Searches for New Physics in Boosted...

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  • Searches for New Physics in Boosted Topologies

    Takuya Nobe*on behalf of ATLAS Collaboration

    *University of Tokyo

    Rencontres de Moriond QCD and High Energy Interactions

    La Thuile, 21/3/2016

  • 2

    CERN Courier

    [email protected]!

    http://cerncourier.com/cws/article/cern/61866

  • 3

    100 10001

    10

    100

    gg Σqq qg

    WJS2013

    ratios of LHC parton luminosities: 13 TeV / 8 TeV

    lu

    min

    osi

    ty r

    atio

    MX (GeV)

    MSTW2008NLO

    _

    Early run-2 physics= focus on high-mass

    [email protected]!

  • Heavy resonances 
in high energy pp collisions

    4

    Heavy Vector Triplet Z’k/MPl=1

    • Many beyond the SMs predict high-mass VV/Vh/Zγ/hh/tt resonances
(V : denotes W and Z boson)

    • Model-independent search is important

    JHEP 09 (2014) 060

  • • A key is tagging high-pT objects from high-mass resonances• Large-R jet

    • ΔR of 2 particles from a 2-body decay :

    • At high-pT region, two quarks from W/Z decay cannot be separated by standard Anti-kT R=0.4 algorithm

    • Reconstruct boosted W/Z→qq, h→bb, and t→qqb as one jet with large cone size (Anti-kT, R=1.0)

    5

    Boosted object tagging

    R = 2M/pT

  • • Pile-up and soft-QCD subtraction

    • Remove sub-constituents of large-R jet if f

  • Jet sub-structure• Using sub-constituents’ kinematics inside the large-R jet, we can define

    good variables to reject backgrounds more• For W/Z-tagging:

    • Using D2β=1 variable (see details in backup)• Mass + D2β=1 cut : 50% signal efficiency v.s. b.g. rejection is factor ~50

    7

    arXiv:1510.05821

    2-prong-like

  • Dibosons [email protected] TeV

    • Full-hadronic channel : 
 local significance : 2.6-3.4σ,
 global 2.5σ@2TeV

    8

    arXiv:1512.05099JHEP 12 (2015) 55• After the combination

    with leptonic modes the local significance is ~2σ

  • • High-centrality to reject QCD b.g.



    • Data-driven b.g. estimation 


    9

    VV→qqqq→JJ

    ����pT,J1 � pT,J2pT,J1 + pT,J2

    ���� < 0.15

    13TeV spectra�y (JJ) < 1.2

    • 1-lepton + missing ET (W mass constraint) 
+ boson-tagged large-R jet

    • b-jet veto to suppress top quarks• Newly applied relative boson-pT cut :


    pT(V)/m(VV) > 0.4 
improves the sensitivity by 10% w.r.t. run-1

    WV→lνJ

    ATLAS-CONF-2015-073

    ATLAS-CONF-2015-068ATLAS-CONF-2015-071

    ATLAS-CONF-2015-075

  • Limits on diboson resonances

    10

    Full-hadronic

    1-lepton

    2-lepton(Z→ll + J)

    missing ET(Z→νν + J)

    m

  • Limits on diboson resonances

    11

  • Limits on diboson resonances

    12

    m

  • Vh resonances• Boosted higgs-tagging technique

    • At least one b-jets inside large-R jet using a new b-tagging technique with ‘track-jets’, R=0.2 (see details in backup)

    • Large-R jet mass peaks at 125 GeV

    13

    ATLAS-CONF-2015-074

    Wh→lνJ Zh→llJZh→ννJ

  • Limits on Vh resonance

    14

    m

  • 3-prong-like

    Boosted top tagging

    • 80% signal efficiency v.s. 
b.g. rejection is factor ~4

    • b-jet tagging using ‘track-jet’ can reduce the b.g. more while keeping high efficiency

    15

    arXiv:1603.03127

    ATL-PHYS-PUB-2015-053

  • boosted top

    1lepton + missing ET

    at least 1 b-jets • Mass and sub-structure• pT>300GeV

    top anti-top resonance

    16

    electron channel

    muon channel

  • Limit on Z’→tt cross-section

    17

    m

  • Vector like quark (VLQ) / four top quarks search

    • Large-R jets to probe boosted higgs/top (no sub-structure cut is applied; m>100GeV)
+ 1-lepton + ET

    miss + multi-jets

    • Signal regions are categorized into 11 sub-regions using number of boosted jets, number of b-jets and number of small-R jets

