Search for physics beyond the standard model in final states with a lepton and missing transverse energy in proton-proton collisions at sqrt(s) = 8 TeV

TL;DR

<3-5 sentence high-level summary> The CMS search targets beyond-Standard-Model physics in final states with a high-$p_T$ lepton and missing transverse energy by examining the transverse-mass distribution in 8 TeV proton-proton collisions. It employs a broad suite of signal models, including a Sequential Standard Model $W'$, helicity-non-conserving contact interactions, dark matter production with a recoiling $W$, split-UED, and TeV$^{-1}$ extra dimensions, with careful treatment of interference effects where relevant. No significant deviations from the SM prediction are observed, leading to 95% CL exclusions such as $M_{W'}^{SSMS,combined}=4.00$ TeV and $M_{W'}^{SSMO,combined}=3.71$ TeV, among others; the results also constrain DM EFT scales and extra-dimensional parameters. The study demonstrates the importance of shape information, higher-order corrections, and data-driven background estimation in tightening limits on a diverse set of BSM scenarios at the LHC.

Abstract

A search for new physics in proton-proton collisions having final states with an electron or muon and missing transverse energy is presented. The analysis uses data collected in 2012 with the CMS detector, at an LHC center-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of 19.7 inverse femtobarns. No significant deviation of the transverse mass distribution of the charged lepton-neutrino system from the standard model prediction is found. Mass exclusion limits of up to 3.28 TeV at a 95% confidence level for a W' boson with the same couplings as that of the standard model W boson are determined. Results are also derived in the framework of split universal extra dimensions, and exclusion limits on Kaluza-Klein W[KK,2] states are found. The final state with large missing transverse energy also enables a search for dark matter production with a recoiling W boson, with limits set on the mass and the production cross section of potential candidates. Finally, limits are established for a model including interference between a left-handed W' boson and the standard model W boson, and for a compositeness model.

Figures (20)

• Figure 1: Production and decay of an SSM ${W}^\prime$ or ${W}_\mathrm{KK}$ boson (left); HNC-CI (center); DM single $\mathrm{W}$ boson production (right).
• Figure 2: Feynman diagrams for dark matter interference, shown as an example with an up and a down quark. The same initial and final state can have different particles coupling to the dark matter particles.
• Figure 3: Signal shapes at generator level: SSM model compared to the SSMS and SSMO models for $g_{{W}^\prime\xspace}/g_{\mathrm{W}\xspace}=1$ (top left); HNC-CI model for various values of $\Lambda$ (top right); DM for various values of $\xi$ (middle left); ${W}^\prime$ with $\mathrm{W}$ boson interference and a varying coupling strength $g_{\mathrm{W}}/g_{{W}^\prime\xspace}$ in the same sign scenario (middle right); and TeV$^{\mathrm{-1}}$ model (bottom).
• Figure 4: The distribution in $p_{\mathrm{T}}$/$E_{\mathrm{T}}^{\text{miss}}$ (top) and $\Delta \phi(\ell,\vec{p}_{\text{T}}^{\text{miss}}\xspace)$ (bottom), for data, background, and some signals in the muon channel with an $M_\mathrm{T}$ threshold of 220$\,\text{Ge\spaceV}$. The simulated background labeled as 'diboson' includes $\mathrm{W}\mathrm{W}$, ${Z}\xspace{Z}\xspace$ and $\mathrm{W}{Z}\xspace$ contributions, while 'DY' denotes the Drell--Yan process.
• Figure 5: Observed $M_\mathrm{T}$ distributions for the electron (top) and muon (bottom) channels. The horizontal bars on the data points indicate the widths of the bins. The asymmetric error bars indicate the central confidence intervals for Poisson-distributed data and are obtained from the Neyman construction as described in Ref. Garwood1936.