Search for Heavy Quarks

Transcription

1 Search for Heavy Quarks with the ATLAS detector Huong Lan Tran Laboratoire de l'accélérateur Linéaire LAL Orsay (IN2P3) On behalf of the ATLAS collabora2on VIIIth Rencontres du Vietnam Beyond the Standard Model Quy Nhon, Vietnam 6-22 December 202

2 Outline. Mo&va&ons for heavy quarks searches Implica&ons of Higgs searches on fourth genera&on Vector- like Quarks 2. Analysis with Data 20 7 TeV : Heavy top : t't' à WbWb : lepton + jets Heavy boiom : b'b' à WtWt à 4W2b : 2 same- sign leptons (similar signature as same- sign top quark pair, or T 5/3 pair, or four tops) Vector- like quarks T,B (Fourth genera9on searches become a sub- set) 3. Conclusion & Perspec&ve EFSS202 7 December 202 2

3 Motivations for Heavy Quarks Searches (.) Standard Model fourth genera&on (SM4) : simplest extension Beyond Standard Model extension Mo2va2on for searches : u c t SM4? SM does not predict number of genera&ons New source of CP viola&on could explain maier- an&maier asymmetry d s b Dynamical electroweak symmetry breaking Very heavy Other theore&cal aspects (Flavour hierarchy, Higgs boson mass naturalness...) EFSS202 7 December 202 3

4 Implications of Higgs Searches on Fourth Generation (.2) Up to > D - : within SM3 all range excluded but a Higgs at 25 GeV EFSS202 7 December 202 4

5 Implications of Higgs Searches on Fourth Generation (.2) 95% CL Limit on / SM ATLAS Preliminary Observed Expected ± ± 2 th 4 CLs Limits Generation Model Ldt = fb s = 7 TeV ATLAS- CONF m H [GeV] With just 2.3 D - within SM4 : m H in all range GeV is excluded EFSS202 7 December 202 5

6 Implications of Higgs Searches on Fourth Generation (.2) 95% CL Limit on / SM ATLAS Preliminary Observed Expected ± ± 2 th 4 CLs Limits Generation Model Ldt = fb s = 7 TeV ATLAS- CONF m H [GeV] Discovery of a Higgs boson with mass of 25 GeV and cross sec&on compa&ble to SM3 rules out minimal SM4 (?) Direct searches for non- minimal models are s&ll needed, e.g. : Two- Higgs doublets Vector- like Quarks EFSS202 7 December 202 6

7 Vector-like Quarks (VLQ) (.3) Lec and Right components behave iden&cally w.r.t. SU(2) U() Ø Allows SM gauge invariant mass term Predicted in various models of physics Beyond Standard Model Mass genera&on not through Yukawa coupling to Higgs Looser constraint from Higgs cross sec&on measurement Decay through Flavour Changing Charged & Neutral Currents t' à Wb, th, tz b' à Wt, bh, bz EFSS202 7 December 202 7

8 2. Analyses and results 2.. t't'à WbWb (Single Lepton + Jets) W + 2b (Same Sign Leptons + Jets) 2.3. b'b' à Zb+X 2.4. Single Vector-like Quark Production EFSS202 7 December 202 8

9 t't'à WbWb (Single Lepton + Jets) (2.) (For high mass t' : q- qbar annihila&on dominant) Analysis published with D - set an observed (expected) 95%CL lower limit on t' mass : m t' > 404 (394) GeV with BR(t'à Wb) = High mass t' : W is boosted à 2 jets from hadronic W can be merged or very close to each other Strategy for analysis at 4.7 D - changed to adapt to this scenario ! R(q,q) W p [GeV] EFSS202 7 December 202 T 9 R(q,q)! ATLAS Preliminary - Simulation Pythia Z " tt, t " Wb

10 t't'à WbWb (Single Lepton + Jets) (2.) Analysis for 4.7 D - : Boosted W reconstruc&on Jet an&- k t algorithm, size R = 0.4 Latest paper with 4.7 D - arxiv : Channel Channel 2 One jet with p T > 250 GeV and 60 < m j < GeV Events/ GeV Data / Bkg type I W had s = 7 TeV ATLAS L dt = 4.7 fb Data t t (500) tt Non-tt Tot bkg unc W had candidate mass [GeV] Dijet system with p T > 50 GeV ΔR(j,j) < < m jj < GeV Events/ GeV Data / Bkg type II W had ATLAS Data t t (500) tt Non-tt Tot bkg unc. s = 7 TeV L dt = 4.7 fb W had candidate mass [GeV] q W q q W 0.8 q 2 EFSS202 7 December 202

