Search for a pair of BEH production with ATLAS University of Birmingham N. Andari (NIU) 25-11-2015 1
Large Hadron Collider pp collider, designed for √ s = 14 TeV (7 TeV in 2011, 8 TeV in 2012, 13 TeV in 2015) • 27 km circumference, 100 m underground, 1232 superconducting dipole magnets, magnetic field nominally 8.3 T, max instantaneous luminosity 10 34 cm -2 s -1 • 4 detectors at collision points: ATLAS, CMS, LHCb, ALICE (TOTEM and LHCf) 2
Run I (2009-2012) data taking 2.07 × 10 32 3.65 × 10 33 7.73 × 10 33 ~20 fb-1 of 8 TeV + 5 fb-1 of 7 TeV used for Run I analyses Z → µ + µ − candidate with 25 reconstructed vertices 3
Higgs boson discovery 4 July 2012 seminar@CERN The puzzle being completed, the two experiments ATLAS and CMS enter the era of properties measurement of the newly discovered particle and the search for New Physics beyond the Standard Model. 4
Higgs production at the LHC a) Gluon-gluon fusion (ggH) b) Vector boson fusion (VBF) c) Associated V=W,Z production (VH) d) Associated tt production (ttH) 1 LHC HIGGS XS WG 2011 Higgs BR + Total Uncert b b WW • H-->bb: high BR but suffers from ZZ large QCD background • H--> ττ : sensitivity enhanced in VBF gg t t -1 τ τ 10 production c c • H--> γγ : narrow resonance over a continuum background -2 10 • H-->ZZ: -->4l golden channel excellent mass resolution and S/B --> Z γ γ γ llqq and ll νν -3 10 • H-->WW: -->l ν l ν and l ν qq 100 200 300 400 500 1000 M [GeV] H 5
Properties measurement ATLAS-CONF-2015-044 CMS-PAS-HIG-15-002 PRL 114, 191803 (2015) ATLAS and CMS Syst Total Stat LHC Run 1 Total Stat Syst ATLAS H 126.02 0.51 ( 0.43 0.27) GeV ± ± ± → γ γ CMS H 124.70 ± 0.34 ( ± 0.31 ± 0.15) GeV → γ γ ATLAS H ZZ 4 l 124.51 ± 0.52 ( ± 0.52 ± 0.04) GeV → → CMS H ZZ 4 125.59 0.45 ( 0.42 0.17) GeV l ± ± ± → → ATLAS + CMS 125.07 0.29 ( 0.25 0.14) GeV ± ± ± γ γ ATLAS + CMS 4 125.15 0.40 ( 0.37 0.15) GeV l ± ± ± ATLAS + CMS +4 l 125.09 ± 0.24 ( ± 0.21 ± 0.11) GeV γ γ 123 124 125 126 127 128 129 (GeV) m H m H ¼ 125 . 09 � 0 . 24 GeV ¼ 125 . 09 � 0 . 21 ð stat Þ � 0 . 11 ð syst Þ GeV ; µ = 1 . 09 + 0 . 11 − 0 . 10 = 1 . 09 + 0 . 07 − 0 . 07 ( stat ) + 0 . 04 − 0 . 04 ( expt ) + 0 . 03 − 0 . 03 ( thbgd ) + 0 . 07 − 0 . 06 ( thsig ) , The exclusion of all non-SM spin hypotheses at a more than 99.9% CL in favour of the SM 0 + arXiv:1506.05669, Phys. Rev. D 92, 012004 So far, compatibility with the SM properties —> SM Higgs boson discovered 6
Higgs self-coupling The Higgs potential is directly to its self-coupling: 2 4 2 V ( H ) H H ... = µ + λ + 0 1 ( % H → & # & # h 2 υ + ' $ 1 Expressed in terms of mass, trilinear and quartic couplings: ' $ 1 λ 2 2 3 4 4 h V ( h ) m h h h ... = + λ υ + + h 3 h 2 4 2 2 2 m / 2 λ = λ = υ 3 h 4 h h = λ h λ h 4 3 Accessible Extremely challenging in Higgs pair production 7
