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## NON-OBSERVATION OF HEAVY NEUTRAL SCALARS AT THE LHC

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**NON-OBSERVATION OF HEAVY NEUTRAL SCALARS AT THE LHC**Pedro Ferreira ISEL and CFTC, UL Scalars 2013, Warsaw 14/09/2013 Workwith A. Arhriband R. Santos Sponsored in partby PTDC/FIS/117951/2010**LHC discovered a new particle (a scalar?) with mass ~125**GeV. • Up to now, all is compatible with the Standard Model (SM) scalar particle. See yesterday’s talks by K. Moenig and G. Tonelli. BORING! (not the talks…) Two Higgs Dublet model, 2HDM (Lee, 1973) : one of the easiest extensions of the SM, with a richer scalar sector. Can help explain the matter-antimatter asymmetry of the universe, provide dark matter candidates, … G.C. Branco, P.M. Ferreira, L. Lavoura, M. Rebelo, R. Santos, M. Sher, J.P Silva, Physics Reports 716, 1 (2012)**TWO HIGGS DOUBLET MODELS**• They are the simplest Standard Model extension – instead of a single scalar doublet, we have two, Φ1 and Φ2. • They do not affect the most successful predictions of the Standard Model. • They have a richer scalar particle spectrum. • They are included in more general models, such as the Supersymmetric one. • They allow for the possibility of minima with spontaneous breaking of CP... (T.D. Lee, Phys. Rev. D8 (1973) 1226)**The Two-Higgs Doublet potential**Most general SU(2) × U(1) scalar potential: m212, λ5, λ6andλ7complex - seemingly 14 independent real parameters Most frequently studied model: softly broken theory with a Z2 symmetry, Φ2 → -Φ2, meaning λ6, λ7 = 0. It avoids potentially large flavour-changing neutral currents.**Softly broken Z2 potential**• EIGHTreal independent parameters. • The symmetry must be extended to the whole lagrangian, otherwise the model would not be renormalizable. Coupling to fermions MODEL I: Only Φ2 couples to fermions. MODEL II: Φ2 couples to up-quarks, Φ1 to down quarks and leptons. . . .**Scalar sector of the 2HDM is richer => more stuff to**discover Two dublets => 4 neutral scalars (h, H, A) + 1 charged scalar (H±). h, H → γ γ h, H → ZZ, WW (real or off-shell) h, H → ff H → hh (if mH>2mh) … h H A - CP-odd scalar (pseudoscalar) CP-even scalars A→ γ γ A→ ZZ, WW A→ ff … Certain versions of the model provide a simple and natural candidate for Dark Matter – INERT MODEL, based on an unbroken discrete symmetry. Deshpande, Ma (1978); Ma (2006); Barbieri, Hall, Rychkov (2006); Honorez, Nezri, Oliver, Tytgat (2007)**THEORETICAL BOUNDS ON 2SDM SCALAR PARAMETERS**Potential has to be bounded from below: Theory must respect unitarity:**EXPERIMENTAL BOUNDS ON 2HDM SCALAR PARAMETERS**• Precision electroweak data (via the S, T, U parameters) constrain the scalar sector. • The charged scalar has potentially large contributions to B-physics phenomena –model II is very highly constrained ( ), model I less so. The contraints involve also the value of tanβ, which determines the coupling of the charged scalar to the fermions. • ATLAS and CMS themselves have set new bounds on the mass/couplings of the heavier states (charged or neutral). • The observed rates of production × decay for the observed scalar relative to the SM further limits the allowed parameter space. • We will assume that the observed scalar is the lightest Higgs h! Maybe it isn’t the only possibility…**Generate random values for all potential’s parameters,**such that mh = 125 GeV (all masses > 90 GeV, < 800 GeV, 1 < tan β < 30). NO BENCHMARKS, “blind” scan. • Ensure the potential obeys all theoretical constraints (unitarity, vacuum stability, etc.). • Impose current experimental bounds from electroweak precision data (S, T, U parameter bounds, B-physics data, etc.). • Calculate all branching ratios and production rates at the LHC. • Compare with ATLAS and CMS results. • Serve shaken, not stirred: • The 2HDM can fit the current LHC data as well as the SM. • That’s not entirely surprising – the 2HDM has a DECOUPLING LIMIT, in which it “reduces to the SM”. • 2HDM would be perfectto explain an eventual γγ excess – the model has one extra charged particle contributing for that loop decay, but which wouldn’t affect the gluon-gluon production, for instance.