New physics in final states with HEAVY Standard Model particles
@ CMS
Tulika BoseBoston University
(On behalf of the CMS Collaboration)March 21st, 2016
Rencontres de Moriond: QCD and High Energy Interactions
The Energy Frontier
Outline:• Strategies for analyzing final states with heavy Standard Model particles• Subset of results focusing on recent 13 TeV LHC searches
• Di-‐bosons [WW, WZ, VH]• Vector-‐like quarks• ttbar, tb resonances
2
LHC @ 13 TeV
Higher energy → boost
Higher luminosity → pileup
Higher reach to new energy regimes(heavier particles, higher pT particles)
For a comprehensive list of searches undertaken by CMS: https://cms-‐results.web.cern.ch/cms-‐results/public-‐results/publications/ [B2G, EXO]
Strategies for boosted analyses
Leptonic final states: • Lepton is no longer isolatedHadronic final states:• Jets with large distance parameter (R) pick up all the radiation from original decay • Use “substructure” techniques to analyze constituents of “fat” jets
• Is it a 1-‐prong, 2-‐prong or 3-‐prong decay ?• Is the energy equally split among “sub-‐jets” ? ….• Many observables/discriminators 3
Resolved Boosted
These strategies need to be kept in mind not only for the offline analysis but also for the trigger!
Top taggingW taggingHiggs tagging
1τ/2τ0 0.2 0.4 0.6 0.8 1
Nor
mal
ized
Dis
tribu
tion
0
0.1
0.2
0.3
, Pythia6LWL W→X + <PU> = 22 + sim. + <PU> = 12 + sim.W+jets, MG+Pythia6 + <PU> = 22 + sim. + <PU> = 12 + sim.
= 8 TeV, W+jetssCMS Preliminary Simulation,
CA R=0.8 < 350 GeV
T250 < p
|<2.4η|
Strategies for boosted analysesExamples:N-‐subjettiness Thaler, Tilburg, JHEP03(2011)240001
• τN: Topological compatibility with hypothesis of N subjets• As τN à0, jet is more consistent with having
N subjets• Ratios typically used as discriminators
• τ2/τ1 : separate “W” jets from QCD• τ3/τ2 : separate “top” jets from “W” jets
Jet mass• “groom” the fat jet to remove unwanted soft QCD
contributions & pileup • pushes the jet mass scale of the background to
lower values while preserving the hard scale of the heavy resonance
4pruned jet mass
0 50 100 150
arb
itrary
units
0
0.1
0.2
SM Higgs, m = 600 GeV
ungroomed jet mass
W+Jets, MadGraph+Pythia6
ungroomed jet mass
CMS Simulation
HIG-‐13-‐008
JME-‐13-‐006
Searches forDi-‐boson Resonances
5
• Comprehensive set of dibosonsearches in Run 1
• Cover many different final states• All hadronic, semi-‐leptonic
and fully leptonic signatures
• Cover different theoretical interpretations:– composite heavy vector
triplet (HVT) spin-‐1 model • Randall-‐Sundrum Graviton
(RSG) spin-‐2 model• Radion in Warped Extra
Dimensions (WED) spin-‐0 model
Diboson Resonances
6
Resonance mass [TeV]1 1.5 2 2.5 3
X) [
pb]
→(p
p 95
%σ
-210
-110
1
(EXO-12-025)ν lll→ WZ →X qqqq (EXO-12-024)→ WV →X
qq (EXO-13-009)ν l→ WV →X qqll (EXO-13-009)→ WZ →X
bb (EXO-14-010)ν l→ WH →X (EXO-13-007)ττ qq→ VH →X
qqbb,6q (EXO-14-009)→ VH →X )0 X→(pp THσ)+- X→(pp THσ)++ X→(pp THσ
= 3)V
HVT Model B (gWH)→ BR(X≈WZ) →BR(X
ZH)→ BR(X≈WW) → BR(X≈
, V = W / Z0 / X±X = X
(8 TeV)-119.7 fbCMS Preliminary
Dibosonsà qqqq, qqlν @ 13 TeV
7
All-‐hadronic & semi-‐leptonic channels:• High pT bosons• V → q ̄q tagger based on τ21 and jet mass • Dedicated trigger with substructure info (had.)
