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Philipp Roloff - CLIC
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summary of important processes in e+e- vs c.o.m. energy
interesting:
HZ Higgsstrahlung for Higgs factory
ttbar threshold 350GeV
ttbar continuum >365GeV
HHZ double-Higgsstrahlung (~600GeV)
two-beam acceleration scheme, 100MV/m
energy from 380GeV to 3TeV in stages
e- polarization at 80% level
CLIC detector concept
4T B field; 1.5m Si tracker; ECAL w/ 22X0, HCAL w/ 7.5lambda
precision timing (IBS 0.5ns) for background suppression: ~1ns calo, 20ns traacker
3 stages: 380GeV, 1.5TeV, 3TeV; 1, 2.5, 5/ab respectively
projections for Higgs measurements, for unpolarized electron beams
comments on systematics
need more knowledge about detector
use Higgs projections as input for detector R&D
seems useful to collect, each year for 2-3 weeks, data at Z pole to calibrate momentum scale and JES...
luminosity spectrum
plot of collisions vs c.o.m.: there is tail at low energy
could be used, but need to measure w/ Bhabha
at 3TeV, hard to have polarimeters at interaction point -> use single W, Z and gamma events
total luminosity crucial for rate measurements: can reach accuracy of 0.1% w/ luminometer designed for CLIC (and better at lower energies)
convinced that luminosity will not be limiting systematic
some new results
e+e- -> ZH in full simulation
two fat jets for Z, two b jets for H
first application of b-tagging in boosted Higgs decays
impact of having longer run at 380GeV
could increase repetition rate from 50Hz to 100Hz, modest cost (5%) and power (170MW -> 220MW) increase, and can double luminosity
if one also ran for 13 years instead of 8, could increase integrated luminosity at 380GeV by factor 4 (total of 4/ab instead of 1/ab)
some plots showing impact of having 4 times statistics, in e+e- -> W+W-, ttbar
EWPO at Z pole: not looked at before, but topic came up at ESG
return-to-Z case: in 380GeV stage, can end up at Z mass via ISR and beamstrahlung
can beat LEP in left-right asymmetry, and AFB, due to beam polarization
systematic error on polarization: 0.1%
impact on Higgs couplings generally small, some improvements from return-to-Z events on TGC
if operating at Z pole, could get 100/fb in a few years: 4.5B Zs, 3B Z(qq)
about three orders of magnitude more than the return-to-Z events
uncertainty on beam polarization ~ 0.1%
similar to Giga-Z option for ILC
references to CLIC physics potential: Higgs analyses; kappa fits; Higgs self-coupling; top; EW and EFT fits
Manqi: slide 8: do the ZH events include PUs? Is the leakage effects dominant/significant in the width of the reconstructed Boson Mass?
A: yes, normal fullsim includes PU; leakage due to finite thickness of calorimeter is not so much (total is 8.5lambda), larger effect from b decays w/ neutrinos, i.e.,
MET. Still see some tail, after correction in fit
Manqi: substructure method can be applied directly to VBS (vvWW and vvZZ final state), any plan?
A: there is analysis on WW+MET and ZZ+MET, but not using boosted topologies
Gauthier Duriex: is it ongoing the usage of optimal observables in full simulation?
A: yes, ongoing work on kinematic fit, shall have results in 2 months
GD: comment on ESG update?
A: not much, beside what is publicly known; ESG did not mention CLIC, but there is budget for continuing R&D on accelerator
Jakob Beyer: impact on TGC of return-to-Z
Gauthier Duriex: return-to-Z pole can improve Z-e-e couplings which are present together with TGCs in e+e- -> WW
Aram Apyan - VBS
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focus on VV->VV scattering
longitudinal scattering key to understand EWSB and window for NP: unitarized by interference w/ amplitudes w/ Higgs
recent LHC results: WZjj and same-sign WWjj w/ full Run-2 datasets
first differential measurement of ssWW, and 10% precision on fiducial cross section
EW WZ measurement w/ 6.8sigma
cross-sections compared w/ theory predictions including NLO corrections
observation of EW ZZjj production, observation (ATLAS) and evidence (CMS)
MVA discriminator
HE-LHC and HL-LHC prospects for WW scattering
questions for discussion:
which future collider maximizes BSM physics potential of VBS?
not yet thought how much precision Higgs measurements provide
benchmarks to use to compare collider options: dim-6, dim-8 operators? NP models?