**What we compare to data:**Plenty of different production processes possible at the LHC: J. Baglio and A. Djouadi, JHEP 03 (2011) 055 VBF**For searches for the heavier neutral states, we will have to**consider the following ratios: Relative to a SM-like scalar, with mass equal to mH or mA. ATLAS and CMS already have a wealth of data on several channels for a wide range of masses. How much do they exclude? (see also C. Chen, S. Dawson, M. Sher, arXiv:1305.1624)**HIGH MASS WW EXCLUSION**In blue, without B-physics constraints. In green, with B-physics constraints. All Type-II points generated with mH+ > 360 GeV, so B-physics constraints automatically satisfied.**HIGH MASS ZZ EXCLUSION**Quite a lot of parameter space points get excluded by these bounds… … but many more survive! All this is telling us is that H cannot couple very strongly to gauge bosons… … and that is to be expected: if h couples strongly to ZZ and WW, H must couple weakly: (probably need to worry a little about interference with background… Be conservative)**HIGH MASS ττ EXCLUSION**Not much happens for H – it is decaying mostly to ZZ and WW (and hh!) below ~350 GeV… … but Acan be very sensitive to an improvement in these bounds! The reason is, below 350 GeV A “has nothing else to decay to” (except hZ!).**LOW MASS γγ EXCLUSION**Both in Type I and Type II, the di-photon channel doesn’t provide major exclusion for both H and A. All of these exclusions, combined, eliminate a Sizeable chunk of the 2HDM parameter space – but not enough to restrict the h rates, for instance.**AND WHAT IF THESE HEAVY STATES ARE DECAYING MOSTLY TO OTHER**STUFF?? H → hh A → Zh**CRAZY IDEA: what if some of the h’s we’re observing at**LHC are coming from the decays of the other heavy scalar states? There are new contributions to the lightest Higgs rates: This is the “usual” rate, which includes only “direct” production There are however “indirect” contributions as well: An H, an A or a H+ is produced first, and THEN decays to a light h – CHAIN HIGGS PRODUCTION.**For instance, for H the new contribution would be given by**With being the “expectation value of h’s produced in H decays”.**Does it make any difference…?**Manage to get larger values of RZZ, which couldn’t occur for Type I… Also for Rγγ. Plenty of Green points in the middle of blue ones => DIRECT + CHAIN PRODUCTION CAN YIELD PERFECTLY REASONABLE VALUES OF THE R’S!**HOW IMPORTANT CAN CHAIN PRODUCTION BE?**• Take all R’s of h within 20% of their SM values. • Consider the ratio between the DIRECT production cross section and the TOTAL. • This ratio is always > 75% => CHAIN PRODUCTION CAN BE UP TO 25% OF THE TOTAL PRODUCTION OF HIGGSES AT THE LHC.**CONCLUSIONS**• Non-observation of heavier scalars in 2HDM at the LHC imposes mild restrictions on the model. • Plenty of parameter space left to accomodate scalars with reasonable masses (> 130, < 600 GeV). • ττ rates in function of the masses might be able to put serious constraints on the model through the pseudoscalar expected rates. • Chain production of lightest scalars h possible and can amount to 25% of total h’s produced! • In that sense, we may already be observing H, A or H without realising ! • How do we test this? How do we disentangle chain production from direct one? How to concile chain production with observed gluon-gluon and VBF productions? Can chain production “mimic” direct production processes? • TO KNOW MORE…**Workshop on**Multi-HiggsModels 2009 Lisbon, Portugal … AND COME TO LISBON IN ONE YEAR’S TIME! Workshop on Multi-HiggsModels 2012 Lisbon, Portugal Workshop on Multi-HiggsModels 2014 Lisbon, Portugal