Higgs phenomenology with antenna subtraction Juan M Cruz Martinez IPPP (Durham University) Supervisor: E.W.N. Glover NNLOJET Collaboration Juan M Cruz Martinez (IPPP) Higgs Pheno 1 / 63
Outline Introduction 1 Phenomenological challenges of NNLO calculations 2 Testing grounds 3 Vector Boson Fusion Higgs Production 4 Summary 5 Juan M Cruz Martinez (IPPP) Higgs Pheno 2 / 63
HEP Introduction The Standard Model (SM) is one of the most robust theories known to phyisicists. As it stands, the SM fails to explain many aspects of High Energy Physics (neutrino masses, gravity, baryion assymetry, etc). Despite its many flaws, we are uncapable of finding any significant deviations from the SM in our current experiments at collideres. Juan M Cruz Martinez (IPPP) Higgs Pheno 3 / 63
The Higgs Boson Just five years ago... Juan M Cruz Martinez (IPPP) Higgs Pheno 4 / 63
The Higgs Boson Why is the Higgs that important? The High Energy Physics community have been looking for hints of new physics for many years now. As it stands, the newly discovered boson (which could be just one of many Higgs, a composite particle or the standard model elemental scalar proposed fifty years ago) could provide some clues about where to find new physics. Sadly it looks very standard model-like... Juan M Cruz Martinez (IPPP) Higgs Pheno 5 / 63
Some motivation: Higgs boson couplings From hep-ex/1507.04548 Experimental efforts are currently focused on finding deviations from the Standard Model in all the different channels that can be measured at the LHC. Confirming that the Higgs boson is not the one predicted by the Standard Model will open the door for many theories that would be ruled out otherwise. Juan M Cruz Martinez (IPPP) Higgs Pheno 6 / 63
Some motivation: Higgs boson Even assuming all couplings were to be fully compatible with the SM, the Higgs would still have some problems of its own. The Higgs parameters require some fine tunning that could be avoided (thus restoring naturalness) by supersymmetry (SUSY) or by being a composite scalar with an inverse length of the order of the TeV scale. In the light of these issues, we expect (we hope) to find new physics at the TeV scale associated with EWSB and the Higgs. Juan M Cruz Martinez (IPPP) Higgs Pheno 7 / 63
We need precision These are just some of the reasons we need more precision, both in the theoretical and experimental side. However, even when we have the most precise measurement and calculations, the comparison between theory and experiment with the minimum loss of information is still highly non trivial. Juan M Cruz Martinez (IPPP) Higgs Pheno 8 / 63
The Big Picture Juan M Cruz Martinez (IPPP) Higgs Pheno 9 / 63
The Big Picture Juan M Cruz Martinez (IPPP) Higgs Pheno 9 / 63
The experimental side After a very sucessful run I at 7 and 8 TeV, the LHC is currently delivering 13 TeV data. Five years ago, during Run I, it was able to confirm the existence of a boson which was compatible with the highly anticipated Higgs Boson. And only one year ago the HEP community was turned upside down by a misterious resonance Juan M Cruz Martinez (IPPP) Higgs Pheno 10 / 63
The experimental side After a very sucessful run I at 7 and 8 TeV, the LHC is currently delivering 13 TeV data. Five years ago, during Run I, it was able to confirm the existence of a boson which was compatible with the highly anticipated Higgs Boson. And only one year ago the HEP community was turned upside down by a misterious resonance Sadly the world is not always that beautiful Juan M Cruz Martinez (IPPP) Higgs Pheno 10 / 63
The experimental side Juan M Cruz Martinez (IPPP) Higgs Pheno 11 / 63
An example: φ ∗ There are other ways of improving the precision of a theory-experiment comparison without the need to get more data or better calculations. By selecting the right observable for the right process we can compare results that are bound by different (better behaved) errors. Juan M Cruz Martinez (IPPP) Higgs Pheno 12 / 63
An example: φ ∗ One simple example of this is the low p t regime of the Z boson. In this case the p t of the Z is computed using the energy of its decay products, which could introduce big relative errors due to the energy resolution of the detector. The observable φ ∗ , sensible to the same physics as the p t in the low energy regime, is computed using the direction of the decay products of the Z, which are measured with far better resolution. Juan M Cruz Martinez (IPPP) Higgs Pheno 12 / 63