EXO-‐15-‐002
Exclusion (HVTB) :W' bosons < 2TeV
semi-‐leptonic bkg:W + jets:normalization, shape from datat ̄t : normalization and shape from MC with scale factors from data control regions data
All-‐hadronic bkg: di-‐jets events modeled with a power-‐law functionvalidated in MC, data control regions
qqqq
qqlν
qqqq + qqlν
Pruned jet mass (GeV)40 60 80 100 120 140
data
σD
ata-
Fit
-202
Even
ts /
( 5 G
eV )
20406080
100120140160180200220240
→ signal region ←
νe→Data W W+jets
WW/WZ tt
Single Top Uncertainty
(13 TeV)-12.3 fb
CMSPreliminary
lνqq low mass extension @ 13 TeV
8
• Extension of the X-‐>VW-‐>l ν qq analysis to “low mass” i.e. 600 – 1000 GeV and optimized for X à WW
• probes region of di-‐photon excess
• Optimized event selection:• lower trigger threshold (isolated
lepton triggers instead of higher non-‐isolated triggers)
• lower offline lepton pT cuts, looser lepton IDs
• tau21 optimized for lower masses• Jet mass window optimized for W-‐
only selection
• Background/Signal modeling: same strategy as EXO-‐15-‐002; narrow resonance approximation, Bulk graviton as benchmark
B2G-‐16-‐004 (GeV)WWM0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5
310×
data
σD
ata-
Fit
-202
Even
ts /
( 50
GeV
)
100
200
300
400
500
600
700νl→Data W W+jets
WW/WZ tt
Single Top Uncertainty
20)×=750 GeV (G MBulkG
(13 TeV)-12.3 fb
CMSPreliminary
9
lνqq low mass extension @ 13 TeV
Obs. Limits: 623 – 63 fb(mG = 600-‐1000 GeV)
B2G-‐16-‐004
(GeV)GM600 700 800 900 1000
WW
)(pb)
→ Bu
lk x
BR(
G95
%σ
-310
-210
-110
1
10
210 (13 TeV)-12.3 fb
CMSPreliminary Expected
SAsympt. CL
1 s.d.± Expected S
Asympt. CL 2 s.d.± Expected
SAsympt. CL
, k = 0.5 WW→BulkG BR× THσ
ObservedS
Asympt. CL
ν l→W
Improves over EXO-‐15-‐002 in the common range (800-‐1000 GeV)
VH à (0,1,2) leptons + bb @ 13 TeV
10
• Search for heavy resonances (mX > 1 TeV) decaying into a V (Z, W) + H→ bb boson
(0 ch. lepton, 1 ch. lepton, 2 ch. leptons)
• Look for peaks in invariant mass spectrum (mX )• Standard W and Z candidate reco• 0 lepton:
• Main backgrounds:• V + jets: normalization and shape from
data (jet mass sideband à signal region transfer factor from MC)
• t ̄t : normalization and shape from simulation with scale factors from control regions in data
• Separated by lepton flavor and number, for 1 and 2 (subjet) b-‐tag categories separately
b tag subjets
B2G-‐16-‐003
𝑍 → 𝜈𝜈, 𝑊 → ℓ𝓁𝜈, 𝑍 → ℓ𝓁ℓ𝓁
(GeV)VhTm
1000 1500 2000 2500 3000
Even
ts /
100.
0 G
eV2−10
1−10
1
10
210
(13 TeV)-12.17 fb
CMSPreliminary
)bbνν,ν (ll,l→ Vh →X
0l, 1 b-tag
DataV+jetsTop, STVV, VHBkg. unc.
