AF Zarnecki, CLIC for top quark studies

CLIC workshop March 2017

Transcript

1. Status and plans for CLIC top quark studies Aleksander Filip ˙ Zarnecki Faculty of Physics, University of Warsaw on behalf of the CLICdp collaboration CLIC workshop 2017 March 10, 2017 A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 1 / 26
2. Motivation Credit: Hitoshi Murayama Top quark the heaviest known elementary particle Yukawa coupling to Higgs boson yt ∼ 1 ⇒ key to understanding of EWSB decays before hadronizing: the only “naked” quark ⇒ test ground for QCD large loop contributions to many precision measurements sensitive to many BSM scenarios ⇒ a window to “new physics” A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 2 / 26
3. Status and prospects at LHC LHC Run I data demonstrated that both ATLAS and CMS experiments are capable of making very precise measurements of copiously produced tops. Top mass [GeV] top m 165 170 175 180 185 ATLAS+CMS Preliminary = 7-8 TeV s summary, top m LHC top WG shown below the line (*) Superseded by results Aug 2016 World Comb. Mar 2014, [7] 0.67) GeV ± 0.76 (0.36 ± = 173.34 top m stat total uncertainty total stat syst) ± total (stat ± top m Ref. s ATLAS, l+jets (*) 7 TeV [1] 1.35) ± 1.55 (0.75 ± 172.31 ATLAS, dilepton (*) 7 TeV [2] 1.50) ± 1.63 (0.64 ± 173.09 CMS, l+jets 7 TeV [3] 0.97) ± 1.06 (0.43 ± 173.49 CMS, dilepton 7 TeV [4] 1.46) ± 1.52 (0.43 ± 172.50 CMS, all jets 7 TeV [5] 1.23) ± 1.41 (0.69 ± 173.49 LHC comb. (Sep 2013) 7 TeV [6] 0.88) ± 0.95 (0.35 ± 173.29 World comb. (Mar 2014) 1.96-7 TeV [7] 0.67) ± 0.76 (0.36 ± 173.34 ATLAS, l+jets 7 TeV [8] 1.02) ± 1.27 (0.75 ± 172.33 ATLAS, dilepton 7 TeV [8] 1.30) ± 1.41 (0.54 ± 173.79 ATLAS, all jets 7 TeV [9] 1.2) ± 1.8 (1.4 ± 175.1 ATLAS, single top 8 TeV [10] 2.0) ± 2.1 (0.7 ± 172.2 ATLAS, dilepton 8 TeV [11] 0.74) ± 0.85 (0.41 ± 172.99 ATLAS, all jets 8 TeV [12] 1.01) ± 1.15 (0.55 ± 173.80 ) l+jets, dil. June 2016 ( ATLAS comb. 7+8 TeV [11] 0.61) ± 0.70 (0.34 ± 172.84 CMS, l+jets 8 TeV [13] 0.48) ± 0.51 (0.16 ± 172.35 CMS, dilepton 8 TeV [13] 1.22) ± 1.23 (0.19 ± 172.82 CMS, all jets 8 TeV [13] 0.59) ± 0.64 (0.25 ± 172.32 CMS, single top 8 TeV [14] 0.95) ± 1.22 (0.77 ± 172.60 CMS comb. (Sep 2015) 7+8 TeV [13] 0.47) ± 0.48 (0.13 ± 172.44 [1] ATLAS-CONF-2013-046 [2] ATLAS-CONF-2013-077 [3] JHEP 12 (2012) 105 [4] Eur.Phys.J.C72 (2012) 2202 [5] Eur.Phys.J.C74 (2014) 2758 [6] ATLAS-CONF-2013-102 [7] arXiv:1403.4427 [8] Eur.Phys.J.C75 (2015) 330 [9] Eur.Phys.J.C75 (2015) 158 [10] ATLAS-CONF-2014-055 [11] arXiv:1606.02179 [12] ATLAS-CONF-2016-064 [13] Phys.Rev.D93 (2016) 072004 [14] CMS-PAS-TOP-15-001 FCNC decays A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 3 / 26
4. Status and prospects at LHC LHC Run I data demonstrated that both ATLAS and CMS experiments are capable of making very precise measurements of copiously produced tops. The HL-LHC will provide much larger samples for precision top physics ∼ 3 billion top-quark pairs produced, ∼1 billion tops produced singly Top mass [GeV] t Total uncertainty on m 0 0.5 1 1.5 2 2.5 3 CMS Preliminary Projection (8 TeV) Run I 0.3/ab, 14 TeV 3/ab, 14 TeV , arXiv:1608.03560 Ψ J/ ), JHEP08 (2016) 029 t (t σ sec. vtx, PRD 93(2016)2006 single t, PAS-TOP-15-001 l+jets, PRD 93(2016)2004 “mass scheme” uncertainty not included CMS CR-2017/029 FCNC decays ATL-PHYS-PUB-2012-001 Most measurements will be systematics limited A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 3 / 26
5. Physics studies for CLIC Assumed running scenario CERN-2016-004 Three construction stages (each 5 to 7 years of running) √ s = 380 GeV with 500 fb−1 + 100 fb−1 at t¯ t threshold selected as an optimal choice for precision Higgs and top physics √ s = 1.5 TeV with 1500 fb−1 √ s = 3 TeV with 3000 fb−1 with ±80% electron beam polarisation (baseline design) Full simulation studies CDR detector models based on the SiD and ILD concepts for the ILC dedicated detector concept, CLICdet, implemented recently Luminosity spectra and overlay events taken into account Event reconstruction with the “Particle Flow” approach Excellent flvour tagging possible with a high precision pixel vertex detector see presentation by Dominik Dannheim for more details A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 4 / 26
