arXiv subjects

Shoaib Munir

Publications and source records attributed to Shoaib Munir.

34 records · Page 2Linked to original sources

arXiv2015

Two Higgs bosons near 125 GeV in the complex NMSSM and the LHC Run-I data

We analyse the impact of explicit CP-violation in the Higgs sector of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) on its consistency with the Higgs boson data from the Large Hadron Collider (LHC). Through detailed scans of the parameter space of the complex NMSSM for certain fixed values of one of its CP-violating (CPV) phases, we obtain a large number of points corresponding to five phenomenologically relevant scenarios containing $\sim 125$ GeV Higgs boson(s). We focus, in particular, on the scenarios where the visible peaks in the experimental samples can actually be explained by two nearly mass-degenerate neutral Higgs boson states. We find that some points corresponding to these scenarios give an overall slightly improved fit to the data, more so for non-zero values of the CPV phase, compared to the scenarios containing a single Higgs boson near 125 GeV.

hep-ph↗

arXiv2015

$\mathcal{O}$(1) GeV dark matter in SUSY and a very light pseudoscalar at the LHC

We analyze the prospects of the detection of a $\mathcal{O}(1)$ GeV neutralino dark matter, $\widetildeχ^0_{1}$, in the Next-to-Minimal Supersymmetric Standard Model at the 14 TeV LHC. We perform dedicated scans of the relevant parameter space of the model and find a large number of points where the thermal relic abundance due to such a dark matter is consistent with the PLANCK measurement. We note that this dark matter is highly singlino-dominated and is always accompanied by a pseudoscalar, $A_1$, with a mass around twice its own, which is responsible for its resonant annihilation. For two benchmark points from our scan, we then carry out a detector-level signal-to-background analysis of the pair production of a heavier higgsino neutralino and a chargino. The higgsino thus produced decays into the dark matter and either the $Z$ boson or the $A_1$. For the $Z$-associated production of $\widetildeχ^0_{1}$, we investigate the scope of the trilepton search channel. For the $A_1$-associated production mode, in order to identify the two collimated muons coming from the decay of the $A_1$, we employ an unconventional method of clustering them together into one jet-like object. Using this method, for certain parameter space configurations, a much larger sensitivity can be obtained at the 14 TeV LHC for the $A_1\widetildeχ^0_{1}$ channel compared to the $Z\widetildeχ^0_{1}$ channel, with an integrated luminosity of 300 fb$^{-1}$.

hep-ph↗

arXiv2015

$H^\pm$ in the $W^\pm h$ channel at the LHC Run 2

We analyse the discovery prospects of the charged Higgs boson, $H^\pm$, via its decay in the $W^\pm h$ channel in the minimal supersymmetric Standard Model (MSSM) as well as several 2-Higgs Doublet Models (2HDMs). $h$, the lightest scalar Higgs boson in these models, is identified with the recently discovered $\sim 125$ GeV state, $H_\text{obs}$, at the Large Hadron Collider (LHC). We find that, while it provides an important input in the kinematic selection of signal events, the measured $H_\text{obs}$ mass renders this channel inaccessible in the MSSM. In the 2HDMs though, through a dedicated signal-to-background analysis for the $pp\to t(\bar{b})H^-\to \ell^\pmν_\ell jj bb\bar{b}(\bar{b})$+h.c process, we establish that some parameter space regions will be testable at the LHC with $\sqrt{s}=14$ TeV.

hep-ph↗

arXiv2015

Accessing the core of naturalness, nearly degenerate higgsinos, at the LHC

The presence of two light higgsinos nearly degenerate in mass is one of the important characteristics of suspersymmetric models meeting the naturalness criteria. Probing such higgsinos at the LHC is very challenging, in particular when the mass-splitting between them is less than 5 GeV. In this study, we analyze such a degenerate higgsino scenario by exploiting the high collinearity between the two muons which originate from the decay of the heavier higgsino into the lighter one and which are accompanied by a high-$p_T$ QCD jet. Using our method, we can achieve a statistical significance $\sim 2.9\,σ$ as well as a $S/B \sim 17\%$ with an integrated luminosity of 3000 fb$^{-1}$ at the 14 TeV LHC, for the pair production of higgsinos with masses 124 GeV and 120 GeV. A good sensitivity can be achieved even for a smaller mass-splitting when the higgsinos are lighter.