11 t't'à WbWb (Single Lepton + Jets) (2.) v Analysis : H T (*) > 750 GeV & p T leading b- jet > 60 GeV & p T subleading b- jet > 60 GeV Reconstruct hadronic t' mass m reco 4 combina&ons from one hadronic W, one leptonic W (2 neutrino solu&ons from W mass constraint) and 2 b- jets Choose combina&on giving the smallest difference between hadronic and leptonic mass arxiv : Addi&onal cuts : minδr(lepton neutrino) <.4 minδr(w both b- jets) >.4 & minδr(lepton both b- jets) >.4 Ø Help to reject boosted top events 4 H T = ET miss + p lepton jet (*) T + p T Distribu9on of minδr(w both b- jets) and j j= minδr(lepton both b- jets) Signal prefer to have high values EFSS202 7 December 202

12 t't'à WbWb (Single Lepton + Jets) (2.) arxiv : Events / 50 GeV tight ATLAS Data t t (500) BR(t Wb) = t t (500) BR(t Wb) = 0.5 BR(t Ht) = 0.5 tt Non-tt Tot. BG uncertainty Total Bkg Data t' SM4 500 GeV t' VLQ 500 GeV.3 ± ± ±.5 s = 7 TeV L dt = 4.7 fb m reco [GeV] Distribu9on of m reco axer event selec9on and axer applying isola9on cuts Result : Observed (expected) limit : m t' > 656 (638) GeV for BR(t'à Wb) = EFSS202 7 December 202 2

13 VLQ Interpretation from t't'à WbWb Analysis (2.) Heavy vector- like t' : Decay modes : t' à Wb t' à th t' à tz (sum of 3 BRs equal, BR values are model dependent) BR(t Ht) Forbidden Forbidden mt = 400 GeV = 450 GeV m t arxiv : ATLAS s = 7 TeV, 95% CL expected exclusion 95% CL observed exclusion Forbidden L dt = 4.7 fb SU(2) singlet SU(2) doublet = 500 GeV m t t' SU(2) singlet (BR(t'à Wb) 0.5) with mass in range GeV excluded Forbidden = 550 GeV m t Forbidden = 600 GeV m t BR(t Wb) EFSS202 7 December 202 3

14 3W + 2b (Same Sign Leptons + Jets) (2.2) Preliminary result with 4.7 D - ATLAS Note ATLAS- CONF : Inclusive searches for 4 exo&c processes (b'b', T 5/3 T 5/3, single T 5/3, 4 tops) Event selec2on : ü At least 2 lepton candidates with same charge and at least 2 "good" jets ü In ee or μμ channel : inv. mass of 2 leptons must exceed 5 GeV & m ll - m Z > GeV ü Missing transverse momentum exceed 40 GeV Signal region : Addi&onal cut : H T (jets+leptons) > 550 GeV Distribu9on of H T axer applying the selec9on except the H T cut for eμ channel EFSS202 7 December 202 4

15 3W + 2b (Same Sign Leptons + Jets) (2.2) ATLAS Note ATLAS- CONF v λ << : No single produc&on m b' and m T5/3 (pair produc&on) > 670 (640) GeV (T 5/3 quasi- stable à R- hadrons- like searches) BR(b!tW) # [pb] " ATLAS Preliminary $ Ldt = 4.7 fb, s = 7 TeV v λ : Single produc&on added u W + d T 5/3 t + W t λ - W t q 3 q 4 b + W! e + e! e + e % Expected limit at 95% CL Observed limit Expected limit ± # Expected limit ± 2 # Theory approx. NNLO Expected $ Observed [TeV] m b /T5/3 Ldt = 4.7 fb s= 7 TeV b λ = : m T5/3 > 680 (640) GeV λ = 3 : m T5/3 > 700 (660) GeV expected 95% CL observed 95% CL ATLAS Preliminary << [TeV] m T5/3 EFSS202 7 December 202 5

