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Higgs production via gluon fusion in the POWHEG approach in the SM and in the MSSM

E. Bagnaschi (Milan U. & INFN, Milan & Paris, LPTHE) , G. Degrassi (INFN, Rome3 & Rome III U.) , P. Slavich (Paris, LPTHE) , A. Vicini (Milan U. & INFN, Milan)

JHEP 1202 (2012) 088

DOI: 10.1007/JHEP02(2012)088

RM3-TH-11-5, IFUM-990-FT

e-Print: arXiv:1111.2854 [hep-ph]

Abstract

We consider the gluon fusion production cross section of a scalar Higgs boson at NLO QCD in the SM and in the MSSM. We implement the calculation in the POWHEG approach, and match the NLO-QCD results with the PYTHIA and HERWIG QCD parton showers. We discuss a few representative scenarios in the SM and MSSM parameter spaces, with emphasis on the fermion and squark mass effects on the Higgs boson distributions.

Towards precise predictions for Higgs-boson production in the MSSM

E. Bagnaschi (UPMC, Paris (main) & Paris, LPTHE) , R.V. Harlander (Wuppertal U.) , S. Liebler (U. Hamburg (main)) , H. Mantler (CERN) , P. Slavich (UPMC, Paris (main) & Paris, LPTHE) , A. Vicini (Milan U. & INFN, Milan)

JHEP 1406 (2014) 167

DOI: 10.1007/JHEP06(2014)167

CERN-PH-TH-2014-048, DESY-14-040, IFUM-1024-FT, LPN14-061, MCNET-14-07, WUB-14-01

e-Print: arXiv:1404.0327 [hep-ph]

Abstract

We study the production of scalar and pseudoscalar Higgs bosons via gluon fusion and bottom-quark annihilation in the MSSM. Relying on the NNLO-QCD calculation implemented in the public code SusHi, we provide precise predictions for the Higgs-production cross section in six benchmark scenarios compatible with the LHC searches. We also provide a detailed discussion of the sources of theoretical uncertainty in our calculation. We examine the dependence of the cross section on the renormalization and factorization scales, on the precise definition of the Higgs-bottom coupling and on the choice of PDFs, as well as the uncertainties associated to our incomplete knowledge of the SUSY contributions through NNLO. In particular, a potentially large uncertainty originates from uncomputed higher-order QCD corrections to the bottom-quark contributions to gluon fusion.

Higgs Mass and Unnatural Supersymmetry

Emanuele Bagnaschi (UPMC, Paris (main) & Paris, LPTHE) , Gian F. Giudice (CERN) , Pietro Slavich (UPMC, Paris (main) & Paris, LPTHE) , Alessandro Strumia (Pisa U. & INFN, Pisa & NICPB, Tallinn)

JHEP 1409 (2014) 092

DOI: 10.1007/JHEP09(2014)092

CERN-PH-TH-2014-131, IFUP-TH-2014

e-Print: arXiv:1407.4081 [hep-ph]

Abstract

Assuming that supersymmetry exists well above the weak scale, we derive the full one-loop matching conditions between the SM and the supersymmetric theory, allowing for the possibility of an intermediate Split-SUSY scale. We also compute two-loop QCD corrections to the matching condition of the Higgs quartic coupling. These results are used to improve the calculation of the Higgs mass in models with high-scale supersymmetry or split supersymmetry, reducing the theoretical uncertainty. We explore the phenomenology of a mini-split scenario with gaugino masses determined by anomaly mediation. Depending on the value of the higgsino mass, the theory predicts a variety of novel possibilities for the dark-matter particle.

An extensive survey of the estimation of uncertainties from missing higher orders in perturbative calculations

Emanuele Bagnaschi (Diderot U., Paris & Paris, LPTHE & DESY) , Matteo Cacciari (Diderot U., Paris & Paris, LPTHE) , Alberto Guffanti (Bohr Inst.) , Laura Jenniches (Bohr Inst. & Wurzburg U.)

