The Compact Muon Solenoid Experiment. Conference Report. Mailing address: CMS CERN, CH-1211 GENEVA 23, Switzerland

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1 Available on CMS information server CMS CR -017/130 The Compact Muon Solenoid Experiment Conference Report Mailing address: CMS CERN, CH11 GENEVA 3, Switzerland 08 May 017 (v3, 11 May 017) Searches for dark matter and new physics with unconventional signatures Livia Soffi for the Exotica, all searches expt SUSY, ATLAS, CMS and SUSY collaborations. Common ATLAS CMS talkcms Abstract Presented at Moriond/QCD017 5nd Rencontres de Moriond on QCD and High Energy Interactions

2 Searches for dark matter and new physics with unconventional signatures at CMS and ATLAS Livia Soffi on behalf of the CMS and ATLAS Collaboration Cornell University, NY, United States Abstract Selected results on searches for dark matter and unconventional signatures with the CMS and ATLAS detectors at LHC are presented. Dark matter searches in channels with jets, single photons, vector bosons, or Higgs bosons combined with missing momentum in the final states are described. Unusual signatures such as displaced objects, disappearing or kinked tracks, delayed or stopped particles have also been explored. The analyses were performed with proton-proton data recorded at LHC centre-of- mass energies up to 13 TeV. 1 Introduction Clear evidence for abundance of matter in the Universe cannot be explained by the visible matter only. While the ordinary atomic matter accounts only for at most 5% the so called Dark Matter (DM) constitutes about 5% of the content of the Universe. Nowadays proofs of evidence for DM come only from the observations of the effects of its gravitational interaction with ordinary matter. Two scenarios for producing DM at LHC can be envisaged, depending whether a contact interaction within an effective field theory approach is appropriate or whether a mediator between ordinary and dark matter comes into a mass range where it could be accessible at the LHC 1. In Sec. of this paper results of searches for direct production of WIMPs with the ATLAS and CMS 3 experiments at the LHC at CERN are presented. The searches have been performed using up to 36 fb 1 of proton-proton collision data delivered during LHC Run- at 13 TeV centre-of-mass energy in 015 and 016. Alternative ways in searching for new physics at LHC involves exploring finals states with unusual signatures such as displaced objects, disappearing or kinked tracks, delayed or stopped particles. An overview of relevant current beyond- the-standard-model physics searches with displaced signatures at both ATLAS and CMS experiments is given in Sec. 3. Dark Matter Searches at LHC If produced, DM would escape the detector without leaving signs of its passage. Its production can be inferred by measuring the amount of energy imbalance in the plane transverse to colliding beams(et miss ). The presence of further objects recoiling against WIMPs in the final state can be used to flag the interaction and identify it. A variety of signatures are exploited at LHC in order to look for DM. Both ATLAS and CMS look for DM production in association with jets 4,5 (mono-jet search). The strategy followed by the two experiments is very similar: events are required to have at least one jet with large transverse momentum (p T ) together with ET miss. Such search strategy is exploited to study also the production of DM candidates in association with a vector boson (W/Z) decaying hadronically (mono-v search). In this case the jets produced in the vector boson decay are reconstructed as a single fat jet with a cone size larger than what is generally used to reconstruct jets at LHC. In addition tagging algorithms based

