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Maria Krawczyk

Publications and source records attributed to Maria Krawczyk.

At least 55 records · Page 3Linked to original sources
arXiv2001

The new (g-2) for muon measurement and limits on the light Higgs bosons in 2HDM (II)

We discuss how new data for a_{mu}= (g-2)_{mu}/2 improve constraints on new physics. Using two types of estimations of a_{mu}^{had} (Davier & H"{o}cker (case A) and Jegerlehner2000 (case B)) we evaluate 95% CL intervals for a new contribution, which can be used to constrain any model beyond the Standard Model. We apply these intervals to the general 2HDM ("Model II"), where up to now one light neutral Higgs particle, h or A, was allowed by the data. Assuming that only one Higgs boson contributes to a_{mu}^{2HDM} the two-loop calculation based on the case A leads to the exclusion of scalar $h$ while a pseudoscalar with mass between 10 and 70 GeV (for tan beta > 20) is allowed. For case B the upper limits for tan beta for both scalar and pseudoscalar are obtained.

hep-ph↗
arXiv2001

Photoproduction of the isolated photon at HERA in NLO QCD

The NLO QCD calculation for the photoproduction of the isolated photon with a large pT at the HERA ep collider is presented. The single resolved photon contribution and the QCD corrections of order alpha_s to the Born term are consistently included. The NNLO contributions, the box and the double resolved photon subprocesses, are sizeable and are taken into account in addition. The importance of the isolation cut, as well as the influence of other experimental cuts on pT and final photon rapidity distributions are discussed in detail. The investigation of the renormalization scale dependence is performed in order to estimate the size of missing higher order QCD corrections. Results are compared with experimental data and with the prediction of a different NLO calculation.

hep-ph↗
arXiv2001

Standard-Model-like scenarios in the 2HDM and Photon Collider potential

After operations at the LHC and e^+e^- Linear Colliders it may be found that a Standard-Model-like scenario is realized. In this scenario no new particle will be discovered, except a single Higgs boson having partial widths or coupling constants with fundamental particles, whose squares are close, within anticipated experimental uncertainty, to those of the SM. Experiments at a Photon Collider can resolve whether the SM or e.g. the Two-Higgs-Doublet Model is realized in Nature. For the SM-like realizations of the 2HDM (II) we study the loop couplings of the Higgs boson with γγand Z γ, and also with gluons. The deviation of the two-photon width from its SM value is generally higher than the expected inaccuracy in the measurement of Γ_{γγ} at a Photon Collider. The deviation is sensitive to the parameters of the Higgs self interaction.

hep-ph↗
arXiv2001

Potential of Photon Collider in resolving SM-like scenarios

After operations at the LHC and e^+e^- Linear Colliders it may be found that a Standard-Model-like scenario is realized. In this scenario no new particle will be discovered, except a single Higgs boson having partial widths or coupling constants squared with fundamental particles close, within anticipated experimental uncertainty, to those of the SM. Experiments at a Photon Collider can resolve whether the SM model or e.g. the Two Higgs Doublet Model is realized in Nature. For the SM-like version of the 2HDM (II) we study the loop couplings of the Higgs boson with γγand Z γ, and also with gluons. The deviation of the two-photon width from its SM value is generally higher than the expected inaccuracy in the measurement of Γ_{γγ} at a Photon Collider. The result is sensitive to the parameters of the Higgs self interaction.

hep-ph↗
arXiv2001

Resolving SM-like scenarios via Higgs boson production at a Photon Collider: I. 2HDM versus SM

We consider the possibility that after operations at the LHC and e^+e^- Linear Colliders a Higgs boson will be discovered, but no signal of New Physics will be found (Standard-Model-like scenario). This can occur in the Standard Model (SM) as well as in other models, including the Two-Higgs-Doublet Model (2HDM), the MSSM, etc. Experiments at a Photon Collider can resolve these cases. In this paper we compare the SM and the 2HDM~(II). In the analysis we use as independent quantities the ratios, to the SM values, of couplings of the observed Higgs boson to gauge bosons, and to up and down-type quarks (basic couplings). We derive a relation between these ratios within the 2HDM~(II), a pattern relation. With the aid of this relation, different possible realizations of an SM-like scenario are found. For these realizations, we calculate the loop couplings of the Higgs boson with γγand Z γ, and also with gluons, taking into account the expected accuracy in the measurements of the basic couplings. The obtained deviation of the two-photon width from its SM value is generally higher than the expected inaccuracy in the measurement of Γ_{γγ} at a Photon Collider. The result is sensitive to the parameters of the Higgs self interaction.

hep-ph↗
arXiv2000

Structure Functions for the Virtual and Real Photons

Development of concepts related to the photon and its high energy hadronic interaction is briefly reviewed. A photon considered as an ideal probe of hadron structure, paradoxically is also considered as an ideal target to test the perturbative QCD. The present status of the theoretical and experimental analysis of the structure functions for a virtual and real photon is presented.

hep-ph↗
arXiv2000

Survey of present data on photon structure functions and resolved photon processes