The theoretical side Juan M Cruz Martinez (IPPP) Higgs Pheno 13 / 63
The theoretical side Even with that knowledge at hand, there are still many known unknowns and unknown unknowns: Strong CP problem Dark Matter Neutrino masses The Higgs Boson Gravity ... ... and the list goes on Juan M Cruz Martinez (IPPP) Higgs Pheno 14 / 63
The theoretical side Even with that knowledge at hand, there are still many known unknowns and unknown unknowns: Strong CP problem Dark Matter Neutrino masses The Higgs Boson � Gravity ... ... and the list goes on Juan M Cruz Martinez (IPPP) Higgs Pheno 14 / 63
The theoretical side And, even knowing there exists a Higgs, there are still many open questions: Is it a fundamental particle? Is it composite? Is it just part of a spectrum, as SUSY predicts? Is it the Higgs of the Standard Model, as simple as that? Improving our theoretical knowledge of the Higgs boson could help find a deviation from the Standard Model: maybe the couplings are not quite right? Maybe we are seeing more (or less) Higgses than we should? Juan M Cruz Martinez (IPPP) Higgs Pheno 15 / 63
And how do we improve precision: There are many things that can be improved in the theory side of particle physics: Parton Distribution Fuctions Juan M Cruz Martinez (IPPP) Higgs Pheno 16 / 63
And how do we improve precision: There are many things that can be improved in the theory side of particle physics: Parton Distribution Fuctions Parton shower Juan M Cruz Martinez (IPPP) Higgs Pheno 16 / 63
And how do we improve precision: There are many things that can be improved in the theory side of particle physics: Parton Distribution Fuctions Parton shower Fixed order calculations Juan M Cruz Martinez (IPPP) Higgs Pheno 16 / 63
And how do we improve precision: Better precision in fixed order calculations means, basically, two things p 1 p 1 p 2 2 p More legs More loops Juan M Cruz Martinez (IPPP) Higgs Pheno 17 / 63
State of the art Many legs calculations can be obtained with tools currently on the market in a mostly automatised manner. The only actual limitation is the computational power. Ie, Leading Order (LO) calculation are, up to a certain point, a solved problem. The challenges that arise for Next to Leading Oredr (NLO) calculations (one extra loop with respect to LO) reduce the number of processes that can be currently automatised. Nonetheless, many processes have been already computed with many legs (and one loop) in the final state (W+5j, Z+4j, 5j, WW+3j). Many techniques and tools have been developed to address the challenges of NLO calculations. Juan M Cruz Martinez (IPPP) Higgs Pheno 18 / 63
State of the art Next-to-Next-to Leading Order (NNLO) calculations (two extra loops with respecto to LO) are currently the state of the art and they will continue be as long as most two loop matrix element are still unknown. Two loops amplitude are known for some processes as H (+ one extra jet), Weak Vector Boson (+ one extra jet) and jet inclusive cross section. Some N 3 LO calculations have been performed for some processes on very particular approximations (inclusive VBF, Higgs production on EFT) Juan M Cruz Martinez (IPPP) Higgs Pheno 19 / 63
State of the art At NLO, new channels for production of a given final state can appear. This means that, for NLO calculations we might be taking into account certain channels with Leading Order precision. At two loops or NNLO the theoretical results are much more reliable as any new channels will be expected to be small in comparison with LO and NLO and the scale dependence stabilises Juan M Cruz Martinez (IPPP) Higgs Pheno 20 / 63
State of the art At NLO, new channels for production of a given final state can appear. This means that, for NLO calculations we might be taking into account certain channels with Leading Order precision. At two loops or NNLO the theoretical results are much more reliable as any new channels will be expected to be small in comparison with LO and NLO and the scale dependence stabilises Although this is not always necessaryly true. Juan M Cruz Martinez (IPPP) Higgs Pheno 20 / 63
Higgs at Next-to-Next-to-Next-to Leading Order A very well known case for this is the production of Higgs boson through gluon fusion. The scale uncertainty is still quite large at NNLO and a N 3 LO calculation has been performed in hep-ph/1504.06056 by C. Anastasiou, C. Duhr, F. Dulat, F. Herzog and B. Mistlberger Juan M Cruz Martinez (IPPP) Higgs Pheno 21 / 63
Recommend
More recommend
