Dr. Sascha Mehlhase Ludwig-Maximilians Universität München for the ATLAS Collaboration Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology Dark Matter • ample evidence for existence of dark matter • stable, neutral and weakly interacting massive particle (WIMP) might be best candidate ➙ need to go beyond Standard Model • no unambiguous direct evidence so far • complement direct detection limits at the LHC Sascha Mehlhase for the ATLAS Collaboration 2 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches • general mono-X+ E Tmiss strategy egy:(( • invisible DM particles escape detection • tag events using recoil object(s) X (Standard Model particle from ISR) • measure E Tmiss ➙ infer DM candidate • variety of X’s under investigation ' 7' Sascha Mehlhase for the ATLAS Collaboration 3 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches ➙ • general mono-X+ E Tmiss strategy • effective field theory (EFT) • approximation of contact qq χχ interaction through heavy mediator • agnostic search, suited for comparison to other searches • poor approximation when interaction’s momentum transfer larger than intermediate state’s mass • results parameterised by ( full list of operators in Goodman et. al, Phys. Rev. D82: 116010, 2010 DM scale (M χ ) and ( d ( interaction strength (M*) 7 ( ( 6 ( • different recoil objects probe 6 ( 6 ( different operators ( 7 ( 6 ( 6 Sascha Mehlhase for the ATLAS Collaboration 4 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches • mono-jet + E Tmiss (arXiv:1502.01518, submitted to EPJC) • event selection • central leading jet with p T > 120 GeV and p T > 0.5 * E Tmiss • 9 signal regions with E Tmiss EFT simplified model thresholds from 150 to 700 GeV • jet and E Tmiss back to back / recoiling Δφ (sel. jets, E Tmiss ) > 1.0 • lepton and isolated track veto • main background • Z( νν ) + jets, constrained using W(l ν ) and Z(ll) control regions • W(l ν ) + jets, mostly when l= τ Sascha Mehlhase for the ATLAS Collaboration 5 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches due to very low-energy recoil • mono-jet + E Tmiss (arXiv:1502.01518, submitted to EPJC) induced by DM particles • all measurements are consistent with SM • limits for six EFT operators better (D1, D5, D8, D9, D11, C5) • most sensitive signal region is used in each case • truncation procedure applied to searches dominate whole range in spin-dependent case collider ensure EFT validity (simplest: only use events where Q tr < M med ) better • complementarity of direct/indirect detection and colliders ➙ each experiment has its strength Sascha Mehlhase for the ATLAS Collaboration 6 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches off-shell | resonant prod | contact int (arXiv:1502.01518, submitted to EPJC) • mono-jet + E Tmiss (ATL-PHYS-PUB-2014-007) Suppression scale • simplified model results also available better • more model parameters • complete description for EFT physics at the LHC • improved sensitivity expected with first months of LHC run 2 • stronger focus on simplified models in run 2 better Sascha Mehlhase for the ATLAS Collaboration 7 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches • mono-photon (arXiv:1411.1559, PRD 91, 012008 (2015)) • event selection • high-energy photon • large E Tmiss • no leptons, at most one jet • main background • Z( νν ) + γ • W γ / Z γ with lost leptons • W / Z with leptons / jets misidentified as γ • estimated via dedicated control regions Sascha Mehlhase for the ATLAS Collaboration 8 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches • mono-photon (arXiv:1411.1559, PRD 91, 012008 (2015)) • all measurements are consistent with SM • truncation procedure applied to ensure EFT validity • limits for three EFT operators (D5, D8, D9) Suppression scale better better Sascha Mehlhase for the ATLAS Collaboration 9 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches • mono-photon (arXiv:1411.1559, PRD 91, 012008 (2015)) • simplified model with Z’-like mediator Suppression scale better mediator mass Sascha Mehlhase for the ATLAS Collaboration 10 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology q( ATLAS searches q( • mono-W/Z (hadronic) (arXiv:1309.4017, PRL 112, 041802 (2014)) • event selection • very central, large-radius jet with Signal'Region ( p T > 250 GeV, 50 GeV < mj < 120 GeV, momentum balance of subjets • two signal regions with E Tmiss > 350 / 500 GeV • max. one narrow jet with p T > 40 GeV • lepton and photon veto • main background • Z( νν ) + jets • Z(ll) + jets and W(l ν ) + jets, with lost lepton Sascha Mehlhase for the ATLAS Collaboration 11 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches • mono-W/Z (hadronic) (arXiv:1309.4017, PRL 112, 041802 (2014)) • all measurements are consistent with SM • limits for four EFT operators (C1, D1, D5, D9) better better Sascha Mehlhase for the ATLAS Collaboration 12 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches (arXiv:1407.7494, JHEP 09 (2014) 037) • mono-W/Z boson (leptonic) (arXiv:1404.0051, PRD 90, 012004 (2014)) • event selection W • one high-p T lepton /W • E Tmiss • large m T , incompatible with directly produced W • event selection Z • two leptons with invariant mass consistent with Z • large E Tmiss • jet and third-lepton vetoes Sascha Mehlhase for the ATLAS Collaboration 13 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches (arXiv:1407.7494, JHEP 09 (2014) 037) • mono-W/Z boson (leptonic) (arXiv:1404.0051, PRD 90, 012004 (2014)) • main background • W: W(l ν ) tail, Z(ll) lost lepton, leptonic taus in W( τν ), Z( ττ ), diboson • Z: diboson Sascha Mehlhase for the ATLAS Collaboration 14 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches (arXiv:1407.7494, JHEP 09 (2014) 037) • mono-W/Z boson (leptonic) (arXiv:1404.0051, PRD 90, 012004 (2014)) • all measurements are consistent with SM • limits for three EFT operators (D1, D5(c/d), D9) better better Sascha Mehlhase for the ATLAS Collaboration 15 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches EFT • heavy quarks + E Tmiss (arXiv:1410.4031, EPJC 75 (2015) 92) • simplified model with “b-flavoured” DM proposed to explain gamma ray excess from galactic centre seen by Fermi-LAT and interpreted as DM annihilating to b quark pairs simplified model • event selection • four signal regions with varying jet/b-jet multiplicity, 0/1 lepton, E Tmiss > 200 - 300 GeV, kinematic cuts to reduce SM top pairs • main background • top-antitop-quark pairs estimated using dedicated control regions • single top production, W/Z + jets Sascha Mehlhase for the ATLAS Collaboration 16 07-2015
Dark Matter searches at ATLAS IX International Conference on Interconnections between Particle Physics and Cosmology ATLAS searches • heavy quarks + E Tmiss (arXiv:1410.4031, EPJC 75 (2015) 92) • all measurements are consistent with SM • limits for three EFT operators (C1, D1, D9) D1 limits in top-quark SR better than in mono-jet, as scalar operators proportional to quark mass • simplified model excludes mediator masses between 300 and 500 GeV for WIMP mass around 35 GeV “b-flavoured” DM simplified model Suppression scale better better Fermi-LAT favoured scalar-mediator mass Sascha Mehlhase for the ATLAS Collaboration 17 07-2015
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