hep-ph↗

arXiv2015

A light NMSSM pseudoscalar Higgs boson at the LHC Run 2

We revisit the light pseudoscalar $A_1$ in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with partial universality at some high unification scale in order to delineate the parameter space regions consistent with up-to-date theoretical and experimental constraints and examine to what extent this state can be probed by the Large Hadron Collider (LHC) during Run 2. We find that it can be accessible through a variety of signatures proceeding via $A_1\to τ^+τ^-$ and/or $b\bar b$, the former assuming hadronic decays and the latter two $b$-tags within a fat jet or two separate slim ones. Herein, the light pseudoscalar state is produced from a heavy Higgs boson decay in either pairs or singly in association with a $Z$ boson (in turn decaying into electrons/muons).

hep-ph↗

arXiv2015

Revisiting a light NMSSM pseudoscalar at the LHC

The discovery of a light, singlet-like pseudoscalar Higgs boson, $A_1$, of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) could provide a hallmark signature of non-minimal supersymmetry. We review here the potential of the LHC to probe such a light $A_1$ in the decays of one of the heavier scalar Higgs bosons of the NMSSM. We find the production of pairs of the $A_1$, with a mass below 60 GeV or so, via decays of the two lightest scalar states to be especially promising, for an integrated luminosity as low as 30/fb. For heavier masses, the decay of the heaviest scalar into a $Z$ boson and an $A_1$ could lead to its detection at the LHC.

hep-ph↗

arXiv2015

A light NMSSM pseudoscalar Higgs boson at the LHC redux

The Next-to-Minimal Supersymmetric Standard Model (NMSSM) contains a singlet-like pseudoscalar Higgs boson in addition to the doublet-like pseudoscalar of the Minimal Supersymmetric Standard Model. This new pseudoscalar can have a very low mass without violating the LEP exclusion constraints and it can potentially provide a hallmark signature of non-minimal supersymmetry at the LHC. In this analysis we revisit the light pseudoscalar in the NMSSM with partial universality at some high unification scale. We delineate the regions of the model's parameter space that are consistent with the up-to-date theoretical and experimental constraints, from both Higgs boson searches and elsewhere (most notably $b$-physics), and examine to what extent they can be probed by the LHC. To this end we review the most important production channels of such a Higgs state and assess the scope of its observation at the forthcoming Run-2 of the LHC. We conclude that the $b\bar{b}$-associated production of the pseudoscalar, which has been emphasised in previous studies, does not carry much promise anymore, given the measured mass of the Higgs boson at the LHC. However, the decays of one of the heavier scalar Higgsbosons of the NMSSM can potentially lead to the discovery of its light pseudoscalar. Especially promising are the decays of one or both of the two lightest scalar states into a pseudoscalar pair and of the heaviest scalar into a pseudoscalar and a $Z$ boson. Since the latter channel has not been explored in detail in the literature so far, we provide details of some benchmark points which can be probed for establishing its signature.

hep-ph↗

arXiv2015

Charged Higgs boson in the $W^\pm$ Higgs channel at the Large Hadron Collider

In light of the recent discovery of a neutral Higgs boson, $H_{\rm obs}$, with a mass near 125 GeV, we reassess the LHC discovery potential of a charged Higgs boson, $H^\pm$, in the $W^\pm H_{\rm obs}$ decay channel. This decay channel can be particularly important for a $H^\pm$ heavier than the top quark, when it is produced through the $pp \rightarrow tH^\pm$ process. The knowledge of the mass of $H_{\rm obs}$ provides an additional handle in the kinematic selection when reconstructing a Breit-Wigner resonance in the $H_{\rm obs} \rightarrow b\bar{b}$ decay channel. We consider some extensions of the Standard Model Higgs sector, with and without supersymmetry, and perform a dedicated signal-to-background analysis to test the scope of this channel for the LHC running at the design energy (14 TeV), for 300/fb (standard) and 3000/fb (high) integrated luminosities. We find that, while this channel does not show much promise for a supersymmetric $H^\pm$ state, significant portions of the parameter spaces of several two-Higgs doublet models are testable.

hep-ph↗

arXiv2015

Search for Charged Higgs bosons via decays to $W^\pm$ and a 125 GeV Higgs at the Large Hadron Collider

