Status of the measurements of Higgs boson properties

Status of the measurements of Higgs boson properties with the ATLAS detector B. Mellado University of the Witwatersrand SAIP 2015, Port Elizabeth, 30 th. June – 4 th July 2015

Outline q. Habemus Novum Boson q. Production mechanisms and decay q. Mass q. Spin-CP quantum numbers q. Fiducial cross-sections q. Signal/coupling strength q. Prospects with Run II q. Outlook and Conclusions 2

Habemus novum Boson Phys. Lett. B 716 (2012) 1 -29 Phys. Lett. B 716 (2012) 30 -61 On July 4 th 2012 reported both experiments reported ~5σ effects 3

Higgs production at Hadron Colliders and decays Gluon-gluon fusion Vector Boson Fusion Associated Production 4

Higgs Cross-Sections at LHC 5

Main Decay Modes 6

Mass measurement The Higgs boson mass is a fundamental parameter of nature that is not predicted by theory 7

ATLAS and CMS measurements are compatible and lead to 0. 2% accuracy measurement 8

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Consistency with SM hypothesis + 0 The SM predicts that the Higgs boson have the quantum number J CP = 0+ 10

Spin/CP in H->ZZ->4 l Phys. Lett. B 726 (2013) 120 -144 Exploit full 4 lepton kinematics, combined into a multivariate analysis (BDT) Most sensitive channel in decay to 0 - 11

Data show compatibility with the SM 0+ hypothesis while other alternative hypotheses considered are excluded at a confidence levels above 95% Observation Phys. Lett. B 726 (2013) 120 -144 12

ATLAS-CONF-2015 -008 Compatibility with the SM hypothesis 13

Fiducial Total and Differential Cross-sections 14

Differential Cross-section Measurements 15

When assuming the Standard Model the signal strength of H->γγ is 1. 17 when releasing that condition we get 1. 42. Still these two numbers are statistically compatible 16

When measuring the Higgs boson transverse momentum certain discrepancies were found with the Standard Model 17

Look at other talks in this session for BSM interpretations of this plot Compatibility with the SM (HRes) is 2% Combination 18

Exploration of Coupling Strengths The ATLAS and CMS experiments perform global fits to their available data in order to check compatibility with the Standard Model. Higgs boson couplings are assumed to be that of the SM and scaling parameters are introduced. SM production mechanisms are assumed. 19

In the standard model there is a physical state, a Higgs boson with well defined couplings to weak bosons, fermions and self interactions The exploration of the coupling to weak bosons plays now a pivotal role in understanding the nature of the scalar boson observed experimentally. New physics can be hidden in these couplings. 20

Overall, good consistency with the SM. Need to remember that these measurements assume production mechanisms 21

Coupling strength to fermions Overall, good consistency with the SM Coupling strength to weak bosons 22

23 Prospects for 2015

Outlook and Conclusions q. With the unequivocal discovery of a new boson its exploration has come to the fore q. Mass measurement with 0. 2% accuracy q. Spin/CP quantum numbers exploration consistent with SM hypothesis and rules our other hypotheses considered with a CL better than 99% q. ATLAS pioneered the measurement of fiducial total and differential cross-section measurements. These measurements have least possible model dependence § Need to keep an eye on these measurements with new data q. Signal and coupling strength measurements, assuming SM production mechanisms, consistent with SM q. Run II is progressing well. Expect to reach sensitivity similar to Run I by the end of the year. 24

Recent Progress in QCD Higher Order Corrections How robust is the total gluon-gluon fusion and differential transverse momentum distribution? 25

ar. Xiv: 1503. 06056 v 1, C. Anastasiou et al. First Complete N 3 LO calculation for the total gluon-gluon fusion crosssection showing small N 3 LO/NNLO corrections Perturbative series have converged adding strong confidence on the calculation 26

ar. Xiv: 1504. 07922 v 1, R. Boughezal et al. First complete calculation of gg. F+1 j at NNLO, showing strong reduction of scale variation Corrections to Higgs p. T are moderate and up to 25% 27