Monte Carlo Fails At Leptonic Summit Couplet Production

The LHC collaborations convey produced hundreds of papers that generally state "everything agrees alongside the Standard Model, cypher novel to hold upwards seen here".

Well, a novel CMS preprint

Measurements of differential cross sections for \(t \bar t\) production inwards proton-proton collisions at \(\sqrt{s} = 13\TeV\) using events containing ii leptons

says something completely different.




Go to the page 58/64 as well as you lot volition come across something like:

Measurements were made of the cross department for the appearance of the superlative quark as well as its antiparticle inwards the proton-proton collisions. Some overall cross sections could concord alongside the theory. However, the next-to-leading Monte Carlo simulations inwards whatever combinations suck at predicting the jet multiplicity. They suck at predicting the transverse momentum of the leptons, quarks, invariant masses, as well as all other kinematic observables you lot could intend of. Higher-order models seem to suck, too.

Nice.




What should you lot intend nearly it? I am non sure. This is a surprising disagreement, I think, because the superlative quarks should hold upwards relatively easy. They're real heavy as well as thus they should hold upwards created similar novel uncomplicated particles that don't assist much nearly the weak gum that attaches them to other quarks as well as gluons. The theoretical simulations shouldn't hold upwards this bad.

On the other hand, the real fact that the Monte Carlo simulators convey to hold upwards used indicates that the QCD phenomena must matter. This is non an experiment whose results could hold upwards easily predicted only yesteryear considering the uncomplicated particles such every bit superlative quarks – the gluons as well as their interactions matter. So I would state that this is a failure of the theory inwards a government where both the simple Feynman diagrams describing high-mass superlative quarks; as well as messy calculations where Monte Carlo calculations are useful convey to hold upwards combined.

When the combination is needed, theoretical predictions seem to hold upwards off.



MG5 aMC@NLO, MG5 aMC@NLO, PYTHIA8, MADSPIN as well as other calculations convey to hold upwards made inwards Monte Carlo because the casino produces the random numbers that are needed inwards the calculations. Donald Trump is planning the American answer to the Monte Carlo simulations inwards several casinos he owns. The commencement generator volition hold upwards MLVGA1 (Make Las Vegas Great Again One).

Of course, this could hold upwards a hint of novel physics. Perhaps the superlative quark is composite. Or something else. But this is a complicated plenty experiment – lots of processes are combined to hit the end results – that it may hold upwards real difficult to opposite engineer the discrepancy. In other words, the discrepancy is no straightforward guide towards the correct means to create our theory if our theory is incomplete at all.