    • Final discriminant : effective mass, meff = Σ pT,i; i is all of lepton, jets and ETmiss

    18

  • Limits on VLQ TT and tttt productions

    19

    m

  • Limit on branching fraction of VLQ

    20

  • No

    trev

    iew

    ed

    ,fo

    rin

    tern

    al

    circu

    la

    tio

    no

    nly

    Model ℓ, γ Jets EmissT

    ∫L dt[fb−1] Limit Reference

    Ext

    rad

    ime

    nsi

    on

    sG

    au

    ge

    bo

    son

    sC

    ID

    ML

    QH

    eavy

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    ADD GKK + g/q − ≥ 1 j Yes 3.2 n = 2 Preliminary6.86 TeVMDADD non-resonant ℓℓ 2 e, µ − − 20.3 n = 3 HLZ 1407.24104.7 TeVMSADD QBH→ ℓq 1 e, µ 1 j − 20.3 n = 6 1311.20065.2 TeVMthADD QBH − 2 j − 3.6 n = 6 1512.015308.3 TeVMthADD BH high

    ∑pT ≥ 1 e, µ ≥ 2 j − 3.2 n = 6, MD = 3 TeV, rot BH ATLAS-CONF-2016-0068.2 TeVMth

    ADD BH multijet − ≥ 3 j − 3.6 n = 6, MD = 3 TeV, rot BH 1512.025869.55 TeVMthRS1 GKK → ℓℓ 2 e, µ − − 20.3 k/MPl = 0.1 1405.41232.68 TeVGKK massRS1 GKK → γγ 2 γ − − 20.3 k/MPl = 0.1 1504.055112.66 TeVGKK massBulk RS GKK →WW → qqℓν 1 e, µ 1 J Yes 3.2 k/MPl = 1.0 ATLAS-CONF-2015-0751.06 TeVGKK massBulk RS GKK → HH → bbbb − 4 b − 3.2 k/MPl = 1.0 ATLAS-CONF-2016-017475-785 GeVGKK massBulk RS gKK → tt 1 e, µ ≥ 1 b, ≥ 1J/2j Yes 20.3 BR = 0.925 1505.070182.2 TeVgKK mass2UED / RPP 1 e, µ ≥ 3 b, ≥ 3 j Yes 3.2 Tier (1,1), BR(A(1,1) → tt) = 1 Preliminary1.46 TeVKK mass

    SSM Z ′ → ℓℓ 2 e, µ − − 3.2 ATLAS-CONF-2015-0703.4 TeVZ′ massSSM Z ′ → ττ 2 τ − − 19.5 1502.071772.02 TeVZ′ massLeptophobic Z ′ → bb − 2 b − 3.2 Preliminary1.5 TeVZ′ massSSM W ′ → ℓν 1 e, µ − Yes 3.2 ATLAS-CONF-2015-0634.07 TeVW′ massHVT W ′ →WZ → qqνν model A 0 e, µ 1 J Yes 3.2 gV = 1 ATLAS-CONF-2015-0681.6 TeVW′ massHVT W ′ →WZ → qqqq model A − 2 J − 3.2 gV = 1 ATLAS-CONF-2015-0731.38-1.6 TeVW′ massHVT W ′ →WH → ℓνbb model B 1 e, µ 1-2 b, 1-0 j Yes 3.2 gV = 3 ATLAS-CONF-2015-0741.62 TeVW′ massHVT Z ′ → ZH → ννbb model B 0 e, µ 1-2 b, 1-0 j Yes 3.2 gV = 3 ATLAS-CONF-2015-0741.76 TeVZ′ massLRSM W ′

    R→ tb 1 e, µ 2 b, 0-1 j Yes 20.3 1410.41031.92 TeVW′ mass

    LRSM W ′R→ tb 0 e, µ ≥ 1 b, 1 J − 20.3 1408.08861.76 TeVW′ mass

    CI qqqq − 2 j − 3.6 ηLL = −1 1512.0153017.5 TeVΛCI qqℓℓ 2 e, µ − − 3.2 ηLL = −1 ATLAS-CONF-2015-07023.1 TeVΛCI uutt 2 e, µ (SS) ≥ 1 b, ≥ 1 j Yes 20.3 |CLL | = 1 1504.046054.3 TeVΛ

