CMS-PAS-EXO-24-028

CMS-PAS-EXO-24-028
Search for microscopic black holes and sphalerons in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
CMS Collaboration
2025-10-06

Abstract: A search for microscopic black holes and sphalerons using proton-proton collisions at $ \sqrt{s} = $ 13 TeV recorded by the CMS detector during the 2016-2018 data taking, and corresponding to an integrated luminosity of 138 fb$^{-1} $, is presented. Two data-driven search strategies are used. Model independent limits on the cross section of a new physics signal with multiple jets and leptons are set using a method that relies on the shape invariance of the scalar sum of the transverse momenta of all objects in the event. Model dependent limits on black hole and sphaleron production are set using a newly introduced method that has been developed for the identification of collider events with distinct kinematic features by separating them into classes based on phase-space proximity. In the context of models with large extra dimensions, semiclassical black holes with masses below 9.0-11.4 TeV are excluded, significantly extending the reach in comparison to limits from previous searches. At 95% confidence limit, more than 3 extra dimensions are excluded for most models probed. Results of a dedicated search for electroweak sphalerons are used to derive an upper limit of 0.0025 at 95% confidence level on the fraction of all quark-quark interactions above the nominal threshold of 9 TeV energy for the sphaleron transition.
Links: CDS record (PDF) ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The $ S_\text{T} $ distribution (left) and sphericity distribution (right) for various black hole (with $ n = $ 2) and sphaleron signal models, together with simulated QCD multijet background.
png pdf	Figure 1-a: The $ S_\text{T} $ distribution (left) and sphericity distribution (right) for various black hole (with $ n = $ 2) and sphaleron signal models, together with simulated QCD multijet background.
png pdf	Figure 1-b: The $ S_\text{T} $ distribution (left) and sphericity distribution (right) for various black hole (with $ n = $ 2) and sphaleron signal models, together with simulated QCD multijet background.
png pdf	Figure 2: SVM score distributions for simulated QCD multijets and selected black hole (with $ n = $ 2) and sphaleron models, before (left) and after (right) the sphericity requirement.
png pdf	Figure 2-a: SVM score distributions for simulated QCD multijets and selected black hole (with $ n = $ 2) and sphaleron models, before (left) and after (right) the sphericity requirement.
png pdf	Figure 2-b: SVM score distributions for simulated QCD multijets and selected black hole (with $ n = $ 2) and sphaleron models, before (left) and after (right) the sphericity requirement.
png pdf	Figure 3: The SVM score vs. the $ S_\text{T} $ distributions for simulated QCD multijet background (left) and a black hole signal model with $ M_\text{D} = $ 2 TeV, $ M_\text{BH} = $ 10 TeV and $ n = $ 2 (right).
png pdf	Figure 3-a: The SVM score vs. the $ S_\text{T} $ distributions for simulated QCD multijet background (left) and a black hole signal model with $ M_\text{D} = $ 2 TeV, $ M_\text{BH} = $ 10 TeV and $ n = $ 2 (right).
png pdf	Figure 3-b: The SVM score vs. the $ S_\text{T} $ distributions for simulated QCD multijet background (left) and a black hole signal model with $ M_\text{D} = $ 2 TeV, $ M_\text{BH} = $ 10 TeV and $ n = $ 2 (right).
png pdf	Figure 4: The $ S_\text{T} $ distribution in the SI-VR region in data, indicated by the black markers. The background prediction is represented by the red line, and the gray band corresponds to the background modeling uncertainty.
png pdf	Figure 5: Post-fit $ S_\text{T} $ distributions in the PS-VR-FAIL (left) and PS-VR-PASS (right) regions in data. The gray shaded areas include both statistical and systematic uncertainties on the background prediction. The red line corresponds to the signal model with B1, $ M_\text{D} = $ 2 TeV, $ M_\text{BH} = $ 10 TeV, and $ n = $ 2.
png pdf	Figure 6: The $ S_\text{T} $ distribution in the $ N \geq $ 4 SI-SR region in data, indicated by the black markers, with background prediction, represented by the red line, and its uncertainty, denoted with the gray band.
png pdf	Figure 7: Expected and observed model independent 95% CL limits for $ N \geq $ 4 (left) and observed limits with different minimum object multiplicity requirements (right).
png pdf	Figure 7-a: Expected and observed model independent 95% CL limits for $ N \geq $ 4 (left) and observed limits with different minimum object multiplicity requirements (right).
png pdf	Figure 7-b: Expected and observed model independent 95% CL limits for $ N \geq $ 4 (left) and observed limits with different minimum object multiplicity requirements (right).
png pdf	Figure 8: Post-fit $ S_\text{T} $ distributions in the PS-FAIL (left) and PS-PASS (right) regions in data. The gray shaded area includes both statistical and systematic uncertainties on the background prediction while the red and blue lines are B1 signal examples as noted in the legends.
