Supersymmetry discovery potential in future LHC and HL-LHC running with the CMS detector

Link to the document CMS-PAS-SUS-14-012 in CDS
Note: Some plots in this PAS were updated in the CMS Phase II upgrade technical proposal Links to CDS. The updated plots are now linked below.

Abstract:

The search for supersymmetry (SUSY) is a major goal of the LHC physics program. The range of SUSY scenarios is broad, and both high luminosity data samples and the full set of CMS detector capabilities are required to provide sensitivity to the range of signatures, cross sections, and decay branching fractions that can arise. If evidence for a spectrum of new particles is discovered, an extensive program of measurements will be required to determine its properties. Results are presented from a set of studies that address key questions related to the anticipated program of SUSY searches, assuming integrated luminosities from 300 fb^-1 (LHC Run 2+3) to 3000 fb^-1 (High Luminosity LHC). Natural SUSY models, which are motivated by the puzzle of how the low value of the Higgs mass is stabilized (the gauge hierarchy problem), are one of the most important areas of investigation. Three full-spectrum natural SUSY scenarios are considered in detail, as well as other scenarios that lead to challenging experimental signatures, such as compressed mass spectra. For some studies, simplified model spectra (SMS) are used to study scenarios in which a small number of SUSY particles dominate the event sample for a particular experimental signature. Using these complementary approaches, results are presented on the sensitivities of searches with a varying numbers of jets, b-tagged jets, and leptons, and with a variety of different kinematic variables. These studies, together with results from previous investigations, demonstrate the tremendous potential for discovering and elucidating SUSY with the CMS detector in future LHC running.

Contents:

Overview

Figure/Table	Links	Description
	pdf, png	Figure 1: Mass reach of searches for supersymmetry based on simplified models.
	(a) pdf, png, (b) pdf, png, (c) pdf, png, (d) pdf, png, (e) pdf, png	Figure 2: Masses of the SUSY particles in different models and their decay lines, which are drawn for branching ratios above 5%. Shown are (a) NM1, (b) NM2, (c) NM3, (d) STC, and (e) STOC. SLHA files can be also found here: [NM1], [NM2], [NM3], [STC], [STOC].
	pdf, png	Table 1: Overview of the different analyses and their application to the different models. Details of the five full-spectrum SUSY models, natural model (NM) 1, 2, and 3, stau coannihilation model (STC), and stop coannihilation model (STOC), can be found here.

Inclusive search in the all-hadronic final state with H_T and H_T^miss variables

Figure/Table	Links	Description
	pdf, png	Table 2: All-hadronic inclusive search with HT and HTmiss: Background and signal event yields corresponding to 3000 fb-1. The vector boson denoted by "V" refers to W, Z, and $\gamma$.
	(a) pdf, png (b) pdf, png	Figure 3: All-hadronic inclusive search with HT and HTmiss: (a) the b-tag multiplicity distribution for events passing all the search selections except for the b-tag multiplicity requirement, and (b) HTmiss distribution for events passing all the search selections except for the HTmiss requirement. The version of plots that appeared in the Phase II upgrade technical proposal are linked here.
	(a) pdf, png (b) pdf, png	Figure 4: All-hadronic inclusive search with HT and HTmiss: (a) the HT distribution for the background and STOC signal events in the search region. At high values of HT we are sensitive to squarks with masses of about 3.4 TeV. (b) Discovery significance as a function of the integrated luminosity.

Inclusive search in the all-hadronic final state with the M_T2 variable

Figure/Table	Links	Description
	pdf, png	Table 3: All-hadronic search with MT2: Estimated event yields for signal samples and SM background processes corresponding to 3000 fb-1.
	(a) pdf, png (b) pdf, png	Figure 5: All-hadronic inclusive search with MT2: (a) The distribution of the number of jets with the medium b-tag requirement, using the signal selection given in the text including a requirement of MT2 > 500 GeV, and (b) the distribution of MT2 after the full selection except the MT2 requirement itself. For (b), the version of the plot that appeared in the Phase II upgrade technical proposal is linked here.
	pdf, png	Figure 6: All-hadronic inclusive search with MT2: Significance for the models NM1, NM2, and NM3. The model NM3 has the highest discovery significance.