6. Status and plans for CLIC top quark studies Presented in this contribution 1 Top reconstruction 2 Top mass and width measurement 3 Electroweak couplings 4 Yukawa coupling 5 Rare decays A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 5 / 26
7. Top event reconstruction Final state e+e− −→ t¯ t −→ 6 j at √ s = 380 GeV At low energy stage, top decay products (jets) well separated. Direct reconstruction of the decay kinematics possible. Crucial for efficient background suppression A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 6 / 26
8. Top event reconstruction Final state e+e− −→ t¯ t −→ 6 j at √ s = 3 TeV At higher energy stages, top quarks produced with large boost. Decay products cluster in two “fat” jets. ⇒ dedicated tools needed to discriminate between top and background events A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 7 / 26
9. Top event reconstruction Final state Invariant mass for “fat jets” (events clustered into 2 jets) √ s = 1.4 TeV t¯ t −→ 6j R.Str¨ om t¯ t −→ 4j l ν A.Winter Two analyses ongoing A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 8 / 26
10. Top tagging Using jet substructure to distinguish boosted top jets from light-quark and gluon jets using Method proposed in Kaplan et al. Phys. Rev. Lett. 101, 142001 Structure of a single top jet Cluster event into two jets, top candidates Try to recluster candidate jet into three subjets to reconstruct decay kinematics A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 9 / 26
11. Top tagging Using jet substructure to distinguish boosted top jets from light-quark and gluon jets using Method proposed in Kaplan et al. Phys. Rev. Lett. 101, 142001 Structure of a single top jet Cluster event into two jets, top candidates Try to recluster candidate jet into three subjets to reconstruct decay kinematics Impose kinematic constraints Look also at relative angles, jet multiplicity... A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 9 / 26
12. Top reconstruction Reconstruction of top production angle In semi-leptonic decay channel: e+e− −→ t¯ t −→ 4j l ν ⇒ determination of Forward-Backward asymmetry important observable for top coupling determination 500 fb−1 at 380 GeV I.Garcia Tight quality cuts required to assure proper charge determination 1.5 ab−1 at 1.4 TeV ) top θ cos( 1 − 0.5 − 0 0.5 1 ) -1 Eff. no. events (1.5 ab 0 200 400 600 800 1000 1200 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 generated reconstructed correctly reconstructed Purity R.Str¨ om corrected for event selection efficiency A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 10 / 26
13. Threshold scan Top pair production cross section around threshold: resonance-like structure corresponding to narrow t¯ t bound state. Very sensitive to top properties and model parameters: [GeV] s 345 350 355 cross section [pb] 0 0.2 0.4 0.6 0.8 1 1.2 1.4 threshold - 1S mass 174 GeV t t TOPPIK NNLO CLIC350 LS only ISR only CLIC350 LS+ISR CLIC top quark mass mt top quark width Γt strong coupling αs top Yukawa coupling yt Significant cross section smearing due to luminosity spectra and ISR A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 11 / 26
14. Top mass determination Already 100 fb−1 at the threshold sufficient for top mass measurement Energy scan: 10 cross section measurements, 10 fb−1 each (to be optimised) [GeV] s 345 350 355 cross section [pb] 0 0.2 0.4 0.6 0.8 threshold - 1S mass 174.0 GeV t t TOPPIK NNLO + CLIC350 LS + ISR /point -1 simulated data: 10 fb 200 MeV ± top mass CLIC top mass [GeV] 173.95 174.00 174.05 s α 0.116 0.118 0.120 σ 1 σ 2 [174.00 GeV; 0.1179] CLIC K.Seidel et al., Eur. Phys. J. C73 (2013) 2530 Expected statistical uncertainty on top mass: 15–20 MeV on top width: ∼40 MeV A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 12 / 26
