PPC07, May 2007 Dan Tovey 1 Dark Matter Searches at ATLAS Dan Tovey University of Sheffield Dan Tovey University of Sheffield

PPC07, May 2007 Dan Tovey 2 ATLAS Length: ~45 m Radius: ~12 m Weight: ~7000 tons

PPC07, May 2007 Dan Tovey 3

PPC07, May 2007 Dan Tovey 4 First cosmic muons observed by ATLAS in the underground cavern on June 20 th 2005 (recorded by hadron Tilecal calorimeter) Tower energies: ~ 2.5 GeV First Astroparticle Data…

PPC07, May 2007 Dan Tovey 5 Main asset of LHC: huge event statistics thanks to high  s and L Allows precision measurements/tests of SM Searches for new particles with unprecedented precision. Event Rates Process Events/s Events per year Total statistics collected at previous machines by 2008 W  e LEP / 10 7 Tevatron Z  ee LEP tt Tevatron bb – Belle/BaBar? H m=130 GeV ? m= 1 TeV Black holes m > 3 TeV (M D =3 TeV, n=4) L = cm -2 s -1

PPC07, May 2007 Dan Tovey 6 Dark ATLAS Characteristic signature for Dark Matter production at ATLAS: Missing Transverse Energy (‘MET’) Valid for any DM candidate (not just SUSY) Observation of MET signal necessary but not sufficient to prove DM signal (DM particle could decay outside detector) MET 0101 0101 ~ ~ Conclusive proof of both existence and identity of DM by combining LHC data with astroparticle data

PPC07, May 2007 Dan Tovey 7 Complementarity   p si h2h2 ZEPLIN-MAX GENIUS XENON ZEPLIN-4 ZEPLIN-2 EDELWEISS 2 CRESST-II ZEPLIN-I EDELWEISS CDMS DAMA Aim to test compatibility of e.g. SUSY signal with DM hypothesis (data from astroparticle experiments) –Fit SUSY model parameters to ATLAS measurements –Use to calculate DM parameters   h 2, m ,   p si etc. Measurements at ATLAS complementary to direct and indirect astroparticle searches / measurements –Uncorrelated systematics –Measures different parameters   p si (cm 2 ) log 10 (   p si / 1pb) h2h2 No. MC Experiments DM particle mass m  (GeV) Polesello et al JHEP 0405 (2004) 071 CDMS-II Provides strongest possible test of Dark Matter model   p si mm

PPC07, May 2007 Dan Tovey 8 SUSY DM Strategy 1)SUSY Discovery phase 2)Inclusive Studies (measurement of SUSY Mass Scale, comparison of significance in inclusive channels). 3)Exclusive studies and interpretation within specific model framework (e.g. Constrained MSSM / mSUGRA) –Specific model needed to calculate e.g. relic density  general SUSY studies will be less model dependent. 4)Less model-dependent interpretation –Relax model-dependent assumptions SUSY Dark Matter studies at ATLAS will proceed in four stages:

PPC07, May 2007 Dan Tovey 9 Stage 1: SUSY Discovery

PPC07, May 2007 Dan Tovey 10 SUSY Signatures Q: What do we expect SUSY LHC to look like? A: Look at typical decay chain: Strongly interacting sparticles (squarks, gluinos) dominate production. Heavier than sleptons, gauginos etc.  cascade decays to LSP. Long decay chains and large mass differences between SUSY states –Many high p T objects observed (leptons, jets, b-jets). If R-Parity conserved LSP (lightest neutralino in mSUGRA) stable and sparticles pair produced. –Large E T miss signature (c.f. W  l ). Closest equivalent SM signature t  Wb. l q q l g ~ q ~ l ~  ~  ~ p p

PPC07, May 2007 Dan Tovey 11 ATLAS 55 Use 'golden' Jets + n leptons + E T miss discovery channel. Map statistical discovery reach in mSUGRA m 0 -m 1/2 parameter space. Sensitivity only weakly dependent on A 0, tan(  ) and sign(  ). Syst.+ stat. reach harder to assess: focus of current & future work. Inclusive Searches ATLAS 55

