Results on low mass WIMPs using an upgraded CRESST-II detector

A search for a Higgs boson produced via vector-boson fusion and decaying into invisible particles is presented, using 20.3 fb −1 of proton-proton collision data at a centreof-mass energy of 8 TeV recorded by the ATLAS detector at the LHC. For a Higgs boson with a mass of 125 GeV, assuming the Standard Model production cross section, an upper bound of 0.28 is set on the branching fraction of H → invisible at 95% confidence level, where the expected upper limit is 0.31. The results are interpreted in models of Higgsportal dark matter where the branching fraction limit is converted into upper bounds on the dark-matter-nucleon scattering cross section as a function of the dark-matter particle mass, and compared to results from the direct dark-matter detection experiments. The ATLAS collaboration 28 IntroductionAstrophysical observations provide strong evidence for dark matter (see ref.[1] and the references therein). Dark matter (DM) may be explained by the existence of weakly interacting massive particles (WIMP) [2,3]. The observed Higgs boson with a mass of about 125 GeV [4,5] might decay to dark matter or neutral long-lived massive particles [6][7][8][9][10], provided this decay is kinematically allowed. This is referred to as an invisible decay of the Higgs boson [11][12][13][14][15][16][17][18]. This paper presents a search for invisible decays of a Higgs boson produced via the vector-boson fusion (VBF) process. In the Standard Model (SM), the process H → ZZ → 4ν is an invisible decay of the Higgs boson, but the branching fraction (BF) is 0.1% [19, 20], which is below the sensitivity of the search presented in this paper. In addition to the VBF Higgs boson signal itself, there is a contribution to Higgs boson production from the gluon fusion plus 2-jets (ggF+2-jets) process, which is smaller than the VBF signal in the phase space of interest in this search. The ggF+2-jets contribution is treated as signal. The search is performed with a dataset corresponding to an integrated luminosity of 20.3 fb −1 of proton-proton collisions at √ s = 8 TeV, recorded by the ATLAS detector at the LHC [21].-1 - JHEP01(2016)172The signature of this process is two jets with a large separation in pseudorapidity 1 and large missing transverse momentum 2 E miss T . The VBF process, in its most extreme topology (high dijet invariant mass for example), offers strong rejection against the QCDinitiated (W, Z)+jets (V +jets) backgrounds. The resulting selection has a significantly better signal-to-background ratio than selections targeting the ggF process.The CMS Collaboration obtained an upper bound of 58% on the branching fraction of invisible Higgs boson decays using a combination of the VBF and ZH production modes [22]. Weaker limits were obtained using the Z(→ )H + E miss T signature by both the ATLAS and CMS collaborations [22, 23], giving upper limits at 95% CL of 75% and 83% on the branching fraction of invisible Higgs boson decays, respectively. By combining the searches in the Z(→ )H and Z(→ bb)H channels, CMS obtained...

Section: Model Interpretationmentioning

confidence: 73%

“…ments which search for dark-matter particles via their direct interaction with the material of a detector [34][35][36][37][38][39][40][41][42]. The paper is organized as follows.…”

Section: Jhep01(2016)172mentioning

confidence: 99%

Search for invisible decays of a Higgs boson using vector-boson fusion in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

Aad¹,

Abbott²,

Abdallah³

et al. 2016

“…The hashed bands indicate the uncertainty resulting from varying the form factor f N by its uncertainty. Excluded and allowed regions from direct detection experiments at the confidence levels indicated are also shown [119][120][121][122][123][124][125][126][127]. These are spin-independent results obtained directly from searches for nuclei recoils from elastic scattering of WIMPs, rather than being inferred indirectly through Higgs boson exchange in the Higgs portal model.…”

Section: Discussionmentioning

confidence: 83%

“…The hashed bands indicate the uncertainty resulting from the systematic variation of the form factor f N . They are compared with limits from direct searches for dark matter [119][120][121][122][123][124][125][126][127] at the confidence levels indicated. The ATLAS limits on the WIMP-nucleon scattering cross section are proportional to those on the invisible decay branching ratio, as evident from eqs.…”

Section: Jhep11(2015)206mentioning

confidence: 99%

Constraints on new phenomena via Higgs boson couplings and invisible decays with the ATLAS detector

