Search for BSM Higgs Bosons with ATLAS Jochen Dingfelder - PowerPoint PPT Presentation

Search for BSM Higgs Bosons with ATLAS Jochen Dingfelder University of Bonn On behalf of the ATLAS Collaboration SEARCH 2012 Workshop University of Maryland, March 17-19, 2012

Overview New prelim. results (4.9 fb -1 ) New prelim. results (4.6 fb -1 ) Published in PRD (1.6 fb -1 ) 2

Fermiophobic Higgs • Suppressed Higgs couplings to fermions in 2HDM and Higgs triplet models Here: simple benchmark model (LEP) • no fermion-Higgs couplings • SM boson-Higgs couplings • Production: Vector-boson fusion and associated production with W/Z • Decays to γγ , WW, ZZ, Z γ Here: focus on H ➝ γγ γγ ⇒ larger σ× BR than SM for light Higgs ⇒ higher Higgs p T 3

Fermiophobic Higgs ➝ γγ • Selection: (identical to SM H ➝ γγ ) • 2 isolated photons with p T > 40, 20 GeV • Di-photon mass: 100 < m γγ γγ < 160 GeV • 9 categories based on p Tt < 40 GeV • presence of γ conversions • γ calorimeter impact point • p Tt : related to di-photon p T ATLAS-CONF-2012-013 • Signal m γγ γγ model Crystal Ball (core) + wide Gaussian (tail) p Tt > 40 GeV • Background m γγ γγ model Exponential 4

Fermiophobic Higgs ➝ γγ : Exclusion limits Largest excess at m H =125.5 GeV Including look-elsewhere effect: Significance: 1.6 σ Prob. of background fluctuation: 5% Observed m H exclusion: [110.0, 118.0], [119.5, 121.0] Expected m H exclusion: [110.0, 123.5] 5

Neutral MSSM Higgs gluon-gluon fusion: gg ➝ h/H/A b-associated production: bbh/H/A • MSSM requires 2 Higgs doublets ⇒ 5 Higgs bosons: Φ = h, H, A ; H + ,H - • h/H and A nearly mass degenerate • 2 parameters at tree level: m A , tan β • Enhanced couplings to b and τ in large parts of parameter space σ bbh/H/A ∝ tan 2 β 6

Tau signature and identification Hadronic τ decay ( τ had ): • Narrow, collimated jet • isolated energy deposits and tracks • large electromagnetic component • low track multiplicity ( 1 or 3 ) τ had identification • high leading track momentum fraction 7

Neutral MSSM Higgs : Selection τ had + τ had e/ µ + τ had e + µ • Di- τ had trigger • 1 isolated e / µ with • 1 isolated e with p T > 25 / 20 GeV p T > 25 GeV • 2 τ had with • 1 τ had with • 1 isolated µ with p T > 45 / 30 GeV p T > 20 GeV p T > 20 GeV • Opposite charges • Opposite charges • Opposite charges • E T miss > 25 GeV • Di-lepton veto (Z, top) • E T miss + p T e + p T µ < 120 GeV (QCD suppression) • E T miss > 20 GeV (QCD) ΔΦ ΔΦ ( e ,µ) ,µ) > 2.0 rad • m T < 30 GeV (W) (top, WW, ZZ suppression) Multi- Z ➝ ττ jet top W+jet 8

Neutral MSSM Higgs : Mass reconstruction • Visible mass : (invariant mass of visible tau decay products) • Effective mass: A.Elagin, P.Murat, A.Pranko, A.Safonov, Nucl. Inst. Meth. A654 (2011) 481 Effective mass • Missing mass calculator (MMC): • 7 unknown parameters: two “missing” 3-momenta, m νν • 4 constraints from E x miss , E y miss , m τ 1 , m τ 2 MMC mass ⇒ scan over ΔΦ ( ν , l ), ΔΦ ( ν , h ), m νν ⇒ weight solution according to probability of 3D angle in solution ⇒ MMC mass = Max. of weighted m ττ distribution 9

Neutral MSSM Higgs : Background estimation Background estimation based on data control samples : • Z/ γ * ➝ ττ ττ from τ -embedded Z/ γ * ➝ µµ data sample • Multijet background from samples with same-sign charges and low E T miss or inverted lepton isolation • W+jets from high-m T (l,E T miss ) sample W+jets (OS) W+jets (SS) + other bkg • No significant charge correlation • Expect no large E T miss From high-m T control sample • Mostly non-isolated or fake leptons 10

Neutral MSSM Higgs : Results τ had + τ had e/ µ + τ had e + µ 11

Neutral MSSM Higgs : Exclusion limits σ × BR ( Φ ➝ ττ ) (m A , tan β ) plane • Assume only one resonance ( Φ ): • Need to assume specific 100% gg ➝ Φ or (c)MSSM scenario 100% bb Φ production • Here: m h max scenario (acceptances similar) • Useful to test arbitrary models ATLAS-CONF-2011-132 12

Neutral MSSM Higgs : Exclusion limits Comparison of search channels Update to full 4.9 fb -1 data set & inclusion of b-tagging in progress! 13

Charged Higgs • Predicted in Higgs doublet (e.g. MSSM) and triplet models • m H+ < m t : dominant production in top quark decays • m H+ > m t : gb → tH + production important, but more data needed • for tan β > 3, preferred decay mode is H ➝ τν (here: assume BR of 100%) τν : lepton + jets : τ had + lepton : τ had + jets 14