JHEP 1502 (2015) 133

DOI: 10.1007/JHEP02(2015)133

LPN14-115

e-Print: arXiv:1409.5036 [hep-ph]

Abstract

We consider two approaches to estimate and characterise the theoretical uncertainties stemming from the missing higher orders in perturbative calculations in Quantum Chromodynamics: the traditional one based on renormalisation and factorisation scale variation, and the Bayesian framework proposed by Cacciari and Houdeau. We estimate uncertainties with these two methods for a comprehensive set of more than thirty different observables computed in perturbative Quantum Chromodynamics, and we discuss their performance in properly estimating the size of the higher order terms that are known. We find that scale variation with the conventional choice of varying scales within a factor of two of a central scale gives uncertainty intervals that tend to be somewhat too small to be interpretable as 68% confidence-level-heuristic ones. We propose a modified version of the Bayesian approach of Cacciari and Houdeau which performs well for non-hadronic observables and, after an appropriate choice of the relevant expansion parameter for the perturbative series, for hadronic ones too.

The pMSSM10 after LHC Run 1

K.J. de Vries (Imperial Coll., London) , E.A. Bagnaschi (DESY) , O. Buchmueller (Imperial Coll., London) , R. Cavanaugh (Fermilab & Illinois U., Chicago) , M. Citron (Imperial Coll., London) , A. De Roeck (CERN & Antwerp U.) , M.J. Dolan (SLAC & ARC, CoEPP, Melbourne) , J.R. Ellis (King's Coll. London & CERN) , H. Flächer (Bristol U.) , S. Heinemeyer (Cantabria Inst. of Phys.) et al.

Eur.Phys.J. C75 (2015) no.9, 422

DOI: 10.1140/epjc/s10052-015-3599-y

KCL-PH-TH-2015-15, LCTS-2015-07, CERN-PH-TH-2015-066, DESY-15-046, FTPI-MINN-15-13, UMN-TH-3427-15, SLAC-PUB-16245, FERMILAB-PUB-15-100-CMS

e-Print: arXiv:1504.03260 [hep-ph]

Abstract

We present a frequentist analysis of the parameter space of the pMSSM10, in which the following ten soft SUSY-breaking parameters are specified independently at the mean scalar top mass scale $ M_{SUSY} \equiv \sqrt{m_{\tilde{t}_1} m_{\tilde{t}_2} }$ : the gaugino masses $M_1$,$M_2$,$M_3$ , the first-and second-generation squark masses $m_{\tilde{q}_1}= m_{\tilde{q}_2}$ , the third-generation squark mass $m_{\tilde{q}_3}$ , a common slepton mass $m_{\tilde{l}}$ and a common trilinear mixing parameter A, as well as the Higgs mixing parameter μ , the pseudoscalar Higgs mass $M_A$ and $\tan\beta$ , the ratio of the two Higgs vacuum expectation values. We use the MultiNest sampling algorithm with ∼ 1.2 ×109 points to sample the pMSSM10 parameter space. A dedicated study shows that the sensitivities to strongly interacting sparticle masses of ATLAS and CMS searches for jets, leptons + signals depend only weakly on many of the other pMSSM10 parameters. With the aid of the Atom and Scorpion codes, we also implement the LHC searches for electroweakly interacting sparticles and light stops, so as to confront the pMSSM10 parameter space with all relevant SUSY searches. In addition, our analysis includes Higgs mass and rate measurements using the HiggsSignals code, SUSY Higgs exclusion bounds, the measurements of BR(Bs→μ+μ−) by LHCb and CMS, other B-physics observables, electroweak precision observables, the cold dark matter density and the XENON100 and LUX searches for spin-independent dark matter scattering, assuming that the cold dark matter is mainly provided by the lightest neutralino χ~01 . We show that the pMSSM10 is able to provide a supersymmetric interpretation of $(g−2)_{\mu}$ , unlike the CMSSM, NUHM1 and NUHM2. As a result, we find (omitting Higgs rates) that the minimum χ2=20.5 with 18 degrees of freedom (d.o.f.) in the pMSSM10, corresponding to a χ2 probability of 30.8 %, to be compared with χ2/d.o.f.=32.8/24 (31.1/23) (30.3/22) in the CMSSM (NUHM1) (NUHM2). We display the one-dimensional likelihood functions for sparticle masses, and we show that they may be significantly lighter in the pMSSM10 than in the other models, e.g., the gluino may be as light as ∼ 1250 GeV at the 68 % CL, and squarks, stops, electroweak gauginos and sleptons may be much lighter than in the CMSSM, NUHM1 and NUHM2. We discuss the discovery potential of future LHC runs, e+e− colliders and direct detection experiments.