100TeV hadron collider: link to interesting studies on ssWW, WZjj, ZZjj, WWjj and dim-8 operators
VBS example on mu collider
cross section calculations, up to few TeV
promising results: VBS and VBF cross sections grow as log, s-channels decrease as 1/s -> looking for sweet spot in c.o.m. energy (Juergen Reuter in chat notes that this
is property of any machine running with fundamental fermions)
VBS example at TeV e-collider
links to studies of scattering W/Z
Georgi-Machacek model: complete BSM model usable as benchmark
have singly and doubly-charged Higgs bosons
summary:
preliminary considerations for VBS studies
question is which future collider option most interesting
road map to unified VBS study: select collider, endorsed by Snowmass community; agree on benchmarks; generator tools
Juergen Reuter: look for more generic BSM models in which you have a few more particles; G-M is quite specific model; generic model could be used as more general
benchmark for other studies
implemented in WHIZARD; and can be implemented straightforwardly in UFO
Ayres: defining benchmarks is tough; e.g., dim-8 _and_ dim-6 operators should be added at the same time, is there then leftover sensitivity to dim-8?
ultimate way could be using both processes at same time, and constrain dim-6 with the inclusive process and dim-8 with VBS process
Marc-Andre Pleier: slide 6, confused by cross section: cross section gets bigger after cut is applied?
A: indeed ;-) could be typo, shall check!
Marc-Andre Pleier: what is phase-space? N colliders, M energies... run out of steam quicky; is there any guidance? At last Snowmass, there was one collider and one
energy, now there are many options
Ayres: very good question; there is no top-down restriction this time around; in some sense, our group can decide what is reasonable
shall have some discussion and restrict to a few (~3?) scenarios
HL-LHC is a given, any estimate there good as a baseline
when discussing where the field go, need to look beyond HL-LHC
Philipp Roloff: a CLIC study of WWvv and ZZvv in full simulation is described in this thesis: https://cds.cern.ch/record/2293158?ln=en
Juergen Reuter: a muon collider collaboration is forming _now_ at CERN; shall wait a day to see whom to talk to
Cen Zhang - Improving positivity bounds on aQGC
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currently aQGC parameterized w/ dim-8 operators
VBS HL/HE-LHC show sensitivity at TeV scale on QGC
SMEFT is right way to go, adding also dim-6 operators
issue: SMEFT connect experimental data w/ concrete UV-complete model
relevant at dim-8: positivity bounds tell us which part of parameter space _cannot_ be UV-completed (e.g., if wrong sign in dim-8 coefficient)
this affects aQGC parameterization
slide 3: green is _only_ area allowed,in rest one cannot get UV completion
in future, more dim-8 effects may become accessible (e.g., new observables in DY)
bounds need to be studied to identify meaningful parameter space (and help focus search)
idea is that certain linear combinations of dim-8 coefficients must be positive
not a new idea, links to papers
want to understand full set of bounds on all QGC operators, and guide future VBS and QGC measurements
dispersion relation to obtain positivity bounds
traditional (elastic positivity) and new approach
dispersion relation: 2->2 scattering can be computed with optical theorem cutting diagrams in two sides
traditional approach to extract bounds: take 2->2 with same particles, get a square term, >0, hence discrete set of inequalities
new approach
instead of using pairs of complex vectors to extract bounds, use symmetries of system: it is a 2->2, use rotations around axis
look at projective operators, generate convex cone, compute all projectors, and their convex hull determines the cone: positivity bounds are the facets of the cone
(maybe it is not cone, but sort of pyramid)
looked at WW->WW
old method gives 4 bounds; new method gives 6 inequalities, 2 of which cannot be obtained by elastic method
problems of interest:
- get full of bounds on all QGC
- establish systematic algorithm
- numerical alternatives for new approach? what to do when continuous generators (and have circular cone instead of pyramid)?
first step: bounds on transversal QGC
note that a couple of them had been missed so far
started with traditional: problem is that there are 8 SM modes -> problem is equivalent to asking determination of positivity of 4th-order polynomial w/ 32 variables...
assume superposition can be factorized -> get conservative results
obtained linear, quadratic, and some cubic bounds: constrained parameter space to 0.8% of total (better than the 2.1% had before)
new approach: problem now expressed by list of projectors, question is: what is cone spanned by these vectors? what its boundary?
problem has linear, quadratic, cubic... and more inequalities
looked at linear and quadratic; constrained parameter space to 0.687%
still conservative (truncated the set of inequalities)
tried to solve numerically, and got 0.681% (1-79.3/N^2)
idea is to determine if given point is included in convex hull or not, and sample large number of discrete points
summary:
- 99.32% of transversal QGC parameters is redundant: it is not UV-completable
- new approach to derive analytical bounds on coefficients
questions:
- implication on experimental analysis? global fits? there has to be implication: 99% of parameter space is excluded...
- beside VBS, other opportunities to test positivity of dim-8 operators?
Ayres: question is whether we can make use of these constraints, but is there idea of how they can be communicated to groups doing fits?
A: indeed, lots of constraints, can tell analyzers, but complicate...