurement of δKπD in quantum-correlated DD¯ decays.
Using 9.9 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between 4.15 and 4.30 GeV, we search for the processes e+e−→γX(3872) with X(3872)→π0χc0 and X(3872)→ππχc0. Depending on the fitting model, the statistical significance for X(3872)→π0χc0 ranges from 1.3σ to 2.8σ. We set upper limits (at 90\% C.L.) of B(X(3872)→π0χc0)B(X(3872)→π+π−J/ψ)<3.6, B(X(3872)→π+π−χc0)B(X(3872)→π+π−J/ψ)<0.68, and B(X(3872)→π0π0χc0)B(X(3872)→π+π−J/ψ)<1.7. Combined with the BESIII measurement of X(3872)→π0χc1, we also set an upper limit of B(X(3872)→π0χc0)B(X(3872)→π0χc1)<4.4.
Using 9.9 fb−1 of e+e− collision data collected by the BESIII detector at center-of-mass energies between 4.15 and 4.30 GeV, we search for the processes e+e−→γX(3872) with X(3872)→π0χc0 and X(3872)→ππχc0. Depending on the fitting model, the statistical significance for X(3872)→π0χc0 ranges from 1.3σ to 2.8σ. We set upper limits (at 90\% C.L.) of B(X(3872)→π0χc0)B(X(3872)→π+π−J/ψ)<3.6, B(X(3872)→π+π−χc0)B(X(3872)→π+π−J/ψ)<0.68, and B(X(3872)→π0π0χc0)B(X(3872)→π+π−J/ψ)<1.7. Combined with the BESIII measurement of X(3872)→π0χc1, we also set an upper limit of B(X(3872)→π0χc0)B(X(3872)→π0χc1)<4.4.
Determination of U-spin breaking parameters with an amplitude analysis of the decay D⁰ → K⁰Lπ⁺π⁻
(2022)
We present a study of the resonant structure of the decay D0→K0Lπ+π−, using quantum-correlated D0D¯0 data produced at s√=3.773 GeV. The data sample was collected by the BESIII experiment and corresponds to an integrated luminosity of 2.93 fb−1. This study is the first amplitude analysis of a decay mode involving a K0L, which also results in the first measurement of the complex U-spin breaking parameters (ρ^) related to various CP-eigenstate resonant modes through which the three-body decay proceeds. The moduli of the ρ^ parameters have central values in a wide range from 0.4 to 12.1, which indicates substantial U-spin symmetry breaking. We present the fractional resonant contributions and average strong-phase parameters over regions of phase space for both K0Sπ+π− and K0Lπ+π− modes. We also report the ratio of the branching fractions between K0Lπ+π− and K0Sπ+π− decay modes and the CP-even fraction of the K0Lπ+π− state calculated using the U-spin breaking parameters.
A determination of the CP-even fraction F+ in the decay D0→K+K−π+π− is presented. Using 2.93 fb−1 of e+e−→ψ(3770)→DD¯ data collected by the BESIII detector, one charm meson is reconstructed in the signal mode and the other in a CP eigenstate or the decay D→K0S,Lπ+π−. Analysis of the relative rates of these double-tagged events yields the result F+=0.730±0.037±0.021, where the first uncertainty is statistical and the second is systematic. This is the first model-independent measurement of F+ in D0→K+K−π+π− decays.
The singly Cabibbo-suppressed decay Λ+c→nπ+ is observed for the first time with a statistical significance of 7.3σ by using 3.9 fb−1 of e+e− collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of Λ+c→nπ+ is measured to be (6.6±1.2stat±0.4syst)×10−4. By taking the upper limit of branching fractions of Λ+c→pπ0 from the Belle experiment, the ratio of branching fractions between Λ+c→nπ+ and Λ+c→pπ0 is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with the current predictions of available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays Λ+c→Λπ+ and Λ+c→Σ0π+ are measured to be (1.31±0.08stat±0.05syst)×10−2 and (1.22±0.08stat±0.07syst)×10−2, respectively, which are consistent with previous results.
The singly Cabibbo-suppressed decay Λ+c→nπ+ is observed for the first time with a statistical significance of 7.3σ by using 3.9 fb−1 of e+e− collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of Λ+c→nπ+ is measured to be (6.6±1.2stat±0.4syst)×10−4. By taking the upper limit of branching fractions of Λ+c→pπ0 from the Belle experiment, the ratio of branching fractions between Λ+c→nπ+ and Λ+c→pπ0 is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with the current predictions of available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays Λ+c→Λπ+ and Λ+c→Σ0π+ are measured to be (1.31±0.08stat±0.05syst)×10−2 and (1.22±0.08stat±0.07syst)×10−2, respectively, which are consistent with previous results.
Using 4.7fb−1 of e+e− collision data at center-of-mass energies from 4.661 to 4.951 GeV collected by the BESIII detector at the BEPCII collider, we observe the X(3872) production process e+e−→ωX(3872) for the first time. The significance is 7.5σ, including both the statistical and systematic uncertainties. The e+e−→ωX(3872) Born cross section and the corresponding upper limit at 90\% confidence level at each energy point are reported. The line shape of the cross section indicates that the ωX(3872) signals may be from the decays of some non-trivial structures.