The Higgs transverse momentum distribution in gluon fusion as a multiscale problem

Emanuele Bagnaschi (DESY) , Alessandro Vicini (INFN, Milan & Milan U.)

JHEP 1601 (2016) 056

DOI: 10.1007/JHEP01(2016)056

DESY-15-067, TIF-UNIMI-2015-3

e-Print: arXiv:1505.00735 [hep-ph]

Abstract

We consider Higgs production in gluon fusion and in particular the prediction of the Higgs transverse momentum distribution. We discuss the ambiguities affecting the matching procedure between fixed order matrix elements and the resummation to all orders of the terms enhanced by $\log(p^T_H/M_H)$ factors. Following a recent proposal [1], we argue that the gluon fusion process, computed considering two active quark flavors, is a multiscale problem from the point of view of the resummation of the collinear singular terms. We perform an analysis at parton level of the collinear behavior of the O(αs) real emission amplitudes, relying on the collinear singularities structure of the latter, we derive an upper limit to the range of transverse momenta where the collinear approximation is valid. This scale is then used as the value of the resummation scale in the analytic resummation framework or as the value of the h parameter in the POWHEG-BOX code. A variation of this scale can be used to generate an uncertainty band associated to the matching procedure. Finally, we provide a phenomenological analysis in the Standard Model, in the Two Higgs Doublet Model and in the Minimal Supersymmetric Standard Model. In the two latter cases, we provide an ansatz for the central value of the matching parameters not only for a Standard Model-like Higgs boson, but also for heavy scalars and in scenarios where the bottom quark may play the dominant role.

Supersymmetric Dark Matter after LHC Run 1

E.A. Bagnaschi (DESY) , O. Buchmueller (Imperial Coll., London) , R. Cavanaugh (Fermilab & Illinois U., Chicago) , M. Citron (Imperial Coll., London) , A. De Roeck (CERN & Antwerp U.) , M.J. Dolan (SLAC & Melbourne U.) , J.R. Ellis (King's Coll. London & CERN) , H. Flächer (Bristol U.) , S. Heinemeyer (Cantabria Inst. of Phys.) , G. Isidori (Zurich U.) et al.

Eur.Phys.J. C75 (2015) 500

DOI: 10.1140/epjc/s10052-015-3718-9

KCL-PH-TH-2015-33, LCTS-2015-24, CERN-PH-TH-2015-167, DESY-15-132, FTPI-MINN-15-36, UMN-TH-3445-15, SLAC-PUB-16350, FERMILAB-PUB-15-333-CMS

e-Print: arXiv:1508.01173 [hep-ph]