SM Higgs pair production SM hh production: destructive interference between the trilinear coupling diagram and the box diagram g g h t, b t, b h - t, b t, b t, b h h t, b t, b g g h arXiv:1309.6594v2 2000 Cross sections computed at NNLO NNLO 1000 NLO 500 LO 8 TeV 14 TeV E cm 100 TeV 200 Σ � fb � 3.0 9 . 76 fb 40 . 2 fb 1638 fb σ NNLO 100 2.5 Scale [%] +9 . 0 − 9 . 8 +8 . 0 − 8 . 7 4 + +5 . 9 − 5 . 8 2.0 50 PDF [%] +6 . 0 − 6 . 1 +4 . 0 − 4 . 0 + 6 +2 . 3 − 2 . 6 K 1.5 PDF+ α S [%] +9 . 3 − 8 . 8 +7 . 2 − 7 . 1 + 0 +5 . 8 − 6 . 0 20 1.0 0.5 10 20 40 60 80 100 20 40 60 80 100 Difficult to probe due to the low predicted E cm � TeV � rate ~ several order of magnitudes smaller than the single h 8
HL-LHC prospects ATL-PHYS-PUB-2014-019 40 Projected limit on the total HH yield (events) Total Yield (3000 fb − 1 ) Decay Channel Branching Ratio 35 bb + bb 33% 40,000 bb γγ bb + W + W − 25% 31,000 30 bb + τ + τ − 7.3% 8,900 25 ZZ + bb 3.1% 3,800 W + W − + τ + τ − 2.7% 3,300 20 ZZ + W + W − 1.1% 1,300 15 ATLAS Simulation Preliminary γγ + bb 0.26% 320 -1 s = 14 TeV: 3000 fb γγ + γγ 0.0010% 1.2 10 Exp. 95% CLs 1 σ ± 5 2 σ ± Considering bb γγ decay channel 0 -2 0 2 4 6 8 10 λ / λ in ATLAS: SM ATL-PHYS-PUB-2015-046 S/ √ B ~ 1.3 in the full 3000fb -1 dataset SM ATLAS Simulation Preliminary σ 8 An exclusion of 95%CL of BSM models / σ 95% CL upper limit on with values <~ -1.3SM and >~8.7SM 7 bb ττ Expected 0.6 σ for bb ττ and 6 exclusions of <-4SM and >12SM 5 4 The CMS collaboration showed 3 (CMS-PAS FTR-15-002) that combining the bb γγ and the bb ττ decay Exp. 95% CL 2 σ 1 ± ∫ -1 σ 2 ± L dt = 3000 fb channels, the expected significance of a Higgs had-had selection 1 lep-had e selection pair production is 1.9 σ s = 14 TeV lep-had µ selection 0 − − 9 10 5 0 5 10 15 λ λ / SM
New Physics A variety of extensions of the SM would enhance Higgs boson pair production ATL-PHYS-PUB-2014-019 Non resonant production HH) [pb] LO 10 NLO non SM Yukawa couplings - → NNLO (pp 1 direct tthh vertex (composite models) - σ addition of light colored scalars - -1 10 dimension-6 gluon Higgs operators … - -2 10 -10 -5 0 5 10 SM λ / λ HHH HHH � Resonant production SUSY: 2HDM the heavier H —>hh (—>1pb) - Production and decay of exotic particles: graviton, radion or stoponium.. - Hidden sector mixing with the observed h - 10
Search for hh in Run I ATLAS Collaboration Searches for Higgs boson pair production in the hh → bb ττ , γγ WW ∗ , γγ bb,bbbb channels • with the ATLAS detector Phys. Rev. D 92, 092004 (2015) Search for Higgs boson pair production in the $b\bar{b} b\bar{b}$ final state from $pp$ • collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector Eur. Phys. J. C (2015) 75:412 Search For Higgs Boson Pair Production in the γγ b b Final State using pp Collision Data • at √ s=8 TeV from the ATLAS Detector Phys. Rev. Lett. 114, 081802 (2015) CMS Collaboration Search for the resonant