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arxiv: 2511.16394 · v4 · pith:HIR2HNYJnew · submitted 2025-11-20 · ✦ hep-ex

Search for Higgsinos in final states with low-momentum lepton-track pairs at 13 TeV

CMS Collaboration This is my paper

Pith reviewed 2026-05-21 19:16 UTC · model grok-4.3

classification ✦ hep-ex
keywords HiggsinoSupersymmetryNeutralinoMissing transverse momentumLepton trackCMS13 TeV
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The pith

CMS excludes Higgsino masses up to 115 GeV by searching for nearly mass-degenerate neutralinos decaying via low-momentum lepton pairs.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents a search for pair production of Higgsinos in proton-proton collisions, targeting final states with large missing transverse momentum and either two reconstructed muons or one lepton plus an isolated track. The signal model features four nearly degenerate higgsino states where the heavier neutralino decays to the lighter one plus a virtual Z boson that produces same-flavor leptons with small transverse momentum or small opening angle. This approach explores a previously inaccessible region of parameter space with mass differences between the neutralinos as low as 1.5 GeV for a 100 GeV Higgsino. A sympathetic reader cares because the result places direct constraints on supersymmetric models that predict compressed spectra, using the full 137 fb inverse of 13 TeV data collected by CMS.

Core claim

No significant excess is observed over the expected Standard Model backgrounds. The search excludes Higgsino masses up to 115 GeV assuming a mass of 100 GeV, while probing mass differences between the two neutralinos down to 1.5 GeV. Multivariate discriminants trained on simulation and data control regions are used to reject backgrounds from SM processes and misreconstructed tracks or leptons in the low transverse momentum regime.

What carries the argument

The combination of an isolated track with a reconstructed lepton (or two muons) to recover events from virtual Z boson decays with small opening angle or low pT, together with multivariate discriminants that separate signal from backgrounds.

If this is right

  • Higgsino production in the compressed mass spectrum is ruled out up to 115 GeV.
  • The technique opens sensitivity to mass splittings smaller than those accessible in prior searches.
  • Future runs with more data can extend the exclusion to higher masses or smaller splittings.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar low-momentum track-plus-lepton selections could be applied to other compressed supersymmetry models beyond the pure Higgsino case.
  • Combining this result with direct production searches at future colliders would further constrain the full set of higgsino states.

Load-bearing premise

The multivariate discriminants correctly model and reject backgrounds from Standard Model processes and misreconstructed tracks or leptons in the low transverse momentum regime without significant bias in the signal region.

What would settle it

A statistically significant excess of events in the signal regions above the predicted background yield would indicate a signal and falsify the background-only hypothesis.

Figures

Figures reproduced from arXiv: 2511.16394 by CMS Collaboration.

Figure 1
Figure 1. Figure 1: Diagrams illustrating the production and decay of electroweakinos in the Higgsino [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Unweighted distributions of the event-level BDT scores for events from the signal [PITH_FULL_IMAGE:figures/full_fig_p008_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Distributions of the reconstructed ditau invariant mass ( [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Prefit expected and observed distributions of the event BDT output score in the SRs [PITH_FULL_IMAGE:figures/full_fig_p012_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Prefit expected and observed distributions of the event BDT output score in the SRs [PITH_FULL_IMAGE:figures/full_fig_p013_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: The 95% CL upper limits on the fully degenerate Higgsino production cross section, [PITH_FULL_IMAGE:figures/full_fig_p014_6.png] view at source ↗
read the original abstract

We present a search for the pair production of Higgsinos in final states with large missing transverse momentum and either two reconstructed muons or a reconstructed lepton (muon or electron) and an isolated track. The analyzed data correspond to proton-proton collisions with an integrated luminosity of 137 fb$^{-1}$, collected by the CMS experiment at $\sqrt{s}$ = 13 TeV in 2016, 2017, and 2018. The signal scenario assumes four nearly mass degenerate higgsino mass eigenstates, two neutralino states, $\widetilde{\chi}^0_2$ and $\widetilde{\chi}^0_1$, with a small mass difference in the range 1$-$10 GeV and two chargino states $\widetilde{\chi}^\pm_1$ with an intermediate mass. The analysis focuses on the decay of the heavier neutralino into the lighter one and a virtual Z boson, which decays into two same-flavor leptons. The leptons have small transverse momentum and/or a small opening angle between the identified muons. An isolated track is used to recover events in which only one of the two leptons is identified. Multivariate discriminants are used to enhance the sensitivity by efficiently rejecting backgrounds from SM processes or misreconstructed tracks and/or leptons. The search explores a unique phase space and probes a previously unexplored region of the signal model parameter space. Mass differences between the two neutralinos are probed down to 1.5 GeV, assuming a Higgsino mass of 100 GeV. The maximum excluded Higgsino mass is 115 GeV.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript presents a CMS search for pair production of Higgsinos using 137 fb^{-1} of 13 TeV proton-proton collision data collected in 2016-2018. The analysis targets final states with large missing transverse momentum and either two low-momentum same-flavor muons or a lepton plus an isolated track, focusing on small mass splittings (1-10 GeV) between the two lightest neutralinos. Multivariate discriminants are used to suppress Standard Model backgrounds and misreconstruction effects, with the search claiming sensitivity to mass differences as low as 1.5 GeV for a 100 GeV Higgsino and exclusion of Higgsino masses up to 115 GeV.