16 b'b' à Zb+... (2.3) Event selec2on : ² At least b- jet ² Z candidate : At least two opposite- charge electron candidates and m ee m Z < 5 GeV p T (Z,b- jet) > 50 GeV Latest paper with 2 D - arxiv : Phys.Rev.Le]. 9 (202) 0780 Total SM Data b' VLS 350 GeV b' 450 GeV ± ± 7 4 ± 2 Reconstruct m(zb) : if more than one b- tagged jet choose the leading p T Mass distribu9on of b' candidate for events passing selec9on EFSS202 7 December 202 6

17 b'b' à Zb+... (2.3) Result : arxiv : Phys.Rev.Le]. 9 (202) 0780 b' with mass m b' < 400 GeV decaying en&rely via b' à Z + b are excluded For vector- like singlet b' mixing solely with the third Standard Model genera&on : m b' > 358 GeV alldecaymodesofthez and W bosons! = 2 BR(b Zb) BR(b Zb) 2 ion of signal events with at least one : Frac&on of signal events with at least one b'à Zb decay as a func&on of BR(b'à Zb) EFSS202 7 December 202 7

18 Single Vector-like Quark Production (2.4) ATLAS Note ATLAS- CONF Q can be U(+2/3), D(- /3) or X(+5/3) Q decays to W/Z and light quarks 2 possible final states : Wu (for D and X) : Charged Current (CC) Zu (for U) Neutral Current (NC) q q' W * /Z * Q q" W/Z q l ν/l q W * /Z * Single produc9on of VLQ in t- channel and s- channel q' q" Q q W/Z l ν/l Ø Analysis divided into 4 channels : CC or NC, electrons or muons in final state Event selec2on : At least 2 jets CC - W reconstructed using lepton candidate and neutrino candidate - m T W > 40 GeV and η(w) < 2.5 NC - 2 same flavour, opposite sign leptons - 66 GeV < m ll < 6 GeV EFSS202 7 December 202 8

19 Events / 50 GeV te Carlo estimated backgrounds for the combined electron and muon channels for the C (bottom) channel. A. TeV VLQATLAS signal is overlaid Preliminary in each case, normalized to the NC Channel κqq = and 0% branching fraction to light quark. The data is also plotted. 6 Note that Data for20 calculation of sensitivity and setting 3 R the background estimate is taken from a fitfitted to data. Background s = 7 TeV 2 Ldt = 4.64 fb Events cross section assuming a coupling of κ qq = mq v Single Vector-like Quark Production (2.4) Results : ATLAS Preliminary NC Channel Ldt = 4.64 fb s = 7 TeV Data 20 Z+jets tt Diboson U, 0 GeV NC m(lepton, lepton, leading jet) [GeV] backgrounds (combined electron MadGraph, and D-quark muon MadGraph, X -quark 95% C.L. upper limits: channels) for NC channel Observed Expected ±σ ±2σ BR(Q Wq) [pb] Qq) most significant devia9on region bounded by σ(pp s = 7 TeV blue lines. The width of BumpHunter bin roughly -2 Ldt = 4.64 fb ATLAS Preliminary equal to VLQ mass resolu9on BR(Q Zq) [pb] Qq) σ(pp [GeV] ATLAS Note ATLAS- CONF Comparison of data and expected SM Plot bo]om- lex : BumpHunter result show the m Q MadGraph, U-quark 95% C.L. upper limits: Observed Expected ±σ ±2σ significance m(lepton, lepton, leading jet) [GeV] 3-2 s = 7 TeV Ldt = 4.64 fb ATLAS Preliminary [GeV] m Q Ø U(+2/3) with mass below 20 GeV excluded (NC) Ø Mass of X(+5/3), D(- /3) greater than 420 GeV and 80 GeV respec&vely Figure 4: Expected and observed 95% C.L. upper limits on σ(pp qq) BR(Q Wq) whe is a D or X (top) and σ(pp qu) BR(U Zq) (bottom) calculated in the CC and NC chan respectively. The nominal theoretical predictions are overlaid. Both cases assume a coupling κ qq and 0% branching fraction to a W or Z boson and a light quark. The band around the theore predictions is the uncertainty due to the PDF set and the factorization and renormalization scales. EFSS202 7 December 202 9

