top mass
- top mass definition - do we need to use a consistent scheme for snowmass studies? how do we enable comparisons properly?
- something that is needed now to prepare for studies later in the year?
- Ferbel: what limits the dilepton mass measurement at hadron collider? Sensitivity to top mass not that large, currently 2GeV and more uncertainty
- experimental projects:
- from theory side: need to determine what can be done about dilepton events - NLO simulation to yet done. this exists for J/Psi determination
- also possible updates to theory description of top mass, but not clear if/what would happen here
- also need to integrate with ME analysis - project on how to do this at NLO
top couplings theory:
- so many operators, hierarchy of what to look for? Matt: operators tell you what leading correction is. Once you look only at that, then automatically reduces it to dimension 6 and interference with SM. At that level, have to stop to be model independent. Scott Thomas and Michael Grasser have looked at this (though not published), and yes, there are some specific kinematics that are sensitive to only a small number of operators.
- Ferbel: tt unpolarized at Tevatron, is there some way to produce polarized top pairs? Matt: Can have new physics which can induce polarization transverse to top production plane. Could try to observe this in hadron collider, but any effect from new operators will be sub-leading. Brock: longitudinal polarization is parts per mil from EW corrections.
top couplings experiment:
- should link experimental limits and measurements to coupling operator constraints.
- Kaustubh: will also have to compare to linear collider for these coupling measurements. Yes, this is being studied for ILC.
- Andy: ATLAS vs CMS ttH sensitivity? Andrey and Jahred: CMS looked at more inclusive sample and CMS uses MVA and is less conservative on systematics. This is being worked on.
- Keith Ellis: some information on ttbar bb at NLO, not a complete calculation, but some information is available.
- Cecilia: those thinking about couplings, please come up with specific bullets on what can be done in next 6 months. Both experimentally and theoretically. Kirill: yes, good project would be to update the projections to LHC 300fb-1 from Baur paper which is ten years old. Andrey: true, but studies have shown that projections from that paper still hold true today.
vanilla stop searches:
- Kaustubh: do pheno papers have top tagger? Yes. But experiments are not using this. Improved tau-jet rejection? In pheno papers this is only classified, very sensitive to details of detector simulation and performance.
- Reinhard: top to all-hadronic best channel since no tau bkg? Daniel: no, in fact that's where the background from tau is largest.
- Reinhard: goal is to extend to the right and up, but beveled edge at upper right will always be there. Lower left is addressed in Mat Reece's talk.
Top partners:
- Adiana, postdoc at Kansas State: (responsible for 2 of the analyses shown): CMS will show update at Moriond of scan of all possible cross section branching ratios. Work ongoing in overlap with stop group. will also see dilepton update with 5/3 charge T'. in discussion with theorists, in particular Matt Strassler.
- Cecilia: try to go beyond LHC specific work, explore other scenarios and colliders.
- Reinhard: specific projects for the summer: exploring full space of possible parameters and how to match experimental searches to them, which experimental searches are missing, and also which theory models and couplings and final states are missing and could be explored, at LHC and lepton colliders.
top AFB:
- can map these types of new physics models onto the operators shown by the couplings group? Are these
- Matt Baumgart: could use 4-top final state to make constraints, eg from axigluon pairs?
- Tom: what is meant by "robust" on page 7? After all, uncertainties in pt are quite large. Also some discrepancy between D0 and CDF as function of mass. D0 analysis will not be done as function of top pair pT since not enough resolution.
top FCNC:
- Kaustubh: yes, should also study this for ILC, for example top-charm-Z
RPV susy, tt like final states:
- yes, it is possible to have final states that look like top with extra stuff not very detectable
- Reinhard: should limit be on mass? or on coupling? Limit is on mass because QCD production through strong interaction. Whether scenario can get ruled out or not depends on model. David Miller: explicit evaluation of couplings would also be interesting, RPV provides large range of phase space. If can push these couplings down to where it looks like long-ranged would be interesting. Yevgeny: Indirect limits depend on flavor structure of RPV scenario. For most couplings, there are no indirect limits sufficiently strong to actually constrain these. David: yes, these are the types of models I have in mind. For example minimal flavor violation not explored in detail experimentally yet. Yevgeny: So far, in reinterpretation, using only total tttbar XS, not any kinematics. Yevgeny: there is also RPV SUSY group within BSM which also study these types of scenarios. Yevgeny and Jared are doing both studies.
