This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a ...minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations.
In this report we discuss appropriate strategies for the tracking of charged particles in the limit of zero curvature. The suggested approach avoids special treatments and precision issues that ...frequently arise in that limit. We provide explicit expressions for transport, refitting and vertexing in regions where magnetic field inhomogeneities or detector interaction effects can be approximately ignored.
In this white paper for the 2021 Snowmass process, we give a description of the proposed Future Circular Collider (FCC) project and its physics program. The paper summarizes and updates the ...discussion submitted to the European Strategy on Particle Physics. After construction of an approximately 90 km tunnel, an electron-positron collider based on established technologies allows world-record instantaneous luminosities at center-of-mass energies from the Z resonance up to tt thresholds, enabling a rich set of fundamental measurements including Higgs couplings determinations at the sub percent level, precision tests of the weak and strong forces, and searches for new particles, including dark matter, both directly and via virtual corrections or mixing. Among other possibilities, the FCC-ee will be able to (i) indirectly discover new particles coupling to the Higgs and/or electroweak bosons up to scales around 7 and 50 TeV, respectively; (ii) perform competitive SUSY tests at the loop level in regions not accessible at the LHC; (iii) study heavy-flavor and tau physics in ultra-rare decays beyond the LHC reach, and (iv) achieve the best potential in direct collider searches for dark matter, sterile neutrinos, and axion-like particles with masses up to around 90 GeV. The tunnel can then be reused for a proton-proton collider, establishing record center-of-mass collision energy, allowing unprecedented reach for direct searches for new particles up to the around 50 TeV scale, and a diverse program of measurements of the Standard Model and Higgs boson, including a precision measurement of the Higgs self-coupling, and conclusively testing weakly-interacting massive particle scenarios of thermal relic dark matter.
The Compact Muon Solenoid (CMS) experiment prepares its Phase-2 upgrade for the high-luminosity era of the LHC operation (HL-LHC). Due to the increase of occupancy, trigger latency and rates, the ...full electronics of the CMS Drift Tube (DT) chambers will need to be replaced. In the new design, the time bin for the digitization of the chamber signals will be of around 1 ns, and the totality of the signals will be forwarded asynchronously to the service cavern at full resolution. The new backend system will be in charge of building the trigger primitives of each chamber. These trigger primitives contain the information at chamber level about the muon candidates position, direction, and collision time, and are used as input in the L1 CMS trigger. The added functionalities will improve the robustness of the system against ageing. An algorithm based on analytical solutions for reconstructing the DT trigger primitives, called Analytical Method, has been implemented both as a software C++ emulator and in firmware. Its performance has been estimated using the software emulator with simulated and real data samples, and through hardware implementation tests. Measured efficiencies are 96 to 98% for all qualities and time and spatial resolutions are close to the ultimate performance of the DT chambers. A prototype chain of the HL-LHC electronics using the Analytical Method for trigger primitive generation has been installed during Long Shutdown 2 of the LHC and operated in CMS cosmic data taking campaigns in 2020 and 2021. Results from this validation step, the so-called Slice Test, are presented.
We classify the possible deviations from the Standard Model in the QED-dominated \(\mathrm{e^+e^-}\rightarrow\gamma\gamma\) process under the assumption of a preserved \(SU(2)_L \times U(1)_Y\) ...symmetry. We find that the only deviations really observable in practice correspond to a correction of the differential cross section by a factor \((1 + \frac{c_8~s^2}{8\pi\alpha\Lambda^4}~\sin^2\theta)\), where \(\Lambda\) is the scale of new physics, \(\theta\) is the polar angle of any of the final state photons and \(c_8\) is a constant of order 1. We also provide sensitivity estimates for QED deviations at future \(\mathrm{e^+e^-}\) facilities. An \(\mathrm{e^+e^-}\) collider operating at \(\sqrt{s}=3\) TeV could provide sensitivity to \(\Lambda\) scales as large as 15 TeV, provided that acceptances and efficiencies are controlled at the per mille level. Finally, we also discuss the possibility of a measurement of the luminosity at the FCC-ee with \(\lesssim 10^{-4}\) precision, using analyses of the \(\mathrm{e^+e^-}\rightarrow\gamma\gamma\) process at \(\sqrt{s}\approx m_\mathrm{Z}\) energies.