Aad

Bergeås

Brenner

et al. 2015

194

198

Abstract:The ATLAS experiment at the LHC has measured the Higgs boson couplings and mass, and searched for invisible Higgs boson decays, using multiple production and decay channels with up to 4.7 fb −1 of pp collision data at √ s = 7 TeV and 20.3 fb −1 at √ s = 8 TeV. In the current study, the measured production and decay rates of the observed Higgs boson in the γγ, ZZ, W W , Zγ, bb, τ τ , and µµ decay channels, along with results from the associated production of a Higgs boson with a top-quark pair, are used to probe the scaling of the couplings with mass. Limits are set on parameters in extensions of the Standard Model including a composite Higgs boson, an additional electroweak singlet, and two-Higgs-doublet models. Together with the measured mass of the scalar Higgs boson in the γγ and ZZ decay modes, a lower limit is set on the pseudoscalar Higgs boson mass of m A > 370 GeV in the "hMSSM" simplified Minimal Supersymmetric Standard Model. Results from direct searches for heavy Higgs bosons are also interpreted in the hMSSM. Direct searches for invisible Higgs boson decays in the vector-boson fusion and associated production of a Higgs boson with W/Z (Z → , W/Z → jj) modes are statistically combined to set an upper limit on the Higgs boson invisible branching ratio of 0.25. The use of the measured visible decay rates in a more general coupling fit improves the upper limit to 0.23, constraining a Higgs portal model of dark matter. Conclusions 26The ATLAS collaboration 36 IntroductionThe ATLAS and CMS Collaborations at the Large Hadron Collider (LHC) announced the discovery of a particle consistent with a Higgs boson in 2012 [1,2]. Since then, the collaborations have together measured the mass of the particle to be about 125 GeV [3][4][5]. Studies of its spin and parity in bosonic decays have found it to be compatible with a J P = 0 + state [6][7][8]. Combined coupling fits of the measured Higgs boson production and decay rates within the framework of the Standard Model (SM) have found no significant deviation from the SM expectations [4,9, 10]. These results strongly suggest that the newly discovered particle is indeed a Higgs boson and that a non-zero vacuum expectation value of a Higgs doublet is responsible for electroweak (EW) symmetry breaking [11][12][13].The observed CP-even Higgs boson is denoted as h throughout this paper. A crucial question is whether there is only one Higgs doublet, as postulated by the SM, or whether the Higgs sector is more complex, for example with a second doublet leading to more than one Higgs boson of which one has properties similar to those of the SM Higgs -1 - JHEP11(2015)206boson, as predicted in many theories beyond the Standard Model (BSM). 1 The "hierarchy problem" regarding the naturalness of the Higgs boson mass, the nature of dark matter, and other open questions that the SM is not able to answer also motivate the search for additional new particles and interactions. Astrophysical observations provide strong evidence of dark matter that could be explained by the e...

“…Direct detection experiments [29][30][31][32] and the observation of a Standard Model-like 125 GeV Higgs with a small invisible decay width [33,34] have severely constrained Z-and Higgs boson-mediated scenarios [21]. As a result, much recent work has been devoted to studying various possibilities for new mediator particles coupling weakly to the Standard Model degrees of freedom.…”

Section: Jhep04(2015)046mentioning

confidence: 99%

Extending LHC coverage to light pseudoscalar mediators and coy dark sectors

Kozaczuk

Martin

2015

Many dark matter models involving weakly interacting massive particles (WIMPs) feature new, relatively light pseudoscalars that mediate dark matter pair annihilation into Standard Model fermions. In particular, simple models of this type can explain the gamma ray excess originating in the Galactic Center as observed by the Fermi Large Area Telescope. In many cases the pseudoscalar's branching ratio into WIMPs is suppressed, making these states challenging to detect at colliders through standard dark matter searches. Here, we study the prospects for observing these light mediator states at the LHC without exploiting missing energy techniques. While existing searches effectively probe pseudoscalars with masses between 5-14 GeV and above 90 GeV, the LHC reach can be extended to cover much of the interesting parameter space in the intermediate 20-80 GeV mass range in which the mediator can have appreciable Yukawa-like couplings to Standard Model fermions but would have escaped detection by LEP and other experiments. Models explaining the Galactic Center excess via a light pseudoscalar mediator can give rise to a promising signal in this regime through the associated production of the mediator with bottom quarks while satisfying all other existing constraints. We perform an analysis of the backgrounds and trigger efficiencies, detailing the cuts that can be used to extract the signal. A significant portion of the otherwise unconstrained parameter space of these models can be conclusively tested at the 13 TeV LHC with 100 fb −1 , and we encourage the ATLAS and CMS collaborations to extend their existing searches to this mass range.