15. Top mass determination Threshold scan Main advantage: mass well defined from theoretical point of view Enormous progress in precision of theoretical calculations 340 342 344 346 348 s (GeV) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 R NNNLO NNLO NLO M.Beneke et al., Phys. Rev. Lett. 115, 192001 (2015) Estimates for top mass systematic uncertainties: theoretical predictions (NNNLO): ∼40 MeV parametric αs uncertainty: ∼30 MeV (for today’s WA) other uncertainties (backgrounds, spectra, etc.): on 10–20 MeV level ⇒ total uncertainty on the top mass of ∼50 MeV feasible dominated by systematics A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 13 / 26
16. Top mass determination Direct reconstruction Possible for all energies above the threshold (continuum) High statistical precision: 80 MeV estimated for 100 fb−1 at 500 GeV entries / (2 GeV) 200 400 600 800 1000 fully-hadronic t t simulated data fit with final pdf background t non t CLIC top mass [GeV] 100 150 200 250 residuals norm. -2 0 2 entries / (2 GeV) 200 400 600 semi-leptonic t t simulated data fit with final pdf background t non t CLIC top mass [GeV] 100 150 200 250 residuals norm. -2 0 2 K.Seidel et al., Eur. Phys. J. C73 (2013) 2530 Suffers from significant theoretical uncertainties when converting to particular mass scheme (as in LHC). A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 14 / 26
17. Top mass determination Radiative events M.Boronat @ CLIC’2016 At higher energies, we are still sensitive to t¯ t threshold in radiative events. When measuring the ISR photon, we can calculate “true” collision energy. Reconstructed energy spectra Particle level √ s = 380 GeV ζs = √ s Parton and particle level studies indicate that statistical uncertainty of ∼100 MeV can be obtained by combining the ISR and FSR measurements Full simulation study is under development A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 15 / 26
18. Electroweak couplings Pair production: direct access to top electroweak couplings Possible higher order corrections ⇒ sensitive to “new physics” Form factor approach: A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 16 / 26
19. Electroweak couplings Pair production: direct access to top electroweak couplings Possible higher order corrections ⇒ sensitive to “new physics” Couplings can be constrained through measurement of: total cross-section forward-backward asymmetry helicity angle in top decays Form factor approach: A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 16 / 26
20. Electroweak couplings Pair production: direct access to top electroweak couplings Possible higher order corrections ⇒ sensitive to “new physics” Couplings can be constrained through measurement of: total cross-section forward-backward asymmetry helicity angle in top decays Alternative, more universal approach: effective field theory (EFT) ⇒ allows to connect different physics processes (sharing same operator) ⇒ allows to combine/compare different experiments ⇒ includes additional terms (i.e. four-fermion contact interactions) Under development. Focus on 2-fermion and 4-fermion dim-6 operators. A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 16 / 26
21. Electroweak couplings Expected coupling precision at LHC, ILC (500 GeV) and CLIC (380 GeV) initial stage CP conserving couplings CP violating couplings IFIC-LAL Collaboration, M.Perello @ ECFA LC’2016 A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 17 / 26
22. Electroweak couplings EFT prospects M.Perello, this workshop Sensitivity of σ(e+e− → t¯ t) to dimension-6 operators    four-fermion operators    two-fermion operators Multi-TeV operation gives high sensitivity to four-fermion operators High sensitivity to two-fermion operators at the initial stage A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 18 / 26
23. Yukawa coupling Threshold scan ILC: A.Ishikawa @ TopLC’2015 Pair production at threshold: 9% Higgs exchange contribution ⇒ yt can be extracted with statistical uncertainty ∼6% (100 fb−1) assuming αs can be constrained from other measurements large theoretical uncertainties (∼20%) need to be reduced A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 19 / 26