Stealth stop:
- Kaustubh: covered case where stop is near top and neutralino is very light. This is complementary to Daniel's talk on heavy neutralino, but small stop/neutralino mass difference. Matt: that corresponds more to compressed spectrum.
- Reinhard: specific experimental talk would be to check experimental cuts like eta or isolation cuts and to see if there are any experimental show-stoppers to sensitivity to variables like MT2.
boosted top:
- Reinhard: overlap with boosted Higgs and boosted other stuff: we cover boosted top in particular, generic boosting algorithms and jet substructure covered in QCD group.
- interplay with detector - important question. limited by detector resolution? only hcal? also tracking? or ecal?
- last page: also need to determine impact of and limitation of boosted tops at muon collider
- Andrey - thought b-tagging was used. Emily: ATLAS ttbar resonance search did use b-tagging, but had large uncertainties. Cecilia: similar at CMS.
Top kinematics:
- how much are linear collider (and muon collider) predictions limited by theory XS prediction? Markus: there are studies for ttbar, nothing beyond LO for associated production processes. Should find out if this is limiting lepton collider studies.
- are there differential cross sections that people aren't looking at yet that are sensitive to NP? Or that have a distinct shape? Can write down specific suggestions for phase space that should be studied? ATLAS jet veto study to constrain PDF is one example, are there more?
- Keith: what about width of top quark and including it? Markus: corrections are of the order of 1 per mille to 1 per cent.
- Susanne: on ttbar+jet, looking at distributions or measuring charge asymmetry? Could also be sensitive to forward-backward asymmetry. what is experimental status? Andy: At Tevatron, adding one jet to ttbar is limited in statistics. At LHC more statistics, so should be studying this. Good specific topic for snowmass study.
top mass scan at linear collider:
- are there aspects of uncertainty that could be improved through hadron collider measurements in near future? Difficult to answer. threshold scan will definitely provide most precise measurement of top properties, doesn't require any input here.
- Width determination from top decay reconstruction? much larger uncertainties, but in principle yes, possible.
- how do beam effects change from ILC to CLIC? ILC is better, better control over beam. Beamstrahlung wider at CLIC.
- studies from ten years ago should be extended once updated XS cross section is available.
Discussion:
- Andreas Jung: would be nice to get simulation samples. Samples don't exist yet. Sergei Chekanov: have samples that were used for recent arXiv study. Will send email with location of those. Chip: BSM group is generating samples with pileup to study this in delphes.
- Higgs and BSM groups are discussing common background samples. Trying to get this organized, but not there yet.
- Reinhard: can do parton level studies right now, even if full detector simulation (or even Delphes) requires coordination amongst groups.
- For European study, ATLAS used smeared objects, better than fastsim, not as good as full detector simulation. Probably won't be used for this study for Snowmass because it's quite special for ATLAS. Robin: CMS has something similar. Can we get something like that or the parameters for it out? Especially regarding pileup.
- Delphes has these parameters from ATLAS inside the Delphes smearing functions. Sergei: passing hepmc event record to Delphes, thus will have many gigs of data in that record. Output of Delphes then is only root files, pretty small.
- Chip will send out link to decks of cards to be used with Delphes. Tom LeCompte is putting twiki page together with information on this, but that page is not ready yet for public consumption.
- Continue to have regular meetings. Next meeting in 2 or 3 weeks.
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