Aug 5, 2016 - Search for new quarks with the. ATLAS detector .... 5/3 m. T5/3. > 990 GeV. mKK > 4 TeV for symmetri
Search for new quarks with the ATLAS detector
G. Azuelos, on behalf of the ATLAS Collaboration
Outline
Motivation Summary of results from Run1 at 8 TeV Selected recent results at s = 13 TeV with 3.2 fb−1 ¤
Events with b-jets and same-sign leptons : o VLQ TT, BB, T5/3T5/3 and 4-top analysis ATL-CONF-2016-032
¤
lepton+jets final state: o Vector-like TT pair and four tops ATL-CONF-2016-013, ATL-CONF-2016-020
¤
Single production o VLQ T/Y → Wb ATL-CONF-2016-072
Aug. 5 2016
ICHEP 2016
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Heavy quarks
Fourth generation chiral quarks are ruled out ¤ ¤
precision electroweak measurements in context of SM, o would enhance Higgs production by a factor ~ 9 o contributes to Higgs quartic coupling λ and leads to vacuum instability
Vector-like quarks ¤ ¤
unlike SM, both L and R chiralities are in the same SU(2) representation: singlets, doublets or triplets mass does not arise from Yukawa couplings 2/3
−1/3
TL,R , BL,R " 5/3 $$ T 2/3 # T " 5/3 $ T 2/3 $ T $ −1/3 # B ¤
Aug. 5 2016
% '' , &L,R % ' ' , ' &L,R
" 2/3 $$ T −1/3 # B " 2/3 $ T −1/3 $ B $ −4/3 # Y
% '' , &L,R
" −1/3 $$ B −4/3 # Y
% '' &L,R
Aguilar-Saavedra et al., 1306.0572
% ' ' ' &L,R
top partners enter in radiative corrections and protect Higgs mass from quadratic divergence with Q2: composite Higgs models, Little Higgs, extra dimensions ICHEP 2016
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Pair production of 3rd generation partners g T
T g
g
b,t,t
t,b,b B
W ,Z ,H b,t,t
B
W ,Z ,H
g
W ,Z ,H t,b,b W ,Z ,H
In the limit of very high mass, the vlq’ BR’s follow
BR(Q →Wq ) : BR(Q → Zq ) : BR(Q → Hq ) = 2 :1:1
no mixing between B-1/3 and b for (T,B)R doublet in these plots (θ Rd = 0) Aug. 5 2016
ICHEP 2016
Aguilar-Saavedra, 1306.0752
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pair-production in Run I:
0.7
arXiv:1504.04605
Zb/t + X JHEP11(2014)104
0.6
Wt+X
700
PRD91,112011(2015)
0.5
Hb+X arXiv:1505.04306
0.4 0.3 0.2
900 850 800 750 700 650 600 550
0.1 800
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Vector-like B
500
BR(B → Wt)
single production ¤
0.8
0 75
¤
s = 8 TeV, 20.3 fb-1 Summary results: Same-Sign dil.
0 75
¤
0.9 0
¤
same-sign dileptons: JHEP10(2015) 150, (1504.04605) o m(B, singlet) > 620 GeV o m(T, singlet) > 590 GeV o m(T5/3) > 750 GeV Zb/t + X: JHEP11(2014)104, (1409.5500) o m(B in (B,Y) doublet) > 755 GeV Wt + X: PRD91, 112011 (2015) o m(T5/3) > 840 GeV Q → Hb, Ht,Wb + X: JHEP08(2015) 105, (15050.04306) o m(T in (T,B) doublet) > 855 GeV o m(Y in (B,Y) doublet) > 770 GeV o m(B, singlet) > 735 GeV
ATLAS 65
¤
950
1
Observed 95% CL mass limit [GeV]
BR(B → Hb)
Previous limits at 8 TeV from ATLAS
T/Y – Wb (1602.05606) o m(T/Y) > 950 GeV (for coupling =1)
single production via heavy gluon ¤
Aug. 5 2016
G* → Bb → Hbb → 4b (1602.06034) o m(B) vs m(G*) ICHEP 2016
Vector-like T 5
b-jets, same-sign leptons, missing ET
ATLAS-CONF-2016-032
Vector-like quarks: ¤
g
TT , BB
bb,t,t
T
B →Wt, Zb, Hb T →Wb, Zt, Ht Events generated with Protos cross section at NNLO
T g
+ ,H + W W,Z →ℓ ν
t →W −b b,t,t Z ,Z →,H ℓ+ℓ− W
¤ T5/3T5/3 (doublet)
BR(T5/3 →Wt) = 100%
Strong enhancement of cross section between 8 and 13 TeV
Aug. 5 2016
ICHEP 2016
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b-jets, same-sign leptons, missing ET
ATLAS-CONF-2016-032
4-top ¤
SM: low cross section: ~9.2 fb at 13 TeV o same sign leptons, missing ET, multiple light-quark and b jets
¤
contact interaction o compositeness, sgluons, …
¤
two universal extra dimensions under real projective plane geometry (2UED/RPP) k +ℓ o KK parity conservation (−1) o dark matter candidate
mKK ≡ m (1,0) =
1 R4
ξ=
R4 R5
m (1,1) = 1+ ξ 2 mKK
Cacciapaglia et al., 0907.4993 Aug. 5 2016
ICHEP 2016
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b-jets, same-sign leptons, missing ET
¤
ATLAS-CONF-2016-032
Signal Basic signatures:
same-sign leptons, high HT, MET, number of jets, b-jets → 8 event categories for signal regions
Backgrounds ¤ ¤
Aug. 5 2016
ttV , ttWW , ttH
MadGraph rescaled to NLO
VV ,VVV
Sherpa
→ systematic uncertainties on cross section 8-57%, depending on signal region Detector-related backgrounds o charge mis-ID • probability measured in Z → ee events, as a function of pT and η • background estimated from opposite sign ee and eµ events • systematic uncertainty ~ 3-8 % of total background o non-prompt and fake leptons • estimated by matrix method: measure how “loose” and “tight” leptons relate to “real” and “fake” leptons and derive the fraction of “fake” leptons in the data. • systematic uncertainty ~ 13-26% of total background ICHEP 2016
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Limits for B and T VLQ’s ATLAS-CONF-2016-032
BB (singlet)
TT (singlet)
mB > 830 GeV
mT > 780 GeV
BB (singlet)
Aug. 5 2016
TT (singlet)
ICHEP 2016
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T5/3, 4-t contact and 2UED/RPP ATLAS-CONF-2016-032
T5/3T5/3
σ (pp → 4t) < 95 fb (SM kinematics) < 67fb (contact interaction) C 4t Λ 2 < 3.5 TeV −2 mKK > 1.4 TeV (R4 = R5 ) mT > 990 GeV 5/3
mKK > 4 TeV for symmetric 2UED/RPP case Aug. 5 2016
ICHEP 2016
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VLQ, 4-tops, in lepton + jets TT → HtHt, HtZt, HtWb also : ZtZt, ZtWb, Z → bb
Selection: one isolated lepton ¤ ETmiss > 20 GeV ¤ mT(W) > 60 GeV ATL-CONF-2016-013 ¤ up to 6-8 jets, ≥ 2 b-tagged ¤ 0-2 high mass jets from boosted tops when pT(top) > 300 GeV ¤ large-R jets (R=1.0) with at least 2 small-R (R=0.4) subjets o trimmed: remove small-R subjets with pT < 5% of pT of large-R jet ATL-CONF-2016-20 ¤ 4-top analysis ¤ 9-10 jets ¤ at least 3-4 b-jets
N (small-R jet)
¤
Aug. 5 2016
N (b-jets)
N (large-R jet)
m(large-R jet)
meff =
ICHEP 2016
∑
pTi
meff
ℓ,j ,miss
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VLQ, 4-tops, in lepton + jets
Backgrounds
ATLAS-CONF-2016-013 ATLAS-CONF-2016-020
tt + jets,Wt → Powheg-Box, MadGraph, rescaled to NNLO W + jets,VV → Sherpa2.1, rescaled to NNLO ttV , ttH
Systematic uncertainties ¤ ¤ ¤ ¤ ¤
MadGraph5_aMC@NLO
luminosity, 5% lepton reconstruction, ~ 1.7% jet energy scale, resolution, ~6% (signal), ~13% (tt background) heavy-flavor jet tagging efficiencies main background modelling uncertainties o tt, ~ 6% o tt + b’s, ~50% o V+jets, dibosons, ~ 5% o ttV, ttH, 11-13% o misidentified lepton: 50%
Limit extraction ¤
Aug. 5 2016
Likelihood fit of all signal regions, with systematic errors as nuisance parameters
ICHEP 2016
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VLQ, 4-tops, in lepton + jets: limits ATLAS-CONF-2016-013
mT > 900 GeV (if BR(T → Ht) = 1) > 750 GeV (T singlet) > 800 GeV (T in doublet)
σ (pp → 4t) < 190 fb (SM kinematics) < 140 fb (contact interaction) C 4t Λ 2 < 4.8 TeV −2 small- and large-R jets:
ATLAS-CONF-2016-013
High jet multiplicity: ATLAS-CONF-2016-020
mKK > 1.45 TeV mKK > 1.3 TeV
Aug. 5 2016
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Single Production T,Y → Wb ATLAS-CONF-2016-072
Single production is sensitive to high mass, if coupling is sufficiently large Aguilar-Saavedra et al., 1306.0572
sin θ L/R or cWb L/R
Coupling QWb ¤
Aguilar-Saavedra et al., 1306.0572
mixing term ! ! t $ cos θ L/R # & =# " T %L/R #" sin θ L/Re −iφ
−sin θ L/Re cos θ L/R
iφ
$! 0 &# t & #" T 0 %
$ && %L/R
tan θ Rq = tan θ Lq =
mq mQ mq mQ
tan θ Lq
(singlets, triplets)
tan θ Rq
(doublets)
similarly for b-B mixing or, more generally, phenomenological Lagrangian, in effective model with coupling cWb = 2 sin θ L/R 2 2 L/R o
¤
σ (Qb ) ~ (cL +cR )
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O. Matsedonskyi et al., 1409.0100 14
Single Production T,Y → Wb ¤
width vary with coupling
Backgrounds ¤ tt → Powheg & Pythia
V + jets → Sherpa2.2 single t → Powheg & Pythia dibosons → Sherpa fake electrons → matrix method
¤ ¤ ¤ ¤
¤
18 16
ATLAS Preliminary s = 13 TeV, 3.2 fb-1 Q → Wb, Q = T or Y SR Post-Fit
Data Single top Other SM bkg.