20 Single Vector-like Quark Production (2.4) ATLAS Note ATLAS- CONF Events / 50 GeV ATLAS Preliminary NC Channel Ldt = 4.64 fb s = 7 TeV Data 20 Z+jets tt Diboson U, 0 GeV Comparison of data and expected SM backgrounds (combined electron and muon channels) for NC channel m(lepton, lepton, leading jet) [GeV] Carlo estimated backgrounds for the combined electron and muon channels for the (bottom) channel. A. TeV VLQ signal is overlaid in each case, normalized to the ss section assuming a coupling of κ qq = mq v κqq = and 0% branching fraction to ght quark. The data is also plotted. 6 Note that for calculation of sensitivity and setting the background estimate is taken from a fit to data. EFSS202 7 December

21 Conclusion & Perspective 202 has seen a huge progress on various searches for New Physics So far no hint for signal! Limits were set for different models th 4 generation : t't'! WbWb th 4 generation : b'b'(t T 5/3 )! WtWt 5/3 New quark b' : b'b'! Zb+X, m Zb Top partner : TT! tt + A 0 A 0 (dilepton, M ) Vector-like quark : CC, Vector-like quark : NC, T2 m l" q m llq L=4.7 fb, 7 TeV [2.5468] L=4.7 fb, 7 TeV [ATLAS-CONF-20230] L=2.0 fb, 7 TeV [ ] L=4.7 fb, 7 TeV [ ] L=4.6 fb, 7 TeV [ATLAS-CONF-20237] L=4.6 fb, 7 TeV [ATLAS-CONF-20237] 400 GeV 483 GeV t' mass b' (T ) mass 5/3 b' mass T mass (m(a ) < 0 GeV) 0.2 TeV VLQ mass (charge /3, coupling, qq = "/m Q ).08 TeV VLQ mass (charge 2/3, coupling, qq = "/m Q ) 656 GeV 670 GeV ATLAS Physics Summary Plot for HCP 202 EFSS202 7 December 202 2

22 Conclusion & Perspective 202 has seen a huge progress on various searches for New Physics So far no hint for signal! Limits were set for different models ² > 20fb 8 TeV p-p physics run data from 202 promises an exciting year of analysis! EFSS202 7 December

23 Conclusion & Perspective 202 has seen a huge progress on various searches for New Physics So far no hint for signal! Limits were set for different models ² > 20fb 8 TeV p-p physics run data from 202 promises an exciting year of analysis! Cross sec9on of heavy quark pair produc9on 3 TeV : Significant enhancement of cross sec&on à Discovery J EFSS202 7 December or High Mass Exclusion (Death of many BSM models!)

24 Backup slides 24

25 Implications of Higgs Searches on Fourth Generation (!(gg"h)xb(h"x)) SM4 /(!(gg"h)xb(h"x)) SM ## (m d4 =TeV) ## (m d4 =400GeV) arxiv : WW, ZZ (m d4 =TeV) WW, ZZ (m d4 =400GeV) m H (GeV) EFSS202 7 December

26 Fourth Generation quark pair production cross section (pb) m t' 7 TeV NNLO 8 TeV NNLO 3 TeV NNLO 4 TeV NLO EFSS202 7 December

27 Some things about VLQ L = q L q L + t R t R +Tr { Q ( MQ ) Q } + T ( M T ) T + Y Tr{ QH} T + h.c + L q L (T,B)+ R t R T + h.c. elementary sector [ ] composite sector Mass terms before EW symm. breaking: mixing terms Yukawa lagrangian ([ T L yuk = Y Tr{ QH} T B = Y Tr T 5/3 T 2/3 = Y ( T φ 0 Bφ + T 5/3 φ + + ][ ]) φ 0 φ + T 2/3 φ 0 ) T φ φ 0 T EFSS202 7 December

28 Some things about VLQ L yuk =Y sin ϕ L sin ϕ R t L φ 0t R b L φ t R + Y cos ϕ L sin ϕ R T φ 0t R Bφ t R + Y sin ϕ L cos ϕ R t L φ T 0 b L φ T + Y sin ϕ R T5/3 φ + t R + T 2/3 φ 0 t R + Y cos ϕ L cos ϕ R TL φ T 0 R B L φ TR + Y TR φ T 0 L B R φ TL + Y cos ϕ R T5/3 φ + T R + T 2/3 φ 0 TR + Y T5/3 φ + T L + T 2/3 φ 0 TL +... We can therefore deduce the couplings of the top p y t = Y sin ϕ ql sin ϕ tr R t L T T h T Z L t L t R T ht L T W L b L T 2/3 Z L t R T 2/3 ht R T Z L t R B W L t R T 5/3 W L t R T 5/3 Z L t R Y sin ϕ L cos ϕ R Y sin ϕ R Y cos ϕ L sin ϕ R Y cos ϕ L sin ϕ R Y sin ϕ R Y sin ϕ R EFSS202 7 December