    Axial-vector mediator (Dirac DM) 0 e, µ ≥ 1 j Yes 3.2 gq=0.25, gχ=1.0, m(χ) < 140 GeV Preliminary1.0 TeVmAAxial-vector mediator (Dirac DM) 0 e, µ, 1 γ 1 j Yes 3.2 gq=0.25, gχ=1.0, m(χ) < 10 GeV Preliminary650 GeVmAZZχχ EFT (Dirac DM) 0 e, µ 1 J, ≤ 1 j Yes 3.2 m(χ) < 150 GeV ATLAS-CONF-2015-080550 GeVM∗

    Scalar LQ 1st gen 2 e ≥ 2 j − 3.2 β = 1 Preliminary1.07 TeVLQ massScalar LQ 2nd gen 2 µ ≥ 2 j − 3.2 β = 1 Preliminary1.03 TeVLQ massScalar LQ 3rd gen 1 e, µ ≥1 b, ≥3 j Yes 20.3 β = 0 1508.04735640 GeVLQ mass

    VLQ TT → Ht + X 1 e, µ ≥ 2 b, ≥ 3 j Yes 20.3 T in (T,B) doublet 1505.04306855 GeVT massVLQ YY →Wb + X 1 e, µ ≥ 1 b, ≥ 3 j Yes 20.3 Y in (B,Y) doublet 1505.04306770 GeVY massVLQ BB → Hb + X 1 e, µ ≥ 2 b, ≥ 3 j Yes 20.3 isospin singlet 1505.04306735 GeVB massVLQ BB → Zb + X 2/≥3 e, µ ≥2/≥1 b − 20.3 B in (B,Y) doublet 1409.5500755 GeVB massVLQ QQ →WqWq 1 e, µ ≥ 4 j Yes 20.3 1509.04261690 GeVQ massT5/3 →Wt 1 e, µ ≥ 1 b, ≥ 5 j Yes 20.3 1503.05425840 GeVT5/3 mass

    Excited quark q∗ → qγ 1 γ 1 j − 3.2 only u∗ and d∗, Λ = m(q∗) 1512.059104.4 TeVq∗ massExcited quark q∗ → qg − 2 j − 3.6 only u∗ and d∗, Λ = m(q∗) 1512.015305.2 TeVq∗ massExcited quark b∗ → bg − 1 b, 1 j − 3.2 Preliminary2.1 TeVb∗ massExcited quark b∗ →Wt 1 or 2 e, µ 1 b, 2-0 j Yes 20.3 fg = fL = fR = 1 1510.026641.5 TeVb∗ massExcited lepton ℓ∗ 3 e, µ − − 20.3 Λ = 3.0 TeV 1411.29213.0 TeVℓ∗ massExcited lepton ν∗ 3 e,µ, τ − − 20.3 Λ = 1.6 TeV 1411.29211.6 TeVν∗ mass

    LSTC aT →W γ 1 e, µ, 1 γ − Yes 20.3 1407.8150960 GeVaT massLRSM Majorana ν 2 e, µ 2 j − 20.3 m(WR ) = 2.4 TeV, no mixing 1506.060202.0 TeVN0 massHiggs triplet H±± → ℓℓ 2 e, µ (SS) − − 20.3 DY production, BR(H±±L → ℓℓ)=1 1412.0237551 GeVH±± massHiggs triplet H±± → ℓτ 3 e,µ, τ − − 20.3 DY production, BR(H±±L → ℓτ)=1 1411.2921400 GeVH±± massMonotop (non-res prod) 1 e, µ 1 b Yes 20.3 anon−res = 0.2 1410.5404657 GeVspin-1 invisible particle massMulti-charged particles − − − 20.3 DY production, |q| = 5e 1504.04188785 GeVmulti-charged particle massMagnetic monopoles − − − 7.0 DY production, |g | = 1gD , spin 1/2 1509.080591.34 TeVmonopole mass

