Constrained S ^ min $$ \sqrt{{\widehat{S}}_{\min }} $$ and reconstructing with semi-invisible production at hadron colliders

Abstract:We have recently established a new method for measuring the mass of unstable particles produced at hadron colliders based on the analysis of the energy distribution of a massless product from their two-body decays. The central ingredient of our proposal is the remarkable result that, for an unpolarized decaying particle, the location of the peak in the energy distribution of the observed decay product is identical to the (fixed) value of the energy that this particle would have in the rest-frame of the decaying particle, which, in turn, is a simple function of the involved masses. In addition, we utilized the property that this energy distribution is symmetric around the location of peak when energy is plotted on a logarithmic scale. The general strategy was demonstrated in several specific cases, including both beyond the standard model particles, as well as for the top quark. In the present work, we generalize this method to the case of a massive decay product from a two-body decay; this procedure is far from trivial because (in general) both the abovementioned properties are no longer valid. Nonetheless, we propose a suitably modified parametrization of the energy distribution that was used successfully for the massless case, which can deal with the massive case as well. We test this parametrization on concrete examples of energy spectra of Z bosons from the decay of a heavier supersymmetric partner of top quark (stop) into a Z boson and a lighter stop. After establishing the accuracy of this parametrization, we study a realistic application for the same process, but now including dominant backgrounds and using foreseeable statistics at LHC14, in order to determine the performance of this method for an actual mass measurement. The upshot of our present and previous work is that, in spite of energy being a Lorentz-variant quantity, its distribution emerges as a powerful tool for mass measurement at hadron colliders.

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“…See also references [56][57][58][59][60][62][63][64][65][66] for other kinematic methods for mass measurement,…”

Section: Jhep04(2016)151mentioning

confidence: 99%

Energy spectra of massive two-body decay products and mass measurement

Agashe

Franceschini

Hong

et al. 2016

J. High Energ. Phys.

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“…Operationally the values are assigned by extremizing some relevant function of the invisible momenta. Often the minimum of the function itself becomes a useful kinematic variable -some well-known examples include the Cambridge M T 2 variable [28,29] and its variants [30][31][32][33], the √ s min variable [34][35][36], a variety of constrained transverse mass variables [37][38][39][40], the M CT 2 variable [41,42], the M 2C variable [43,44], the MAOS method [45][46][47][48], the M 2 class of variables [49][50][51][52][53][54][55][56], etc. While this approach has useful practical applications, it still only represents an approximate treatment and does not lead to a mass reconstruction through a bump.…”

Section: Introductionmentioning

confidence: 99%

Kinematic focus point method for particle mass measurements in missing energy events

Kim

Matchev

Shyamsundar

2019

J. High Energ. Phys.

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We investigate the solvability of the event kinematics in missing energy events at hadron colliders, as a function of the particle mass ansatz. To be specific, we reconstruct the neutrino momenta in dilepton tt-like events, without assuming any prior knowledge of the mass spectrum. We identify a class of events, which we call extreme events, with the property that the kinematic boundary of their allowed region in mass parameter space

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“…which is known [36] to provide the link between transverse invariant mass variables (like the transverse mass m T , the Cambridge m T 2 and others) and their respective 3+1 dimensional analogues [57][58][59][60][61][62][63][64][65][66][67][68]. In order to cast the singularity condition in the desired form (1.1), we must eliminate the invisible 4-momentum q by using four out of the five equations appearing in eqs.…”

Section: Derivation Of a Singularity Coordinatementioning

confidence: 99%

Singularity variables for missing energy event kinematics

Matchev

Shyamsundar

2020

J. High Energ. Phys.

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We discuss singularity variables which are properly suited for analyzing the kinematics of events with missing transverse energy at the LHC. We consider six of the simplest event topologies encountered in studies of leptonic W -bosons and top quarks, as well as in SUSY-like searches for new physics with dark matter particles. In each case, we illustrate the general prescription for finding the relevant singularity variable, which in turn helps delineate the visible parameter subspace on which the singularities are located. Our results can be used in two different ways -first, as a guide for targeting the signal-rich regions of parameter space during the stage of discovery, and second, as a sensitive focus point method for measuring the particle mass spectrum after the initial discovery. 4 The only exception being an invisibly decaying Z-boson, or a leptonically decaying W -boson where the lepton is lost [26].5 For reviews of the large variety of mass measurement methods proposed for SUSY-like events with MET, see [27,28] and references therein.

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Constrained S ^ min $$ \sqrt{{\widehat{S}}_{\min }} $$ and reconstructing with semi-invisible production at hadron colliders

Cited by 17 publications

References 68 publications

Energy spectra of massive two-body decay products and mass measurement

Energy spectra of massive two-body decay products and mass measurement

Kinematic focus point method for particle mass measurements in missing energy events

Singularity variables for missing energy event kinematics

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