arXiv subjects

I. Sahin

Publications and source records attributed to I. Sahin.

At least 19 recordsLinked to original sources

arXiv2020

Photoproduction of mixed radions at a proton-proton collider

We investigate Higgs-radion mixing scenario through single radion photoproduction process $pp\to pγp\to pRqX$ at the LHC where $X$ represents the remnants of one of the initial protons. We consider high luminosity values of $L_{int}=200\;fb^{-1}$, $500\;fb^{-1}$ and $3000\;fb^{-1}$. We obtain bounds on the mixing parameter space by considering $R\to γγ$, $R\to W^+ W^-$ and $R\to ZZ$ decay channels of the radion as the signal. We also perform a similar analysis for a 100 TeV future proton-proton collider and compare its potential with that of LHC.

hep-ph↗

arXiv2017

Non-standard Higgs couplings in single Higgs boson production at the LHC and future linear collider

We investigate the potential of single Higgs boson production at the LHC and at egamma mode of future linear electron-positron collider to probe non-standard HZgamma and Hgammagamma couplings. We consider the semi-elastic production process pp-> p gamma p-> pHqX at the LHC where q represents the quarks and X represents the remnants of one of the initial protons. We also study the single Higgs production through gamma e-> He in the egamma collision at the future linear collider. We perform a model-independent analysis and obtain the sensitivity bounds on the non-standard Higgs couplings for both colliders.

hep-ph↗

arXiv2017

Some surprises in the neutrino cross sections associated with neutrino spin

It is generally assumed that neutrino masses can be neglected to a high degree of approximation in cross section calculations. This assumption seems very reasonable since the neutrino masses are extremely small and the neutrinos are ultrarelativistic fermions at the energy scales of current experiments. Consequently, in cross section calculations in the Quantum Field Theory, the Standard Model neutrinos are frequently assumed to be described by 100% negative helicity states. This assumption is true in a sense that in the Standard Model processes the positive helicity states can be safely neglected for ultrarelativistic neutrinos. On the other hand, the assumption tacitly assert that the neutrino fields are completely longitudinally polarized, i.e., the contribution to the cross section coming from transverse polarization can be neglected. We show that this tacit assertion is not correct. Although the Standard Model cross section for a neutrino with positive helicity goes to zero as m-> 0, the cross section for a neutrino with transverse polarization remains finite in that limit. Thus the contribution coming from transverse polarization cannot be neglected even in the ultrarelativistic/zero-mass limit. We examine the consequences of this fact and deduce that it has some unexpected results in the neutrino cross sections.

physics.gen-ph↗

arXiv2016

Zero-mass limit of a Dirac spinor with general spin orientation

The helicity eigenstates which describe the fermions with a special spin orientation (parallel or antiparallel to the direction of momentum) provide considerable simplification in calculations. Hence, it is generally preferred to use helicity basis during the calculations in Relativistic Quantum Mechanics or Quantum Field Theory. Possibly because of the above reason, the Dirac spinors describing a general spin orientation have been ignored in many textbooks. Although the helicity eigenstates give almost complete understanding of the behavior of the free Dirac solutions, the zero-mass limit is one of its exception. The zero-mass behavior of the free spinor with general spin orientation and its relation with chirality eigenstates has been skipped in textbooks and hence it deserves a clear, detailed investigation. In this paper we obtain the free Dirac spinors describing a general spin orientation and examine their zero-mass limit. We also briefly discuss some of the implications of this small-mass behavior of the spinors on particle physics.

