Invariant mass distributions in cascade decays

Abstract

We derive analytical expressions for the shape of the invariant mass distributions of massless Standard Model endproducts in cascade decays involving massive New Physics (NP) particles, D → Cc → Bbc → Aabc, where the final NP particle A in the cascade is unobserved and where two of the particles a, b, c may be indistinguishable. Knowledge of these expressions can improve the determination of NP parameters at the LHC. The shape formulas are composite, but contain nothing more complicated than logarithms of simple expressions. We study the effects of cuts, final state radiation and detector effects on the distributions through Monte Carlo simulations, using a supersymmetric model as an example. We also consider how one can deal with the width of NP particles and with combinatorics from the misidentification of final state particles. The possible mismeasurements of NP masses through "feet" in the distributions are discussed. Finally, we demonstrate how the effects of different spin configurations can be included in the distributions.

Distinguishing spins in decay chains at the large hadron collider

“…We derive simple analytical formulae for the correlation coefficients in terms of the masses in the decay chain, which should be of general use whatever the mass spectrum might turn out to be. These extend those already given in [4,10]. We show graphical results for two specific mass scenarios, one considered more probable in SUSY and the other in a UED model.…”

Interpreting a CMS excess inlljj+missing-transverse-momentum with the golden cascade of the minimal supersymmetric standard model

“…We use as free parameters the wino soft-mass M 2 , a common first and second generation 3 2 In this chain, theχ 0 2 decays through an off-shell Z, which does not predict an exact triangular dilepton distribution [5,6]. 3 CMS did not release a flavor decomposition of the events.…”

“…Higgsinos only couple extremely weakly to selectrons or smuons and so would result in rates that were far too small if they were involved in the chain. 5 Instead of fixing the Lagrangian parameters for the soft SUSY breaking Higgs mass parameters, we calculate them by minimizing the MSSM Higgs potential after fixing M A and the μ parameter to 3500 GeV [12].…”

Mass determination in SUSY-like events with missing energy

“…Many of these studies use the decay chainq →χ 0 2 q →lℓq →χ 0 1 ℓℓq (figure 1) that occurs for the benchmark point SPS1a [17], for which m e χ 0 1 ∼ 97 GeV, m e ℓ ∼ 143 GeV, m e χ 0 2 ∼ 180 GeV, m e b ∼ 570 GeV and m e g ∼ 610 GeV, see appendix B. The kinematic endpoints of the invariant mass distributions, m ℓℓ , m qℓℓ , m qℓ(high) , and m qℓ(low) , 1 depend on the masses of the super-particles in the decay chain through some complicated relations [9,10,18]. If the end points of these distributions can be accurately determined from the experimental data, we can invert the relations to obtain the masses of the super-particles.…”