The recent observation of a 125 GeV neutral Higgs boson ($H_{\rm obs}$) provides additional input for charged Higgs boson searches in the $H^\pm \to W^\pm H_{\rm obs}$ decay channel at the Large Hadron Collider (LHC). We reassess the discovery potential in this channel, which is important for $H^\pm$ heavier than the top quark mass. When $H_{\rm obs}$ decays to a $b\bar{b}$ pair, knowledge of the Higgs mass aids in the kinematic selection of signal events. We perform a signal-to-background analysis to demonstrate the LHC prospects for charged Higgs discovery in the resulting channel $pp\to t(\bar{b})H^-\to \ell^\pmν_\ell jj bb\bar{b}(\bar{b})$+h.c. for standard (300 fb$^{-1}$) and high (3000 fb$^{-1}$) luminosities at design energy, $\sqrt{s}=14 {\rm TeV}$. We find that regions of the parameter space of several two-Higgs doublet models, consistent with constraints from LHC Higgs searches and $b$-physics observables, are testable in this channel.

hep-ph↗

arXiv2014

Novel Higgs-to-125 GeV Higgs boson decays in the complex NMSSM

In the Next-to-Minimal Supersymmetric Standard Model (NMSSM) a variety of parameter configurations yields a Higgs boson consistent with the one observed at the LHC. Additionally, the Higgs sector of the model can contain explicit CP-violating phases even at the tree level, in contrast with the Minimal Supersymmetric Standard Model (MSSM). In this article we present the one-loop Higgs boson mass matrix of the complex NMSSM in the renormalisation-group-improved effective potential approach. We also present the trilinear Higgs boson self-couplings as well as various partial decay widths of a generic CP-mixed Higgs boson in the model. We then analyse a very interesting phenomenological scenario wherein the decay of a relatively light pseudoscalar-like Higgs boson into ~ 125 GeV SM-like Higgs boson(s) is induced by non-zero CP-violating phases. We discuss in detail a few benchmark cases in which such a decay can contribute significantly to the production of SM-like Higgs bosons at the LHC on top of the gluon fusion process. It can thus be partially responsible for the gamma.gamma excess near 125 GeV due to the subsequent decay of the SM-like Higgs boson. Such a scenario is extremely difficult to realize in the complex MSSM and, if probed at the LHC, it could provide an indication of the non-minimal nature of supersymmetry.

hep-ph↗

arXiv2013

Simultaneous enhancement in gamma.gamma, b.b-bar and tau+.tau- rates in the NMSSM with nearly degenerate scalar and pseudoscalar Higgs bosons

We propose an experimental test of a scenario in the Next-to-Minimal Supersymmetric Standard Model in which both the lightest scalar and the lightest pseudoscalar Higgs bosons have masses around 125 GeV. The pseudoscalar can contribute significantly to the gamma.gamma rate at the LHC due to light Higgsino-like charginos in its effective one-loop coupling to two photons. Such charginos are obtained for small values of the mu_eff parameter which also results in enhanced b.b-bar and tau+.tau- rates compared to those expected for a Standard Model Higgs boson. This scenario should result in a clear discrepancy between the observed rates in these three decay channels and those in the WW and ZZ channels, since the pseudoscalar does not couple to the W and Z bosons. However, in the dominant gluon fusion production mode the pseudoscalar will stay hidden behind the SM-like scalar Higgs boson and in order for it to be observable the associated b.b-bar.h production mode has to be considered, the cross section for which is tiny in the Standard Model but tan.beta-enhanced in supersymmetry. We analyze the constrained NMSSM with non-universal Higgs sector parameters and identify regions of its parameter space where the lightest pseudoscalar with mass around 125 GeV and strongly enhanced gamma.gamma (up to 60%), b.b-bar and tau+.tau- rates in the b.b-bar.h mode can be obtained.

hep-ph↗

arXiv2013

The Constrained NMSSM with a 126 GeV Higgs boson: A global analysis

We present the first global analysis of the Constrained NMSSM that investigates the impact of the recent discovery of a 126 GeV Higgs-like boson, of the observation of a signal for BR(B_s->μ^+μ^-), and of constraints on supersymmetry from ~5/fb of data accumulated at the LHC, as well as of other relevant constraints from colliders, flavor physics and dark matter. We consider three possible cases, assuming in turn that the discovered Higgs boson is: i) the lightest Higgs boson of the model; ii) the next-to-lightest Higgs boson; and iii) a combination of both roughly degenerate in mass. The likelihood function for the Higgs signal uses signal rates in the γγ and ZZ --> 4l channels, while that for the Higgs exclusion limits assumes decay through the γγ, ττ, ZZ and W^+W^- channels. In all cases considered we identify the 68% and 95% credible posterior probability regions in a Bayesian approach. We find that, when the constraints are applied with their respective uncertainties, the first case shows strong CMSSM-like behavior, with the stau coannihilation region featuring highest posterior probability, the best-fit point, a correct mass of the lightest Higgs boson and the lighter stop mass in the ballpark of 1 TeV. The second and the third cases, on the other hand, while allowed are disfavored by the constraints from direct detection of dark matter and from BR(B_s->μ^+μ^-). Without the anomalous magnetic moment of the muon the fit improves considerably, especially for negative effective μ parameter. We discuss how the considered scenarios could be tested furtherly at the LHC and in dark matter searches.