physics.gen-ph↗

arXiv2016

A hypothesis on neutrino helicity

It is firmly established by experimental results that neutrinos are almost 100\% longitudinally polarized and left-handed. It is also confirmed by neutrino oscillation experiments that neutrinos have tiny but non-zero masses. Since their masses are non-zero the neutrinos cannot be strictly described by pure helicity states which coincide with the chirality eigenstates. On the other hand, it is generally assumed that ultrarelativistic massive fermions can be described well enough by the Weyl equations. This assumption obviously explains why the neutrinos are almost 100\% longitudinally polarized. We discuss the validity of this assumption and show that the assumption is fallacious for a fermion with a general spin orientation. For instance, a fermion with a transverse polarization (relative to its momentum) cannot be described by one of the Weyl equations even in the ultrarelativistic limit. Hence, the fact that neutrinos are almost completely longitudinally polarized cannot be explained in the basis of relativistic quantum mechanics or quantum field theory. As a solution to this problem, we propose a new hypothesis according to which neutrinos are strictly described by pure helicity states although they are not massless.

physics.gen-ph↗

arXiv2016

Semi-elastic cross section for a scalar resonance of mass 750 GeV

We assume that the recently reported excess over Standard Model expectations in the diphoton production is originated from a new scalar boson phi which interacts with photons through the coupling proportional to phi F^2. We obtain the cross section for semi-elastic production process pp-> p gamma p-> p phi q X by considering phi-photon-photon and phi-photon-Z couplings and discuss the constraints on the coupling parameters. We investigate the potential of the semi-elastic production process to probe phi-photon-photon and phi-photon-Z.

hep-ph↗

arXiv2015

Graviton production through photon-quark scattering at the LHC

We have investigated real graviton emission in the ADD and RS model of extra dimensions through the photoproduction process pp-> p gamma p-> pGqX at the LHC. We have considered all contributions from the subprocesses gamma q -> G q, where q=u,d,c,s,b,anti-u,anti-d, anti-c, anti-s, anti-b quark. The constraints on model parameters of the ADD and RS model of extra dimensions have been calculated. During numerical calculations we have taken account of 3, 4, 5 and 6 large extra dimensional scenarios. The constraints on RS model parameters have been calculated by considering G -> gamma gamma, e^- e^+, mu^- mu^+ decay channels of the graviton.

hep-ph↗

arXiv2013

Probe of extra dimensions in gamma q->gamma q at the LHC

We have examined TeV scale effects of extra spatial dimensions through the processes gamma q-> gamma q where q=u,d,c,s,b, anti-u, anti-d, anti-c, anti-s, anti-b. These processes have been treated in a photon-proton collision via the main reaction pp-> p gamma p-> p gamma qX at the LHC. We have employed equivalent photon approximation for incoming photon beams and performed statistical analysis for various forward detector acceptances.

hep-ph↗

arXiv2012

Anomalous quartic ZZgammagamma couplings in gamma-proton collision at the LHC

We investigate the constraints on the anomalous quartic $ZZγγ$ couplings through the process $p p\to pγp\to p γq Z X$ at the LHC. Taking into consideration various forward detector acceptances and integrated LHC luminosities, we find 95% confidence level bounds on the anomalous coupling parameters. We show that the bounds on these couplings are at the order of $10^{-6}GeV^{-2}$ which are about four orders of magnitude more restricted with respect to current experimental bounds.

hep-ph↗

arXiv2012

Electromagnetic properties of the neutrinos in gamma-proton collision at the LHC

We have investigated non-standard $ν\bar νγ$ and $ν\bar νγγ$ couplings via $ν\bar ν$ production in a $γp$ collision at the LHC. We obtain 95\% confidence level bounds on $ν\bar νγ$ and $ν\bar νγγ$ couplings by considering three different forward detector acceptances; $0.0015 <ξ< 0.15$, $0.0015 <ξ< 0.5$ and $0.1 <ξ< 0.5$. We show that the reaction $p p\to pγp\to p ν\bar νq X$ provides more than eight orders of magnitude improvement in neutrino-two photon couplings compared to LEP limits.