24. Yukawa coupling Threshold scan ILC: A.Ishikawa @ TopLC’2015 Pair production at threshold: 9% Higgs exchange contribution ⇒ yt can be extracted with statistical uncertainty ∼6% (100 fb−1) assuming αs can be constrained from other measurements large theoretical uncertainties (∼20%) need to be reduced Direct measurement for energies above 500 GeV yt can be extracted from the measured e+e− → t¯ tH cross section Difficult measurement: very low statistics and large backgrounds. Statistical uncertainty of 4.4% expected for 1.5 ab−1 at 1.4 TeV CLICdp-Note-2015-001 New: analysis looking at CP violation in the ttH vertex at 1.4 TeV A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 19 / 26
25. Rare decays FCNC top decays Strongly suppressed in the Standard Model (GIM mechanism + CKM): BR(t → c γ) ∼ 5 · 10−14, BR(t → c Z) ∼ 1 · 10−14, BR(t → c H) ∼ 3 · 10−15 Significant enhancement possible in many “new physics” scenarios A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 20 / 26
26. Rare decays FCNC top decays Strongly suppressed in the Standard Model (GIM mechanism + CKM): BR(t → c γ) ∼ 5 · 10−14, BR(t → c Z) ∼ 1 · 10−14, BR(t → c H) ∼ 3 · 10−15 Significant enhancement possible in many “new physics” scenarios Two channels under study for CLIC at 380 GeV t →c h enhancement up to 10−5−10−2 test of Higgs boson couplings well constrained kinematics seems most difficult for LHC Run II: BR < 0.46% HL-LHC: BR < 2 · 10−4 t →c γ enhancement up to 10−7−10−5 clear signature less constrained kinematics expected limits from HL-LHC BR < 2.5 · 10−5 A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 20 / 26
27. Rare decays Reconstruction of FCNC events Preliminary results from the full simulation study for √ s = 380GeV Invariant mass distributions for “spectator” top candidates (SM decay) t →c h events AF ˙ Z t →c γ events N. van der Kolk A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 21 / 26
28. Rare decays Expected limits on BR(t → ch) × BR(h → b¯ b) at √ s = 380 GeV Comparison with parton level results, different jet energy resolutions AF ˙ Z @ LCWS’16 ] -1 Integrated luminosity [fb 0 500 1000 1500 2000 2500 3000 Expected limit 5 − 10 4 − 10 Parton level E 30%/ E 50%/ hadronic decays only E 80%/ CLICdp preliminary full simulation Kinematic fit performance still to be optimised Background reduction primarily based on flavour tagging! A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 22 / 26
29. Status and plans for CLIC top quark studies Summary of activities Threshold 380 GeV 1.4 TeV 3 TeV Top reconstruction " " w w Top mass " " EW couplings " w w Yukawa coupling + CP % "w FCNC decays w Single top/Vtb w % Top squark production w? " - available, w - under study, % - missing The goal is to prepare the complete top paper draft before the end of 2017 A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 23 / 26
30. Conclusions Precise determination of top parameters is crucial for validation of the Standard Model (or any alternative BSM theory) Wide range of top related measurements under study for CLIC Most of it can be addressed already at the initial stage! Top threshold scan gives unique oportunities for precise mass, width and coupling determination Direct measurement of Yukawa coupling requires higher beam energies Most of processes studied in details, based on full simulation results. A lot of ongoing activities, focus mainly on high energy stages and optimization of the detector performance. ⇒ towards the top paper draft by the end of 2017 A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 24 / 26
31. TopLC17 Invitation to Workshop on top physics at the LC 2017 (TopLC17) TopLC workshops gather theorists and experimentalists to study the potential of future lepton colliders in the area of top quark physics. TopLC17 will be held at CERN on 7-9 June 2017 For details see: http://indico.cern.ch/event/595651/ Registration is already opened A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 25 / 26
32. Thank you! Many thanks to all authors contributing their results to this presentation. CLICdp top study group: Marca Boronat, Tom Coates, Juan Fuster, Ignacio Garcia, Pablo Gomis, Victoria Martin, Philipp Roloff, Martin Perello Rosello, Frank Simon, Lars Rickard Strom, Naomi van der Kolk, Marcel Vos, Alasdair Winter, Yixuan Zhang, Aleksander Filip ˙ Zarnecki A.F. ˙ Zarnecki (University of Warsaw) Top studies at CLIC March 10, 2017 26 / 26