CMS-EXO-17-010

CMS-EXO-17-010 ; CERN-EP-2021-029
Search for strongly interacting massive particles generating trackless jets in proton-proton collisions at $\sqrt{s} = $ 13 TeV
CMS Collaboration
19 May 2021
Eur. Phys. J. C 82 (2022) 213
Abstract: A search for dark matter in the form of strongly interacting massive particles (SIMPs) using the CMS detector at the LHC is presented. The SIMPs would be produced in pairs that manifest themselves as pairs of jets without tracks. The energy fraction of jets carried by charged particles is used as a key discriminator to suppress efficiently the large multijet background, and the remaining background is estimated directly from data. The search is performed using proton-proton collision data corresponding to an integrated luminosity of 16.1 fb$^{-1}$, collected with the CMS detector in 2016. No significant excess of events is observed above the expected background. For the simplified dark matter model under consideration, SIMPs with masses up to 100 GeV are excluded and further sensitivity is explored towards higher masses.
Links: e-print arXiv:2105.09178 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: A Feynman diagram showing SIMP pair production via the s-channel exchange of a new scalar mediator.
png pdf	Figure 2: Left: comparison of the leading jet $ {p_{\mathrm {T}}} $ spectrum between jets clustered at the generator level (dashed lines) and after detector simulation (solid lines), arising from the GEANT4 SIMP simulation at masses of 1 GeV (blue lines) and 1000 GeV (green lines); right : the ratio of the reconstruction-level and generator-level jet transverse momenta for the GEANT4 SIMP simulation at masses of 1 GeV (dark blue, long-dashed line) and 1000 GeV (green, short-dashed line), including a comparison to a simulation where a 1 GeV SIMP is replaced by a neutron (red, solid line).
png pdf	Figure 2-a: Comparison of the leading jet $ {p_{\mathrm {T}}} $ spectrum between jets clustered at the generator level (dashed lines) and after detector simulation (solid lines), arising from the GEANT4 SIMP simulation at masses of 1 GeV (blue lines) and 1000 GeV (green lines).
png pdf	Figure 2-b: The ratio of the reconstruction-level and generator-level jet transverse momenta for the GEANT4 SIMP simulation at masses of 1 GeV (dark blue, long-dashed line) and 1000 GeV (green, short-dashed line), including a comparison to a simulation where a 1 GeV SIMP is replaced by a neutron (red, solid line).
png pdf	Figure 3: Distributions of the number of jets with $ {p_{\mathrm {T}}} > $ 30 GeV and $ {\| \eta \|} < $ 5 (left), and the value of ChF of the two leading jets (right). The simulated QCD multijet background is compared with the signal expected for three different SIMP masses, with their cross sections scaled as indicated in the legend. The baseline selection is applied, except the events with three or more jets with $ {p_{\mathrm {T}}} > $ 30 GeV and $ {\| \eta \|} < $ 5 are included in the number of jets in the left plot.
png pdf	Figure 3-a: Distribution of the number of jets with $ {p_{\mathrm {T}}} > $ 30 GeV and $ {\| \eta \|} < $ 5. The simulated QCD multijet background is compared with the signal expected for three different SIMP masses, with their cross sections scaled as indicated in the legend. The baseline selection is applied. The events with three or more jets with $ {p_{\mathrm {T}}} > $ 30 GeV and $ {\| \eta \|} < $ 5 are included in the plot.
png pdf	Figure 3-b: The value of ChF of the two leading jets. The simulated QCD multijet background is compared with the signal expected for three different SIMP masses, with their cross sections scaled as indicated in the legend. The baseline selection is applied.
png pdf	Figure 4: The number of background events obtained from the 1- and 2-leg predictions using reconstructed objects in simulation, compared to the direct prediction from MC simulation, shown for various upper ChF thresholds. The bottom panel shows the ratios of the MC prediction to the 1-leg and the 2-leg background predictions.
png pdf	Figure 5: The number of background events obtained from the 1- and 2-leg predictions derived from data, together with the direct observation in data, in bins in ChF, where either the leading or subleading jet has a ChF within the bin edges, and both have a ChF below the upper bin threshold. The bottom panel shows the ratios of the observation in data to the 1-leg and the 2-leg background predictions.
png pdf	Figure 6: The expected and observed 95% CL upper limits on the production cross section for SIMPs with masses between 1 and 1000 GeV, with the assumption that the SIMP interaction in the detector can be approximated as neutron-like. The theoretical prediction of a simplified model incorporating this approximation and including a scalar mediator with couplings $g_\chi = $ $-$1 and $g_\mathrm{q} = $ 1 is also shown (red line). For masses above 100 GeV, where the modelling of the SIMP-nucleon interaction becomes more speculative, the obtained cross section upper limits are increasingly uncertain (shaded area).

Tables
png pdf	Table 1: The numbers of background and observed events for different upper bounds on the ChF value. The background estimations are derived using the data-based 2-leg predictions. The expected number of signal events is given for the $m_{\chi} = $ 1, 100, and 1000 GeV scenarios, with the corresponding statistical uncertainties.

Summary

A search has been presented for dark matter in the form of strongly interacting massive particles (SIMPs) manifesting themselves in the detector as trackless jets. The large multijet background is efficiently suppressed using the charged energy fraction of jets as the key discriminator. The remaining background is estimated directly from data. Using proton-proton collision data corresponding to an integrated luminosity of 16.1 fb$^{-1}$ collected by the CMS experiment in 2016, we set first limits on the production cross section for SIMPs with masses between 1 and 1000 GeV at 95% confidence level (CL), using a signal simulation that assumes the SIMP interaction in the detector can be approximated as neutron-like. The signal modelling assumptions stated previously have small uncertainties, and hence a small impact on the cross section upper limits, for SIMP masses up to about 100 GeV, but become increasingly uncertain above 100 GeV, where an improved phenomenology of the SIMP-nucleon interaction would be welcome. Within this framework we exclude SIMPs with masses less than 100 GeV. These limits were obtained for the off-shell production of SIMP pairs, through a new scalar mediator with couplings $g_\chi = $ $-$1 and $g_{\mathrm{q}} = $ 1. An upper limit on the fiducial cross section of 0.18 fb at 95% CL is also provided for a generic signal of high-momentum trackless jets. With this search, strongly interacting massive particles, for which the interaction strength is constrained to generate a trackless jets signature, have been ruled out over a wide mass range.

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