arXiv subjects

Ijaz Ahmed

Publications and source records attributed to Ijaz Ahmed.

35 records · Page 2Linked to original sources

arXiv2023

Pair production of heavy charged gauge bosons in $pp$ collisions at LHC

Two opposite charged new heavy gauge boson pair production at the Large Hadron Collider (LHC) is presented in this paper. These bosons are known as $W^{'}$ boson due to the reason that it is the heavy version of Standard Model's weak force carrier, the $W$ boson. The production cross section and decay width in proton-proton ($pp$) collision at \sqrts~= 8 TeV are calculated for different masses and coupling strengths of $W^{'}$. Efficiencies for different signal regions and branching ratios for different decay channels are computed. In this study, the pair production ($W^{'^{+}}W^{'^{-}}$) is considered in emerging new physics as a result of $pp$ collision at \sqrts~= 8 TeV at the LHC with final state containing two tau ($τ$) leptons and two neutrinos (each $W^{'}$ decay to $τ$ and its neutrino). The event selection efficiency similar to the CMS experiment is used for the mass of $W^{'}$ to set lower limits for different coupling strengths of $W^{'}$ and results are presented in this work. For heavy gauge bosons, when coupling strength is similar to that of Standard Model's $W$ boson, the mass of $W^{'}$ below 305 GeV are excluded at confidence level of $95\%$.

hep-ph↗

arXiv2023

Observability of triple top quark signal at Future Hadron Colliders

This paper is devoted to the Standard Model cross-sections for the production of single top, top quark in pairs, triple-top quarks, and four top-quarks at three different centre of mass-energies e.g., $\sqrt{s}=$7, 10 and 14 TeV at existing particle colliders as well as at Future Hadron Colliders. A fully kinemtaic analysis with the optimized pre-selection cuts along with invariant mass reconstruction of top quarks is performed for triple-top production processes pp$\rightarrow $tttW, tttd,tttb in the presence of Standard Model background. The three signal processes are forced to decay in fully hadronic mode and their significance is computed in High Luminosity Large Hadron Collider (HL$-$LHC) at $\sqrt{s}=$14 TeV and also in High-Energy LHC (HE$-$LHC) at $\sqrt{s}=$27 TeV. It is found that the observability at HL$-$LHC will would not be so easy task and chances are much lower but there are higher chances to observe the signal events at HE$-$LHC. The signal to background ratio and signal significance of all signal and background processes are estimated for both the HL$-$LHC and the HE$-$LHC at $\sqrt{s}$ =14 TeV and $\sqrt{s}$ =27 TeV respectively.

hep-ph↗

arXiv2022

A Comprehensive Study of Energy Dependence of Particle Ratios in $pp$ Collisions from SPS to LHC Energies

A comprehensive study has been performed to estimate the kaon to pion ($K^\pm$/$π^\pm$) yield ratio and total kaon to total pion ($K$/$π$) yield ratio as a function of centre of mass energy in $pp$ collisions at different energies i.e., \sqrts~= 6.3, 17.3, 62.4, 200, 900 GeV, 2.76 TeV, 7 TeV, 13 TeV and 14 TeV using EPOS1.99, EPOS-LHC, HIJING, QGSJETII-03 and Sibyll2.3d model simulations. NA61/SHINE experiment reported that $K^+/π^+$ yield ratio exhibits rapid changes at the SPS energy range. A horn like structure appears in $K/π$ yield ratio as a function of collision energy. Significant presence of horn in $K^+$/$π^+$ and $K^-$/$π^-$ yield ratio is suggested by experimental data at lower energies, which is confirmed by HIJING and EPOS-LHC models. A smooth increase in $K/π$ yield ratio is also seen at higher energies. The model simulations predict similar increase in yield ratio with increasing energies. On the basis of previous available measurements, we also study model predictions of these yield ratios at \sqrts~= 13 and 14 TeV where no data is available. Almost all models suggest a saturation in the yield ratio within statistical fluctuations at these energies except EPOS1.99 and QGSJETII-03 which slightly over predict the yield ratio. These systematic comparisons are helpful to apply possible constraints on various hadronic event generators to significantly improve the predictions of Standard Model physics as well as for the understanding of underlying physics mechanisms in high energy collisions.

hep-ph↗

arXiv2022

Possibility of observing charged Higgs in the single top production via its $τ$ lepton decay at LHC