PPC07, May 2007 Dan Tovey 12 Background Systematics Z  + n jets, W  l + n jets, W   + (n-1) jets (  fakes jet) Estimate from Z  l + l - + n jets (e or  ) Tag leptonic Z and use to validate MC / estimate E T miss from p T (Z) & p T (l) Alternatively tag W  l + n jets and replace lepton with  0l): –higher stats –biased by presence of SUSY ATLAS Preliminary ATLAS Preliminary (Z  ll) (W  l )

PPC07, May 2007 Dan Tovey 13 Stage 2: Inclusive Studies

PPC07, May 2007 Dan Tovey 14 Question 2: Is the LSP the lightest neutralino? –Natural in many MSSM models –If YES then test for consistency with astrophysics –If NO then what is it? –e.g. Light Gravitino DM from GMSB models (not considered here) Following any discovery of SUSY next task will be to test broad features of potential Dark Matter candidate. Question 1: Is R-Parity Conserved? –If YES possible DM candidate –LHC experiments sensitive only to LSP lifetimes < 1 ms (<< t U ~ 13.7 Gyr) Inclusive Studies Non-pointing photons from  0 1  G  ~ ~ GMSB Point 1b (Physics TDR) LHC Point 5 (Physics TDR) R-Parity Conserved R-Parity Violated ~ ATLAS

PPC07, May 2007 Dan Tovey 15 Measuring Parameters First indication of mSUGRA parameters from inclusive channels –Compare significance in jets + E T miss + n leptons channels Detailed measurements from exclusive channels when accessible. Consider here two specific example points studied previously: ATLAS LHC Point 5 (A 0 =300 GeV, tan(  )=2,  >0) Point SPS1a (A 0 =-100 GeV, tan(  )=10,  >0) Sparticle Mass (LHC Point 5) Mass (SPS1a) q L ~690 GeV ~530 GeV  GeV 177 GeV l R 157 GeV 143 GeV  GeV 96 GeV ~ ~ ~ ~ Point m 0 m 1/2 A 0 tan(  ) sign(  ) LHC Point SPS1a

PPC07, May 2007 Dan Tovey 16 Stage 3: Exclusive studies and interpretation within specific model framework

PPC07, May 2007 Dan Tovey 17 Exclusive Studies With more data will attempt to measure weak scale SUSY parameters (masses etc.) using exclusive channels. Different philosophy to TeV Run II (better S/B, longer decay chains)  aim to use model-independent measures. Two neutral LSPs escape from each event –Impossible to measure mass of each sparticle using one channel alone Use kinematic end-points to measure combinations of masses. Old technique used many times before ( mass from  decay spectrum, W (transverse) mass in W  l ). Difference here is we don't know mass of neutral final state particles. lq q l g ~ q ~ lRlR ~  ~  ~ pp

PPC07, May 2007 Dan Tovey 18 Dilepton Edge Measurements ~ ~ 0202 ~ 0101 ll l e + e - +  +  - ~ ~ 30 fb -1 atlfast Physics TDR Point 5 e + e - +  +  - - e +  - -  + e - 5 fb -1 SU3 ATLAS m 0 = 100 GeV m 1/2 = 300 GeV A 0 = -300 GeV tan(  ) = 6 sgn(  ) = +1 When kinematically accessible    can  undergo sequential two-body decay to    via a right-slepton (e.g. LHC Point 5). Results in sharp OS SF dilepton invariant mass edge sensitive to combination of masses of sparticles. Can perform SM & SUSY background subtraction using OF distribution e + e - +  +  - - e +  - -  + e - Position of edge measured with precision ~ 0.5% (30 fb -1 ).

PPC07, May 2007 Dan Tovey 19 Measurements With Squarks Dilepton edge starting point for reconstruction of decay chain. Make invariant mass combinations of leptons and jets. Gives multiple constraints on combinations of four masses. Sensitivity to individual sparticle masses. ~ ~  ~  ll l qLqL q ~ ~  ~  b h qLqL q ~ b llq edge 1% error (100 fb -1 ) lq edge 1% error (100 fb -1 ) llq threshold 2% error (100 fb -1 ) bbq edge TDR, Point 5 TDR, Point 5 TDR, Point 5 TDR, Point 5 ATLAS 1% error (100 fb -1 )