hep-ph↗

arXiv2011

Lepton flavor violation in medium energy setup of a beta-beam facility

We examine lepton flavor violating couplings of the neutrinos to W boson in medium energy setup of a beta-beam experiment. We show that muon production via quasielastic scattering and deep inelastic scattering processes nu_e n-> mu p and nu_e N-> mu X are very sensitive to W-mu-nu_e couplings. We perform a model independent analysis and obtain 95% confidence level bounds on these couplings.

hep-ph↗

arXiv2011

Search for electromagnetic properties of the neutrinos at the LHC

Exclusive production of neutrinos via photon-photon fusion provides an excellent opportunity to probe electromagnetic properties of the neutrinos at the LHC. We explore the potential of processes pp-> p gamma gamma p -> p nu anti-nu p and pp -> p gamma gamma p -> p nu anti-nu Z p to probe neutrino-photon and neutrino-two photon couplings. We show that these reactions provide more than seven orders of magnitude improvement in neutrino-two photon couplings compared to LEP limits.

hep-ph↗

arXiv2011

Anomalous WWgamma couplings in gamma-proton collision at the LHC

We examine the potential of pp-> p gamma p -> p W q X reaction to probe anomalous WWgamma couplings at the LHC. We find 95% confidence level bounds on the anomalous coupling parameters with various values of the integrated luminosity. We show that the reaction pp -> p gamma p -> p W q X at the LHC highly improve the current limits.

hep-ph↗

arXiv2010

Extra dimensions in gamma gamma -> gamma gamma process at the CERN-LHC

Potential of the LHC to explore the phenomenology of the Kaluza-Klein (KK) tower of gravitons in the scenarios of the Arkani-Hamed, Dimopoulos and Dvali(ADD) model and Randall-Sundrum (RS) model is discussed via the process ${γγ\to γγ}$ including the Standard Model one loop diagram. The improved constraints on model parameters have been obtained compared to the LEP and Tevatron sensitivity.

hep-ph↗

arXiv2009

Extra dimensions in photon-induced two lepton final states at the CERN-LHC

We discuss the potential of the photon-induced two lepton final states at the LHC to explore the phenomenology of the Kaluza-Klein (KK) tower of gravitons in the scenarios of the Arkani-Hamed, Dimopoulos and Dvali(ADD) model and Randall-Sundrum (RS) model. The sensitivity to model parameters can be improved compared to the present LEP or Tevatron sensitivity.

hep-ph↗

arXiv2009

Probe of unparticles at the LHC in exclusive two lepton and two photon production via photon-photon fusion

The exclusive production pp->pXp is known to be one of the most clean channels at the LHC. We investigate the potential of processes pp -> p l-l+ p and pp-> p gamma gamma p to probe scalar and tensor unparticles by considering three different forward detector acceptances; 0.0015<xi<0.15, 0.0015<xi<0.5 and 0.1<xi<0.5. We obtain 95% confidence level sensitivity limits on the unparticle couplings for various integrated luminosities.

hep-ph↗

arXiv2009

Probe of anomalous neutrino couplings to W and Z in medium energy setup of a beta-beam facility

Capability of medium energy setup of a beta beam experiment to probe new physics contributions to neutrino-W and neutrino-Z couplings are investigated. We employ the effective lagrangian approach of Buchmuller and Wyler and obtain 95% confidence level limits on neutrino couplings to these gauge bosons without assuming the flavor universality of the coupling of neutrinos. We show that a beta beam facility can place 3 to 20 times more restrictive limits than present ones on the deviations from the electron neutrino couplings in the Standard Model.

hep-ph↗

arXiv2009

Effect of top quark spin on the unparticle couplings in γγ\to t\bar{t}

We investigate the potential of $γγ$ collisions to probe scalar unparticle couplings via top-antitop quark pair production. We find 95% confidence level limits on the unparticle couplings with an integrated luminosity of $500 fb^{-1}$ and $\sqrt{s}=1$ TeV energy. We investigate the effect of top quark spin polarization on the unparticle couplings. It is shown that spin polarization of the top quark leads to a significant improvement in the sensitivity limits.

hep-ph↗