Single top quark production through weak interactions is considered to be an important source of charged Higgs in the Minimal Super Symmetric Standard Model. In the s-channel single top production having largest cross-section may appear as a propagator in the form of heavy resonance state decaying to a pair of top and bottom quark. The process under investigation is $pp \rightarrow H^{\pm}\rightarrow tb \rightarrow b\bar{b}W^{\pm} \rightarrow b\bar{b}τ^{\pm} ν_τ$, where top quark exclusively decays into a pair of bottom quark and W boson while W boson subsequently decays to $τ$ jet and neutrino. So the final state is characterized by the presence of two b jets, hadronic $τ$ decay and missing transverse energy. Within the presence of QCD multijet and electroweak background events at LHC, it has been demonstrated that the charged Higgs signal observability is possible within the available MSSM parameter space (tan$β$, $m_{H^{\pm}})$ respecting all experimental and theoretical constraints. In order to show the observability potential of charged Higgs, the exclusion curves at 95$\%$ confidence level and 5$σ$ contours are plotted at different integrated luminosities with $\sqrt{s}=$14 TeV.

hep-ph↗

arXiv2022

Application of deep learning in top pair and single top quark production at the LHC

We demonstrate the performance of a very efficient tagger applies on hadronically decaying top quark pairs as signal based on deep neural network algorithms and compares with the QCD multi-jet background events. A significant enhancement of performance in boosted top quark events is observed with our limited computing resources. We also compare modern machine learning approaches and perform a multivariate analysis of boosted top-pair as well as single top quark production through weak interaction at $\sqrt{s}=$14 TeV proton-proton Collider. The most relevant known background processes are incorporated. Through the techniques of Boosted Decision Tree (BDT), likelihood and Multlayer Perceptron (MLP) the analysis is trained to observe the performance in comparison with the conventional cut based and count approach.

hep-ph↗

arXiv2021

Charged Higgs Observability via Charged Higgs Pair Production at Future Lepton Collider

The observability of charged Higgs $ H^{\pm} $ has been investigated at future lepton collider by assuming type-I 2HDM, at a centre of mass energy $ \sqrt{s}=1.5$ TeV. The signal process chain is $ e^{+}e^{-} \rightarrow Z^{*}/ γ^{*}\rightarrow H^{+} H^{-}\rightarrow H W^{+} H W^{-}\rightarrow b \overline{b} jjb \overline{b} jj$. The process proceed through virtual gamma and Z-boson exchange in S-channel. Several benchmark points are selected and events are analyzed to reconstruct the mass of charged Higgs bosons $ H^{\pm} $. The value of $\tanβ$ is kept relatively high to enhance the branching ratio of $ H\rightarrow b\overline{b} $ to benefit the signal processes. The main SM background processes produced is $ t\overline{t} $. Signal selection and significance efficiencies are calculated at integrated luminosities of $100 fb^{-1} $ and $ 500 fb^{-1} $. The reconstructed and corrected mass of charged Higgs bosons $ H^{\pm} $ is determined. Through analyzing the results, it is demonstrated that charged Higgs bosons can be discovered through pair production process via its bosonic decays. This study is supposed to provide the experimentalists a good way to examine the Higgs bosons beyond SM, as well as to check the validity of 2HDM models in considered parameter space.

hep-ph↗

arXiv2021

Observability of 2HDM Neutral Higgs Bosons in fully hadronic decay at future linear collider

The study aims to investigate the observability of pseudoscalar Higgs boson $A$ and neutral heavy CP even Higgs boson $H$, at different benchmark points, in the framework of type-I 2HDM. The study is done for $e^{-}e^{+}$ collisions at $\sqrt{s}$ = 1000 GeV centre of mass energy (c.o.m.) a possible scenario in future lepton collider. The associated production of $A$ and $H$ in $e+ e-$ collisions are investigated in fully hadronic final state in two different channels. The first one is $AH \to ZHH \to j\bar{j} b \bar{b}b\bar{b}$ while the other one is $AH \to b \bar{b}b\bar{b}$. The observability of neutral heavy Higgs and pseudoscalar Higgs signal is possible within the parameter space $ (\tan β, m_{A}) $ which satisfies all experimental and theoretical constraints. The CP odd and CP even Higgs bosons in all scenarios are observable when signal exceeds $ 5σ$, which is the final extracted value of signal significance. The signal significance is calculated at different integrated luminosities. It is concluded from current analysis that fully hadronic channel is promising for search and measurement of the neutral Higgs Bosons in 2HDM.

hep-ph↗

arXiv2021

Probing triple higgs self coupling and effect of beam polarization in lepton colliders