PPC07, May 2007 Dan Tovey 20 ‘Model-Independent’ Masses Combine measurements from edges from different jet/lepton combinations to obtain ‘model- independent’ mass measurements. 0101 lRlR 0202 qLqL Mass (GeV) ~ ~ ~ ~ ATLAS Sparticle Expected precision (100 fb -1 ) q L  3%  0 2  6% l R  9%  0 1  12% ~ ~ ~ ~ LHCC Point 5

PPC07, May 2007 Dan Tovey 21 Measuring Model Parameters Alternative use for SUSY observables (invariant mass end-points, thresholds etc.). Here assume mSUGRA/CMSSM model and perform global fit of model parameters to observables –So far mostly private codes but e.g. SFITTER, FITTINO now on the market; –c.f. global EW fits at LEP, ZFITTER, TOPAZ0 etc. Point m 0 m 1/2 A 0 tan(  ) sign(  ) LHC Point SPS1a Parameter Expected precision (300 fb -1 ) m 0  2% m 1/2  0.6% tan(  )  9% A 0  16%

PPC07, May 2007 Dan Tovey 22 Dark Matter Parameters Baer et al. hep-ph/ LEP 2 No REWSB LHC Point 5: >5  error (300 fb -1 )   p = pb   p = pb   p =10 -9 pb Can use parameter measurements for many purposes, e.g. estimate LSP Dark Matter properties (e.g. for 300 fb -1, SPS1a) –   h 2 =  –log 10 (   p /pb) =  0.04 SPS1a: >5  error (300 fb -1 ) Micromegas 1.1 (Belanger et al.) + ISASUGRA 7.69 ATLAS 300 fb -1 pp ATLAS 300 fb -1 DarkSUSY (Gondolo et al.) + ISASUGRA 7.69 h2h2

PPC07, May 2007 Dan Tovey 23 Target Models SUSY (e.g. mSUGRA) parameter space strongly constrained by cosmology (e.g. WMAP satellite) data. mSUGRA A 0 =0, tan(  ) = 10,  >0 'Bulk' region: t- channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts. 'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons ~ Ellis et al. hep-ph/ 0101 0101 l l lRlR ~ ~ ~ 0101 11   /Z/h 11 ~ ~ ~ Disfavoured by BR (b  s  ) = (3.2  0.5)  (CLEO, BELLE)    h 2  (WMAP) Slepton Co- annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult. Also 'rapid annihilation funnel' at Higgs pole at high tan(  ), stop co-annihilation region at large A 0

PPC07, May 2007 Dan Tovey 24 Coannihilation Signatures E T miss >300 GeV 2 OSSF leptons P T >10 GeV >1 jet with P T >150 GeV OSSF-OSOF subtraction applied E T miss >300 GeV 1 tau P T >40 GeV;1 tau P T <25 GeV >1 jet with P T >100 GeV SS tau subtraction Small slepton-neutralino mass difference gives soft leptons –Low electron/muon/tau energy thresholds crucial. Study point chosen within region: –m 0 =70 GeV; m 1/2 =350 GeV; A 0 =0; tanß=10 ; μ>0; Decays of  0 2 to both l L and l R kinematically allowed. –Double dilepton invariant mass edge structure; –Edges expected at 57 / 101 GeV Stau channels enhanced (tan  ) –Soft tau signatures; –Edge expected at 79 GeV; –Less clear due to poor tau visible energy resolution. ATLAS Preliminary 100 fb -1 ~ ~ ~

PPC07, May 2007 Dan Tovey 25 Focus Point Signatures Large m 0  sfermions are heavy Most useful signatures from heavy neutralino decay Study point chosen within focus point region : –m 0 =3550 GeV; m 1/2 =300 GeV; A 0 =0; tanß=10 ; μ>0 Direct three-body decays  0 n →  0 1 ll Edges give m(  0 n )-m(  0 1 ) : flavour subtraction applied ~ ~ ~~ Z 0 → ll 300 fb -1    →    ll ~ ~    →    ll ~ ~ Preliminary ATLAS ParameterWithout cutsExp. value MM 68± M 2 -M ± M 3 -M ± M = m A +m B  m A -m B