    Mass scale [TeV]10−1 1 10

    √s = 8 TeV

    √s = 13 TeV

    ATLAS Exotics Searches* - 95% CL ExclusionStatus: March 2016

    ATLAS Preliminary∫L dt = (3.2 - 20.3) fb−1

    √s = 8, 13 TeV

    *Only a selection of the available mass limits on new states or phenomena is shown. 21

  • Summary• 13TeV pp collisions data opens a whole new world!• Early run-2 = focus on high mass region, where our sensitivity is already

    better than 8 TeV• Boosted object tagging is an important key to probe high-mass new physics• Reported the latest ATLAS search results for VV/Vh/tt/TT/tttt resonances

    22

    Dibosons resonance ttbar resonance

  • Backup slides

    23

  • • Decay of W/Z : 2-prong-like

    • A variable:

is used to enhance signals

    D2β=1 and τ32

    24

    ECF2 =X

    ij

    pT,ipT,j�Rij

    ECF1 =X

    i

    pT,i

    ECF3 =X

    ijk

    pT,ipT,jpT,k�Rij�Rjk�Rki

    There’re 2 high-pT constituents 
with large ΔRij; and no the other constituents 
with high-pT: → large ECF2 but small ECF3

    D�=12 = ECF3

    ✓ECF1ECF2

    ◆3

    • Decay of top : 3-prong-like

    • A variable:

is used to enhance signals

    ⌧32 =

    Pi pT,i min (�Ra1,i,�Ra2,i, Ra3,i)P

    i pT,i min (�Ra1,i,�Ra2,i)

    3-prong-like signal shows small τ32

  • b-tagging in dense environment

    25

    Standard technique (outside-in)

    New technique (inside-out)

    1. Reconstruct jet using energy deposits in calorimeter 2. b-tagging using ‘matched’ tracks and vertices3. Good energy resolution but large contaminations from

    non-b particles’ tracks in dense hadronic environment
i.e. many other charged particles are expected near 
b-quark from boosted top/higgs
(high pT=small ΔR)

    1. Anti-kT algorithm seeded by inner detector tracks are employed (track-jet R=0.2)

    2. Good angular resolution / high secondary vertex reconstruction efficiency even in dense environment

    3. Worse energy resolution:
Track-jet is used only for b-tagging and jet energy is measured in calorimeter

  • b-tagging in dense environment• Data/MC difference is taken into account by ‘b-tag scaling factor’,

    which is estimated using isolated b-quarks from top quark decay

    • After applying the scaling factor, data agree well with MC even if 
b-jet is associated with large-R jet (g→bb enriched sample by muon-in-jet tagging)

    26

    ATLAS-CONF-2016-002

    double b-tag efficiency for large-R jet (assuming g→bb)

    pT and mass scales agree with MC after the b-tagging

  • 27

    Full-hadronic dibosons resonance search

  • 28

    ZV→ννJ• Large missing ET + large-R jet

    • Normalizations of W/Z+jets b.g. are determined in 1-/2-lepton control regions (common with lvJ/llJ)

    • Final discriminant : transverse mass

    The other dibosons spectra• 2-lepton (Z mass constraint) + large-R jet

    • Variable cone-size lepton isolation 
depending on pT

    • pT(V)/m(VV) > 0.4

    ZV→llJ

  • Z+γ resonance

    29

    dilepton+γ Large-R jet +γ

  • hh resonance• hh→bbbb channel (3 b-tag or 4 b-tag)

    • Using boosted higgs tagging technique

    • Data-drived multi-jet b.g. estimation (b-veto → b-tag)

    • Combined with resolved channel

    30

  • VLQ search: event yields in each category

    31

  • [email protected]!

    32

    • c.f. total 8TeV data in 2012 : 20/fb

  • q q

    W/Z

    topo-clusters

    33

    large-R jet

    protonproton

    Illustration of W/Z tagging

    lepton missing ET

  • q qW/Z

    sub-jet

    33

    large-R jet

    protonproton

    Illustration of W/Z tagging

    lepton missing ET

  • 33

    large-R jet

    protonproton

    Illustration of W/Z tagging

    Trimmingremove sub-jet if f

  • 33

    large-R jet

    protonproton

    Illustration of W/Z tagging

    Trimmingremove sub-jet if f