hep-ph↗

arXiv2012

Constrained MSSM favoring new territories: The impact of new LHC limits and a 125 GeV Higgs boson

We present an updated and extended global analysis of the Constrained MSSM (CMSSM) taking into account new limits on supersymmetry from ~5/fb data sets at the LHC. In particular, in the case of the razor limit obtained by the CMS Collaboration we simulate detector efficiency for the experimental analysis and derive an approximate but accurate likelihood function. We discuss the impact on the global fit of a possible Higgs boson with mass near 125 GeV, as implied by recent data, and of a new improved limit on BR(B_s->μμ). We identify high posterior probability regions of the CMSSM parameters as the stau-coannihilation and the A-funnel region, with the importance of the latter now being much larger due to the combined effect of the above three LHC results and of dark matter relic density. We also find that the focus point region is now disfavored. Ensuing implications for superpartner masses favor even larger values than before, and even lower ranges for dark matter spin-independent cross section, σ^{SI}_p<10^{-9} pb. We also find that relatively minor variations in applying experimental constraints can induce a large shift in the location of the best-fit point. This puts into question the robustness of applying the usual chisquare approach to the CMSSM. We discuss the goodness-of-fit and find that, while it is difficult to calculate a p-value, the g-2 constraint makes, nevertheless, the overall fit of the CMSSM poor. We consider a scan without this constraint, and we allow μ to be either positive or negative. We find that the global fit improves enormously for both signs of μ, with a slight preference for μ<0 caused by a better fit to BR(b->sγ) and BR(B_s->μμ).

hep-ph↗

arXiv2011

Z' Bosons at Colliders: a Bayesian Viewpoint

We revisit the CDF data on di-muon production to impose constraints on a large class of Z' bosons occurring in a variety of E_6 GUT based models. We analyze the dependence of these limits on various factors contributing to the production cross-section, showing that currently systematic and theoretical uncertainties play a relatively minor role. Driven by this observation, we emphasize the use of the Bayesian statistical method, which allows us to straightforwardly (i) vary the gauge coupling strength, g', of the underlying U(1)'; (ii) include interference effects with the Z' amplitude (which are especially important for large g'); (iii) smoothly vary the U(1)' charges; (iv) combine these data with the electroweak precision constraints as well as with other observables obtained from colliders such as LEP 2 and the LHC; and (v) find preferred regions in parameter space once an excess is seen. We adopt this method as a complementary approach for a couple of sample models and find limits on the Z' mass, generally differing by only a few percent from the corresponding CDF ones when we follow their approach. Another general result is that the interference effects are quite relevant if one aims at discriminating between models. Finally, the Bayesian approach frees us of any ad hoc assumptions about the number of events needed to constitute a signal or exclusion limit for various actual and hypothetical reference energies and luminosities at the Tevatron and the LHC.

hep-ph↗

arXiv2011

Z' Bosons from E(6): Collider and Electroweak Constraints

Many models beyond the Standard Electroweak Theory, top-down or bottom-up, contain extensions of the gauge symmetry group by extra U(1)' factors which can be understood or treated as subgroups of E(6). A brief overview of such models is followed by a sketch of a systematic classification. We then describe how the resulting extra massive neutral gauge bosons can be searched for and in case of positive evidence diagnosed using electroweak and collider data.

hep-ph↗

arXiv2009

Improved Constraints on Z' Bosons from Electroweak Precision Data

We analyze various models with an extra U(1) gauge symmetry in addition to the Standard Model (SM) gauge group at low energies, and impose limits on the mass of the neutral Z' boson, M_Z', predicted in all such models, and on the Z-Z' mixing angle, theta_ZZ'. The precision electroweak data strongly constrain theta_ZZ' to very small values and for most models we find lower limits on M_Z' of order 1 TeV. In one case we obtain a somewhat better fit than in the SM (although this is only marginally statistically significant) and here we find a weak upper limit at the 90% C.L.

hep-ph↗