PPC07, May 2007 Dan Tovey 26 Stage 4: Less model-dependent interpretation

PPC07, May 2007 Dan Tovey 27 Dark Matter in the MSSM Can relax mSUGRA constraints to obtain more ‘model-independent’ relic density estimate. Much harder – needs more measurements Not sufficient to measure relevant (co-) annihilation channels – must exclude all irrelevant ones also … Stau, higgs, stop masses/mixings important as well as gaugino/higgsino parameters Nojiri, Polesello & Tovey, JHEP 0603 (2006) 063 h2h2 h2h2 σ(m  )= 5 GeV σ(m  )= 0.5 GeV SPA point 300 fb -1 σ(   h 2 ) vs σ(m  )

PPC07, May 2007 Dan Tovey 28 Heavy Gaugino Measurements Potentially possible to identify dilepton edges from decays of heavy gauginos. Requires high stats. Crucial input to reconstruction of MSSM neutralino mass matrix (independent of SUSY breaking scenario). ATLAS 100 fb -1 ATLAS 100 fb -1 ATLAS 100 fb -1 ATLAS SPS1a

PPC07, May 2007 Dan Tovey 29 Summary Following a (SUSY) discovery ATLAS will aim to test the (SUSY) Dark Matter hypothesis. Conclusive result only possible in conjunction with astroparticle experiments (constraints on LSP life-time). Estimation of relic density and direct / indirect DM detection cross-sections in model-dependent scenario will be first goal. Less model-dependent measurements will follow. Ultimate goal: observation of neutralinos at LHC confirmed by observation of e.g. signal in (in)direct detection Dark Matter experiment at predicted mass and cross-section. This would be major triumph for both Particle Physics and Cosmology!

PPC07, May 2007 Dan Tovey 30 BACK-UP SLIDES

PPC07, May 2007 Dan Tovey 31 Supersymmetry Supersymmetry (SUSY) fundamental continuous symmetry connecting fermions and bosons Q  |F> = |B>, Q  |B> = |F> {Q ,Q  }=-2    p   generators obey anti- commutation relations with 4-mom –Connection to space-time symmetry SUSY stabilises Higgs mass against loop corrections (gauge hierarchy/fine-tuning problem) –Leads to Higgs mass  135 GeV –Good agreement with LEP constraints from EW global fits SUSY modifies running of SM gauge couplings ‘just enough’ to give Grand Unification at single scale. LEPEWWG Winter 2006 m H <207 GeV (95%CL)

PPC07, May 2007 Dan Tovey 32   e H-dH-d ~ H+uH+u ~ H0dH0d ~ H0uH0u ~ 0404 ~ 0303 ~ 0202 ~ 0101 ~ SUSY Spectrum Expect SUSY partners to have same masses as SM states –Not observed (despite best efforts!) –SUSY must be a broken symmetry at low energy Higgs sector also expanded SUSY gives rise to partners of SM states with opposite spin-statistics but otherwise same Quantum Numbers. H±H± H0H0 A G   e bt sc du g W±W± Z  h W±W± Z  ~ ~~ g ~ G ~  ± 2 ~  ± 1 ~   e   e bt sc du ~~ ~ ~ ~~ ~~~ ~ ~ ~

PPC07, May 2007 Dan Tovey 33 Model Framework Minimal Supersymmetric Extension of the Standard Model (MSSM) contains > 105 free parameters, NMSSM etc. has more  difficult to map complete parameter space! Assume specific well-motivated model framework in which generic signatures can be studied. Often assume SUSY broken by gravitational interactions  mSUGRA/CMSSM framework : unified masses and couplings at the GUT scale  5 free parameters (m 0, m 1/2, A 0, tan(  ), sgn(  )). R-Parity assumed to be conserved. Exclusive studies use benchmark points in mSUGRA parameter space: LHCC Points 1-6; Post-LEP benchmarks (Battaglia et al.); Snowmass Points and Slopes (SPS); etc… LHCC mSUGRA Points

