Search for Dark Matter in the mono-x* final states with ATLAS

Transcription

1 Search for Dark Matter in the mono-x* final states with (on behalf of the Collaboration) Rencontres de Moriond (EW) 08 *: X = jet, Z, W, H

2 Probing Dark Matter (DM) Underlying assumption: DM has also non-gravitational interactions with the Standard Model particles (SM) Direct detection: scattering of DM particles on nuclei Indirect detection: annihilation products out of WIMP collisions Collider search: produce WIMPs through collision of SM particles DM is assumed to be a weakly interacting massive particle (WIMP) Direct detection SM SM Collider DM DM Indirect detection

3 The theoretical framework A large number of DM models are out there, each with its own assumptions/observables/dm candidates Effective Field Theory: just assume a massive mediator (MMED >> momentum transfer), i.e. contact interaction only valid at low Q Completeness Simplified Models: - MMED ~ MDM - more assumptions on the mediator (e.g. different spin hypotheses) - DM is a Dirac fermion - 4 parameters: MDM, MMED, mediator couplings to DM and SM Complete Models: SUSY, extra-dimensions, etc. /CMS DM Forum: arxiv:

4 Mono-X strategy SM Use SM particles (or objects ) to select and tag the event SM SM DM DM DM particles go through the detector without interacting with it Mono-X: reuire a large amount of ing transverse momentum (due to DM) and a known object (X = jet, photon, W, Z, Higgs, ) recoiling against it Also other strategies are used (e.g. resonance search), but they are not covered in this talk Interesting reading: B. Penning, The pursuit of DM at Collider - an overview arxiv:

5 Summary of results in mono-x mono-jet 36./fb s = 3 TeV JHEP 0 (08) 6 arxiv: mono-γ 36./fb s = 3 TeV Eur. Phys. J. C 77 (07) 393 arxiv: mono-v(had) 3./fb s = 3 TeV Phys. Lett. B 763 (06) 5 arxiv: mono-z(lep) 36./fb s = 3 TeV Phys. Lett. B 776 (07) 38 arxiv: mono-h(bb) 36./fb s = 3 TeV PRL 9, 8804 (07) mono-h(γγ) 36./fb s = 3 TeV Phys. Rev. D 96, 004 (07) 5

6 Summary of results in mono-x mono-jet 36./fb s = 3 TeV JHEP 0 (08) 6 arxiv: mono-γ 36./fb s = 3 TeV Eur. Phys. J. C 77 (07) 393 arxiv: mono-v(had) 3./fb s = 3 TeV Phys. Lett. B 763 (06) 5 arxiv: mono-z(lep) 36./fb s = 3 TeV Phys. Lett. B 776 (07) 38 arxiv: mono-h(bb) 36./fb s = 3 TeV PRL 9, 8804 (07) mono-h(γγ) 36./fb s = 3 TeV Phys. Rev. D 96, 004 (07) 6

7 Mono-jet: analysis summary g χ g g χ up to 3 jets pt > 30 GeV mono -jet pt > 50 GeV η <.4 ΔΦ(MET,jet) > 0.4 ET > 50 GeV Dominant backgrounds are Z( vv)+jets and W( lv)+jets constrained using dedicated control regions in which leptons are treated as invisible (e.g. Z vv estimated from Z μμ) Simultaneous fit of the signal region (SR) and control regions (CR) using ET shape information Z A χ Events / GeV Data / SM Signal Region p (j)>50 GeV, E >50 GeV T T Stat. + Syst. Uncertainties Data Standard Model Z( νν) + jets W( lν) + jets Z( ll) + jets tt + single top Diboson multijets + ncb ~ 0 m( b, χ) ) = (500, 495) GeV (m, M )= (400, 00) GeV DM med ADD, n=4, M =6400 GeV D Main systematic uncertainties comes from ET and affect both signal (-9%) and background (-5%). Signal is also affected by ISR modelling (O(%)). Signal is expected to arise as an excess of events in the ET distribution, ET spectrum is binned to enhance the sensitivity to several models No significant excess is observed, limits are set on the relevant parameters of the model 7

