ATLAS Higgs and SUSY at the LHC Alan Barron behalf of the ATLAS and CMS collaborations ICHEP-17 Aug 2004, Beijing
Outline • Discovery and measurement of: • Higgs sector of MSSM • SUSY partners of SM particles • SUSY and Higgs discovery reviewed • Reach, channels • Focus on some recent work: • Determination of higgs v.e.v. ratio (tan b) • SUSY spin measurement • Mixed Higgs + SUSY cascade decays
(S)particle reminder SM+ MSSM Higgs SUSY quarks (L&R)leptons (L&R) neutrinos (L&?) squarks (L&R)sleptons (L&R)sneutrinos (L&?) Spin-1/2 Spin-0 AfterMixing Z0W± gluon BinoWino0Wino± gluino BW0 Spin-1 4 x neutralino Spin-1/2 gluino ~ h0 H0 A0 H± H0H± ~ 2 x chargino Spin-0 Extended higgs sector (2 doublets)
Neutral Higgs production Mass of H or h
SM-like higgs discovery h → tt requiresexcellent low-pT lepton + tau jet trigger fb-1 1 year @1034 1 year @1033 time 1 month @1033 ATLAS Values for single experiment
h: Number of observable final states Conservative in tan b 1 channel 2 channels 3 channels 4 channels Excluded by LEP 5 channels 300 fb-1 several channels observable allows parameter determination ? Suppressed g coupling Suppressed b, t
Heavy neutral higgs (H,A)
Measuring tan b (1) • Ratio of v.e.v.s of the 2 MSSM Higgs doublets • Important for understanding EWSB • For large (>5) tan b • b Yukawa dominates s • s tan2b • Measure s • Compare to NLO ~
Measuring tan b (2) • Errors dominated by theoretical uncertainty on NLO cross-section • With signal discovery at 5σ, tan b measurable to 35%. N.B. m, M2 kept fixed here
Charged higgs production/decay • Associated production with t and b quarks • Decay H± → • Very complicated final state! • Combinatorial BG • Also H± → t nt • BR decreases as mA increases ~6 jet + lepton + missing energy SM background uncertain?
Charged higgs • When H+ is close to top mass: • H+ -> tbor • t -> H+b • Revised analyses in progress ATLAS
Overall Discovery Potential: 300 fb-1 • Whole plane covered for at least one Higgs • Large wedge area (intermediate tan b) whereonly his observed • No direct evidence for higgs beyond SM ATLAS • Can we distinguish between SM and extended Higgs sectors by parameter measurements?
SM or Extended Higgs Sectors? First look using rate measurements from VBF channels (30fb-1) ATLAS BR(htt) BR(hWW) R = Deviation from SM expectation D=|RMSSM-RSM|/sexp potential for discrimination seems promising! • only statistical errors considered • assumes Higgs mass exactly known
Searching for SUSY • If SUSY was exact we’d have seen it already • Variety of ways to induce SUSY masses: • Minimal super-gravity (mSUGRA) • Anomaly mediated SUSY breaking (AMSB) • Gauge mediated SUSY breaking (GMSB) • Experimental emphasis is on building general toolkit of techniques based on types of signatures of above • Generally search reach ~2 TeV.
SUSY Discovery - mSUGRA • Finial discovery limit ~ 2.5 TeV squark or gluino • Initially will be limited by detector uncertainties, not SUSY stats! • Also need to understand SM backgrounds Gaugino mass term Scalar mass term
~ ~ ~ c02 ~ c01 qL l l l q Slepton, squark, neutralino masses M(c2)-M(c1) ≈ 105 GeV Apply corrections for electron and muon energy scale and efficiency Flavor Subtracted mass to remove the contribution from uncorrelated SUSY decays: e+e- + m+m- - e+m- - e-m+ 5 fb-1
ATLAS ~ ~ Squark – neutralino1mass difference 5 fb-1 qR qR SUSY measurements - mass q • Mass measurements from exclusive cascade decays • Mass differences well measured • Typically limited by detector performance • Of order 1% • Error in overall mass scale • Unknown missing energy • Of order 10% c01 p p c01 q
SUSY SPIN @ LHC Chiral coupling Measure Angle (or inv mass) • SUSY particles have spin differing by ½ from SM • “Discovering SUSY” means measuring spins of new particles • Possible at LHC? • Investigation of mSUGRA “Point 5” Spin-0 Spin-½ Polarise Spin-½, mostly wino Spin-0 Spin-½, mostly bino Final state = jet + l+ + l- + ET ( + decay of other sparticle) Similar technique allows measurement of tanb from muon/electron asymmetry
SUSY spin – observable distributions ATLAS l- parton-level Events Charge asymmetry, spin-0 l+ detector-level ATLAS Lepton+jet invariant mass -> Measure spin-1/2 nature of neutralino-2 -> Also can measure scalar nature of slepton ->Success at several distinct points in parameter space
SUSY produces Higgs ~ q (720 GeV) ~ g (1200 GeV) Strongly interacting, so high rate ~ g (600 GeV) ~ ~ (1000 GeV) ~ Other points & combinations also investigated ~ ~ ~ q (800 GeV) (340 GeV) ~ ~ ~ (400 GeV) h0, H0, A0, H± ~ h0, H0, A0, H± ~ (170 GeV) ~ (200 GeV) ~ (95 GeV) ~ • Provided Heavy higgs are <150 GeV -> produced • Missing energy + jet/lepton + higgs decay->bb • Apply very simple (general) analysis
h 30 fb-1 H,A h H,A : susy signal : susy bkg : SM tt bkg SUSY -> h,H,A -> bb
H0, A0 -> SUSY -> leptons hep-ph/0303095
SUSY -> light higgs • Region of parameter space where h is discoverable • ~ cosmological “bulk region” CMS note 2003-033 for summary
H± -> SUSY • Harder! • Works in restricted area of m, M2 space • Complements tau, tb analysis. H 2,30 1,2 3l+ ETmiss hep-ph/0303093
Conclusions (1) • LHC SUSY and Higgs search strategies well developed • Constantly being reviewed / developed • New techniques in Higgs sector • Production via Vector Boson Fusion • Improves reach for MSSM benchmarks • Couplings if only lightest higgs accessible • Infer non-SM Higgs sector • Measurement of tan b
Conclusions (2) • New SUSY techniques • Lepton asymmetry • Charge -> spin determination • Flavour -> tan b • Full likelihood event reconstruction • 3rd generation squarks + heavy gauginos • (not covered in this talk) • Combined SUSY + Higgs • Complimentary to standard Higgs searches • Could help dis-entangle complex SUSY chains • Much work going on for trigger, calibration, systematics.
Backup slides
SM-like higgs discovery ATLAS h → tt requires multi-object t-jet, lepton trigger
Charged higgs
SUSY spin – lepton asymmetry Back to backin 20 frame quark Probability θ* l+ lepton Phase space Invariant mass l- m/mmax = sin ½θ* Phase space -> factor of sin ½θ* Spin projection factor in |M|2: l+q -> sin2½θ* l-q ->cos2½θ* In presence of spin-correlations, lq invariant mass is different for l+ and l-
mSUGRA Dilepton edge reach
SM-like higgs rate measurement
Overall SummaryTwo experiments, 30 fb-1, charged and neutral higgs.