Abstract

Different mechanisms operate in various regions of the MSSM parameter space to bring the relic density of the lightest neutralino, χ~01 , assumed here to be the lightest SUSY particle (LSP) and thus the dark matter (DM) particle, into the range allowed by astrophysics and cosmology. These mechanisms include coannihilation with some nearly degenerate next-to-lightest supersymmetric particle such as the lighter stau $\tilde{\tau}_1$ , stop $\tilde{t}_1$ or chargino $\chi^{\pm}_1$ , resonant annihilation via direct-channel heavy Higgs bosons H / A, the light Higgs boson h or the Z boson, and enhanced annihilation via a larger Higgsino component of the LSP in the focus-point region. These mechanisms typically select lower-dimensional subspaces in MSSM scenarios such as the CMSSM, NUHM1, NUHM2, and pMSSM10. We analyze how future LHC and direct DM searches can complement each other in the exploration of the different DM mechanisms within these scenarios. We find that the $\tilde{\tau}_1$ coannihilation regions of the CMSSM, NUHM1, NUHM2 can largely be explored at the LHC via searches for MET events and long-lived charged particles, whereas their H / A funnel, focus-point and $\chi^{\pm}_1$ coannihilation regions can largely be explored by the LZ and Darwin DM direct detection experiments. We find that the dominant DM mechanism in our pMSSM10 analysis is $\chi^{\pm}_1$ coannihilation: parts of its parameter space can be explored by the LHC, and a larger portion by future direct DM searches.

Resummation ambiguities in the Higgs transverse-momentum spectrum in the Standard Model and beyond

Emanuele Bagnaschi (DESY) , Robert V. Harlander (Bergische U., Wuppertal (main)) , Hendrik Mantler (CERN & Karlsruhe U., ITP & KIT, Karlsruhe, IKP) , Alessandro Vicini (INFN, Milan & Milan U.) , Marius Wiesemann (Zurich U.)

JHEP 1601 (2016) 090

DOI: 10.1007/JHEP01(2016)090

CERN-PH-TH-2015-242, KA-TP-20-2015, MCNET-15-21, DESY-15-155, TIF-UNIMI-2015-7, WUB-15-06, ZU-TH-31-15, --TIF-UNIMI-2015-7

e-Print: arXiv:1510.08850 [hep-ph]

Abstract

We study the prediction for the Higgs transverse momentum distribution in gluon fusion and focus on the problem of matching fixed- and all-order perturbative results. The main sources of matching ambiguities on this distribution are investigated by means of a twofold comparison. On the one hand, we present a detailed qualitative and quantitative comparison of two recently introduced algorithms for determining the matching scale [1, 2]. On the other hand, we apply the results of both methods to three widely used approaches for the resummation of logarithmically enhanced contributions at small transverse momenta: the MC@NLO and POWHEG Monte Carlo approaches, and analytic resummation. While the three sets of results are largely compatible in the low-p⊥ region, they exhibit sizable differences at large p⊥. We show that these differences can be significantly reduced by suitable modifications of formally subleading terms in the Monte Carlo implementations. We apply our study to the Standard Model Higgs boson and to the neutral Higgs bosons of the Two-Higgs-Doublet Model for representative scenarios of the parameter space, where the top- and bottom-quark diagrams enter the cross section at different strengths.

Vacuum stability and supersymmetry at high scales with two Higgs doublets

Emanuele Bagnaschi (DESY) , Felix Brümmer (Montpellier U.) , Wilfried Buchmüller, Alexander Voigt, Georg Weiglein (DESY)

JHEP 1603 (2016) 158

DOI: 10.1007/JHEP03(2016)158

DESY-15-238

e-Print: arXiv:1512.07761 [hep-ph]

Abstract

We investigate the stability of the electroweak vacuum for two-Higgs-doublet models with a supersymmetric UV completion. The supersymmetry breaking scale is taken to be of the order of the grand unification scale. We first study the case where all superpartners decouple at this scale. We show that contrary to the Standard Model with one Higgs doublet, matching to the supersymmetric UV completion is possible if the low-scale model contains two Higgs doublets. In this case vacuum stability and experimental constraints point towards low values of tan β ≲ 2 and pseudoscalar masses of at least about a TeV. If the higgsino superpartners of the Higgs fields are also kept light, the conclusions are similar and essentially independent of the higgsino mass. Finally, if all gauginos are also given electroweak-scale masses (split supersymmetry with two Higgs doublets), the model cannot be matched to supersymmetry at very high scales when requiring a 125 GeV Higgs. Light neutral and charged higgsinos therefore emerge as a promising signature of a supersymmetric UV completion of the Standard Model at the grand unification scale.