PPC07, May 2007 Dan Tovey 34 SUSY & Dark Matter R-Parity R p = (-1) 3B+2S+L Conservation of R p (motivated e.g. by string models) attractive –e.g. protects proton from rapid decay via SUSY states Causes Lightest SUSY Particle (LSP) to be absolutely stable LSP neutral/weakly interacting to escape astroparticle bounds on anomalous heavy elements. Naturally provides solution to dark matter problem R-Parity violating models still possible  not covered here. Universe Over-Closed mSUGRA A 0 =0, tan(  ) = 10,  >0 Ellis et al. hep-ph/ 0101 0101 l l lRlR ~ ~ ~ 0101 11   /Z/h 11 ~ ~ ~ Disfavoured by BR (b  s  ) = (3.2  0.5)  (CLEO, BELLE)    h 2  (WMAP-1year)

PPC07, May 2007 Dan Tovey 35 Stop Mass Look at edge in tb mass distribution. Contains contributions from –g  tt 1  tb  + 1 –g  bb 1  bt  + 1 –SUSY backgrounds Measures weighted mean of end-points Require m(jj) ~ m(W), m(jjb) ~ m(t) Subtract sidebands from m(jj) distribution Can use similar approach with g  tt 1  tt  0 i –Di-top selection with sideband subtraction Also use ‘standard’ bbll analyses (previous slide) ~ ~ ~ ~ ~ ~ 120 fb -1 ATLAS LHCC Pt 5 (tan(  )=10) 120 fb -1 ATLAS LHCC Pt 5 (tan(  )=10) m tb max = (443.2 ± 7.4 stat ) GeV Expected = 459 GeV m tb max = (510.6 ± 5.4 stat ) GeV Expected = 543 GeV ~ ~ ~

PPC07, May 2007 Dan Tovey 36 Preparations for 1 st Physics Preparations needed to ensure efficient/reliable searches for/measurements of SUSY particles in timely manner: –Initial calibrations (energy scales, resolutions, efficiencies etc.); –Minimisation of poorly estimated SM backgrounds; –Estimation of remaining SM backgrounds; –Development of useful tools. –Definition of prescale (calibration) trigger strategy Different situation to Run II (no previous  measurements at same  s) Will need convincing bckgrnd. estimate with little data as possible. Background estimation techniques will change depending on integrated lumi. Ditto optimum search channels & cuts. Aim to use combination of –Fast-sim; –Full-sim; –Estimations from data. Use comparison between different techniques to validate estimates and build confidence in (blind) analysis.

PPC07, May 2007 Dan Tovey 37 Black Hole Signatures In large ED (ADD) scenario, when impact parameter smaller than Schwartzschild radius Black Hole produced with potentially large x-sec (~100 pb). Decays democratically through Black Body radiation of SM states – Boltzmann energy distribution. M p =1TeV, n=2, M BH = 6.1TeV Discovery potential (preliminary) –M p < ~4 TeV  < ~ 1 day –M p < ~6 TeV  < ~ 1 year Studies continue … ATLAS w/o pile-up ATLAS

PPC07, May 2007 Dan Tovey 38

PPC07, May 2007 Dan Tovey 39

PPC07, May 2007 Dan Tovey 40 Sbottom/Gluino Mass Following measurement of squark, slepton and neutralino masses move up decay chain and study alternative chains. One possibility: require b-tagged jet in addition to dileptons. Give sensitivity to sbottom mass (actually two peaks) and gluino mass. Problem with large error on input  0 1 mass remains  reconstruct difference of gluino and sbottom masses. Allows separation of b 1 and b 2 with 300 fb -1. lb b l g ~ b ~ lRlR ~  ~  ~ pp 300 fb -1 ~ ~ ~ m(g)-0.99m(  0 1 ) = (500.0 ± 6.4) GeV 300 fb -1 ATLAS SPS1a m(g)-m(b 1 ) = (103.3 ± 1.8) GeV m(g)-m(b 2 ) = (70.6 ± 2.6) GeV ~ ~ ~ ~ ~ ~

PPC07, May 2007 Dan Tovey 41 RH Squark Mass Right handed squarks difficult as rarely decay via ‘standard’  0 2 chain –Typically BR (q R   0 1 q) > 99%. Instead search for events with 2 hard jets and lots of E T miss. Reconstruct mass using ‘stransverse mass’ (Allanach et al.): m T2 2 = min [max{m T 2 (p T j(1),q T  (1) ;m  ),m T 2 (p T j(2),q T  (2) ;m  )}] Needs  0 1 mass measurement as input. Also works for sleptons. q T  (1) +q T  (2) =E T miss ~ ~ ~  qRqR q ~ ATLAS 30 fb fb -1 Left slepton Right squark ~ ~ SPS1a Precision ~ 3%

