Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA heavy neutral gauge boson near the Z boson mass pole via third generation fermions at the LHC
60
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We explore the physics of a new neutral gauge boson, ($Z^prime$), coupling to only third-generation particles with a mass near the electroweak gauge boson mass poles. A $Z^prime$ boson produced by top quarks and decaying to tau leptons is considered. With a simple search strategy inspired by existing analyses of the standard model gauge boson production in association with top quarks, we show that the Large Hadron Collider has good exclusionary power over the model parameter space of the $Z^prime$ boson even at the advent of the high-luminosity era. It is shown that the $tbar{t}Z^prime$ process allows one to place limits on right-handed top couplings with a $Z^prime$ boson that preferentially couples to third generation fermions, which are at present very weakly constrained.
rate research
Read More
Unification at M_{GUT}sim 3times 10^{16} GeV of the three Standard Model (SM) gauge couplings can be achieved by postulating the existence of a pair of vectorlike fermions carrying SM charges and masses of order 300 GeV -- 1 TeV. The presence of these fermions significantly modifies the vacuum stability and perturbativity bounds on the mass of the SM Higgs boson. The new vacuum stability bound in this extended SM is estimated to be 117 GeV, to be compared with the SM prediction of about 128 GeV. An upper bound of 190 GeV is obtained based on perturbativity arguments. The impact on these predictions of type I seesaw physics is also discussed. The discovery of a relatively `light Higgs boson with mass sim 117 GeV could signal the presence of new vectorlike fermions within reach of the LHC.
Family gauge boson production at the LHC is investigated according to a $U(3)$ family gauge model with twisted family number assignment. In the model we study, a family gauge boson with the lowest mass, $A_1^{ 1}$, interacts only with the first generation leptons and the third generation quarks. (The family numbers are assigned, for example, as $(e_1, e_2, e_3)= (e^-, mu^-, tau^-)$ and $(d_1, d_2, d_3)=(b, d, s) $[or $(d_1, d_2, d_3)=(b, s, d)$]). In the model, the family gauge coupling constant is fixed by relating to the electroweak gauge coupling constant. Thus measurements of production cross sections and branching ratios of $A_1^{ 1}$ clearly confirm or rule out the model. We calculate the cross sections of inclusive $A_1^{ 1}$ production and $b bar{b} , (t bar{t})$ associated $A_1^{ 1}$ production at $sqrt{s} = 14~text{TeV}$ and $100~text{TeV}$. With the dielectron production cross section, we discuss the determination of diagonalizing matrix of quark mass matrix, $U_{u}$ and $U_{d}$, respectively.
A heavy Standard Model Higgs boson is not only disfavored by electroweak precision observables but is also excluded by direct searches at the 7 TeV LHC for a wide range of masses. Here, we examine scenarios where a heavy Higgs boson can be made consistent with both the indirect constraints and the direct null searches by adding only one new particle beyond the Standard Model. This new particle should be a weak multiplet in order to have additional contributions to the oblique parameters. If it is a color singlet, we find that a heavy Higgs with an intermediate mass of 200 - 300 GeV can decay into the new states, suppressing the branching ratios for the standard model modes, and thus hiding a heavy Higgs at the LHC. If the new particle is also charged under QCD, the Higgs production cross section from gluon fusion can be reduced significantly due to the new colored particle one-loop contribution. Current collider constraints on the new particles allow for viable parameter space to exist in order to hide a heavy Higgs boson. We categorize the general signatures of these new particles, identify favored regions of their parameter space and point out that discovering or excluding them at the LHC can provide important indirect information for a heavy Higgs. Finally, for a very heavy Higgs boson, beyond the search limit at the 7 TeV LHC, we discuss three additional scenarios where models would be consistent with electroweak precision tests: including an additional vector-like fermion mixing with the top quark, adding another U(1) gauge boson and modifying triple-gauge boson couplings.
For the purpose of cross-fertilising currently separate experimental approaches, we connect results of LHC analyses attempting to access the properties of additional $W^prime$ and $Z^prime$ bosons from Drell-Yan processes. Under theoretical assumptions linking the two new gauge bosons, we take into account that such possible states of nature are wide enough (in relation to the leptonic mass resolution) for the corresponding signals be significantly affected by interference effects with the background from the Standard Model. The shape of the differential cross section may then no longer be a standard Breit-Wigner distribution, and asymmetry observables would become useful for characterisation (and, possibly, discovery) purposes. Under such conditions we concentrate our analysis on specific widely-studied models: the Sequential Standard Model, a model with an additional $SU(2)_L$ gauge symmetry, as well as standard and alternative realisations of the Left-Right Symmetric Model. We show how information gathered in $Z$ boson searches in terms of cross section and/or asymmetry distributions can be used to improve $W$ boson searches in terms of the LHC sensitivity, and {it vice versa}.
We search for signatures of the extra neutral gauge boson $ Z^prime$, predicted in some extensions of the Standard Model, from the analysis of some distributions for $p + p longrightarrow mu^+ + mu^- + X$, where the only exotic particle involved is $ Z^prime$. In addition to the invariant mass and charge asymmetry distributions, we propose in our search to use the transverse momentum distribution ($p_T$) as an observable. We do our calculation for two values of the LHC center of mass energy (7 and 14 TeV), corresponding to 1 and 100 fb$^{-1}$ of luminosity, in order to compare our findings from some models with the distributions following from the Standard Model. By applying convenient cuts in the invariant mass, we show that the final particles $p_T$ distributions can reveal the presence of an extra neutral gauge boson contribution. We also claim that it is possible to disentangle the models considered here and we emphasize that the minimal version of the model, based on ${SU (3)_C times SU (3)_L times U (1)_X}$ symmetry, presents the more clear signatures for $ Z^prime$ existence.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