=2000 GeVXmHVT model B
(GeV)VhTm
1000 1500 2000 2500 3000
Pulls
4−2−024
11
• No significant excess over standard model expectation• Limits on σ(X) × B(X → VH) combined for (ee, μμ, νν) and (eν, μν) • Data interpreted in HVT (A and B) models
(GeV)W'm1000 1500 2000 2500 3000 3500 4000
bb)
(pb)
→ B
(h
× W
h)
→ B
(W'
×(W
') σ
0.0030.004
0.01
0.020.030.04
0.1
0.20.30.4
1
23
95% CL limitsObservedExpected
σ 1±Expected σ 2±Expected
W' (HVT model B)
bbν l→ Wh →W'
1l channel
(13 TeV)-12.17 fb
CMSPreliminary
(GeV)Z'm1000 1500 2000 2500 3000
bb)
(pb)
→ B
(h
× Z
h)
→ B
(Z'
×(Z
') σ
0.0030.004
0.01
0.020.030.04
0.1
0.20.30.4
1
23
95% CL limitsObservedExpected
σ 1±Expected σ 2±Expected
Z' (HVT model B)
)bbνν (ll,→ Zh →Z'
0l, 2l channel
CMSPreliminary
(13 TeV)-12.17-2.52 fb
Obs. Limits: 10 – 200 fbmW’ >= ~1.6 TeV (HVT model B)
Combination of 0 lepton, 2lepton channels Combination of 1 lepton channels
First CMS result in VH-‐>0l, 2l channels!
1 l channel better than CMS Run 1!
B2G-‐16-‐003
VH à (0,1,2) leptons + bb @ 13 TeV
Vector-‐like Quarks
Fermionic Partners
13
• Vector-‐like quarks (VLQs) [non-‐chiral fermions]• Predicted by a large variety of
models• Little Higgs models• Warped extra dimensions• Composite Higgs model…
• Not excluded by Higgs measurements
• Can have same charge as b, t (B, T) or exotic charge (X5/3 or Y-‐4/3) • In many models the X5/3 is the lightest of these top partners, more easily accessible…
• Rich phenomenology with many different final states• Inclusive analyses +
dedicated/optimized searches• Run 1 analyses: mostly pair production
• Single production imp. for Run 2
X5/3 (same-‐sign di-‐lepton) @ 13 TeV
14
• Pair-‐production: same-‐sign di-‐lepton final state (charge 5/3e)• Striking signature -‐> clean channel with
relatively small SM background• 8 TeV CMS analysis: stringent limit of 800
GeV• Require > 5 jets and 2 same-‐sign leptons,
optimize HT (scalar sum of pT of leptons and jets)
• Primary background (fake leptons) estimated using a data-‐driven fake-‐rate method• Charge mis-‐id also taken into account• rare decays from MC (WW, ZZ, ttbarW,
ttbarZ, WWW)
14Exclude RH (LH) X53 < 950 (910) GeV
Better than Run 1!First LHC result in this channel @ 13 TeV
B2G-‐15-‐006
15
• Semi-‐leptonic final state:• 1 W boson decays leptonically, the others
decay hadronically• Boosted X53 decay products (merged jets)
• W tagged jets, jet mass, τ2/τ1• Dominant backgrounds: ttbar, V+jets
• Taken from simulation; checked using control regions in data
• Main discriminating variable: min(M[lepton, b])• 8 event categories:
• (e, μ) [# b tags (1, 2+), # W jets (0, 1+)]
15
X5/3 (semi-‐leptonic) @ 13 TeV
Exclude RH (LH) X53 < 700 (715) GeV First LHC result in this channel!
Combination of same-‐sign di-‐lepton + semi-‐leptonic analyses:Exclude RH (LH) X53 < 960 (940) GeV
Same-‐sign+semi-‐lep.
B2G-‐15-‐006
TT search (semi-‐leptonic) @ 13 TeV• Pair production of vector-‐like T(+2/3e)
• Benchmark: “Nominal” BRs of 50% bW, 25% tZ, tH• 8 TeV exclusion: 696 GeV
• Analysis strategy similar to B2G-‐15-‐006 • Event selection:
• Single lepton, 3+ jets, W-‐tagged jets• Veto Higgs-‐tagged jets (non-‐boosted Higgs
regime)• Main discriminating variable: min(M[lepton, b])• Event categorization: 16 categories
• (e, μ) [# b tags (0, 1, 2, 3+), # W tags(0, 1+)]
𝑇𝑇, 𝑇→ 𝑏𝑊 50% , 𝑡𝑍 25%, 𝑡𝐻 25% Exclude m(T) < 750 GeVAlso scan over BRs and set limits
Better than Run 1!