PPC07, May 2007 Dan Tovey 42 Physics Strategy December 2007(?): 900 GeV calibration run –commence tuning trigger menus / in situ calibration Summer 2008: first 14 TeV physics run (L < cm -2 s -1, L int ~ 1 fb -1 ) –commence tuning trigger menus / in situ calibration –First SM measurements: min bias, PDF constraints, Z / W / top / QCD 2008/9: physics run (L ~ 2x10 33 cm -2 s -1, L int ~ 10 fb -1 ) –First B-physics measurements & rare decay searches (e.g. B s →J/  ) –First searches: high mass dilepton / Z’, inclusive SUSY, Black Hole production, Higgs in ‘easier’ channels e.g. H→4l 2009/10: physics run (L ~ 2x10 33 cm -2 s -1, L int = 10 fb -1 /year) –First precision SM & B-physics measurements (systematics under control) –Improved searches sensitivity –Light Higgs searches (ttH, H→gg, VBF qqH(H→  ) etc.) 2010/11: High luminosity running (L ~10 34, L int = 100 fb -1 /year) –High precision measurements of New Physics (e.g. Higgs/SUSY/ED properties)

PPC07, May 2007 Dan Tovey 43 Inclusive SUSY First SUSY parameter to be measured may be mass scale: –Defined as weighted mean of masses of initial sparticles. Calculate distribution of 'effective mass' variable defined as scalar sum of masses of all jets (or four hardest) and E T miss : M eff =  p T i | + E T miss. Distribution peaked at ~ twice SUSY mass scale for signal events. Pseudo 'model-independent' measurement. With PS typical measurement error (syst+stat) ~10% for mSUGRA models for 10 fb -1, errors much greater with ME calculation  an important lesson … Jets + ETmiss + 0 leptons ATLAS 10 fb -1

PPC07, May 2007 Dan Tovey 44 SUSY Spin Measurement Q: How do we know that a SUSY signal is really due to SUSY? –Other models (e.g. UED) can mimic SUSY mass spectrum A: Measure spin of new particles. One possibility – use ‘standard’ two-body slepton decay chain –charge asymmetry of lq pairs measures spin of  0 2 –relies on valence quark contribution to pdf of proton (C asymmetry) –shape of dilepton invariant mass spectrum measures slepton spin ~ 150 fb -1 spin-0=flat Point 5 ATLAS m lq Straight line dist n (phase-space) Point 5 Spin-½, mostly wino Spin-0 Spin-½ Spin-0 Spin-½, mostly bino Polarise Measure Angle ATLAS 150 fb -1

PPC07, May 2007 Dan Tovey 45 Processing the Data Understand/interpret data via numerically intensive simulations –e.g. 1 event (ATLAS Monte Carlo Simulation) ~20 mins/3 MB Use worldwide computing Grid to solve problem Many events –~10 9 events/experiment/year –~3 MB/event raw data –several passes required  Worldwide LHC computing requirement (2007): –100 Million SPECint2000 (=20,000 of today’s fastest processors) –12-14 PetaBytes of data per year (=100,000 of today’s highest capacity HDD).

PPC07, May 2007 Dan Tovey ns Event rate in ATLAS : N = L x  (pp)  10 9 interactions/s Mostly soft ( low p T ) events Interesting hard (high-p T ) events are rare  Each accompanied by 20 soft events  Also additional soft interactions (UE) ATLAS

PPC07, May 2007 Dan Tovey 47 Background Estimation Inclusive signature: jets + n leptons + E T miss Main backgrounds: –Z + n jets –W + n jets –QCD –ttbar Greatest discrimination power from E T miss (R-Parity conserving models) Generic approach to background estimation: –Select low E T miss background calibration samples; –Extrapolate into high E T miss signal region. Used by CDF / D0 Extrapolation is non-trivial. –Must find variables uncorrelated with E T miss Several approaches being developed. Jets + ETmiss + 0 leptons ATLAS 10 fb -1