Marcel Vos (for all top-philic groups at IFIC)
The top quark and the Higgs force
The top quark - theory
The top quark feels the Higgs force more than any other (SM) particle
This implies that the top quark is part of the (hierarchy) problem, and a key
ingredient to many proposed solutions (i.e. top partners in SUSY, composite Higgs) A calculable quark: precise predictions exist for tt production (NNLO+NNLL ~5%), single top production and many associated production processes
A friendly quark for phenomenology: a quark that produces an isolated lepton,
leaving an unambiguous marker to distinguish top and anti-top and to study its spin The ultimate flavour...
The top quark - experimental
Too heavy for LEP/SLD: the top quark was indirectly “felt”, but not produced - no constraints on g/Z-tt vertices → model-builders promptly used that freedom Discovered in 1995 by the Tevatron experiments
- first characterization of QCD and charged-current interactions The Large Hadron Collider is a top quark factory
- 100.000.000 top quark pairs in ATLAS and CMS in run 2, still x20 to come
The ATLAS top physics program
study top quark production to:
- search for top-philic new physics
- test the SM in precision measurements
- determine fundamental parameters of the SM
- provide a clean source of W-bosons and b-quarks - characterize an important backgrounds for searches - calibrate the detector response
Strong contribution from
t + DM, vector-like top boosted tops
tt, tq’, ttH, ttZ, ttW, tH top mass measurement -
ttW
jet calibration
2 group conveners + several candidates In the following: some highlights, with a focus
on recent results with a recognized role for IFIC
Approximately 350 ATLAS scientists
(+ a similar number in CMS + a few in LHCb and ALICE)
Searches with top quarks
DM searches with top quarks:
- mono-top production: single top in association with invisibles
- bounds on simplified models with dark matter candidate and heavy mediator
Searches top + DM:
M.J. Costa, C. Escobar, C. Garcia, J.E. Garcia, S. Marti, M. Moreno, P.
Sabatini
Ph.D. J Navarro (VLT),
IFIC contact editor for:
Partial Run-2 dataset [JHEP 05 (2019) 41]
HL-LHC potential (ATL-PHYS-PUB-2018-024).
[arXiv:2011.09308, submitted to EPJC]
L. Barranco PhD ‘18 F. Castillo PhD ‘20
Searches with top quarks
SUSY searches with top quarks:
- stop pair production produces top, Z, H
- full run 2 data set expand stop mass reach to > 1 TeV
Searches SUSY top:
X. Poveda
EPJC 80 (2020) 1080 IFIC: contact editor
Boosted top quarks
Boosted top quarks:
- From exotic signal to standard candle
- IFIC isolated the first boosted top quarks in 2011 - Boosted object taggers now mainstream in searches - Used to “boost” BSM sensitivity of SM measurements - Use mass peaks of known resonances (W, top) to calibrate the large-R jet response
[review Kogler et al., Rev. Mod. Phys 91 (2019) 4]
boosted tops:
Miguel Villaplana, J. Salt, S. Gonzalez, M.Vos
Ph.D. Javier Aparisi
ATLAS-CONF-2019-026, EPJC79 (2019) 2, 135, ATLAS-CONF-2020-022
4s evidence for SM effect
Measurement of the tt cross section Top quark pair production:
- NNLO+NNLL calculation is available (~5% uncertainty)
- Cross section measurements at several energies and in multiple channels
ATLAS 13 TeV em analysis EPJC 80 (2020) 528
Uncertainty breakdown
Statistics: 0.4% (36 fb-1!) Detector: 0.6%
Modelling: 1.0% (NLO) Luminosity: 1.9% (→ 1%) Total: 2.4%
Measurement of W branching fractions
Revisit the W branching ratio to charged leptons:
- Inspired by hints of departure from lepton universality - Isolate a clean sample of W-boson in top decays
- Fit templates of the lepton pT and d0
- Resolves a long-standing LEP discrepancy
arXiv:2007.14040, accepted by Nature Physics
Single top quark production
Single top quark production:
- Cross section measurements with 5-15% precision - Legacy results for t-channel, tW and s-channel
- C. Escobar responsible LHC top WG run 1 combinations
boosted tops:
Miguel Villaplana (GENT), J. Salt, S.
