Finding physics signals with shower deconstruction

TL;DR

Shower deconstruction provides a general, information-rich framework for distinguishing hadronically decaying new physics signals from QCD background by computing the observable chi, the ratio of signal- to background- probabilities for a given microjet configuration, using a deliberately simplified but analytically tractable shower. Applied to boosted p p → HZ with H → bb, the method leverages fat jets and microjets, including Sudakov factors, ISR/UE, and Higgs decay probabilities, to outperform traditional approaches like BDRS in this scenario. The results demonstrate substantial discrimination capability and reveal sensitivity to the choice of event generator (Pythia vs. Herwig), underscoring the need for experimental validation and potential refinements. Overall, shower deconstruction is a modular, extensible approach that can be adapted to more complex signals and integrated with matrix-element ideas for robust hadronic new-physics searches.

Abstract

We introduce shower deconstruction, a method to look for new physics in a hadronic environment. The method aims to be a full information approach using small jets. It assigns to each event a number chi that is an estimate of the ratio of the probability for a signal process to produce that event to the probability for a background process to produce that event. The analytic functions we derive to calculate these probabilities mimic what full event generators like Pythia or Herwig do and can be depicted in a diagrammatic way. As an example, we apply this method to a boosted Higgs boson produced in association with a Z-boson and show that this method can be useful to discriminate this signal from the Z+jets background.

Figures (21)

• Figure 1: $d\sigma_\mathrm{MC}(\mathrm{B})/ d\log\chi$ for background events (upper curve) and $d\sigma_\mathrm{MC}(\mathrm{S})/ d\log\chi$ for signal events (lower curve) for samples of signal and background events generated by Pythia. We use the cuts described in Sec. \ref{['sec:EventSelection']}.
• Figure 2: Plot of $s/b$ versus $s$, where $s$ and $b$ are defined in Eq. (\ref{['eq:sandbdef']}). We use samples of signal and background events generated by Pythia as in Fig. \ref{['fig:SandBvschi']}.
• Figure 3: A shower history for a background event. The "star" vertex represents the production of a high $p_T$ parton from the hard interaction. The "diamond" vertices represent production of partons by initial state radiation. Each parton can split into two daughter partons at a shower vertex, represented by a small circle. In this background event, one of the gluons splits into a light $q$-$\bar{q}$ pair.
• Figure 4: A shower history for a signal event. The dashed line is the Higgs boson, produced in the hard interaction. It decays into a $b$-quark and a $\bar{b}$-quark, which carry arrows representing the flow of $b$-flavor. The QCD shower splitting of a $b$-quark is to a $b$-quark plus a gluon. In this event, one of the gluons splits into further gluons.
• Figure 5: A shower history for a background event in which a high $p_T$ gluon splits to a $b + \bar{b}$ pair. The QCD shower splitting of a $b$-quark is to a $b$-quark plus a gluon. The $b$ and $\bar{b}$ quarks radiate gluons and one of the gluons splits into two gluons.