B2G-‐16-‐002
Single Production: T-‐> tH @ 13 TeV• Single production of vector-‐like T quark
• Exclusive decay to tH• bW/tZ coupling in production
• Optimized for leptonic top decay, H à bb• Event reconstruction w/ top and H candidates
• For large masses, top and H are boosted • Merged jets, non-‐isolated leptons
• Forward jet present in events
17
ST: scalar sum over ETmiss, lepton pT, pT of all reco. jets
ΔR(top cand., Higgs cand.) > 2.
B2G-‐15-‐008
• Primary background: ttbar + W+jets• Derived from sideband region in data
(no forward jets, only 1 subjet b-‐tagged)
• No significant excess in T quark mass distribution• Set limits on production cross section
x BR and on T quark coupling parameters
18
Single Production: T-‐> tH @ 13 TeV
Associated Tb prod.RH, bW coupling
B2G-‐15-‐008
First LHC result for singly produced T quarks @ 13 TeV
Coupling limitX-‐section limit
Associated Tb prod.RH, bW coupling
T quark mass / GeV0 500 1000 1500 2000
even
ts /
80 G
eV
10
20
30
40
T quark mass / GeV0 500 1000 1500 2000
MC
Dat
a-M
C
01
DatatH→(1700)lhTtH→(1200)lhT
tH→(700)lhTStat. uncert. BkgBkg. post-fit
(13 TeV)-12.3 fb
CMSPreliminary
electron+muonchannel
Searches for ttbar, tb resonances
19
ttbar, tb resonances
20
• Several models of new physics predict massive gauge bosons decaying into final states with top quarks
• ttbar:• Generic narrow and wide Z’ models, Kaluza
Klein excitations (Randall-‐Sundrum), Heavy Higgs models, generic excess (or deficit) in the ttbar mass spectrum
• tb:• Sequential Standard Model, Little Higgs, Extra
Dimensions, Minimal Higgsless Models…
• Analyses split on the basis of final states:• Hadronic, leptonic (“Resolved” and
“boosted”) and then combined
20
20
W’à tb (comb.): M(W’) > 2.15 TeV
8 TeV JHEP 02 (2016) 122 Narrow (1.2%) Z’ : M(Z’) > 2.4 TeVWide (10%) Z’ : M(Z’) > 2.9 TeVRS KK gluon: M(KKG) > 2.8 TeV
8 TeV PRD 93 (2016) 012001
Complementary to other searches:• (W’) No assumptions wrt M(νR)• Couplings to 3rd generation
fermions may be enhanced
21
ttbar resonances @ 13 TeV
• kinematical reconstruction of the ttbar system • Primary backgrounds: ttbar production, W/Z +
jets• simultaneous max. likelihood fit to the data
• final event categorization based on number of b-‐tagged and t-‐tagged jets:
Lepton (e, µ) + jets analysis optimized for heavy resonance masses:• leptonic top: non-‐isolated lepton, missing ET,
b-‐tagged jet• hadronic top (“fat” jet): use top tagging (e.g.
nsubjettiness)
B2G-‐15-‐002
22
ttbar resonances @ 13 TeVNo significant deviation from the Standard Model prediction⇒ Limits extracted for different BSM scenarios
• Z’ bosons of relative widths 1%, 10%, 30%• KK excitation of a gluon in the RS model
Excluded mass regions [TeV]
Competitive with Run 1!