png pdf	Figure 9: Expected and observed 95% CL upper limits for B1 models with $ M_\text{D} = $ 2 TeV (left) and $ M_\text{D} = $ 4 TeV (right). The blue curves represent the theoretical cross section values.
png pdf	Figure 9-a: Expected and observed 95% CL upper limits for B1 models with $ M_\text{D} = $ 2 TeV (left) and $ M_\text{D} = $ 4 TeV (right). The blue curves represent the theoretical cross section values.
png pdf	Figure 9-b: Expected and observed 95% CL upper limits for B1 models with $ M_\text{D} = $ 2 TeV (left) and $ M_\text{D} = $ 4 TeV (right). The blue curves represent the theoretical cross section values.
png pdf	Figure 10: Excluded $ M_\text{BH} $ values as a function of $ M_\text{D} $ and $ n $ for a variety of BLACKMAX (left) and CHARYBDIS2 (right) BH models.
png pdf	Figure 10-a: Excluded $ M_\text{BH} $ values as a function of $ M_\text{D} $ and $ n $ for a variety of BLACKMAX (left) and CHARYBDIS2 (right) BH models.
png pdf	Figure 10-b: Excluded $ M_\text{BH} $ values as a function of $ M_\text{D} $ and $ n $ for a variety of BLACKMAX (left) and CHARYBDIS2 (right) BH models.
png pdf	Figure 11: Expected and observed 95% CL upper limits on the cross-section of the black hole production as a function of the number of extra dimensions for B1 with $ M_{D} = $ 3 TeV and $ M_{BH}= $ 10 TeV (left), and for $ M_{BH}= $ 11 TeV (right).
png pdf	Figure 11-a: Expected and observed 95% CL upper limits on the cross-section of the black hole production as a function of the number of extra dimensions for B1 with $ M_{D} = $ 3 TeV and $ M_{BH}= $ 10 TeV (left), and for $ M_{BH}= $ 11 TeV (right).
png pdf	Figure 11-b: Expected and observed 95% CL upper limits on the cross-section of the black hole production as a function of the number of extra dimensions for B1 with $ M_{D} = $ 3 TeV and $ M_{BH}= $ 10 TeV (left), and for $ M_{BH}= $ 11 TeV (right).
png pdf	Figure 12: The maximum number of excluded extra dimensions as a function of $ M_D $, $ M_{BH} $ values and various models using BLACKMAX (left) and CHARYBDIS2 (right) generators. The points seen near $ n_{\textrm{extra}}^{\textrm{max}} $ values of 2 and 6 are to be understood as underflow and overflow values given the simulation parameter choices at $ n=$ 2, 4, 6.
png pdf	Figure 12-a: The maximum number of excluded extra dimensions as a function of $ M_D $, $ M_{BH} $ values and various models using BLACKMAX (left) and CHARYBDIS2 (right) generators. The points seen near $ n_{\textrm{extra}}^{\textrm{max}} $ values of 2 and 6 are to be understood as underflow and overflow values given the simulation parameter choices at $ n=$ 2, 4, 6.
png pdf	Figure 12-b: The maximum number of excluded extra dimensions as a function of $ M_D $, $ M_{BH} $ values and various models using BLACKMAX (left) and CHARYBDIS2 (right) generators. The points seen near $ n_{\textrm{extra}}^{\textrm{max}} $ values of 2 and 6 are to be understood as underflow and overflow values given the simulation parameter choices at $ n=$ 2, 4, 6.
png pdf	Figure 13: Expected and observed 95% CL upper limits on the pre-exponential factor for the sphaleron model with $ p({N_\text{CS}})= $ 0.5 (left), and observed limits with $ p({N_\text{CS}})= $ 0.0, 0.5 and 1 (right).
png pdf	Figure 13-a: Expected and observed 95% CL upper limits on the pre-exponential factor for the sphaleron model with $ p({N_\text{CS}})= $ 0.5 (left), and observed limits with $ p({N_\text{CS}})= $ 0.0, 0.5 and 1 (right).
png pdf	Figure 13-b: Expected and observed 95% CL upper limits on the pre-exponential factor for the sphaleron model with $ p({N_\text{CS}})= $ 0.5 (left), and observed limits with $ p({N_\text{CS}})= $ 0.0, 0.5 and 1 (right).

Summary

A dedicated search for black holes and sphalerons produced in proton-proton collisions at $ \sqrt{s} = $ 13 TeV using the CMS detector has been presented. No excesses above SM background predictions are observed, enabling 95% confidence level upper limits to be extracted that are both model independent as a function of $ S_\text{T} $ and object multiplicity, and model dependent on the cross section of numerous black hole and sphaleron models. The model independent results demonstrate approximately a factor of four improvement over the last published CMS analysis. The model dependent results exclude semiclassical black holes with masses below 9.0-11.4 TeV, extending the the exclusion reach by 1-1.6 TeV, depending on the model and the number of extra dimensions. This includes the first reported limits on the number of extra dimensions as a function of $ M_\text{D} $ from the LHC. The limits on the sphaleron pre-exponential factor were strengthened by an order of magnitude compared to previously published results. These are the most stringent limits on the sphaleron pre-exponential factor to date. A significant improvement in the model dependent study over previous results comes from an improved understanding of parton distribution functions. Additional significant gains can be traced to both the increased luminosity and the enhanced background rejection provided by the sphericity and phase space distance event selection requirements.

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