Present data on the partonic content of the photon from LEP, TRISTAN and HERA accelerators are reviewed and the essential aspects of the underlying ideas and methods are pointed out. Results of the unpolarized photon structure function F_2 from DIS_{e gamma} experiments and on large p_T jet production processes in the resolved gamma-gamma collisions are presented for both real and virtual photons. The results of analysis of the hadronic final state accompanying the DIS_{e gamma} measurements, showing some discrepancies with the Monte Carlo models, are collected together and presented as a separate issue. Also results on the DIS_{e gamma} with leptonic final states are shown. The results from resolved real and virtual photon processes at HERA collider based on the single and double jet events, also charged particles and prompt photons, are presented. In the context of virtual photon processes the data for forward jet and forward particle production are included. In addition a short presentation of the recent data on the heavy quark content of the photon is given. Related topics - the polarized (spin dependent) structure functions for the real and virtual photon, the structure function of the electron and the photonic content of the proton are also shortly mentioned.

hep-ph↗
arXiv2000

The light Higgs window in the 2HDM at GigaZ

The sensitivity to a light Higgs boson in the general 2HDM (II), with a mass below 40 GeV, is estimated for an future e+e- linear collider operating with very high luminosity at the Z peak (GigaZ). We consider a possible Higgs boson production via the Bjorken process, the (hA) pair production, the Yukawa process Z -> b {\bar b} h(A), -> tau {\bar tau} h(A), and the decay Z ->h(A)+gamma. Although the discovery potential is considerably extended compared to the current sensitivities, mainly from LEP, the existence of a h or A even with a mass of a few GeV cannot be excluded with two billion Z decays. The need to study the very light Higgs scenario at a linear e+e- collider running at several hundred GeV and the LHC is emphasised.

hep-ph↗
arXiv1999

The forward photon production and the gluonic content of the real and virtual photon at the HERA collider

The discussion on the production of prompt photons with pT of a few GeV in the tagged process ep -> e gamma X with small Q^2 (DIC process) at the HERA collider is presented. Photons produced in the forward (proton) direction are mainly originating from subprocesses involving interactions of the gluonic content of the exchanged photon. The large enhancement over the Born term (direct photon) is found up to a factor of 35 for a real photon and up to 5 for a virtual photon with a squared virtuality 1 GeV^2. It gives a possibility of extracting a gluonic density of the real and of the virtual photon. The BFKL approach to the description of the forward particle production is shortly discussed.

hep-ph↗
arXiv1999

Distinguishing Higgs models at photon colliders

We consider the two effective couplings hZγand hγγinvolving a neutral scalar Higgs boson with a mass around 100 GeV in the Standard Model, in the Two Higgs Doublet Model, and in the Minimal Supersymmetric Standard Model. The couplings can be tested at Photon Colliders, and used to distinguish these models.

hep-ph↗
arXiv1998

Process Z->h(A)+gamma in the Two Higgs Doublet Model and the Experimental Constraints from LEP

The one-loop branching ratios for the process Z->h(A)+gamma are calculated in the general Two Higgs Doublet Model (Model II) taking into account existing constraints on the model parameters. For Higgs boson masses below 50 GeV and tan beta of order 1-10 the fraction of such Z decays are at the level of 10^{-7}, but can be significantly stronger for very low or high tan beta, where the dependence of these results on other model parameters like sin(beta-alpha) and the mass of the charged Higgs boson is found to be of little importance. The results are compared to the LEP measurements, which are sensitive to branching ratios of Z->h(A)+gamma of the order 10^{-5} for masses larger than 20 GeV, but approach 10^{-6} for low masses. Relating the expectation to the experimental limits, constraints on the parameter space of the 2HDM are derived.

hep-ph↗
arXiv1996

Status of 2HDM with a Light Higgs Particle

Present data do not rule out the light neutral Higgs particle h or A with mass below 40--50 GeV in the framework of the general 2HDM ("Model II"). The status of this model in a light of existing LEP I data and a potential of the new muon experiment (g-2), the measurement of photon-gluon and gluon-gluon fusion at HERA as well as photon-photon fusion at low energy gamma gamma NLC is discussed.

hep-ph↗
arXiv1996

Looking for a Light Higgs Particle at Present and Future Colliders

Present data do not rule out the light neutral Higgs particle $h$ or $A$ with mass below 40--50 GeV in the framework of the general 2HDM ("Model II"). The recent limits from LEP I on the parameters of the model, based on the Bjorken process $Z \to Z h$, Higgs pair production $Z \to A h$ and the Yukawa process $Z \to f {\bar f} A$ ($f= b$ quark or $τ$ lepton) are presented. Including limits on Higgs bosons masses from LEP I data additional constraints on the allowed value for $ tan β$ for mass below 2 GeV, can be obtained from the existing $(g-2)_μ$ data. The improvement in the accuracy by factor 20 in the forthcoming $(g-2)_μ$ experiment E821 may lead to more stringent limits on mass of neutral Higgs boson up to 30 GeV, or even higher if the mass difference between $h$ and $A$ is larger than $M_Z$. The exclusion/discovery potential of the gluon-gluon fusion in $ep$ collision at HERA is also discussed. Already for a luminosity $ L_{ep} =25 pb^{-1}$ this measurement may lead to more stringent limits on $ tan β$ for the mass range 5-15 GeV, especially for the pseudoscalar case. In addition the possible search for very light Higgs particle in $γγ$ fusion at low energy (10 GeV) LC is described. It may improve bounds considerably compared to the present limits for mass around between 1.5 and 8 GeV assuming the luminosity $10 fb^{-1}$.

hep-ph↗