B2G-‐15-‐002
W’ -‐-‐> tb @ 13 TeV
23
• Lepton (e, µ) + jets analysis optimized for Run 2• non-‐isolated lepton, use relative momentum
b/w lepton and closest jet for QCD rejection• Consider right-‐handed WRʹ′ with SM-‐like
couplings as benchmark model• Exploit the tb invariant mass distribution• Dominant background contributions:
• ttbar: check top pT distribution in control regions and derive corrections
• W + jets: : 0 b-‐tag region to get shape and normalization
• Treat 1 and 2 b-‐tag categories separately and then combine
Exclude RH W' bosons < 2.38 TeV
B2G-‐15-‐004
Better than Run 1!
Summary & Conclusions
24
• Wide range of searches are being performed in final states with heavy Standard Model particles• ttbar resonances, tb resonances, di-‐boson searches, vector-‐like quark
searches
• Already, with limited 13 TeV data, searches cover comprehensive spectrum of final states• Improve upon Run 1 sensitivity and exclude large regions of parameter space• Lots of progress in exploring difficult regions of parameter
space/complicated/boosted final states and new channels
• Eagerly awaiting the 2016 LHC dataset which will provide even greater sensitivity to new physics discoveries
Stay tuned!
Extra
25
ttbar resonances
26
• Several models of new physics predict massive neutral bosons decaying via a top antitop quark pair
• Generic narrow and wide Z’ models• Kaluza Klein excitations (Randall-‐Sundrum)
• Heavy Higgs models• Generic excess (or deficit) in the ttbar mass spectrum
• Analyses split on the basis of final states:– Hadronic, Di-‐leptonic, Semi-‐leptonic
(“Resolved” and “boosted”)
26
Narrow (1.2%) Z’ : M(Z’) > 2.4 TeVWide (10%) Z’ : M(Z’) > 2.9 TeVRS Kaluza-‐Klein gluon: M(KKG) > 2.8 TeV
8 TeV PRD 93 (2016) 012001
Searches for W’ bosons
2727
Another way to cancel fine-‐tuning problems in top,gauge and Higgs self-‐coupling loops • Predicted by many new physics theories
– Sequential Standard Model, Little Higgs, Extra Dimensions, Minimal Higgsless Models, Technicolor, etc.
Single top quark decay channel is a promising searching ground for a W' that interacts hadronically• Relatively small QCD multijet backgrounds, compared
to the decay to light quarks• Couplings to third generation fermions may be
enhanced in some models • Phys. Lett. B 392 383 (1996) 345, Phys. Lett. B 385 (1996) 304
• No assumptions regarding mass of νR==> Complementary to W’à lν searchesIf right-‐handed neutrino is v. heavy, W’à lν is suppressed
Lepton+jets : M(W’) > 2.05 TeVAll-‐hadronic : M(W’) > 2.02 TeVW’à tb (comb.): M(W’) > 2.15 TeV
8 TeV
JHEP 02 (2016) 122
WW, WZ, ZZ à qqqq @ 13 TeV
28
• All-‐hadronic channel w/high pT bosons • Dedicated trigger with substructure info• V → q ̄q tagger based on τ21 and jet mass
• Dominant background contribution from di-‐jets events modeled with a power-‐law function
• validated in simulation, data control regions • Six signal regions defined based on:
• V-‐jet mass category • WW, WZ, ZZ
• τ21• High purity• Low purity
High Purity
Low Purity
Z: 85-‐105 GeVW: 65-‐85 GeVEXO-‐15-‐002
WW, WZ à qq lν @ 13 TeV
29
• Semi-‐leptonic channel w/high pT bosons
• V → q ̄q tagger based on τ21 and jet mass• Main backgrounds:
• W + jets : normalization and shape from data• t ̄t : normalization and shape from simulation
with scale factors from control regions in data
EXO-‐15-‐002
Exclusion (HVTB) :W' bosons < 2TeV
![Semantic Texture for Robust Dense Trackingjc8515/pubs/semantic_texture.pdf · pitch [rad] 0.2 0.1 0.0 0.1 0.2 yaw [rad] 0.2 0.1 0.0 0.1 0.2 5000 10000 15000 20000 25000 Figure 1.](https://static.documents.pub/doc/80x56/5fbdd04c8e5fb64df2490e3f/semantic-texture-for-robust-dense-jc8515pubssemantictexturepdf-pitch-rad.jpg)
