arXiv subjects
Publications and source records attributed to H. H. Yang.
The Hidden Thresholds technique reconstructs New Physics (NP) masses from two or more simultaneous NP decays at a hadron collider. We show how this works in several MSSM examples: $\widetildeχ_{i}^0 \widetildeχ_{j}^0 \to e^+ e^- μ^+ μ^- \widetildeχ_{1}^0 \widetildeχ_{1}^0$ ($i,j=2,3,4$) and ${\widetildeχ_1}^\pm {\widetildeχ_2}^0 \to {W^\pm}^*(\to \ell^\pm ν) {\widetildeχ_1}^0 ~ {Z^0}^*(\to \ell^\pm \ell^\mp) {\widetildeχ_1}^0 $.
We present an improved method of reconstructing New Physics (NP) masses from invariant mass endpoints. While the traditional method focuses on a single NP decay, our method considers the decays of two or more NP particles ($ABC...$) in a grander decay chain: $ anything \to ABC... \to ... \to jets + leptons$. Though the center-of-mass energy $E_{CM}$ of `anything' varies unpredictably at a hadron collider, a sample of many events nonetheless expresses features of threshold production $E_{CM} = m_A + m_B + ...$: invariant masses constructed from the final jet and lepton momenta are correlated in a way that makes their threshold endpoints visually obvious in a scatterplot. We illustrate this technique for the production of two neutralinos in the MSSM: $anything \to \widetildeχ_{i}^0 \widetildeχ_{j}^0$ ($i,j=2,3,4$) which subsequently decay via on- or off-shell sleptons to four leptons. Assuming the relevant SUSY spectrum is below $1 TeV$ and squarks/gluinos eventually decay to neutralinos, our MC study shows that one low-luminosity year at the LHC ($10-30 fb^{-1}$) can quantitatively determine on- versus off-shell decays and find the relevant neutralino and slepton masses to less than 10 percent.
It is well known that finding and measuring the masses of particles in the Minimal Supersymmetric Standard Model (MSSM) at the Large Hadron Collider (LHC) may be possible using invariant mass distributions in exclusive channels containing n_j jets and n_l leptons. We perform this analysis for the (n_j, n_l) = (0,4) decay of heavy Higgs bosons to neutralinos, pp \to H/A \to χ_i χ_j (i,j =2,3,4), which then decay to four leptons and two lightest neutralinos χ_1 via on-shell sleptons. When i=j and the sleptons are degenerate, our Monte Carlo study shows that the LHC will be able to measure the Higgs and relevant neutralino and slepton masses to roughly 30%; however, if one of these is already known within 5%, the other three may be found to equal or better accuracy. This would provide the first accurate measurement of the H/A mass via invariant mass distribution techniques.