One of the main objectives of almost all future (lepton) colliders is to measure the self-coupling of triple Higgs in the Standard Model. By elongating the Standard Model's scalar sector, using incipient Higgs doublet along with a quadratic (Higgs) potential should reveal many incipient features of the model and the possibility of the emergence of additional Higgs self-couplings. The self-coupling of the Higgs boson helps in reconstructing the scalar potential. The main objective of this paper is to extract Higgs self-coupling by numerically analyzing several scattering processes governed by two Higgs doublet models (2HDM). These scattering processes include various possible combinations of final states in the triple Higgs sector. The determination of production cross-section of scattering processes is carried out using two different scenarios, with and without polarization of incoming beam and is extended to a center of mass energy up to $\sqrt{s}$ = 3 $TeV$. The computation is carried out in Type-1 2HDM. Here we consider the case of exact alignment limit ($s_{βα}$ = 1) and masses of extra Higgs state are equal that is $m_H = m_{H^0} = m_{A^0} = m_{H^\pm}$. This choice is made to minimize the oblique parameters. The decays of the final state of each process are investigated to estimate the number of events at integrated luminosity of $1ab^{-1}$ and $3ab^{-1}$.

hep-ph↗

arXiv2021

Double and Triple Higgs Boson Production at Future Linear Colliders

In this paper such processes which act as a source of double Higgs production (2H) as well as triple Higgs production (3H) at future linear colliders are analyzed with in 2HDM and its special type-II, MSSM at various center of mass energies. The main aim of this study is to compute and also compare the cross-sections in double and triple Higgs production processes at the future linear colliders. The production of double charged Higgs boson ($H^{+}H^{-}$) as well as triple Higgs boson ($H^{+}H^{-}H^{0}$),($H^{+}H^{-}h^{0}$) are considered for study at two center of mass energies (1.5 TeV and 3 TeV) within two models 2HDM and MSSM at future linear colliders. It is observed that for double charged Higgs production process (H${}^{+}$H${}^{-}$) the resulting cross-section values are almost same in both the models (in 2HDM and MSSM). On the other hand in the case of Triple Higgs production process ($H^{+}H^{-}H^{0}$), ($H^{+}H^{-}h{0}$) several orders of enhancement in cross-sections is observed in 2HDM as compared to MSSM. Similarly two types of processes, neutral Higgs pair production ($A^{0} H^{0}$) as well as ($A^{0} h^{0}$) and triple neutral Higgs production ($h^{0}h^{0}A^{0}$) is analyzed in 2HDM type-I at the future linear $μ^{+}$$μ^{-\ }$ collider for various values of center of mass energies from 500 GeV to 3000 GeV (0.5 TeV to 3 TeV). It is observed that the cross-section for neutral Higgs pair production ($A^{0} h^{0}$) process is comparatively greater than that of neutral Higgs pair production ($A^{0} H^{0}$) process. Similarly for neutral Higgs Triple production ($h^{0}h^{0}A^{0}$) an enhancement is seen in cross-sections with increase of tanß.

hep-ph↗

arXiv2021

Correlation between the scaling factor of the yukawa coupling and cross section for the $e^+ e^- \rightarrow hhf\overline{f}$ ($f\neq t$) in type-I 2HD

The objective of this study is to correlate the scaling factor of the Standard Model (SM) like Higgs boson and the cross section ratio of the process $e^+ e^- \rightarrow hhf\overline{f}$ where $f\neq t$, normalized to SM predictions in the type I of the Two Higgs Doublet Model. All calculations have been performed at $\sqrt{s}=500$ GeV and $1 \leq \tanβ \leq 30$ for masses $m_H = m_A = m_{H^\pm} = 300GeV$ and $m_H=300$ GeV, $m_A=m_{H^\pm}=500$ GeV. The working scenario is by taking without alignment limit, that is $s_{β-α}= 0.98$ and $s_{β-α}= 0.99,$ $0.995$, which gives the enhancement in the cross section, particularly a few times greater than the predictions of the SM due to resonant-impacts of the additional heavy neutral Higgs bosons. This shows that enhancement in cross section occurs on leaving the alignment i.e., $s_{β-α}=1$, at which all the higgs that couple to vector bosons and fermions have the same values as in SM at tree level. A large value of enhancement factor is obtained at $s_{β-α}= 0.98$ compared to $s_{β-α}= 0.99,$ $0 .995$. Furthermore, the decrease in the enhancement factor is observed for the case when $m_H=300$ GeV, $m_A=m_{H^\pm}=500$ GeV. The behavior of the scaling factor with $\tanβ$ is also studied, which shows that for large values of $\tanβ$, the scaling factor becomes equal to $s_{β-α}$. Finally a convincing correlation is achieved by taking into account, the experimental and theoretical constraints e.g, perturbative unitarity, vacuum stability and electroweak oblique parameters.