29 Some things about VLQ SM quarks Singlets ( ) Doublets Triplets ( ) ( ) ( ) X ( ) u c t (U) U U X ( ) U d s b (D) D D D U D Y Y SU(2) L q L =2 q R = U() Y q L =/6 u R =2/3 d R = / /3 /3 7/6 /6 5/6 2/3 /3 L Y y i u qi L Hc u i R y i d qi L V i,j CKM Hdj R λ i u q i L Hc U R λ i d qi L HD R λ i uψ L H (c) u i R λ i d ψ LH (c) d i R L m not allowed M ψψ λ i q i L τ a H (c) ψ a R EFSS202 7 December

30 t't'->wbwb (single lepton + jets) Analysis strategy : Boosted W reconstruc&on Selec2on: Electron : Tight, p T > 25 GeV & η < 2.47 not in the crack ( ), isolated Muon : p T > 20 GeV & η < 2.5 Jets : Topocluster an&- kt, cone R = 0.4 p T > 25 GeV & η < 2.5 Event level cuts : > 4 tracks from primary vertex (non- collision background rejec&on) e- channel : E T miss > 35 GeV & E T miss + m T W > 60 GeV mu- channel : E T miss > 20 GeV & E T miss + m T W > 60 GeV EFSS202 7 December

31 t't'->wbwb (single lepton + jets) m u4 (GeV) σ(u 4 ū 4 ) (pb) Scale uncertainties (pb) PDF and α s uncertainties (pb) / / / / / / / / / / / / / / / / Table 3: Theoretical cross section at NNLO for u 4 ū 4 production as a function of m u4 as computed by Hathor, and scale and PDF uncertainties. m T (GeV) BR(WbWb) BR(WbtH) BR(WbtZ) BR(tHtZ) BR(tHtH) BR(tZtZ) Table 2: Protos Branching Ratios (BR) for T T production as a function of m T as computed by Protos. EFSS202 7 December 202 3

32 b'b'à WtWtà 4W2b (Same Sign Leptons + Jets) Selec2on: Electron : Tight, p T > 25 GeV & η < 2.47 not in the crack ( ), isolated Muon : Combined with track, p T > 20 GeV & η < 2.5, isolated, not overlap with jet Back- to- back muon pairs removed Jets : Topocluster an&- kt, cone R = 0.4 p T > 25 GeV & η < 2.5 Remove jets overlapped with electron Event level cuts : E T miss > 40 GeV Heavy-quark and same-sign top-quark signal regions l + l + and l l b m b =350 GeV 2.0% b m b =450 GeV 2.5% b m b =550 GeV 2.7% l + l + l l tt LL 0.7% negligible tt LR 0.8% negligible tt RR 0.8% negligible Low-mass Z boson signal region tt RR,mZ =0 GeV 0.7% negligible tt RR,mZ =50 GeV 0.8% negligible tt RR,mZ =200 GeV.0% negligible EFSS202 7 December

33 b'b'à WtWtà 4W2b (Same Sign Leptons + Jets) Analysis also used to search for same- sign (s- s) top- quark pair produc&on Latest paper with.04 D - arxiv : Event selec2on : At least 2 lepton candidates with same charge and at least 2 "good" jets In ee or μμ channel : inv. mass of 2 leptons must exceed 5 GeV & m ll - m Z > GeV Missing transverse momentum > 40 GeV 3 signal regions : () Heavy quark signal region for b', or s- s top- pair produc&on from high- mass Z' exchange : H T (jets+leptons) > 350 GeV (2) Same- sign top- quark signal region : sa&sfies requirement of () but only for posi&vely- charged leptons (3) Low- mass Z' boson signal region : posi&vely- charged leptons, H T > 50 GeV, m ll >0 GeV Events / 200 GeV " L dt =.04 fb s = 7 TeV l + l + :H T >50GeV,m ll >0GeV data real charge flip fakes uncertainty Z 0GeV(! ) tt RR ATLAS [GeV] H T Comparison of observed data and expected SM backgrounds for H T in region (3) EFSS202 7 December

