Observation of γγ → ττ in proton-proton collisions and limits on the anomalous electromagnetic moments of the τ lepton

The production of a pair of τ leptons via photon–photon fusion, γγ → ττ, is observed for the f irst time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb−1. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of γγ → ττ is σfid obs = 12.4+3.8 −3.1 fb. Constraints are set on the contributions to the anomalous magnetic moment (aτ) and electric dipole moments (dτ) of the τ lepton originating from potential effects of new physics on the γττ vertex: aτ = 0.0009+0.0032 −0.0031 and |dτ| < 2.9×10−17ecm (95% confidence level), consistent with the standard model

The CMS HGCAL trigger data receiver

As part of the CMS Phase-2 upgrade, a prototype receiver for the HGCAL endcap front end has been implemented using the Serenity ATCA platform. The receiver firmware was developed to test the unpacking of data from the front-end endcap trigger concentrator ASIC (ECON-T) and measure its performance and stability. The firmware was integrated with prototype DAQ firmware as well as ancillary blocks to generate a trigger using ECON-T data, process scintillator trigger and timing distribution system, to evaluate the complete HGCAL vertical slice. The data was read out using custom 10G UDP links and upgraded to CMS DTH system at 25 Gbps. The system successfully achieved prototype TPG Stage-1 and DAQ path readout using generated beam triggers and delivered ~20 TB of data containing physics events at an average trigger rate of about 100 kHz

India as an emerging power in international climate negotiations

India's negotiation strategies in international climate policy have considerably changed over the past decade. While core positions have not altered substantially, the way they were presented and supported at the international level reveals major changes. In particular between 2007 and 2011, India's international climate policy shifted from defensive, pure distributive strategies toward mixed strategies with a number of ‘value-creating’ elements, dynamism and flexibility became clearly visible in India's international climate policy. This shift is confirmed by evidence from a novel dataset based on an assessment of country submissions at the UNFCCC negotiations, negotiation summaries and interviews with an Indian delegate and representatives of other delegations. India's change in strategy appears to be driven by several factors: developments in the national political landscape whereby the personality of the delegation leader and minister in charge plays a critical role, a general trend related to rising public awareness of India's vulnerability to climate change, increasing domestic energy constraints, direct economic benefits from the Kyoto Protocol's market mechanisms, reactions to international pressure from other developing countries, and increased reporting by domestic media