A biophysical regulator of inhibitory integration and learning in mesolimbic dopamine neurons
(2022)
Midbrain dopamine neurons are essential for flexible control of adaptive behaviors. DA neurons that project to different target regions have unique biophysical properties, and it is thought that this diversity reflects functional specialization. This assumption implies the presence of specific genetic determinants with precise impacts on behavior. We tested this general hypothesis by homing in on one particular biophysical mechanism, Kv4 channel inactivation, using a combination of molecular, proteomic, electrophysiological, computational, and behavioral approaches. We demonstrate that KChIP4a, a singular Kv4 β-subunit splice variant, prolongs hyperpolarization-rebound delays selectively in dopamine neurons projecting to the nucleus accumbens core, shifts the integration of inhibitory inputs and, in turn, selectively regulates learning from negative prediction-errors. Our results reveal a highly specialized, gene-to-behavior mechanistic chain that is only operative in a particular dopaminergic subsystem, illuminating how molecularly defined biophysical switches are employed for neuron subtype-specific information processing in the brain.
The production of the ψ(2S) charmonium state was measured with ALICE in Pb-Pb collisions at sNN−−−√=5.02 TeV, in the dimuon decay channel. A significant signal was observed for the first time at LHC energies down to zero transverse momentum, at forward rapidity (2.5<y<4). The measurement of the ratio of the inclusive production cross sections of the ψ(2S) and J/ψ resonances is reported as a function of the centrality of the collisions and of transverse momentum, in the region pT<12 GeV/c. The results are compared with the corresponding measurements in pp collisions, by forming the double ratio [σψ(2S)/σJ/ψ]Pb−Pb/[σψ(2S)/σJ/ψ]pp. The ψ(2S) nuclear modification factor RAA was also obtained as a function of both centrality and pT. The results show that the ψ(2S) resonance yield is strongly suppressed in Pb-Pb collisions, by a factor up to ∼3 with respect to pp. Furthermore, the ψ(2S) suppression in Pb-Pb collisions is stronger than the one observed for the J/ψ by a factor ∼2. Comparisons of cross section ratios with previous SPS findings by the NA50 experiment, and of RAA with higher-pT results at LHC energy are also reported. These results and the corresponding comparisons with calculations of transport and statistical models address questions on the existence and properties of charmonium states in the quark-gluon plasma formed in nuclear collisions at the LHC.
The production of the ψ(2S) charmonium state was measured with ALICE in Pb-Pb collisions at sNN−−−√=5.02 TeV, in the dimuon decay channel. A significant signal was observed for the first time at LHC energies down to zero transverse momentum, at forward rapidity (2.5<y<4). The measurement of the ratio of the inclusive production cross sections of the ψ(2S) and J/ψ resonances is reported as a function of the centrality of the collisions and of transverse momentum, in the region pT<12 GeV/c. The results are compared with the corresponding measurements in pp collisions, by forming the double ratio [σψ(2S)/σJ/ψ]Pb−Pb/[σψ(2S)/σJ/ψ]pp. The ψ(2S) nuclear modification factor RAA was also obtained as a function of both centrality and pT. The results show that the ψ(2S) resonance yield is strongly suppressed in Pb-Pb collisions, by a factor up to ∼3 with respect to pp. Furthermore, the ψ(2S) suppression in Pb-Pb collisions is stronger than the one observed for the J/ψ by a factor ∼2. Comparisons of cross section ratios with previous SPS findings by the NA50 experiment, and of RAA with higher-pT results at LHC energy are also reported. These results and the corresponding comparisons with calculations of transport and statistical models address questions on the existence and properties of charmonium states in the quark-gluon plasma formed in nuclear collisions at the LHC.
The ALICE experiment was proposed in 1993, to study strongly interacting matter at extreme energy densities via a comprehensive investigation of nuclear collisions at the LHC. Its physics programme initially focused on the determination of the properties of the Quark-Gluon Plasma (QGP), a deconfined state of quarks and gluons and was extended along the years, covering a diverse ensemble of observables related to Quantum Chromodynamics (QCD), the theory of strong interactions. The experiment has studied Pb-Pb, Xe-Xe, p-Pb and pp collisions in the multi-TeV energy range, during the Run 1 and Run 2 data taking periods at the LHC (2009-2018). The aim of this review article is to gather and summarise a selection of ALICE physics results and to discuss their implications on the current understanding of the macroscopic and microscopic properties of strongly interacting matter at the highest temperature reached in the laboratory. It will be shown that it is possible to have a quantitative description of the properties of the QGP produced in Pb--Pb collisions. We also show that various features, commonly ascribed to QGP formation, are detected for a wide range of interacting system sizes. Precision measurements of QCD-related observables not directly connected to the study of the QGP will also be discussed. Prospects for future measurements with the ALICE detector and its foreseen upgrades will also be briefly described.
Using an e+e− collision data sample with a total integrated luminosity of 3.19 fb−1 collected with the BESIII detector at a center-of-mass energy of 4.178 GeV, the branching fraction of the inclusive decay of the D+s meson to final states including at least three charged pions is measured for the first time to be B(D+s→π+π+π−X)=(32.81±0.35stat±0.82syst)%. In this measurement the charged pions from K0S meson decays are excluded. The partial branching fractions of D+s→π+π+π−X are also measured as a function of the π+π+π− invariant mass.
Using data corresponding to an integrated luminosity of 651 pb−1 accumulated at 22 center-of-mass energies from 2.00 to 3.08 GeV by the BESIII experiment, the process \process is studied. The cross sections for \process are consistent with previous results, but with improved precision. A combine fit to the cross section line shape is performed, which reveals contributions from two structures: the first one has a mass of $M=2174\pm23\pm4\unitmmev$ and a width of $\varGamma=207\pm49\pm5\unitemev$ and the second one has a mass of $M=2276\pm42\pm6\unitmmev$ and a width of $\varGamma=320\pm112\pm6\unitemev$, where the first uncertainties are statistical and the second systematic.