production of two Higgs bosons in the final state with two photons • and two bottom quarks CMS PAS HIG-13-032 Search for resonant pair production of Higgs bosons decaying to two bottom quark- • antiquark pairs in proton-proton collisions at 8 TeV, CMS-HIG-14-013 Searches for a heavy scalar boson H decaying to a pair of 125 GeV Higgs bosons hh or • for a heavy pseudoscalar boson A decaying to Zh, in the final states with h to tautau, CMS-HIG-14-034 11
ATLAS detector Inner Detector EM Calorimeter Sampling calorimeter Pb-LAr Three subdetectors (B=2T) Three longitudinal layers: Pixel detector - layer 1: very fine segmentation along η - Semi-Conductor Tracker - allowing γ / π 0 discrimnation Transition Radiation Tracker - layer 2: bulk of the EM shower deposited - layer 3: tail of the EM shower - Reconstruct charged particles A presampler up to | η |<1.8 corrects for losses upstream the calorimeter 12
hh—>bb γγ 13
hh—>bb γγ Powerful final state: large h—>bb branching ratio - excellent diphoton invariant mass - resolution low backgrounds - clean diphoton trigger - H—> γγ selection • Loose diphoton trigger ~ 100% efficient • pT>0.35 (0.25) m γγ for leading (subleading) photon • | η |<2.37 excluding 1.37<| η |<1.56 • Tight identified photons • Track isolation ( Δ R<0.2) < 2.6 GeV • Calorimetric isolation ( Δ R<0.4) <6 GeV corrected for γ energy leakage and pileup • 105< m γγ <160 GeV 14
hh—>bb γγ ATLAS-CONF-2014-004 1 b-jet efficiency Anti-kT jets (R=0.4) satisfy: ∫ -1 ATLAS Preliminary L dt = 20.3 fb pT>55 (35) GeV for leading (subleading) jets - s = 8 TeV 70% efficiency for b-jets in |eta|<2.5 0.8 - b-tagging use multivariate algorithm with an 70% efficiency for jets from b fragmentation in simulated 0.6 Rejection factor 130x (4x) ttbar events: rejection factor of ~ 130 (4) for light quark (charm) jets 0.4 t t PDF (MC) MV1, = 70% ∈ b t t PDF (Data) Calibrate b-tag scale using dilepton ttbar events 2 2 20 30 40 10 2 10 × Jet p [GeV] T 95< m jj < 135 GeV: mass resolution ~ 13 GeV asymmetric cut since neutrinos from semileptonic b-decays are not measured 0.1 0.1 Fractional JES uncertainty Fractional JES uncertainty ATLAS Preliminary ATLAS Preliminary anti-k R = 0.4, LCW+JES + in situ correction anti-k R = 0.4, LCW+JES + in situ correction t t 0.09 0.09 Data 2012, s = 8 TeV Data 2012, s = 8 TeV 0.08 0.08 jet = 0.0 p = 40 GeV � Total uncertainty Total uncertainty T Absolute in situ JES Absolute in situ JES 0.07 0.07 Relative in situ JES Relative in situ JES Flav. composition, inclusive jets Flav. composition, inclusive jets 0.06 0.06 Flav. response, inclusive jets Flav. response, inclusive jets 0.05 0.05 Pileup, average 2012 conditions Pileup, average 2012 conditions 0.04 0.04 0.03 0.03 0.02 0.02 0.01 0.01 0 0 -4 -3 -2 -1 0 1 2 3 4 2 2 3 3 20 30 40 10 2 10 10 2 10 × × 15 jet p [GeV] � T
Recommend
More recommend
