Multidifferential study of identified charged hadron distributions in ZZ-tagged jets in proton-proton collisions at s=\sqrt{s}=13 TeV

Jet fragmentation functions are measured for the first time in proton-proton collisions for charged pions, kaons, and protons within jets recoiling against a $Z$ boson. The charged-hadron distributions are studied longitudinally and transversely to the jet direction for jets with transverse momentum 20 $< p_{\textrm{T}} < 100$ GeV and in the pseudorapidity range $2.5 < \eta < 4$. The data sample was collected with the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.64 fb$^{-1}$. Triple differential distributions as a function of the hadron longitudinal momentum fraction, hadron transverse momentum, and jet transverse momentum are also measured for the first time. This helps constrain transverse-momentum-dependent fragmentation functions. Differences in the shapes and magnitudes of the measured distributions for the different hadron species provide insights into the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb public pages

Study of the B−→Λc+Λˉc−K−B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-} decay

The decay $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV using data corresponding to an integrated luminosity of 5 $\mathrm{fb}^{-1}$ collected by the LHCb experiment. In the $\Lambda_{c}^+ K^{-}$ system, the $\Xi_{c}(2930)^{0}$ state observed at the BaBar and Belle experiments is resolved into two narrower states, $\Xi_{c}(2923)^{0}$ and $\Xi_{c}(2939)^{0}$, whose masses and widths are measured to be $$m(\Xi_{c}(2923)^{0}) = 2924.5 \pm 0.4 \pm 1.1 \,\mathrm{MeV}, \\ m(\Xi_{c}(2939)^{0}) = 2938.5 \pm 0.9 \pm 2.3 \,\mathrm{MeV}, \\ \Gamma(\Xi_{c}(2923)^{0}) = \phantom{000}4.8 \pm 0.9 \pm 1.5 \,\mathrm{MeV},\\ \Gamma(\Xi_{c}(2939)^{0}) = \phantom{00}11.0 \pm 1.9 \pm 7.5 \,\mathrm{MeV},$$ where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt $\Lambda_{c}^{+} K^{-}$ sample. Evidence of a new $\Xi_{c}(2880)^{0}$ state is found with a local significance of $3.8\,\sigma$, whose mass and width are measured to be $2881.8 \pm 3.1 \pm 8.5\,\mathrm{MeV}$ and $12.4 \pm 5.3 \pm 5.8 \,\mathrm{MeV}$, respectively. In addition, evidence of a new decay mode $\Xi_{c}(2790)^{0} \to \Lambda_{c}^{+} K^{-}$ is found with a significance of $3.7\,\sigma$. The relative branching fraction of $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ with respect to the $B^{-} \to D^{+} D^{-} K^{-}$ decay is measured to be $2.36 \pm 0.11 \pm 0.22 \pm 0.25$, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb public pages

Measurement of the ratios of branching fractions R(D∗)\mathcal{R}(D^{*}) and R(D0)\mathcal{R}(D^{0})

The ratios of branching fractions $\mathcal{R}(D^{*})\equiv\mathcal{B}(\bar{B}\to D^{*}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}\to D^{*}\mu^{-}\bar{\nu}_{\mu})$ and $\mathcal{R}(D^{0})\equiv\mathcal{B}(B^{-}\to D^{0}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(B^{-}\to D^{0}\mu^{-}\bar{\nu}_{\mu})$ are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb${ }^{-1}$ of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $\tau^{-}\to\mu^{-}\nu_{\tau}\bar{\nu}_{\mu}$. The measured values are $\mathcal{R}(D^{*})=0.281\pm0.018\pm0.024$ and $\mathcal{R}(D^{0})=0.441\pm0.060\pm0.066$, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is $\rho=-0.43$. Results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb public pages

Militias in Civil Wars

Militias are an empirical phenomenon that has been overlooked by current research on civil war. Yet, it is a phenomenon that is crucial for understanding political violence, civil war, post-conflict politics, and authoritarianism. Militias or paramilitaries are armed groups that operate alongside regular security forces or work independently of the state to shield the local population from insurgents. We review existing uses of the term, explore the range of empirical manifestations of militias, and highlight recent findings, including those supplied by the articles in this special issue. We focus on areas where the recognition of the importance of militias challenges and complements current theories of civil war. We conclude by introducing a research agenda advocating the integrated study of militias and rebel groups

Large Scale Land Acquisition as Commons Grabbing: A comparative study on cases from Africa

We discuss the results of two research projects carried out by the Institute of Social Anthropology and Geography, University of Bern (Switzerland) regarding large-scale land acquisitions in Africa. Our case-studies are form Morocco, Ghana, Sierra Leone, Kenya, Tanzania, and Malawi. They illustrate the drama of the grabbed commons and economic consequences affecting marginalized groups. The results show that new land deals were made by foreign investors with local state officials and elites. The new rules made the land available for market-oriented productions and transferred the assets into state- or local elites- and international companies-owned properties. These changes adversily affected the traditional property rights scheme. New institutional changes eliminated communal ownership and access to other land-related commons such as water, pasture, fisheries, forestry, non-timber forest products, and wildlife vital for local livelihoods. We analyze how different local groups reacted to these dramas and what strategies they used to reinstall the commons, although with mixed success. Finally, we argue that only bottom-up institutional buildup provides essential basis for securing resilient livelihoods. Our studies allow for understanding the way how to use the commons in the future on local, national, and international level

Search for A′→μ+μ−A'\to\mu^+\mu^- Decays

International audienceSearches are performed for both promptlike and long-lived dark photons, A′, produced in proton-proton collisions at a center-of-mass energy of 13 TeV. These searches look for A′→μ+μ- decays using a data sample corresponding to an integrated luminosity of 5.5  fb-1 collected with the LHCb detector. Neither search finds evidence for a signal, and 90% confidence-level exclusion limits are placed on the γ–A′ kinetic mixing strength. The promptlike A′ search explores the mass region from near the dimuon threshold up to 70 GeV and places the most stringent constraints to date on dark photons with 214<m(A′)≲740  MeV and 10.6<m(A′)≲30  GeV. The search for long-lived A′→μ+μ- decays places world-leading constraints on low-mass dark photons with lifetimes O(1)  ps

Measurement of Ξcc++\mathit{\Xi}_{cc}^{++} production in pppp collisions at s=13\sqrt{s}=13 TeV

International audienceThe production of baryons in proton-proton collisions at a centre-of-mass energy of is measured in the transverse-momentum range and the rapidity range . The data used in this measurement correspond to an integrated luminosity of , recorded by the LHCb experiment during 2016. The ratio of the production cross-section times the branching fraction of the decay relative to the prompt production cross-section is found to be , assuming the central value of the measured lifetime, where the first uncertainty is statistical and the second systematic