arXiv subjects

S. M. Lietti

Publications and source records attributed to S. M. Lietti.

18 recordsLinked to original sources

arXiv2004

Testing Non commutative QED gamma-gamma-gamma and gamma-gamma-gamma-gamma Couplings at LHC

In this work, we investigate the sensitivity of the process p + p --> q + q --> j + j + gamma + gamma at LHC for the photonic 3- and 4- point functions that appear in non commutative QED. We show that this process serves to study the behavior of the space-space as well as of the space-time non commutativity. We also show that this process can probe the non commutative scale in the range of few TeV.

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arXiv2003

Bosonic Quartic Couplings at LHC

We analyze the potential of the CERN Large Hadron Collider (LHC) to study anomalous quartic vector-boson interactions Z Z gamma gamma, Z Z Z gamma, W+ W- gamma gamma, and W+ W- Z gamma through the weak boson fusion processes q q -> q q gamma gamma and q q -> q q gamma Z(-> l+ l-) with l = electron or muon. After a careful study of the backgrounds and how to extract them from the data, we show that the process p p -> j j gamma l+ l- is potentially the most sensitive to deviations from the Standard Model, improving the sensitivity to anomalous couplings by up to a factor 10^4 (10^2) with respect to the present direct (indirect) limits.

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arXiv2002

Radion and Higgs Signals in Peripheral Heavy Ion Collisions at the LHC

We investigate the sensitivity of the heavy ion mode of the LHC to Higgs boson and Radion production via photon-photon fusion through the analysis of the processes photon to photon photon, photon photon to b anti-b, and photon photon to g g in peripheral heavy ion collisions. We suggest cuts to improve the Higgs and Radion signal over standard model background ratio and determine the capability of LHC to detect these particles production.

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arXiv2001

Anomalous Quartic Gauge Boson Couplings at Hadron Colliders

We analyze the potential of the Fermilab Tevatron and CERN Large Hadron Collider (LHC) to study anomalous quartic vector--boson interactions (photon photon Z Z) and (photon photon W+ W-). Working in the framework of SU(2)_L X U(1)_Y chiral Lagrangians, we study the production of photons pairs accompanied by (e+e-), (e nu), and jet pairs to impose bounds on these new couplings, taking into account the unitarity constraints. We compare our findings with the indirect limits coming from precision electroweak measurements as well as with presently available direct searches at LEPII. We show that the Tevatron Run II can provide limits on these quartic limits which are of the same order of magnitude as the existing bounds from LEPII searches. LHC will be able to tighten considerably the direct constraints on these possible new interactions, leading to more stringent limits than the presently available indirect ones.

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arXiv2000

Searching for Anomalous Higgs Couplings in Peripheral Heavy Ion Collisions at the LHC

We investigate the sensitivity of the heavy ion mode of the LHC to anomalous Higgs boson couplings to photons, H-photon-photon, through the analysis of the processes photon photon to b anti-b and photon photon to photon photon in peripheral heavy ion collisions. We suggest cuts to improve the signal over background ratio and determine the capability of LHC to impose bounds on anomalous couplings by searching for a Higgs boson signal in these modes.

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arXiv2000

CP violating Z t anti-t and gamma t anti-t Couplings at a Future e+ e- Collider

The effect of new operators that give rise to CP-violating couplings of the type $Z t \bar{t}$ and $γt \bar{t}$ are examined at future electron positron Linear Colliders (FLC). The impact of these CP-violating interactions over Standard Model predictions was studied for the process e+ e^- -> t anti-t with the subsequent decays t -> b l+ nu_l and anti-t -> anti-b l- anti-nu_l, called as dilepton mode, and t -> b l^+ nu_l and anti-t -> anti-b anti-q q' or t -> b q anti-q' and anti-t -> anti-b l- anti-nu_l, called as single lepton mode, where the final leptons are l = e or mu, and the final quarks are q(q')= u(d) or c(s). Polarized electron beam and CP observables and asymmetries are used to impose bounds on the anomalous couplings.

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arXiv1999

Anomalous Higgs-Photon Interactions in Photon Fusion Processes at NLC

The Standard Model (SM) of the electroweak has proven to be successful in describing all the available precision experimental data. However, the Higgs mechanism, responsible for the electroweak symmetry breaking in the SM, still remains one of the most important open questions of the theory. The effect of new operators that give rise to anomalous Higgs boson coupling to two photons (HAA) is examined in the two-photon processes AA -> H \to bb, AA,W+W-,ZZ at a high energy linear e+ e- collider (NLC).

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arXiv1999

New Higgs Couplings at Tevatron

We investigate the potentiality of CERN LEP and Fermilab Tevatron colliders to establish bounds on new couplings involving the bosonic sector of the standard model. A combined exclusion plot for the coefficients of different dimension-6 anomalous operators is presented. We also discuss the sensitivity that can be achieved at the upgraded Tevatron.

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arXiv1998

New Higgs Couplings at e+ e- and Hadronic Colliders

We examine the potentiality of both CERN LEP and Fermilab Tevatron colliders to establish bounds on new couplings involving the bosonic sector of the standard model. We pay particular attention to the anomalous Higgs interactions with $γ$, $W^{\pm}$ and $Z^0$. A combined exclusion plot for the coefficients of different anomalous operators is presented. The sensitivity that can be achieved at the Next Linear Collider and at the upgraded Tevatron is briefly discussed.