Search for sbottom pair production in the all-hadronic final state

Figure/Table	Links	Description
	pdf, png	Table 4: Search for bottom squarks: The event yields for the STC signal sample and several SM processes with 3000 fb-1 at 14 TeV with 140 pileup interactions. The variable MT is the minimum invariant transverse mass of one of the two b-tagged jets and the missing transverse energy .
	pdf, png	Table 5: Search for bottom squarks: The composition of the inclusive signal sample after applying all selection requirements in the search region. The variable MT is the minimum invariant transverse mass of one of the two b-tagged jets and the missing transverse energy.
	(a) pdf, png (b) pdf, png	Figure 7: Search for bottom squarks: Comparison of the MCT distribution for signal and background from SM and other SUSY processes. All selection requirements are applied. The two figures show the signal region for (a) MT > 750 GeV and (b) MT > 950 GeV, respectively. The endpoint for all signal regions is located at the same position. The background distribution is stacked, while the signal and other SUSY contributions are overlaid. The version of plots that appeared in the Phase II upgrade technical proposal are linked here.
	pdf, png	Figure 8: Search for bottom squarks: Expected sensitivity in different search bins as a function of integrated luminosity.

Search for stop pair production in the single-lepton final state

Figure/Table	Links	Description
	pdf, png	Table 6: Search for direct stop production in the single-lepton channel: The event yields for the inclusive signal samples and several SM processes with 3000 fb-1 at 14 TeV with 140 pileup interactions. The significances are determined by considering a systematic uncertainty on the background prediction of 15 % and 25%. For the high ETmiss search region, only 25 % systematic uncertainty is considered as discussed in the text.
	(a) pdf, png (b) pdf, png (c) pdf, png (d) pdf, png	Figure 9: Search for direct stop production in the single-lepton channel: Comparison of (a) $\Delta \phi$, (b) centrality, (c) MT, and (d) MT2W for signals and SM backgrounds after all selection requirements are applied except on the variables themselves.
	pdf, png	Figure 10: Search for direct stop production in the single-lepton channel: Significance for the different full-spectrum SUSY models. An uncertainty of 15 % is used for the curves of NM1, NM2, NM3, and STC, while a higher uncertainty of 25 % is chosen for the STOC model due to the increased ETmiss threshold.
	(a) pdf, png (b) pdf, png	Figure 11: Search for direct stop production in the single-lepton channel: Comparison of the HT distribution for signals and SM backgrounds after all selection requirements. in Fig. (a), HT distributions for the different SUSY scenarios are overlaid, while in Fig. (b) the signal composition is shown for the NM1 model, where the different production modes are separated from each other and stacked on top of the the SM background. At high values of HT we are sensitive to squarks with masses above 3 TeV. For (b), the version of the plot that appeared in the Phase II upgrade technical proposal is linked here.

Search for compressed supersymmetry spectra in the monojet signature

Figure/Table	Links	Description
	pdf, png	Table 7: Search in the monojet signature: Background and signal event yields corresponding to 3000 fb-1. The "pre-selection" refers to events passing all the requirements except the final tight selection on the leading jet pT and ETmiss.
	(a) pdf, png (b) pdf, png	Figure 12: Search in the monojet signature: (a) Leading jet pT for 3000 fb-1 after the selection given in the text except for the requirement on the leading jet pT itself and (b) the discovery significance as a function of the integrated luminosity. For (a), the version of the plot that appeared in the Phase II upgrade technical proposal is linked here.

Search using a kinematic edge in the opposite-sign dilepton mass distribution

Figure/Table	Links	Description
	pdf, png	Table 8: Search for a kinematic edge: Event yields for the SM background processes and the signals expected from the NM1 model for 3000 fb-1. The "Edge" row is for events satisfying 20 < ml+l- < 70 GeV and the requirement that leptons be the same flavor.
	(a) pdf, png (b) pdf, png (c) pdf, png	Figure 13: Search for a kinematic edge: Distributions of ml+l- for 3000 fb-1 after the selection given in the text. (a) The signal is split between events with a true, properly reconstructed "edge" decay chain and all other signal events. Also shown is an example unbinned fit to the (b) SF and (c) OF dilepton ml+l- distributions. For the SF ml+l- distribution in (b), the solid blue curve is the total PDF, background components are shown in green and magenta. For (b), the version of the plot that appeared in the Phase II upgrade technical proposal is linked here.
	(a) pdf, png (b) pdf, png (c) pdf, png	Figure 14: Search for a kinematic edge: (a) Significance of the ml+l- kinematic edge search from unbinned fits to the SF+OF samples as a function of integrated luminosity, and (b, c) the fractional uncertainty on the ml+l- kinematic edge signal yield and mass as functions of integrated luminosity.