hep-ph↗

arXiv2020

Charged Higgs observability in the single top production channel at LHC

Single top quark production through weak interactions is an important source of charged Higgs in the Minimal Super Symmetric Standard Model. In the s-channel single top production ,charged Higgs having largest cross-section may appear as a propagator in the form of heavy resonance state decaying to a pair of top and bottom quark. In this paper the channel under consideration is $pp \rightarrow H^{\pm}\rightarrow tb \rightarrow b\bar{b}W^{\pm} \rightarrow b\bar{b}τ^{\pm} ν_τ$, where top quark exclusively decays into a pair of b quark and W boson while W boson subsequently decays to $τ$ jet and neutrino. So the final state is characterized by the presence of two b jets, hadronic $τ$ decay and missing transverse energy.It has been demonstrated that the charged Higgs signal observability is possible within the available MSSM parameter space (tan$β$, $m_{H^{\pm}})$ respecting all experimental and theoretical constraints due to presence of QCD multijet and electroweak background events at LHC. In order to show the observability potential of charged Higgs, the charged Higgs signal are well observed or excluded in a wide range of phase space particular ($β> 35$ at 500 $fb^{-1}$ , $β> 25$ at 1000 $fb^{-1}$ , $β> 15$ at 3000 $fb^{-1}$ ) at $\sqrt{s}=$14 TeV.

hep-ph↗

arXiv2020

Constraints on $H^\pm$ parameter space in 2HDM at $\sqrt{s}=$ 8 TeV and $\sqrt{s}=$ 13 TeV

This paper reflects the heavy Higgs scenario where the mass of charged Higgs is equal to or greater than 200 GeV. The CMS observed and expected values of upper limits on the product $σ_H^\pm BR(H^\pm \rightarrow tb^\mp)$, assuming $H^\pm \rightarrow tb^\mp=1$, both at 8 TeV (at integrated luminosity of 19.7 $fb^{-1}$ ) and 13 TeV (at integrated luminosity of 35.9 $fb^{-1}$ ) c.m energies are used. By comparing these expected and observed upper limits with computational values , we find out the expected and observed exclusion regions of charged Higgs parameter space ($ m_H^\pm - tanβ$ space ) in 2HDM both at $\sqrt{s}=$8 and $\sqrt{s}=$ 13 TeV. We compare the expected and observed exclusion regions and observe that exclusion regions made by observed upper limits are always greater than the exclusion made by expected upper limits both at 8 and 13 TeV c.m energies. Only in the mass range from 200 GeV to 220 GeV the expected exclusion region is greater than the observed one only at $\sqrt{s}=$13 TeV. We also equate the exclusion regions at these two different center of mass energies and find that the expected exclusion region and observed exclusion region at $\sqrt{s}=$13 TeV are always greater than the expected exclusion region and observed exclusion region at $\sqrt{S}=$8 TeV respectively.

hep-ph↗

arXiv2019

Automatic Inference of Symbolic Permissions for Sequential Java Programs

In mainstream programming languages such as Java, a common way to enable concurrency is to manually introduce explicit concurrency constructs such as multi-threading. In multi-threaded programs, managing synchronization between threads is a complicated and challenging task for the programmers due to thread interleaving and heap interference that leads to problems such as deadlocks, data races. With these considerations in mind, access permission-based dependencies have been investigated as an alternative approach to verify the correctness of multi-threaded programs and to exploit the implicit concurrency present in sequential programs without using explicit concurrency constraints. However, significant annotation overhead can arise from manually adding permission-based specifications in a source program, diminishing the effectiveness of existing permission-based approaches. In this paper,we present a framework, Sip4J, to automatically extract access permission-based implicit dependencies from sequential Java programs, by performing inter-procedural static analysis of the source code. Moreover, we integrate and extend an existing permission-based verification tool, Pulse, to automatically verify correctness of the inferred specifications and to reason about their concurrent behaviors. Our evaluation on some widely-used benchmarks gives strong evidence of the correctness of the inferred annotations and their effectiveness in enabling concurrency in sequential programs.