We classify the possible deviations from the Standard Model in the
QED-dominated $\mathrm{e^+e^-}\rightarrow\gamma\gamma$ process under the
assumption of a preserved $SU(2)_L \times U(1)_Y$ symmetry. ...We find that the
only deviations really observable in practice correspond to a correction of the
differential cross section by a factor $(1 +
\frac{c_8~s^2}{8\pi\alpha\Lambda^4}~\sin^2\theta)$, where $\Lambda$ is the
scale of new physics, $\theta$ is the polar angle of any of the final state
photons and $c_8$ is a constant of order 1. We also provide sensitivity
estimates for QED deviations at future $\mathrm{e^+e^-}$ facilities. An
$\mathrm{e^+e^-}$ collider operating at $\sqrt{s}=3$ TeV could provide
sensitivity to $\Lambda$ scales as large as 15 TeV, provided that acceptances
and efficiencies are controlled at the per mille level. Finally, we also
discuss the possibility of a measurement of the luminosity at the FCC-ee with
$\lesssim 10^{-4}$ precision, using analyses of the
$\mathrm{e^+e^-}\rightarrow\gamma\gamma$ process at $\sqrt{s}\approx
m_\mathrm{Z}$ energies.
The transverse momentum spectra of charged particles have been measured in pp and PbPb collisions at \(\sqrt{s_{NN}}=2.76~\mathrm{TeV}\) by the CMS experiment at the LHC. In the transverse momentum ...range pT=5–10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 7 compared to the pp yield scaled by the number of incoherent nucleon–nucleon collisions. At higher pT, this suppression is significantly reduced, approaching roughly a factor of 2 for particles with pT in the range pT=40–100 GeV/c.
In order to stimulate new engagement and trigger some concrete studies in areas where further work would be beneficial towards fully understanding the physics potential of an \(e^+e^-\) Higgs / Top / ...Electroweak factory, we propose to define a set of focus topics. The general reasoning and the proposed topics are described in this document.
The 2011 Les Houches workshop was the first to confront LHC data. In the two years since the previous workshop there have been significant advances in both soft and hard QCD, particularly in the ...areas of multi-leg NLO calculations, the inclusion of those NLO calculations into parton shower Monte Carlos, and the tuning of the non-perturbative parameters of those Monte Carlos. These proceedings describe the theoretical advances that have taken place, the impact of the early LHC data, and the areas for future development.
The CMS drift tubes (DT) muon detector, built for withstanding the LHC expected integrated and instantaneous luminosities, will be used also in the High Luminosity LHC (HL-LHC) at a 5 times larger ...instantaneous luminosity and, consequently, much higher levels of radiation, reaching about 10 times the LHC integrated luminosity. Initial irradiation tests of a spare DT chamber at the CERN gamma irradiation facility (GIF++), at large (\(\sim\)O(100)) acceleration factor, showed ageing effects resulting in a degradation of the DT cell performance. However, full CMS simulations have shown almost no impact in the muon reconstruction efficiency over the full barrel acceptance and for the full integrated luminosity. A second spare DT chamber was moved inside the GIF++ bunker in October 2017. The chamber was being irradiated at lower acceleration factors, and only 2 out of the 12 layers of the chamber were switched at working voltage when the radioactive source was active, being the other layers in standby. In this way the other non-aged layers are used as reference and as a precise and unbiased telescope of muon tracks for the efficiency computation of the aged layers of the chamber, when set at working voltage for measurements. An integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC run has been absorbed by this second spare DT chamber and the final impact on the muon reconstruction efficiency is under study. Direct inspection of some extracted aged anode wires presented a melted resistive deposition of materials. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway. Strategies to mitigate the ageing effects are also being developed. From the long irradiation measurements of the second spare DT chamber, the effects of radiation in the performance of the DTs expected during the HL-LHC run will be presented.
PDF