Search for supersymmetry in final states with multileptons and b-jets

Figure/Table	Links	Description
	pdf, png	Table 9: Trilepton + b-tag search: Result table for the 3$\ell$ + b-jets search with 3000 fb$^{-1}$. This table contains events with at least 3$\ell$, $E_\mathrm{T}^\mathrm{miss}$>500 GeV, and some b-jets.
	(a) pdf, png (b) pdf, png	Figure 15: Trilepton + b-tag search: The $E_\mathrm{T}^\mathrm{miss}$ distribution for events with (a) 3 $\ell$ and 2+3 b-tagged jets and (b) 3$\ell$ and $\ge$4 b-tagged jets. The predictions for the SM background processes and full-spectrum SUSY models are shown. For (b), the version of the plot that appeared in the Phase II upgrade technical proposal is linked here.
	pdf, png	Figure 16: Trilepton + b-tag search: Expected sensitivity versus the integrated luminosity for the models STC, NM1, NM2, and NM3.

Search for the electroweak production of charginos and neutralinos

Figure/Table	Links	Description
	(a) pdf, png (b) pdf, png	Figure 17: Simplified models for chargino-neutralino production leading to (a) WZ + $E_\mathrm{T}^\mathrm{miss}$ and (b) WH + $E_\mathrm{T}^\mathrm{miss}$ final states.

Search for $\tilde{\chi}_{1}^{\pm}\tilde{\chi}_{2}^{0}$ production with $\tilde{\chi}_{1}^{\pm}\to\mathrm{W}\tilde{\chi}_{1}^{0}$ and $\tilde{\chi}_{2}^{0}\to\mathrm{Z}\tilde{\chi}_{1}^{0}$ in the multilepton channel

Figure/Table	Links	Description
	(a) pdf, png (b) pdf, png	Figure 18: Multilepton search: (a) Definition of search bins and (b) the M$_{\ell\ell}$ distribution for the different full-spectrum SUSY models compared to the SM background.
	(a) pdf, png (b) pdf, png	Figure 19: Multilepton search: Distributions for the on-Z search region no. 9: (a) the $\mathrm{M}_\mathrm{T}$ distribution for events with $E_\mathrm{T}^\mathrm{miss}$>400 GeV and (b) the $E_\mathrm{T}^\mathrm{miss}$ distribution for events with 200 < $\mathrm{M}_\mathrm{T}$ < 400 GeV. For (b), the version of the plot that appeared in the Phase II upgrade technical proposal is linked here.
	(a) pdf, png (b) pdf, png	Figure 20: Multilepton search: (a) Contours for 5$\sigma$ discovery in the $m_{\tilde{\chi}_{1}^{\pm}}=m_{\tilde{\chi}_{2}^{0}}$ versus $m_{\tilde{\chi}_{1}^{0}}$ plane. (b) Discovery significance as a function of the integrated luminosity.
	pdf, png	Table 10: Multilepton search: Event yields for the SM background, the simplified model (SMS) signal with $m_{\tilde{\chi}_{1}^{\pm}}=m_{\tilde{\chi}_{2}^{0}}$=500 GeV and $m_{\tilde{\chi}_{1}^{0}}$=100 GeV, and the investigated full-spectrum SUSY model signals. The results are split into the on-Z and high-Z signal regions,

Search for $\tilde{\chi}_{1}^{\pm}\tilde{\chi}_{2}^{0}$ production in the WH + E_T^miss final state