3 ] m ATLAS s = 13 TeV, 3. fb Axial Vector Mediator Dirac Fermion DM g = 0.5, g = 1.0 q 95% CL limits m A = m Expected limit (± Observed limit (± Perturbativity Limit Relic Density 1 exp ) PDF, scale 1 ) theory m A [cm σ SI DM-nucleon CMS obs. 90% CL LUX CDMSLite PandaX-II CRESST-II 1.9 fb CMS Scalar med, Dirac DM, g = 1, g = 1 q DM (13 TeV) 3 m DM Figure 1 Expected and observed exclusion limits on DM produced in association with jets assuming a vector mediator (left, CMS 5 ), axial-vector mediator (ATLAS, center 4 ) simplified model. On the right the interpretation of the dijet search in terms of DM models 6 on the jet sub=structures are applied in order to discriminate such decays from standard multijet events. Constraints on the mass of the fat are applied requiring it to be close to the vector boson mass. Both searches observe a good agreement of data with SM background expectation. Exclusion limits are set on the DM production cross section. These limits are then translated in lower limits on the mass of the heavy mediator as a function of DM mass and shown in Fig. 1. A translation to the DM-nucleon elastic scattering cross section versus the dark matter particle mass plane is also performed to allow a comparison of LHC results to direct detection experiments and shown in Fig. 1. Limits on DM production obtained from the mono-jet searches are easily combined with those from dijets searches when considering models in which DM particles couple to quarks through a DM leptophobic vector and axialvector mediator 1. Figure 1 right shows an example of exclusion region in the phase space of the DM mass and the mediator mass obtained from CMS for a given set of vector mediator simplified model parameters when performing the dijet search 6. Results from this search are also translated in limits on invisible branching ratio decay of the Higgs boson. A summary of the most recent limits set by ATLAS and CMS on DM production using the jet signatures is shown in Tab. 1. Table 1: Observed excluded phase space regions on DM models obtained analyzing mono-jet and mono-v signatures at LHC Theory interpretation CMS(1.9 fb 1 mono-jet+mono-v) ATLAS (3. fb 1 ) Scalar (Pseudo) Mediator M med < 0 (430) GeV Vector (Axial) Mediator M med < 1.95 TeV M med < 1 TeV Large Extra-Dimensions M D < 6.58 (4.31) TeV for n = (6) Higgs Invisible BR < 0.56 Although the mono-jet/v signatures are the most sensitive signatures for the most benchmarks due to the large statistics in the region of interest with high ET miss, other DM production processes are worth to investigate. Among them, signatures with high ET miss and electroweak vector bosons have lower backgrounds with respect to mono-jet signature and are sensitive to different benchmark models. Mono-photon, mono-higgs searches are performed by both ATLAS and CMS. The mono-photon analyses 7,8 follow a strategy similar to the mono-jet search. Events with a well identified high p T photon and large ET miss are selected. Table summarize the most recent public results on mono-photon search from both ATLAS and CMS with 015 and 016 data. The discovery of the Higgs boson opens a new collider probe of dark matter. ATLAS and CMS experiments explore mono-higgs signature with Higgs signals in three final state channels: H(b b)+et miss, H(γγ)+ET miss and H(ZZ)+ET miss. There is an important difference

4 Table : Observed excluded phase space regions on DM models obtained analyzing mono-photon signature at LHC Theory interpretation CMS(1.9 fb 1 ATLAS (36 fb 1 ) Vector (Axial) Mediator M med < 0.76 TeV M med < 1. TeV Additional Extra-Dimensions M D <.6 TeV for n =6 Zγ production UL<6-43 fb for m [ - 5] TeV EFT Dim 7 Λ < 60 GeV Λ < 790 GeV Events / 5 GeV.3 fb (13 TeV) Data DY + jets CMS Vh EW + γ Z' DM+h(γγ) SM h γγ γ + jets EW + γγ γγ Stat. Unc. m A = 300 GeV, m = 600 GeV Z' m A = 300 GeV, m = 800 GeV Z' = 300 GeV, m = 00 GeV 1 m A Z' 1 Data/MC 4 MC uncert. (stat) pmiss T Figure E miss T after final selection in mono-higgs searches for H(b b) (left, ATLAS ), H(γγ) (center, CMS 13 ) and H(ZZ) (right, ATLAS 1 ) between mono-higgs and other mono-x searches. In proton-proton collisions, a j//w/z can be emitted directly from a light quark as initial state radiation (ISR) through the usual SM gauge interactions, or it may be emitted as part of the new effective vertex coupling DM to the SM. In contrast, since Higgs boson ISR is highly suppressed due to the small coupling of the Higgs boson to quarks, a mono-higgs is preferentially emitted as part of the effective vertex itself 9. The distribution of the ET miss after the final selection for mono-higgs searches are shown in Fig for the so far analyzed channels,11,1,13 : H(b b) and H(γγ) (ATLAS and CMS) and H(ZZ) (ATLAS only). Results from mono-higgs searches are interpreted in terms of simplified models with a vector mediator which radiates a Higgs boson, and decays into two DM particles and a two- Higgs-doublet-model (HDM) where a vector mediator is produced resonantly and decays into a Higgs boson plus an intermediate heavy pseudoscalar. Table 3 summarize the most recent public results on mono-higgs searches from both ATLAS and CMS with 015 and 016 data. 3 Unconventional Signatures Long-lived particles are predicted in many beyond-standard-model theories such as in gaugeor anomaly-mediated supersymmetry (SUSY) breaking scenarios, in R-parity violating SUSY and split SUSY models, or in hidden valley scenarios implying a dark sector. An inclusive search for long-lived particles decaying to various combinations of jets and leptons is performed by CMS with full 015 data 15. The analysis exploits the information originating from the CMS calorimeters to reconstruct jets and measure their energies. The analysis sensitivity is maximal for ( < c0 < 00) mm. Fig. 3 left shows for example the excluded pair-production cross section for the Jet-Jet model. Cross sections as small as 1. fb are excluded for c0 = 50 mm. ATLAS search for disappearing tracks 14 find its motivation under the hypothesis that a charged SUSY particle produced in a high energy collider acquires a relatively long lifetime and leave multiple hits in the traversed tracking layers before decaying. A track arising from a long-lived chargino for example, can disappear and leave hits only in the innermost layers and no hits in the portions of the detector at higher radius. Figure 3 right shows the