tt W+jets Total unc.
14 12
8
exactly one lepton high pT b-tagged jet pT > 350 GeV a forward jet, |η|>2.5 veto hard central jet with pT > 250 GeV (reduce tt background) large Δφ (lepton, leading jet) > 2.5
Control regions ¤
20
10
Event selection ¤
Events / 100 GeV
Signal generated with MadGraph
W + jets o leading jet not b-tagged, pT > 250 GeV ttbar o leading jet pT > 200 GeV o at least one hard jet
6 4 2
1.50 1.25 1 0.75 0.5 400
Data / Pred.
ATLAS-CONF-2016-072
600
800
1000
1200
1400
1600
mVLQ [GeV] ATLAS-CONF-2016-072
Systematic uncertainties ¤ ¤
Aug. 5 2016
dominated by b-tagging efficiency uncertainty, ~ 10% mismodelling of tt (6%) and W+jets at high pT(W) ~ 25% ICHEP 2016
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σ × BR [pb]
Limit on T, Y from single production 102
ATLAS Preliminary s = 13 TeV, 3.2 fb-1
10
ATLAS-CONF-2016-072
Observed Expected
95% CL Exclusion Limits on σ × BR
Expected ± 1 σ Expected ± 2 σ
1 10−1
Theory (NLO), BR(Q->Wb)=1 σth, c2L + c2R = 1/ 2
−2
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T or Y
σth, c2L + c2R = 1
mT /Y > 1.44 TeV
σth, c2L + c2R = 0.32 3 10−0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5 1.6 mQ [TeV]
BR(Y →Wb) = 100%
BR(T →Wb) ∼ 50%
T − t mixing angle θ L , T singlet
Aug. 5 2016
B −b mixing angle θ Rb , (B,Y ) doublet
ICHEP 2016
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Conclusion Improved limits on vector-like quarks with first 3.2 fb-1 at 13 TeV
pair production: ¤
single production
same-sign leptons
ATLAS-CONF-2016-072
ATLAS-CONF-2016-032
m(B singlet) > 830 GeV m(T singlet) > 780 GeV
cWb L
c4t Λ < 3.5 TeV
2
+ cWb r
( ) ( )
m(T5/3 ) > 990 GeV 2
! # for "
mY > 1.44 TeV 2
cWb L
2
+ cWb r
( ) ( )
2
$ = 1/ 2 & %
< 0.33 for Y quark < 0.45 for T quark
−2
T − t mixing angle dominantly θ Lt , T singlet
σ (4t) < 95 / 67 fb (SM, contact kinematics) mKK > 1.4 TeV (2ED/RPP, R4 = R5 )
sin θ L < 0.32 − 0.69 for m(T ) between 1 TeV and 1.5 TeV B −b mixing angle dominantly θ Rb , (B,Y ) doublet sin θ R < 0.23− 0.56 for m(Y ) between 1 TeV and 1.5 TeV
¤
lepton + jets
ATLAS-CONF-2016-013 ATLAS-CONF-2016-020
m(T singlet) > 750 GeV (900 GeV if BR(T →Wb) = 1) m(T doublet) > 800 GeV c4t Λ 2 < 4.8 TeV −2
σ (4t) < 190 / 140 fb (SM/contact kinematics) mKK > 1.45 TeV Aug. 5 2016
ICHEP 2016
More data coming in fast è expect stronger limits (or discovery!)! 17
Backup
Limit on mixing angles
! mT /Y > 1.44 TeV # for " Wb L
2
Wb r
(c ) + (c )
2
Wb L
2
Wb r
(c ) + (c )
2
$ = 1/ 2 & %
< 0.33 for Y quark < 0.45 for T quark
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