8 Mono-jet: results Axial-vector mediator Vector mediator m χ 00 Axial-Vector Mediator Dirac Fermion DM g = 0.5, g =.0 χ 95% CL limits Expected limit ± σ exp Expected limit (± σ exp ) PDF, scale Observed limit (± σ theory ) Perturbativity Limit Relic Density (MadDM) s = 3 TeV, 3. fb m χ 00 Vector Mediator Dirac Fermion DM g = 0.5, g =.0 χ 95% CL limits Expected limit ± σ exp Expected limit (± σ exp ) Observed limit (± σ Relic Density (MadDM) PDF, scale theory ) 500 m ZA = m χ 500 m ZV = m χ m ZA m ZV ] (χ-proton) [cm σ SD m χ 90% CL limits PICO-60 Axial-Vector Mediator Dirac Fermion DM g = 0.5, g χ 3 =.0 4 If strong assumptions are made, collider searches can play a role in the field of direct searches (here results from PICO-60 are shown) Assume AV mediator and couplings (and DM composition) points in (xsec, mχ) correspond to points in (MMED, mχ) C. Amole et al., DM search results from the PICO-60 C3F8 Bubble Chamber arxiv:

9 Mono-H(bb) Higgs radiation from the initial state is Yukawasuppressed, mono-h signatures are sensitive to different (more complex) DM models Z 0 h A b-jets for high-et a fat jet with two bs inside Background contamination varies as a function of the kinematic range: top uark production at low pt, Z+jets at high pt backgrounds are constrained in CRs defined using leptons other soft jets allowed ET > 50 (500) GeV Main systematic uncertainties come from the modelling of background processes Since no SM Higgs is expected in the final state, here we look for the presence of the Higgs boson itself, which would appear in this topology thanks to DM signatures Several signal regions defined depending on the ET and the number of b-tagged jets Events / 0 GeV Data SM SR (Merged) : 0 lepton > 500 GeV b-tags Data SM Vh Diboson tt + single top Z+jets W+jets Background Uncertainty Pre-fit Background h + Z'-HDM m Z' =.4 TeV, m = 0.6 TeV A = 3.75 fb σ Signal m J 9

10 Mono-H(bb): results In this search, limits are set on the parameters of this specific Z -HDM model: scan (mz, ma) for fixed values of the other parameters Z 0 h A m A h(bb) + E, all limits at 95% CL T Z -HDM tanβ =, g = 0.8, m χ = 0 GeV Z m H = m ± H = 300 GeV Kin. limit : m A = m Z - m h Observed limit Expected limit ±σ s = 3 TeV, 3. fb Not to be confused with the (mmed, mdm) plane from other mono-x searches m Z Z -HDM: a Two Higgs Doublet Model (which foresees h, H, H± and A) with an additional Z

11 Mono-Z(lep) H e + e - /μ + μ - In addition to the ISR of a Z boson, here one can probe the presence of H χχ direct coupling Z jets are not vetoed ΔΦ(MET, Zlep) >.7 ET > 90 GeV SM Higgs has an invisible BR of ~ -3 (via H ZZ* vvvv) a direct coupling to DM would enhance this BR Z Events / GeV 4 3 s=3 TeV, 36. fb ee Data ZZ WZ Z+jets Non-resonant-ll Others Stat. + Syst. =500, 0 GeV)x0.7 DM(m, m med χ ZH(ll+inv) with B(H inv)=0.3 Main systematic uncertainties come from signal theory and jet/et scale and resolution Fitting the ET spectrum allows to set upper limits on the BR(H inv.) Events / bkg