cs.SE↗

arXiv2016

Sources of Charged Higgs Pair Through Double or Triple Higgs Production in Two Higgs Doublet Model Type II at Linear Colliders

The production of triple Higgs $(H^+H^-H^0)$, $(H^+H^-h^0)$ and pair wise charged Higgs boson $(H^+H^-)$ is studied in the context of future linear colliders within the Two-Higgs Doublet Model (2HDM) type II. The aim is to compare sources of charged Higgs pair through the above processes, i.e., double and triple Higgs production. Cross-sections are calculated at the leading order in 2HDM type II and Minimal Supersymmetric Standard Model (MSSM). Several orders of magnitude ($\sim 10^{4}$) enhancement is observed in 2HDM compared to MSSM, while no sizable enhancement is seen in muon collider versus electron-positron collider. The analysis is based on a heavy charged Higgs with mass above 500 GeV. It is found that double charged Higgs production cross-section (being the same in 2HDM and MSSM) is few femtobarns while the triple Higgs production can not exceed a fraction of femtobarn within the parameter space under study.

hep-ph↗

arXiv2016

The $s$-channel Charged Higgs in the Fully Hadronic Final State at LHC

With the current measurements performed by CMS and ATLAS experiments, the light charged Higgs scenario ($m_{H^{\pm}}$ $<$ 160 GeV), is excluded for most of the parameter space in the context of MSSM. However, there is still possibility to look for heavy charged Higgs boson particularly in the $s$-channel single top production process where the charged Higgs may appear as a heavy resonance state and decay to $t\bar{b}$. The production process under consideration in this paper is $pp \ra H^{\pm} \ra t\bar{b}~+~h.c.$, where the top quark decays to $W^{+}b$ and $W^{+}$ boson subsequently decays to two light jets. It is shown that despite the presence of large QCD and electroweak background events, the charged Higgs signal can be extracted and observed at a large area of MSSM parameter space ($m_{H^{\pm}}$,tan$β$) at LHC. The observability of charged Higgs is potentially demonstrated with 5$σ$ contours and $95\%$ confidence level exclusion curves at different integrated LHC luminosities assuming a nominal center of mass energy of $\sqrt{s}$ = 14 TeV.

hep-ph↗

arXiv2015

Charged Higgs Study through Triple or Double Higgs Production in a General Two Higgs Doublet Model at Future Lepton Collide

In this study the charged Higgs signal through triple or double Higgs production in a general two Higgs doublet model (2HDM) is investigated. The main production process is $e^+e^- \rightarrow H^+H^-H^0$ followed by the charged Higgs decay to a pair of $τν$ and the neutral Higgs decay to $b\bar{b}$. The alternative process $H^+W^-H^0$ is also included as a source of charged Higgs signal in the analysis having comparable cross-section. The focus is on a future $e^+e^-$ linear collider operating at $\sqrt{s}=1.5$ TeV. The final state under consideration ($τ^+ τ^- b \bar{b} E^{\textnormal{miss}}_{T}$) is suitable for electroweak background rejection using the $b-$tagging tools. It is shown that although the signal cross section is small, with a reasonable background suppression, high signal significance values are achievable at an integrated luminosity $500 fb^{-1}$ depending on the charged Higgs mass, $\tanβ~$ and the CP-odd neutral Higgs mass. Finally results are quoted in terms of the signal significance for charged Higgs in the mass range $170<m_{H^{\pm}}<400$ GeV.

hep-ph↗

arXiv2014

Observability of Charged Higgs through Triple or Double Higgs Production in a General Two Higgs Doublet Model at an e+e- Linear Collider

In this paper the triple Higgs production in a general two Higgs doublet model (2HDM) is studied. The production process is e+e- -> H+H-H0 followed by the charged Higgs decay to a pair of tau nu and the neutral Higgs decay to bb. The alternative process H+W-H0 is also included as a source of charged Higgs signal in the analysis. The focus is on a future e+e- linear collider operating at sqrt(s) = 1.5 TeV. The final state under consideration (tau tau bb ETmiss) is suitable for electroweak background rejection using the b-tagging tools. It is shown that although the signal cross section is small, with a reasonable background suppression, high signal significance values are achievable at an integrated luminosity 500 fb-1 depending on the charged Higgs mass, tanbeta and the CP-odd neutral Higgs mass. Finally results are quoted in terms of the signal significance for charged Higgs in the mass range 170 < mH+ < 400 GeV.

hep-ph↗