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arXiv1998

Testing Anomalous Higgs Couplings in Triple Photon Production at the Tevatron Collider

We derive bounds on Higgs and gauge--boson anomalous interactions using the CDF data for the process $p \bar{p} \to γγγ+ X$. We use a linearly realized $SU_L(2) \times U_Y(1)$ invariant effective Lagrangian to describe the bosonic sector of the Standard Model, keeping the fermionic couplings unchanged. All dimension--six operators that lead to anomalous Higgs interactions involving $γ$ and $Z$ are considered. We also show the sensitivity that can be achieved for these couplings at Fermilab Tevatron upgrades.

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arXiv1998

Bounds on Higgs and Gauge--Boson Interactions from LEP2 Data

We derive bounds on Higgs and gauge--boson anomalous interactions using the LEP2 data on the production of three photons and photon pairs in association with hadrons. In the framework of $SU(2)_L \otimes U(1)_Y$ effective Lagrangians, we examine all dimension--six operators that lead to anomalous Higgs interactions involving $γ$ and $Z$. The search for Higgs boson decaying to $γγ$ pairs allow us to obtain constrains on these anomalous couplings that are comparable with the ones originating from the analyses of $p\bar{p}$ collisions at the Tevatron. Our results also show that if the coefficients of all ``blind'' operators are assumed to have same magnitude, the indirect constraints on the anomalous couplings obtained from this analyses, for Higgs masses $M_H \lesssim$ 140 GeV, are more restrictive than the ones coming from the $W^+W^-$ production.

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arXiv1997

Search for Non-standard Higgs Boson in Diphoton Events at p pbar Collisions

We estimate the attainable limits on the coupling of a non-standard Higgs boson to two photons taking into account the data collected by the Fermilab collaborations on diphoton events. We based our analysis on a general set of dimension--6 effective operators that give rise to anomalous couplings in the bosonic sector of the Standard Model. If the coefficients of all ``blind'' operators are of the same order of magnitude, bounds on the anomalous triple vector-boson couplings can also be obtained.

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arXiv1997

Anomalous Higgs Couplings in Triple Gauge Boson Production at the NLC

We present the sensitivity limits on the coefficients of a dimension-6 effective operators that parametrizes the possible effects of new physics beyond the Standard Model. Our results are based on the study of the processes $e^+ e^- \to W^+ W^- γ$, $Z Zγ$, and $Zγγ$ at NLC energies. In our calculations, we include all the anomalous interactions involving vector and Higgs bosons, and take into account the Standard Model irreducible background. We analyse the impact of these new interactions on the total cross section and on some kinematical distributions of the final state particles.

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arXiv1997

New Higgs Interactions in ZZγand ZγγProduction

The effect of new operators that only modify the bosonic couplings of the Higgs boson, without altering the WWγor WWZ three-point functions, are examined in the e+e- -> ZZγand Zγγprocesses. We analyse the constraints on these interactions that can be imposed by the LEP II collider at CERN and at the Next Linear Collider.

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arXiv1997

Anomalous Couplings in e^+ e^- --> W^+ W^- gamma at LEP2 and NLC

We present sensitivity limits on the coefficients of a dimension-6 effective Lagrangian that parametrizes the possible effects of new physics beyond the Standard Model. Our results are based on the study of the process $e^+ e^- \to W^+ W^- γ$ at LEP2 and NLC energies. In our calculations, we include all the new anomalous interactions, involving vector and Higgs bosons, and take into account the Standard Model irreducible background. We analyse the impact of these new interactions on the total cross section, including the effects of the initial electron and final W polarizations. We then focus on the operators that will not be constrained by the $e^+ e^- \to W^+ W^-$ process, obtaining limits based on the photon energy distribution.

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arXiv1996

Probing Higgs Couplings in e^+ e^- \to γγγ

We investigate the existence of anomalous Higgs boson couplings, $Hγγ$ and $HZγ$, through the analysis of the process $e^+ e^- \to γγγ$ at LEP2 energies. We suggest some kinematical cuts to improve the signal to background ratio and determine the capability of LEP2 to impose bounds on those couplings by looking for a Higgs boson signal in this reaction.

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arXiv1996

Anomalous Higgs Boson Contribution to e^+ e^- \to b \bbar γat LEP2

We study the effect of anomalous $Hγγ$ and $HZγ$ couplings, described by a general effective Lagrangian, on the process $e^+ e^- \to b \bar{b} γ$ at LEP2 energies. We include the relevant irreducible standard model background to this process, and from the photon energy spectrum, we determine the reach of LEP2 to unravel the anomalous couplings by analyzing the significance of the signal for Higgs boson with mass up to $150$ GeV.

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arXiv1994

$ε_b$ Constraints on Self--Couplings of Vector Bosons

We analyze the constraints on possible anomalous contributions to the $W^+W^-Z$ vertex coming from non-universal radiative corrections to the $Z \rightarrow b \bar{b}$ width. We parametrize these corrections in terms of $ε_b$ and use the LEP data to establish the allowed values for the anomalous triple couplings. We examine all CP conserving effective operators that exhibit $SU(2)_L\times U(1)_Y$ gauge invariance and do not give any tree level contribution to the present experimental observables. For some of these operators our constraints are comparable with the bounds coming from a global fit of the oblique parameters, which evidences the increasing relevance of the precise measurement of the $b$--quark parameters at LEP for the search of new physics.

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