Gonzalez, M.Vos Ph.D. Javier Aparisi
10
IFIC Editor [JHEP 05 (2019) 088]
Single top:
M.J. Costa, S. Cabrera, J.E. Garcia, C. Escobar, C. Garcia, S. Marti
Ph.D. Galo Gonzalvo Mariam Chitisvili
Single top quark production Single top quark production:
A source of highly polarized top quarks at the LHC
Aguilar-Saavedra, Bernabeu, NP B840 (2010) → ATLAS-CONF-2013-032 Aguilar-Saavedra, Bernabeu, PRD93 (2016) 011301. → JHEP 04 (2017) 124 Aguilar-Saavedra,Escobar et al., EPJC (2017) 77:200 → JHEP 12 (2017) 017
full polarisation vector for top/anti-top quarks
- Full Run-2 result at 13 TeV
- Particle-level normalized cross sections - EFT bounds on the tWb dipole operator:
O.Estrada PhD ‘20 J. Jimenez PhD ‘18
M. Moreno PhD ‘14 L. Barranco PhD ‘18 S. Pedraza PhD ‘17
Partial run 2 result, full run 2 paper under approval
V. Lacuesta PhD ‘16
Clearly recognized as IFIC effort, in collaboration with other institutes
(U. Pittsburgh, NIKHEF)
G. Gonzalvo PhD ‘21
Top quark mass
Top quark mass:
E. Fullana, J. Fuster, M.Vos
Ph.D. Alberto Prades, Luis Monsonis,
Javier Aparisi
Ph.D. Melini ‘19 Ph.D. Irles ‘15
Clearly recognized as IFIC effort, in collaboration with theory groups
- IFIC develops MC mass calibration
Top quark mass:
- One of the most hotly debated areas of (top quark) physics
- World average of “direct” measurements: 172.8 ± 0.3 GeV [PDG 2020]
- IFIC proposed and executed pole (and MS) mass extraction from tt+jet events - Full run 2 analysis aiming for 0.5 GeV precision in well-understood mass scheme
[EPJC77 (2017) 11, EPJC73 (2013) 2438]
[A. Hoang, what’s the top mass, Ann. Rev. Nucl. Part. Sci. 70 (2020)]
Associated top quark production
Top + X production:
Top and Z Top and Z:
- Associated ttZ production; first direct probe of top-Z couplings - Differential cross section measurement on full run 2 data
ttZ:
M. Moreno, F. Cardillo
arXiv:2103.12603, submitted to EPJC analysis contact + 2 paper editors
Inclusive cross-section:
(compatible with SM, precision of 9%)
Top and W Top and W:
- The ttW process is an interesting process; tW scattering - Important background for three-lepton searches
ttW:
M. Moreno
Ph.D. Marcos Miralles
Improve ttW modelling and estimate missing higher-order effects:
* scale dependence * EW corrections
ATL-PHYS-PUB-2020-024
Top and more tops Top and more tops:
- Four-top production: a spectacular final state with a tiny rate (~10 fb) - The backgrounds (ttH, ttZ, ttW) were discovered just yesterday
ATLAS published “evidence” in same-sign multi-lepton channel EPJC 80 (2020) 1085
Some further support in 1/2-lepton ATLAS-CONF-2021-013
Discovery soon? Stay tuned?
Top and Higgs Top and Higgs:
The “Brangelina” of the SM
- Loop production and decays discovered in 2012 offer indirect sensitivity to top (+ heavy new particles)
- ttH production discovered in 2018: direct measurement of the Yukawa coupling
ttH:
X. Poveda ttH-CP M. Moreno New particles in
Higgs loops would enhance gg→ H and H→gg, but not ttH and H→ZZ
Top and Higgs Top and Higgs:
- Use pp→ ttH, H→ gg to probe CP nature of the top-Higgs interaction - Reconstruction & classification of a tiny signal using BDTs
Particle physics is an exciting game, but in the end the SM usually wins:
CP-even interaction strongly preferred by the data
|a|< 43o at 95% CL yt <0 disfavoured
Phys.Rev.Lett.125,061802 (2020) IFIC (contact editor)
Top and Higgs and taus Top and Higgs and taus:
- Use pp→ ttH, H→ tt with hadronic tau candidates - New effort: no public results yet,
ttH with taus:
X. Poveda, L. Fiorini
Enrique Valiente (JAE ICU)
(single) top and Higgs (single) top and Higgs:
- tiny cross section (74 fb) and hard to distinguish from ttH - tHq vertex is sensitive to the sign of yt.
- New effort in multi-lepton final states (no public results yet)
tH:
S. Cabrera, F. Cardillo, C. Escobar
PhD Jesus Guerrero, Pablo Martínez
SMEFT interpretation
SMEFT interpretations to benchmark the BSM potential of precision measurements
IFIC + U. Michigan, J.A. Aguilar, 2016 IFIC (M. Perelló, J. Aparisi), 2019
“massacre in model zoo” “do I even dare to mention Tevatron AFB in a polite conversation?”
SMEFT interpretation
SMEFT interpretations to compare the reach of different machines
Comparison of LHC, HL-LHC, and electron-positron collider (aka Higgs factory) Operation above the tt threshold is a must to measure top EW couplings
[JHEP12 (2019) 098] and the (running) top mass [PLB804 (2020) 135353]
SMEFT interpretation
SMEFT interpretations to project all data on BSM world (much more in Martín’s talk) A very helpful map to understand the inter-relations of the top and Higgs programs
Inventory of the top quark EW couplings after LHC run 2
(LEP Z→bb, Tevatron single top, LHC W-helicities, single top, associated production) IFIC top EFT
M. Moreno, A. Peñuelas, M. Vos
Ph.D. M. Miralles, V.
Miralles
IFIC theory & experiment
Dipoles; CtW very tightly bound; CtZ benefits from differential measurements
Right-handed coupling:
(weak) bound from ttg, ttZ Left-handed coupling:
LEP + LHC synergy
Yukawa from ttH
Summary
The LHC “top factory” physics programme is in full swing:
- searches for top-philic BSM exploring the TeV scale - precision measurements at %-level at a hadron collider - top mass measurements to deep-sub-GeV precision
- rare processes characterizing previously unseen top EW interactions - first light on the interactions of the top quark with the Higgs boson
IFIC top effort
Implication of the experimental groups in the ATLAS programme well recognized Healthy two-way interplay with theory departement
measurements
phenomenology interpretation
