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Searching and Constraining Dark Matter in Colliders

Searching and Constraining Dark Matter in Colliders . Vasiliki A. Mitsou IFIC Valencia. XXIX Workshop on Recent Advances in Particle Physics and Cosmology 14–16 April 2011, University of Patras. Outline. D ark matter astrophysical evidence theoretical models predicting WIMPs

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Searching and Constraining Dark Matter in Colliders

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  1. Searching and Constraining Dark Matter in Colliders Vasiliki A. Mitsou IFIC Valencia XXIX Workshop on Recent Advances in Particle Physics and Cosmology14–16 April 2011, University of Patras

  2. V. A. Mitsou Outline • Dark matter • astrophysical evidence • theoretical models predicting WIMPs • DM in colliders • missing energy • search strategy • constraints • massmeasurements • distinguishmodels • determine modelparameters • Conclusions & outlook Energy budget of the Universe LHC

  3. V. A. Mitsou Dark matter cosmological evidence • Astrophysical observations (gravitational) • galaxy clusters rotation curves • velocity dispersions of galaxies • gravitational lensing • structure formation  Cold Dark Matter: non-relativistic matter • Precise DM measurements • Cosmic MicrowaveBackground(CMB) • + other (BAO, H0, …) • DM particlerelicdensity: Ωχ≈0.23 Optical –X-rays - Dark Matter Bradac et al,ApJ652 (2006) 937 BULLET CLUSTER sensitive to DM CMB power spectrum D Larson et al [WMAP] arXIv:1001.4635

  4. Weakly Interacting Massive Particles (WIMPs) • 1 GeV < mχ < 50 TeV • thermal relics from Big Bang • being stable and weakly-interacting only, if produced at a collider, escape detection ➔ large missing energy • Possible WIMPs predicted in models with a symmetry preventing lightest new particle from decaying • lightest supersymmetric particle (neutralino, massO(100 GeV)) • Kaluza-Klein states (UED, …) • T-odd states in “Little Higgs” • axino, gravitino (extremely WIPs) in R-parity violating SUSY V. A. Mitsou Dark matter candidates WIMP miracle thermally-averaged WIMP annihilation cross section EW cross section for annihilation of non-relativistic particles ~ • Other DM explanations • axions (solve strong CP problem) • non-thermal (superheavy) relics focus on SUSY in this talk search strategy at LHC similar to that of SUSY

  5. V. A. Mitsou R-parity violating SUSY & dark matter • R-parity conservation is an ad-hoc assumption • rapid proton decay avoided if only B or L is violated • RPV SUSY & DM • seemingly incompatible concepts • can be reconciled in models with a gravitino or axino LSP with a lifetime exceeding the age of the Universe • If RPV is induced by bilinear terms in the superpotential that can also explain neutrino masses and mixings without invoking any GUT-scale physics • RPV couplings can lead to interesting expectations for collider phenomenology • standard SUSY signatures: multi-lepton and multi-jet events • + explicit lepton number violation at the final state • Nevertheless determining whether R-parity is conserved or broken may not be trivial • WIMPs, whether absolutely stable or quasi-stable, cannot be detected directly in collider experiments • merely observed as missing energy R = (-1)3(B-L)+2s Takayama & Yamaguchi PLB 485 (2000) 388 Buchmulleret al JHEP03(2007)037 Chun& Kim JHEP10(2006)082 Hirsch, Porod, RestrepoJHEP03(2005)062

  6. V. A. Mitsou Missing (transverse) energy • = imbalance of total measured (transverse) momentum • True ME(T) indicates invisible, i.e. weakly interacting, particles • e.g. neutrinos, WIMPs • Observable directly connected to dark-matter particles independent of underlying model simulated event

  7. l l q V. A. Mitsou DM search strategy at LHC qualitative picture – no mass scale mSUGRA Standard signature:multi jets + missing ET+ (leptons) p p ~ ~ ~ q ~ c10 ~ c20 g l q WMAP constraints on neutralinorelicdensityΩχ(*) (g – 2)μ measurements Kakizaki, Matsumoto, Senami, PRD 74 (2006) 023504 • (*)Caution: neutralinorelicdensitypredictiondependsonassumptionsmadeonSUSY/UED/cosmologicalmodel • otherchannelsmay be favourablefordiscovery UED

  8. V. A. Mitsou Supercritical String Cosmology (SSC) • The presence of the time-dependent dilaton affects the relic density calculation, since it modifies the Boltzmann equation • O(10) dilution for dark matter (neutralinos) ➞ more room for Supersymmetry at colliders • LHC signatures also affected • h(➞bb) + jets + MET • Z(➞ℓℓ) + jets + MET • 2τ + jets + MET favouredin new regions Dutta et al, PRD 79 (2009) 055002 SSC-allowed ordinary cosmology-allowed Lahanas et al, PLB 649 (2007) 83 [hep-ph/0612152]