5 Table 3: Observed excluded phase space regions on DM models obtained analyzing mono-higgs signature at LHC Theory interpretation H(b b) H(γγ) H(ZZ) H(b b)+ H(γγ) ATLAS (3. fb 1 ) ATLAS (36 fb 1 ) ATLAS (3.6 fb 1 ) CMS (3. fb 1 ) Vector Mediator M med <700 GeV M med <850 GeV σ < 1-5 fb HDM M med <1950 GeV M med <00 GeV M med <1800 GeV Heavy Scalar σ <.7 fb σ < -4 fb upper limit 95% CL [fb] σ x BR CMS Preliminary Jet-Jet 1.6 fb (13 TeV) 3 cτ 0 [mm] Exp. Limit ± 1 σ exp Obs. Limit m X 0=50 GeV m X 0=0 GeV m X 0=300 GeV m X 0=00 GeV Figure 3 Expected and Observed exclusion limits on pair produced long-lived particles decaying to jets as presented by CMS (left 15 ) and on disappearing tracks in SUSY by ATLAS (right 14 ) exclusion limits in the m χ ± τ 1 χ ± plane for the electroweak channel, where τ χ ± 1 is the lifetime 1 of the chargino. For a chargino lifetime of 0. ns, gluino 1.05 TeV are excluded assuming very compressed spectra with a mass difference between the gluino and the chargino of less than 00 GeV. The existing searches do not fully cover the enormous parameter space of masses, crosssections and decay possibilities of all possible new particles. Signals might be hidden in so far unexplored kinematic regimes and final states, motivating a structured, global and automated way to search for new physics. Therefore model-independent general searches are performed by both ATLAS 16 and CMS 17 to detect discrepancies between data and the prediction which serve as an alert to perform more precise and model-dependent analyses in the potentially interesting final states. Such analyses partition all recorded events into exclusive classes according to the number of high p T reconstructed objects: electrons, muons, photons, jets, b-tagged jets and ET miss. The largest discrepancy observed by ATLAS in the 1mu+1e+4b-jets+jets class, with a local p0-value of 5 4, is expected in about 70% of the pseudo-experiments. While the largest excess observe by CMS, with a local significance of less than 3σ is observed in the 1e+1γ+ET miss channel. All observed excesses are however compatible with background expectation when considering the look-elsewhere-effect. 4 Conclusion In the search for Dark Matter and new physics unusual signatures, the ATLAS and CMS experiments covered a huge range of final states during the 015 and 016 data-taking runs of the LHC. Although observations are consistent with SM background expectation, stringent limits have been set on different benchmark models, emphasising for what concerns the Dark Matter investigation, the complementarity of collider searches and direct detection searches. The preliminary analyses of 13 TeV data result in a significant expansion of previous limits

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