Charged Higgs: Lepton + jets channel Selection: • 1 isolated e / µ with p T > 25 / 20 GeV _ • ≥ 4 jets (2 b-tagged) with p T > 20 GeV τ ➝ e/ µ νν • E T miss > 40 GeV if | Φ l,miss | > π /6 q E T miss × |sin( Φ l,miss )| > 20 GeV if | Φ l,miss | < π /6 _ q’ • Identify “hadronic side” by choosing combination of 1 b-jet and 2 light jets that minimizes Discriminating variables: generator generator level level Lower bound ~ Discriminates mass of charged between leptons boson (H + or W) from τ and W 15

Charged Higgs: Lepton + jets channel Signal region: cos θ l * < - 0.6, m T (l,E T miss ) < 60 GeV Dominant background from top pairs ! Simulated with MC@NLO, normalized in -0.2 < cos θ * l < 1 Misidentified-lepton background determined from control sample with loosened lepton ID 16

Charged Higgs: τ had + lepton channel Selection: • 1 isolated e / µ with p T > 25 / 20 GeV τ ➝ had ν • 1 τ had with p T > 20 GeV e/ µ • ≥ 2 jets ( ≥ 1 b-tagged) with p T > 20 GeV • Sum of primary-vertex track p T : ν ν Discriminating variable: E T miss • Background contributions with misidentified taus : µ: 0.05%, e: 1%, jets: 55% ; jet ➝ τ had mis-ID measured with W+jets • True-tau background taken from simulation 17

A candidate event in τ had + lepton channel 18

Charged Higgs: τ had + jets channel Selection: • τ + E T miss trigger • 1 τ had with p T > 40 GeV τ ➝ had ν q • ≥ 4 jets ( ≥ 1 b-tagged) with p T > 20 GeV _ • E T miss > 65 GeV q’ • E T miss significance: • jjb combination (hightest p T ) consistent m top Discriminating variable: • True-tau background estimated with τ embedding in µ+jets events (with top-pair like event topology) • Mis-id. tau background: as for τ had +lepton 19

Charged Higgs: τ had + jets channel Multijet background estimated by fitting E T miss shapes to data . Multijet shape from control sample with inverted τ and b ID 20

Charged Higgs: Exclusion limits ATLAS-CONF-2012-011 Tevatron limits: BR < 10-15% Combined 21

Charged Higgs: Exclusion limits (MSSM) ATLAS-CONF-2012-011 Combined …we will probably be able to rule out low-mass charged Higgs with 2012 data, if it doesn’t exist! 22

_ Charged Higgs: H + ➝ cs c ATLAS-CONF-2011-094 _ s e/ µ ν _ • H ➝ cs dominates for tan β < 1 • Require large E T miss and m T to suppress multijet background • Kinematic fit with W and top mass contraints to find best H + candidate T evatron • Set limits on BR(t ➝ H + b) assuming _ BR(H + ➝ cs) = 100% 23

Doubly-charged Higgs H ++ H ++ H -- • Relevant e.g. in Higgs triplet , Little Higgs and Left-Right Symmetric models WZ, ZZ, W ± W ± , ttW • Select µ pairs with same-sign charges and p T > 20 GeV • Look for resonance in µ ± µ ± mass spectrum • No significant excess over SM background found 24

Doubly-charged Higgs: Exclusion limits Assuming predicted cross Set limits on H ++ H -- pair production via section, set limits on BR Drell Yan process pp ➝ Z/ γ * ➝ H ++ H -- Tevatron (CDF) upper limit: 205-245 GeV 25 Phys.Rev.D 88 (2012) 032004

NMSSM a 1 ➝ µ + µ - • NMSSM : introduces singlet scalar field to solve µ problem ⇒ 3 CP-even scalars (h 1 , h 2 , h 3 ) 2 CP-odd scalars ( a 1 , a 2 ) • a 1 can be very light ! m a1 < 2 m B Analysis: • Opposite-sign di-muons (P T >4GeV) • Likelihood ratio selection based on µ + µ - vertex χ 2 and µ isolation • Set limits by fitting to mass spectrum • Y region excluded 26 ATLAS-CONF-2011-020

Conclusions • Various interesting BSM Higgs scenarios are being probed in parallel to SM Higgs search • No indication for BSM Higgs bosons yet … but lots of upper limits on cross sections/branching ratios • Searches continue with more data and improved methods ⇒ There is still significant room for BSM Higgs searches for the year ahead … and after! 27

Backup Slides 28

Fermiophobic Higgs ➝ γγ : Exclusion limits 29

Fermiophobic Higgs ➝ γγ : Systematics 30

MSSM Higgs sector • MSSM: 2 Higgs doublets ⇒ 5 Higgs bosons: h 0 (CP=1) , H 0 (CP=1) , A 0 (CP=-1), H ± • At tree level described by two parameters: m A , tan β = v u /v d • Fixed mass relations at tree level: • Upper mass bound modified by radiative corrections (depend on SUSY parameters, e.g. mixing in stop sector) 31

MSSM Higgs production 32

Estimation of Z ➝ τ τ Background • Reliable Z ➝ τ τ model important for low-mass Higgs • Desirable to use real data, but cannot be selected signal-free • Instead, use high-purity Z ➝ µ µ sample (~ signal-free due to small Higgs-µ coupling) 33