  9. V. A. Mitsou SUSY searches at LHC • No SUSY(-like) signal observed at LHC so far (~35 pb-1) • (see talks by R. Hawking & G. Gómez) • Huge potential still to be explored …even this year • If a positive signal is to be found, what and how can we learn about dark matter from it? All-hadronicchannel 95% exclusion limits 5σdiscoveryreach for 0,1 and 2 lepton channels simulation studies ATLAS-PHYS-PUB-2010-010 CMS-NOTE-2010-008

  10. V. A. Mitsou Mass combinations • LSPs escaping the detector make reconstruction of mass peaks impossible • Mass measurement strategy • apply kinematics on long decay chains to link endpoints with combinations of masses • measure endpoints (edges, thresholds) in invariant mass distributions • Cuts applied depend on the SUSY mass scale; has to be known from Meff distribution • Method does not depend on underlying model (pure kinematics) Allanach et al., JHEP 09 (2000) 004

  11. V. A. Mitsou Dileptonendpoint 1 fb-1 14 TeV • Event selection based on: • 2 or 3 leptons + at least 2 jets + ETmiss • Flavoursubtraction is applied (OSSF-OSOF) to remove SUSY/SM background • Fit triangular distribution with Gaussian smearing SU3 0.5 fb-1 14 TeV SU4 +bkg ATLAS collab, CSC note, ATL-COM-PHYS-2008-063

  12. V. A. Mitsou Adding the squarks • Di-lepton edge starting point for reconstruction of decay chain • Make invariant mass combinations of leptons and jets • Gives multiple constraints on combinations of four masses ATLAS collab, CSC note, ATL-COM-PHYS-2008-063 with 1 fb-1 0.5 fb-1 1 fb-1 0.5 fb-1 SU3 SU4 SU4

  13. Measurement of masscombinations- endpoints … V. A. Mitsou Model masses/parameters determination Sparticlesmassesdeterminationwithhighuncertaintyevenfor SU3 (optimum case) 1 fb-1 FittingmasscombinationswithSfitter Determination of mSUGRApara-meters with a precision at % level 300 fb-1 ATLAS collab, CSC note, ATL-COM-PHYS-2008-063 • mSUGRAparametersdetermination: • m0, m1/2 at 1–3% • tanβ, A0onlyorder of magnitude • Higgswidthmeasurement➔ tanβ determination 1 fb-1 If sgn(μ) fixed Lafaye et al, hep-ph/0512028 For a more precise parameterdetermination, e+e-colliderisneeded

  14. ATLAS Point 5 150 fb-1 Mℓℓ Mℓq ATLAS Point 5 150 fb-1 non-flat anglular distribution spin-0 spin-½ spin-0=flat spin-0triangulardistribution polarised spin-½ mostly wino spin-½ mostly bino spin-0 V. A. Mitsou Is it Supersymmetry? • Determination of new particles’ spin can distinguish different models, e.g. SUSY vs. UED • Charge asymmetry reflects primary production asymmetry: squarks – anti-squarks • Consider usual two-body slepton decay chain • charge asymmetry of lq pairs sensitive to spin of ~χ20 • shape of dilepton invariant mass spectrum indication of sleptonspin Barr, PLB 596 (2004) 205 see also Barr, JHEP02 (2006) 042

  15. V. A. Mitsou Beyond LHC… e+e- colliders FengJPhysG 32 (2006) R1 Bagger, Nojiri, Belanger • Dark matter relic density Ωχpredictions in colliders requires determination of variousparameters • LSP properties • other particles contributing to LSP annihilation • squarks, gluinos • heavy Higgs boson • Gain in sensitivity by combining LHC and ILC data is spectacular Baltzet al PRD 74 (2006) 103521

  16. V. A. Mitsou Returning to RPV SUSY • RPV through bilinear terms: • relevant for neutrino masses and mixing • BRs of LSP sensitive to neutrino mixing parameters • Search ongoing in the ATLAS experiment Hirsch, Diaz, Porod, Romao, Valle, PRD 62 (2000) 113008 De Camposet al, PRD 82 (2010) 075002 CLIC study e+e- 5 TeV generatorlevel LHC √s=14 TeV Accomando et al arXiv:hep-ph/0412251 sparticles masses measurement 10% M(μjj) [GeV] E. Torró, VAM, C. García, E. Romero, ongoing analysis

  17. V. A. Mitsou Outlook • Discovery of dark matter in colliders: search for deviation from SM in inclusive signatures like missing energy + jets (+leptons) • Scheme developed for SUSY, but applicable to other BSM scenarios, e.g. extra dimensions, Little Higgs, ... • LHC capable of discovering generic WIMP dark matter • non-trivial to prove that it has the right properties •  LHC upgrade, ILC/CLIC: extend LHC observations • improve on LHC capability of identifying DM model • more precise determination of model parameters • Complementarity between LHC and astroparticle detectors • uncorrelated systematics • measure different parameters see also: VAM, arXiv:1104.1149 [hep-ph]

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