LHC signature of the minimal SUGRA model with a large soft scalar mass

Abstract

Thanks to the focus point phenomenon, it is quite natural for the minimal SUGRA model to have a large soft scalar mass (m 0 > 1 TeV). A distinctive feature of this model is an inverted hierarchy, where the lighter stop has a significantly smaller mass than the other squarks and sleptons. Consequently, the gluino is predicted to decay dominantly via stop exchange into a channel containing 2b and 2W along with the LSP. We exploit this feature to construct a robust signature for this model at the LHC in leptonic channels with 3-4 b tags and a large missing-E T . 1The minimal SUGRA model represents the most attractive model of low energy supersymmetry in terms of simplicity and economy of parameters [1]. Besides it can naturally account for the electroweak symmetry breaking as well as the suppression of flavour changing neutral current effects. The basic parameters of the model are m 0 , M 1/2 , A, B and µ -i.e. the soft supersymmetry breaking scalar and gaugino masses, the trilinear and bilinear couplings, along with the supersymmetric Higgs mass parameter. The last two can be determined in terms of the two Higgs vacuum expectation values, v 1 and v 2 , using the two minimisation conditions. The first one determines the B parameter in term ofand the ratio v 2 /v 1 ≡ tan β. The second condition giveswhere the last term comes from the radiative correction to the Higgs potential. Thus for any tan β, the naturalness of the electroweak scale requires m for tan β > ∼ 5. Moreover, contrary to some earlier apprehensions, a large value of m 0 seems to lead to a cosmologically interesting dark matter density [5]. Besides a large m 0 would also alleviate the potential conflict of the minimal SUGRA model with the electric dipole moments of electron and neutron [6]. Thus the minimal SUGRA model with a large soft scalar mass (m 0 > 1 TeV) seems to be attractive both on theoretical and phenomenological grounds. We shall analyse the signature of this model at the large hadron collider (LHC) by exploiting the distinctive characteristics of the large m 0 limit. Indeed we shall see that they lead to a more robust signal at LHC compared to the canonical SUGRA model. The ModelFor qualitative understanding of the model it is instructive to look at the approximate expressions for the electroweak scale scalar masses in terms of the universal soft mass parameters at the GUT scale. We shall neglect the GUT scale A parameter, which is unimportant for the present consideration; and assume not too large tan β where the b Yukawa coupling is relatively less significant. Then analytic solutions to the one-loop RGE givewhere U and Q refer to the 3rd generation singlet and doublet squarks [7]. Herewhere the subscript f denotes the fixed point values of the top Yukawa coupling and the corresponding tan β at the electroweak scale. The numerical coefficients of y in (3) which is in turn related to the physical top quark mass M t viaThe QCD and SUSY radiative corrections add about 6% and 4% respectively to the running mass to arrive at the phys...

Phenomenological aspects of gauge mediation with sequestered supersymmetry breaking in light of dark matter detection

“…It is expected that sizable mixing of the Bino and Higgsino and possibly Higgs or Z 0 pole effects are important. In this case, the third family quark jets are expected to be characteristic signals just like a focus-point in the gravity mediation [30,31,32,33], if the gluino is relatively light, compared to the masses of the squarks.…”

How light a higgsino or a wino dark matter can become in a compressed scenario of MSSM

“…In this analysis, since we are looking for slepton and squark coannihilations with the LSP while trying to probe the lower mass limit of the latter, we undertake a minimalistic approach of considering not too much different mass values for the scalars among themselves. We also limit µ so as to have only an adequate degree of wino purity of the LSP while trying to respect naturalness [26][27][28][29][30][31][32][33][34][35][174][175][176] as far as possible. Hence, we will prefer not to take very large values for the scalar masses or µ.…”

“…This makes bulk annihilation rather an inefficient mechanism for obtaining the right relic density [20][21][22][23][24][25]. It is however possible to have a bino-LSP giving the correct abundance of DM in some specific regions of parameter space of mSUGRA, like the stau coannihilation, funnel (resonant Higgs annihilation) or hyperbolic branch (HB) [26][27][28]/ focus point (FP) [29][30][31][32][33][34][35] regions. While most of the former two regions of parameter space are ruled out by the Higgs data [17][18][19], a large part of the HB/FP region, which corresponds to a significant degree of bino-higgsino mixing, is disfavored by DM direct detection experiments [36][37][38][39].…”

Mixed neutralino dark matter in nonuniversal gaugino mass models

“…[8]. It should be mentioned here that a very important example of the mixed bino-higgsino LSP occurs in the so-called hyperbolic branch/focus point (HB/FP) [9][10][11][12] region of mSUGRA model. This is a narrow strip at the edge of the mSUGRA parameter space, corresponding to very large (multi-TeV) scalar masses.…”