507 research outputs found

    Draft genome sequence of the Tibetan antelope

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    The Tibetan antelope (Pantholops hodgsonii) is endemic to the extremely inhospitable high-altitude environment of the Qinghai-Tibetan Plateau, a region that has a low partial pressure of oxygen and high ultraviolet radiation. Here we generate a draft genome of this artiodactyl and use it to detect the potential genetic bases of highland adaptation. Compared with other plain-dwelling mammals, the genome of the Tibetan antelope shows signals of adaptive evolution and gene-family expansion in genes associated with energy metabolism and oxygen transmission. Both the highland American pika, and the Tibetan antelope have signals of positive selection for genes involved in DNA repair and the production of ATPase. Genes associated with hypoxia seem to have experienced convergent evolution. Thus, our study suggests that common genetic mechanisms might have been utilized to enable high-altitude adaptation

    Functional traits and phenotypic plasticity modulate species coexistence across contrasting climatic conditions

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    Functional traits are expected to modulate plant competitive dynamics. However, how traits and their plasticity in response to contrasting environments connect with the mechanisms determining species coexistence remains poorly understood. Here, we couple field experiments under two contrasting climatic conditions to a plant population model describing competitive dynamics between 10 annual plant species in order to evaluate how 19 functional traits, covering physiological, morphological and reproductive characteristics, are associated with species’ niche and fitness differences. We find a rich diversity of univariate and multidimensional associations, which highlight the primary role of traits related to water- and lightuse- efficiency for modulating the determinants of competitive outcomes. Importantly, such traits and their plasticity promote species coexistence across climatic conditions by enhancing stabilizing niche differences and by generating competitive trade-offs between species. Our study represents a significant advance showing how leading dimensions of plant function connect to the mechanisms determining the maintenance of biodiversity

    Observation of the electromagnetic Dalitz decay D∗0 →d0e+e-

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    Does or did the supernova remnant Cassiopeia A operate as a PeVatron?

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    For decades, supernova remnants (SNRs) have been considered the prime sources of Galactic Cosmic rays (CRs). But whether SNRs can accelerate CR protons to PeV energies and thus dominate CR flux up to the knee is currently under intensive theoretical and phenomenological debate. The direct test of the ability of SNRs to operate as CR PeVatrons can be provided by ultrahigh-energy (UHE; Eγ100E_\gamma \geq 100~TeV) γ\gamma-rays. In this context, the historical SNR Cassiopeia A (Cas A) is considered one of the most promising target for UHE observations. This paper presents the observation of Cas A and its vicinity by the LHAASO KM2A detector. The exceptional sensitivity of LHAASO KM2A in the UHE band, combined with the young age of Cas A, enabled us to derive stringent model-independent limits on the energy budget of UHE protons and nuclei accelerated by Cas A at any epoch after the explosion. The results challenge the prevailing paradigm that Cas A-type SNRs are major suppliers of PeV CRs in the Milky Way.Comment: 11 pages, 3 figures, Accepted by the APJ

    Measurement of ultra-high-energy diffuse gamma-ray emission of the Galactic plane from 10 TeV to 1 PeV with LHAASO-KM2A

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    The diffuse Galactic γ\gamma-ray emission, mainly produced via interactions between cosmic rays and the interstellar medium and/or radiation field, is a very important probe of the distribution, propagation, and interaction of cosmic rays in the Milky Way. In this work we report the measurements of diffuse γ\gamma-rays from the Galactic plane between 10 TeV and 1 PeV energies, with the square kilometer array of the Large High Altitude Air Shower Observatory (LHAASO). Diffuse emissions from the inner (15<l<12515^{\circ}<l<125^{\circ}, b<5|b|<5^{\circ}) and outer (125<l<235125^{\circ}<l<235^{\circ}, b<5|b|<5^{\circ}) Galactic plane are detected with 29.1σ29.1\sigma and 12.7σ12.7\sigma significance, respectively. The outer Galactic plane diffuse emission is detected for the first time in the very- to ultra-high-energy domain (E>10E>10~TeV). The energy spectrum in the inner Galaxy regions can be described by a power-law function with an index of 2.99±0.04-2.99\pm0.04, which is different from the curved spectrum as expected from hadronic interactions between locally measured cosmic rays and the line-of-sight integrated gas content. Furthermore, the measured flux is higher by a factor of 3\sim3 than the prediction. A similar spectrum with an index of 2.99±0.07-2.99\pm0.07 is found in the outer Galaxy region, and the absolute flux for 10E6010\lesssim E\lesssim60 TeV is again higher than the prediction for hadronic cosmic ray interactions. The latitude distributions of the diffuse emission are consistent with the gas distribution, while the longitude distributions show clear deviation from the gas distribution. The LHAASO measurements imply that either additional emission sources exist or cosmic ray intensities have spatial variations.Comment: 12 pages, 8 figures, 5 tables; accepted for publication in Physical Review Letters; source mask file provided as ancillary fil

    Amplitude analysis of Ds+π+ππ+D_s^{+} \rightarrow \pi^{+} \pi^{-} \pi^{+}

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    Utilizing the data set corresponding to an integrated luminosity of 3.193.19 fb1^{-1} collected by the BESIII detector at a center-of-mass energy of 4.178 GeV, we perform an amplitude analysis of the Ds+π+ππ+D_s^+\to\pi^+\pi^-\pi^+ decay. The sample contains 13,797 candidates with a signal purity of \sim80%. The amplitude and phase of the contributing ππ\pi\pi S{\cal S} wave are measured based on a quasi-model-independent approach, along with the amplitudes and phases of the P{\cal P} and D{\cal D} waves parametrized by Breit-Wigner models. The fit fractions of different intermediate decay channels are also reported.Comment: 14 pages, 6 figure