34 b'b'à WtWtà 4W2b (Same Sign Leptons + Jets) Results : Heavy down- type quark m b' > 450 GeV For s- s top quarks produc&on : Solid red line presents result from analysis, measurements of forward- backward produc&on at Tevatron lie above SM expecta&on Upper limit for cross sec&on : 2pb arxiv : EFSS202 7 December

35 BB à Zb+X m of Z and st b fraction / 20 GeV MC Backgrounds 250 GeV b', ZbZb 400 GeV b', ZbZb 550 GeV b', ZbZb 700 GeV b', ZbZb Selec&on of objects is exactly the same as the 2 previous analyses m(zb) [GeV] ass of 5 the Zb system, for all backgrounds combined! (fb) 4 QQ Tbj, Ybj 3 Bbj Xtj 2 Ttj V = 0. Branching ratio T " Wb T " Zt T " Ht B " Wt B " Zb B " Hb m Q (GeV) m Q (GeV) Figure. Left:Heavy quark production cross sections at LHC.Right:branching ratios for T and B decays. EFSS202 7 December

36 Single Vector-like Quark Production Selec2on: Object selec&on is the same as for the previous analyses Addi&onal cuts : CC Channel: η(w, leading jet) < 2.3 φ(w, leading jet) > 2. rad φ(l, E miss T ) <.3rad η(w, associated jet) >.6 η(leading jet, associated jet) >.3 E T miss > 50 GeV p T leading jet > 60 GeV NC Channel: φ(l, l) <.5rad η(l, l) <.6 φ(z, leading jet) > 2.rad η(z, leading jet) <. η(z, associated jet) > 0.9 η(leading jet, associated jet) > 0.9 EFSS202 7 December

37 Results : Single Vector-like Quark Production ATLAS Note ATLAS- CONF Events / 50 GeV ATLAS Preliminary CC Channel Ldt = 4.64 fb s = 7 TeV Data 20 W +jets tt Multi-jet Single Top Z+jets Diboson D, 0 GeV Same kind of plots but for CC channel 2 Events CC m(lepton, ν, leading jet) [GeV] ATLAS Preliminary Data 20 ATLAS Preliminary CC Channel Z+jets NC Channel Data 20 tt Fitted Ldt = 4.64 fb s = 7 TeV Diboson Background su, = 0 7 TeV GeV Ldt = 4.64 fb Qq) BR(Q Wq) [pb] σ(pp MadGraph, D-quark MadGraph, X -quark 95% C.L. upper limits: Observed Expected ±σ ±2σ significance Events m(lepton, ν, leading jet) [GeV] ATLAS Preliminary 4 NC Channel Data 20 nte Carlo 3 estimated backgrounds for the combined Fitted Background electron and muon channels for the NC (bottom) channel. A. TeV VLQ signal is overlaid s = 7 TeV in each case, normalized to the 2 cross section assuming a coupling of κ qq = mq v κ qq = and 0% branching fraction to a light quark. The data is also plotted. 6 Ldt = 4.64 fb Note that for calculation of sensitivity and setting BR the background estimate is taken from a fit to data. 3 BR(Q Zq) [pb] q) -2 s = 7 TeV Ldt = 4.64 fb ATLAS Preliminary [GeV] Ø Mass of X(+5/3), D(- /3) greater than 420 GeV and 80 GeV respec&vely Ø U(+2/3) with mass below 20 GeV excluded (NC) m Q MadGraph, U-quark 95% C.L. upper limits: Observed Expected ±σ ±2σ EFSS202 7 December

38 Single Vector-like Quark Production Figure 7: Event display for the W eν channel event with the highest three body invariant mass. Here, the invariant mass of the three body system is M(e, ν, leading jet) = 65 GeV. EFSS202 7 December

39 Single Vector-like Quark Production Figure 9: Event display for the Z ee channel event with the highest three body invariant mass. Here, the invariant mass of the three body system is M(e, e, leading jet) = 859 GeV. EFSS202 7 December