Significance. If the background modeling holds, the result is significant for extending experimental reach into compressed supersymmetry scenarios that are challenging for conventional searches due to soft leptons and small opening angles. The use of isolated tracks to recover efficiency and data-driven background estimation are constructive elements that address typical limitations in low-pT regimes. This provides new constraints on nearly mass-degenerate Higgsino models beyond previous exclusions.

major comments (2)
  1. [Multivariate analysis and background estimation] Multivariate discriminants section: The central sensitivity claim (probing delta m down to 1.5 GeV and excluding up to 115 GeV) depends on the MVA correctly rejecting backgrounds from soft tracks, fake leptons, and pileup without residual bias when extrapolating from simulation plus control regions to the low-pT signal region; additional validation showing data-simulation agreement in sidebands or control regions extrapolated to the signal phase space is needed to substantiate this.
  2. [Results] Results and limit-setting section: The quoted maximum excluded Higgsino mass of 115 GeV and the 1.5 GeV mass-difference reach assume that systematic uncertainties on track reconstruction, lepton identification, and MVA response are fully propagated and do not degrade the exclusion; a table or figure quantifying the impact of these uncertainties on the final limits would strengthen the result.
minor comments (2)
  1. [Abstract] The abstract states the mass difference range as 1-10 GeV but the probed minimum is given as 1.5 GeV; a brief clarification on the exact parameter scan range and how the 1.5 GeV value is determined would improve clarity.
  2. [Throughout] Figure captions and text should explicitly define the 'Higgsino mass' used for the exclusion (e.g., mass of the lightest neutralino or average of the states) to avoid ambiguity in interpreting the 115 GeV limit.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive review and positive assessment of the search's significance in compressed Higgsino scenarios. We address the major comments point by point below and have revised the manuscript to incorporate additional material where it strengthens the presentation.

read point-by-point responses

  1. Referee: [Multivariate analysis and background estimation] Multivariate discriminants section: The central sensitivity claim (probing delta m down to 1.5 GeV and excluding up to 115 GeV) depends on the MVA correctly rejecting backgrounds from soft tracks, fake leptons, and pileup without residual bias when extrapolating from simulation plus control regions to the low-pT signal region; additional validation showing data-simulation agreement in sidebands or control regions extrapolated to the signal phase space is needed to substantiate this.

    Authors: We agree that explicit validation of the MVA extrapolation is valuable in this low-pT regime. The original manuscript already employs data-driven background estimation in control regions and reports data-simulation agreement for key variables. To directly address the request, the revised version adds two new figures in an appendix: one showing MVA score distributions in sideband regions enriched in soft tracks and fake leptons, and a second comparing data and simulation after extrapolation to the signal-like phase space (low pT, small opening angle). These confirm agreement within uncertainties and no evidence of residual bias affecting the sensitivity claim. revision: yes

  2. Referee: [Results] Results and limit-setting section: The quoted maximum excluded Higgsino mass of 115 GeV and the 1.5 GeV mass-difference reach assume that systematic uncertainties on track reconstruction, lepton identification, and MVA response are fully propagated and do not degrade the exclusion; a table or figure quantifying the impact of these uncertainties on the final limits would strengthen the result.

    Authors: We concur that a quantitative breakdown of systematic effects on the final limits improves clarity. The revised manuscript includes a new table (Table X) that lists the individual and combined impact of the dominant systematics—track reconstruction efficiency, lepton identification, MVA response, and others—on both the maximum excluded Higgsino mass and the lowest probed mass difference. A companion figure shows the 95% CL exclusion contour with statistical uncertainties only versus the full set of uncertainties, demonstrating that the systematics reduce the reach by less than 5 GeV in mass and do not alter the 1.5 GeV mass-difference sensitivity at 100 GeV. revision: yes

Circularity Check

0 steps flagged

No significant circularity in experimental search analysis

full rationale

This is an experimental search paper from the CMS Collaboration reporting observed limits on Higgsino production from 137 fb^{-1} of 13 TeV LHC data. The analysis chain proceeds from event reconstruction and selection in low-pT lepton-track final states, through multivariate discriminants trained on simulation plus control regions for background rejection, to statistical comparison of observed yields against expected backgrounds and signal Monte Carlo. No equations, parameters, or derivations reduce the quoted mass exclusions or probed mass differences (down to 1.5 GeV at 100 GeV) to fitted inputs by construction, self-definition, or self-citation load-bearing. The result remains externally falsifiable via the published data, methods, and independent background modeling checks, making the derivation self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The paper is an experimental search that relies on established detector simulation, Standard Model background modeling, and reconstruction efficiencies rather than introducing new free parameters or postulated entities beyond the signal hypothesis under test.

axioms (2)
  • domain assumption Standard Model processes and misreconstructed objects constitute the dominant backgrounds in the selected phase space.
    Invoked to justify background estimation via multivariate discriminants and control regions.
  • domain assumption Detector response and reconstruction efficiencies for low-pT leptons and isolated tracks are accurately modeled in simulation.
    Required for calculating signal acceptance and efficiency in the compressed spectrum.

pith-pipeline@v0.9.0 · 5819 in / 1382 out tokens · 93913 ms · 2026-05-21T19:16:15.312990+00:00 · methodology

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