    Search for New Hadronic Decays of hch_c and Observation of hcK+Kπ+ππ0h_c\rightarrow K^{+}K^{-}\pi^{+}\pi^{-}\pi^{0}

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    Ten hadronic final states of the hch_c decays are investigated via the process ψ(3686)π0hc\psi(3686)\rightarrow \pi^0 h_c, using a data sample of (448.1±2.9)×106(448.1 \pm 2.9) \times 10^6 ψ(3686)\psi(3686) events collected with the BESIII detector. The decay channel hcK+Kπ+ππ0h_c\rightarrow K^{+}K^{-}\pi^{+}\pi^{-}\pi^{0} is observed for the first time with a significance of 6.0σ6.0 \sigma. The corresponding branching fraction is determined to be B(hcK+Kπ+ππ0)=(3.3±0.6±0.6)×103\mathcal{B}(h_c\rightarrow K^{+}K^{-}\pi^{+}\pi^{-}\pi^{0}) =(3.3 \pm 0.6 \pm 0.6)\times 10^{-3} (the first uncertainty is statistical and the second systematical). Evidence for the decays hcπ+ππ0ηh_c\rightarrow \pi^{+} \pi^{-} \pi^{0} \eta and hcKS0K±ππ+πh_c\rightarrow K^{0}_{S}K^{\pm}\pi^{\mp}\pi^{+}\pi^{-} is found with a significance of 3.6σ3.6 \sigma and 3.8σ3.8 \sigma, respectively. The corresponding branching fractions (and upper limits) are obtained to be B(hcπ+ππ0η)=(7.2±1.8±1.3)×103\mathcal{B}(h_c\rightarrow \pi^{+} \pi^{-} \pi^{0} \eta ) =(7.2 \pm 1.8 \pm 1.3)\times 10^{-3} (<1.8×102)(< 1.8 \times 10^{-2}) and B(hcKS0K±ππ+π)=(2.8±0.9±0.5)×103\mathcal{B}(h_c\rightarrow K^{0}_{S}K^{\pm}\pi^{\mp}\pi^{+}\pi^{-}) =(2.8 \pm 0.9 \pm 0.5)\times 10^{-3} (<4.7×103)(<4.7\times 10^{-3}). Upper limits on the branching fractions for the final states hcK+Kπ0h_c \rightarrow K^{+}K^{-}\pi^{0}, K+KηK^{+}K^{-}\eta, K+Kπ+πηK^{+}K^{-}\pi^{+}\pi^{-}\eta, 2(K+K)π02(K^{+}K^{-})\pi^{0}, K+Kπ0ηK^{+}K^{-}\pi^{0}\eta, KS0K±πK^{0}_{S}K^{\pm}\pi^{\mp}, and ppˉπ0π0p\bar{p}\pi^{0}\pi^{0} are determined at a confidence level of 90\%.Comment: 10 pages, 2 figure

    Study of the doubly Cabibbo-suppressed decays Ds+K+K+πD^+_s\to K^+K^+\pi^- and Ds+K+K+ππ0D^+_s\to K^+K^+\pi^-\pi^0

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    Based on 7.33 fb1^{-1} of e+ee^+e^- collision data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, the experimental studies of the doubly Cabibbo-suppressed decays Ds+K+K+πD^+_s\to K^+K^+\pi^- and Ds+K+K+ππ0D^+_s\to K^+K^+\pi^-\pi^0 are reported. We determine the absolute branching fraction of Ds+K+K+πD^+_s\to K^+K^+\pi^- to be (1.230.25+0.28(stat)±0.06(syst){1.23^{+0.28}_{-0.25}}({\rm stat})\pm0.06({\rm syst})) ×104\times 10^{-4}. No significant signal of Ds+K+K+ππ0D^+_s\to K^+K^+\pi^-\pi^0 is observed and the upper limit on its decay branching fraction at 90\% confidence level is set to be 1.7×1041.7\times10^{-4}.Comment: 10 pages, 4 figures, 4 table

    Observation of χcJΛΛˉη\chi_{cJ}\to \Lambda\bar \Lambda \eta

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    By analyzing (448.1±2.9)×106(448.1\pm2.9)\times10^6 ψ(3686)\psi(3686) events collected with the BESIII detector operating at the BEPCII collider, the decays of χcJΛΛˉη\chi_{cJ} \to \Lambda\bar \Lambda \eta (J=0J=0, 1 and 2) are observed for the first time with statistical significances of 13.9σ13.9\sigma, 6.7σ6.7\sigma, and 8.2σ8.2\sigma, respectively. The product branching fractions of ψ(3686)γχcJ\psi(3686)\to\gamma\chi_{cJ} and χcJΛΛˉη\chi_{cJ}\to \Lambda\bar \Lambda \eta are measured. Dividing by the world averages of the branching fractions of ψ(3686)γχcJ\psi(3686)\to\gamma\chi_{cJ}, the branching fractions of χcJΛΛˉη\chi_{cJ}\to \Lambda\bar \Lambda \eta decays are determined to be (2.31±0.30±0.21)×104(2.31\pm0.30\pm0.21)\times10^{-4}, (5.86±1.38±0.68)×105(5.86\pm1.38\pm0.68)\times10^{-5}, and (1.05±0.21±0.15)×104(1.05\pm0.21\pm0.15)\times10^{-4} for J=0J=0, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.Comment: 9 pages, 4 figure
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