Figure/Table	Links	Description
	(a) pdf, png (b) pdf, png	Figure 21: Ewkino WH search: Distributions of ETmiss for (a) the Phase I 50 pileup scenario and (b) the Phase II 140 pileup scenario, after all other selections are applied.
	(a) pdf, png (b) pdf, png	Figure 22: Ewkino WH search: (a) Contours for 5$\sigma$ discovery and 95% CL exclusion in the SMS plane of $m_{\tilde{\chi}_{1}^{\pm}}=m_{\tilde{\chi}_{2}^{0}}$ versus $m_{\tilde{\chi}_{1}^{0}}$ for the Phase I 50 pileup and Phase II 140 pileup scenarios, assuming a background systematic uncertainty of 12.5%. The observed exclusion contour based on the 2012 data is also overlaid. (b) The same contours in the Phase II 140 pileup scenario, showing the impact of different branching ratios for $\tilde{\chi}_{1}^{\pm} \tilde{\chi}_{2}^{0} \rightarrow (W \tilde{\chi}_{1}^{0})(H \tilde{\chi}_{1}^{0})$.
	pdf, png	Figure 23: Ewkino WH search: Contours for 5$\sigma$ discovery in the SMS plane of $m_{\tilde{\chi}_{1}^{\pm}}=m_{\tilde{\chi}_{2}^{0}}$ versus $m_{\tilde{\chi}_{1}^{0}}$ for scenarios of 300 fb-1 with the Phase I detector and 50 pileup interactions, 1000 fb-1 with the aged detector and 140 pileup interactions, and both 1000 fb-1 and 3000 fb-1 with the Phase II detector and 140 pileup interactions. Note: This plot was updated in the Phase II upgrade technical proposal with updated performance evaluation of the aged detector. For the aged detector 140 pileup scenario, the b-tagging efficiency is now degraded by about 0.8 instead of 0.67 and the missing ET resolution is degraded by 20 GeV instead of 40 GeV in the DELPHES simulation for the Phase II 140 pileup scenario.
	pdf, png	Table 11: Ewkino WH search: Yields for the Phase I scenario with 50 pileup events, 300 fb-1, after all signal selections except for the ETmiss requirement listed.
	pdf, png	Table 12: Ewkino WH search: Estimated significance in $\sigma$ for a few signal points in the Phase I, 50 pileup scenario with 300 fb-1. The yields from Table 11 are used, and two different choices of background systematic uncertainty are presented.
	pdf, png	Table 13: Ewkino WH search: Yields for the Phase II scenario with 140 pileup events, 3000 fb-1, after all signal cuts except for the ETmiss requirement listed.
	pdf, png	Table 14: Ewkino WH search: Estimated significance in $\sigma$ for a few signal points in the Phase II, 140 pileup scenario with 3000 fb-1. The yields from Table 13 are used, and two different choices of background systematic uncertainty are presented.

Combined results for $\tilde{\chi}_{1}^{\pm}\tilde{\chi}_{2}^{0}$ production

Figure/Table	Links	Description
	(a) pdf, png (b) pdf, png	Figure 24: (a) Contours for 5$\sigma$ discovery are shown in the simplified model parameter space of $m_{\tilde{\chi}_{1}^{\pm}}=m_{\tilde{\chi}_{2}^{0}}$ versus $m_{\tilde{\chi}_{1}^{0}}$ three different branch fraction assumptions of $\mathcal{B}(\tilde{\chi}_2^0\to\mathrm{Z}\tilde{\chi}_1^0)=100$%, $\mathcal{B}(\tilde{\chi}_2^0\to\mathrm{H}\tilde{\chi}_1^0)=100$%, and $\mathcal{B}(\tilde{\chi}_2^0\to\mathrm{Z}\tilde{\chi}_1^0)=1-\mathcal{B}(\tilde{\chi}_2^0\to\mathrm{H}\tilde{\chi}_1^0)=50$%. For the last assumption, the sensitivity is obtained from the combination of the WZ + $E_\mathrm{T}^\mathrm{miss}$ and WH + $E_\mathrm{T}^\mathrm{miss}$ searches. The excluded regions based on the 8 TeV data collected in 2012 are also shown. (b) The discovery sensitivities for the natural model NM2 from the combination of the WZ + $E_\mathrm{T}^\mathrm{miss}$ and WH + $E_\mathrm{T}^\mathrm{miss}$ searches are also shown as a function of integrated luminosity, together with the sensitivities from the individual WZ + $E_\mathrm{T}^\mathrm{miss}$ and WH + $E_\mathrm{T}^\mathrm{miss}$ searches. For (a), the version of the plot that appeared in the Phase II upgrade technical proposal is linked here.

Detailed model information

Figure/Table	Links	Description
	pdf, png	Table 15: Overview of the most relevant sparticle masses for the models NM1, NM2, NM3, STC, and STOC. $\tilde{\mathrm{q}}$ denotes the first two generation squarks, and their average mass is listed.
	pdf, png	Table 16: Cross sections of main SUSY particle production processes for the models NM1, NM2, NM3, STC, and STOC. The cross sections are calculated at the next-to-leading-order accurancy. The cross sections below 0.01 fb are not listed.
	pdf, png	Table 17: Main branching fractions of SUSY particles for the models NM1, NM2, NM3, STC, and STOC.
$\tilde{\chi}_{2}^{0} \tilde{\chi}_{1}^{\pm}$ production slha	slha file	Slha file that was used to produce the $\tilde{\chi}_{2}^{0} \tilde{\chi}_{1}^{\pm}$ scan
$\tilde{\chi}_{2}^{0} \tilde{\chi}_{1}^{\pm}$ cross section table	txt file	Cross sections used for the $\tilde{\chi}_{2}^{0} \tilde{\chi}_{1}^{\pm}$ scan