12 Where do mono-x analyses contribute? DM Mass [TeV] DM Simplified Model Exclusions Preliminary July Dijet + ISR Dijet TLA Dijet 8 TeV Dijet DM Mass = Mediator Mass Dijet s = 3 TeV, 37.0 fb arxiv: [hep-ex] Dijet 8 TeV s = 8 TeV, 0.3 fb Phys. Rev. D (05) Dijet TLA s = 3 TeV, 3.4 fb -CONF γ +jet Thermal Relic Ω c h = 0. Dijet + ISR s = 3 TeV, 5.5 fb -CONF γ Eur. Phys. J. C 77 (07) 393 DM Mass [TeV] Z Vector mediator, Dirac DM g = 0.5, g = 0, g = l All limits at 95% CL DM Mediator Mass [TeV] DM Simplified Model Exclusions Preliminary July 07. DM Mass = Mediator Mass Thermal Relic Ω c h = 0. +jet -CONF Z -CONF Dijet Dijet 8 TeV s = 8 TeV, 0.3 fb Phys. Rev. D (05) Dijet s = 3 TeV, 37.0 fb arxiv: [hep-ex] Dijet TLA s = 3 TeV, 3.4 fb -CONF Dijet + ISR s = 3 TeV, 5.5 fb -CONF X E +γ T Eur. Phys. J. C 77 (07) 393 E +jet T -CONF Varying the couplings (even with the same hypotheses on the mediator) the reach and the importance of the different signatures varies wildly 0.4 Dilepton Dijet Dilepton CERN-EP X Vector mediator, Dirac DM g = 0., g = 0.0, g = l All limits at 95% CL DM Mediator Mass [TeV]

13 Summary Search for DM is an highly interdisciplinary challenge, and each field has its own strengths and weaknesses Collider searches are particularly powerful at low WIMP masses and can play a relevant role also compared to direct and indirect DM searches Mono-X signatures are a powerful tool - offer a clear signature to select and identify events - depending on the nature of X, allow direct probe of a number of different models 3

14 Backup

15 The detector Run : collected ~36/fb during 05 and 06 data taking at s = 3 TeV 5

16 Relevant performances Normalised Events / GeV Preliminary 33 fb, s=3 TeV Z µµ topology, 07 Data Track Soft Term (TST) EM+JES jets Tight Inclusive Jets 0 Jets η >.4 0 Jets 7 Identification Efficiency Simulation Preliminary s = 3 TeV Z ee Simulation Loose Medium Tight Efficiency Data / MC E T Preliminary s = 3 TeV, 5.4 fb Medium muons η >0. Stat only Sys Stat J/ψ µµ Data J/ψ µµ MC Z µµ Data Z µµ MC p T 6

17 Mono-jet: other interpretations 95% CL upper limit on µ 4 3 Pseudo-scalar mediator Pseudo-Scalar Mediator Dirac Fermion DM m χ = GeV, g = g χ 95% CL limits = Expected limit ± σ exp Expected limit (± σ exp ) PDF, scale Observed limit (± σ theory ) m χ Coloured scalar mediator 95% CL limits Coloured scalar mediator g = m η = m χ Expected limit ± σ exp Expected limit (± σ exp ) PDF,scale Observed limit (± σ theory ) Relic density (MadDM) m ZP m η 7

18 Other models for mono-h search results from mono-h(γγ) h Z 0 Z 0 Pure Z model which couples both to Higgs and DM m χ 3 H(γγ) + E, Z', Dirac DM T B sinθ = 0.3, g = /3, g = χ σ obs / σ th = Expected Expected + σ Expected - σ m Z'B m Z' = m χ 3 σ obs /σ th 95% CL observed limit on B(h γγ) [fb] 95% CL limit on σ(pp hχχ) 3 Observed Expected Expected ± σ Expected ± σ B σ th pp h( γ γ ) + sinθ = 0.3, g χ χ, Z' B = /3, g χ model =, m χ = GeV m Z'B 8

19 DM searches AV mediator with non-zero couplings to leptons DM Mass [TeV] DM Simplified Model Exclusions Preliminary July 07 Perturbative Unitarity +X Dijet Dilepton DM Mass = Mediator Mass Axial-vector mediator, Dirac DM g = 0., g = 0., g = Thermal Relic Ω c h All limits at 95% CL l = 0. DM Dijet Dijet 8 TeV s = 8 TeV, 0.3 fb Phys. Rev. D (05) Dijet s = 3 TeV, 37.0 fb arxiv: [hep-ex] Dijet TLA s = 3 TeV, 3.4 fb -CONF Dijet + ISR s = 3 TeV, 5.5 fb -CONF E T +X +γ Eur. Phys. J. C 77 (07) 393 E T +jet -CONF Dilepton CERN-EP Mediator Mass [TeV] 9