60 research outputs found
Comparative analysis of the four-fermion contact interactions at e^+e^- and e^-e^- colliders
We study electron-electron contact-interaction searches in the process
e^+e^-\to e^+e^- at a future e^+e^- Linear Collider with both beams
longitudinally polarized. We evaluate the model-independent constraints on the
coupling constants, emphasizing the role of beam polarization, and make a
comparison with the case of e^+e^-\to\mu^+\mu^-.Comment: 5 pages with 3 figures. Talk given at the VII-th International School
- Seminar ``The Actual Problems of Microworld Physics'', Gomel, 28 July - 8
August, 200
Signals of Warped Extra Dimensions at the LHC
We discuss the signatures of the spin-2 graviton excitations predicted by the
Randall-Sundrum model with one warped extra dimension, in dilepton and diphoton
production at LHC. By using a specific angular analysis, we assess the ranges
in mass and coupling constant where such gravitons can be discriminated against
competitor spin-1 and spin-0 objects, that potentially could manifest
themselves in these processes with the same mass and rate of events. Depending
on the value of the coupling constant to quarks and leptons, the numerical
results indicate graviton identification mass ranges up to 1.1-2.4 TeV and
1.6-3.2 TeV for LHC nominal energy of 14 TeV and time-integrated luminosity of
10 and 100~, respectively.Comment: 8 pages, Talk given at QCD@Work - International Workshop on QCD -
Theory and Experiment, 20 - 23 June, 2010, Martina Franca Ital
Revealing the large extra dimension effective interaction at an e^+e^- collider with polarized beams
Contactlike nonstandard effective interactions can be revealed through
deviations of observables from the Standard Model predictions. If such
deviations were observed, the relevant source should be identified among the
possible models that could explain them. We estimate the expected
discrimination reach on the ADD model of gravity in large compactified extra
dimensions, against the compositeness-inspired four-fermion contact
interaction. As basic observables we take the differential cross sections for
fermion-pair production at a 0.5-1 TeV electron-positron linear collider with
both beams longitudinally polarized. For the four-fermion contact interaction,
we assume a general linear combination of the individual models with definite
chiralities, and arbitrary coupling constants. Accordingly, the estimated
identification reach on the ADD scenario can be considered as
`model-independent'. We emphasize the substantial role of beams polarization in
enhancing the identification sensitivity.Comment: 14 pages, 2 figure
Sneutrino identification in dilepton events at the LHC
Heavy neutral resonances appearing in the clean Drell-Yan channel may be the
first new physics to be observed at the proton-proton CERN LHC. If a new
resonance is discovered at the LHC as a (narrow) peak in the dilepton invariant
mass distribution, the characterization of its spin and couplings will proceed
via the measurement of production rates and angular distributions of the decay
products. We discuss the discrimination of a spin-0 resonance (sneutrino)
predicted by supersymmetric theories with R-parity breaking against the spin-1
of Z^\prime bosons and the Randall-Sundrum graviton resonance (spin-2) with the
same mass and producing the same number of events under the observed peak. To
assess the region of sneutrino parameters (couplings and masses) where the spin
determination can be performed to a given confidence level, we focus on the
event rate and the angular distributions of the Drell-Yan leptons, in
particular using the center-edge asymmetry, A_{\rm CE}. We find that although
the measured event rate permits solving the above problem partially, the
center-edge asymmetry, on the contrary allows to differentiate the various
spins entirely with a minimal number of events around 200.Comment: 20 pages; version to appear in PR
Spin and model identification of Z' bosons at the LHC
Heavy resonances appearing in the clean Drell-Yan channel may be the first
new physics to be observed at the proton-proton CERN LHC. If a new resonance is
discovered at the LHC as a peak in the dilepton invariant mass distribution,
the characterization of its spin and couplings will proceed via measuring
production rates and angular distributions of the decay products. We discuss
the discrimination of the spin-1 of Z' representative models (Z'_{SSM},
Z'_{psi}, Z'_{eta}, Z'_{chi}, Z'_{LR}, and Z'_{ALR}) against the
Randall-Sundrum graviton resonance (spin-2) and a spin-0 resonance (sneutrino)
with the same mass and producing the same number of events under the observed
peak. To assess the range of the Z' mass where the spin determination can be
performed to a given confidence level, we focus on the angular distributions of
the Drell-Yan leptons, in particular we use as a basic observable an
angular-integrated center-edge asymmetry, A_{CE}. The spin of a heavy Z' gauge
boson can be established with A_{CE} up to M_{Z'} \simeq 3.0 TeV, for an
integrated luminosity of 100 fb^{-1}, or minimal number of events around 110.
We also examine the distinguishability of the considered Z' models from one
another, once the spin-1 has been established, using the total dilepton
production cross section. With some assumption, one might be able to
distinguish among these Z' models at 95% C.L. up to M_{Z'} \simeq 2.1 TeV.Comment: 18 pages, 6 figure
Distinguishing New Physics Scenarios at a Linear Collider with Polarized Beams
Numerous non-standard dynamics are described by contact-like effective
interactions that can manifest themselves through deviations of the cross
sections from the Standard Model predictions. If one such deviation were
observed, one should try to identify to a given confidence level the actual
source among the possible non-standard interactions that in principle can
explain it. We here estimate the potential identification reach on different
New Physics effective interactions, obtainable from the angular distributions
of lepton pair production processes at the planned International Linear
Collider with polarized beams. The models discussed are the interactions based
on gravity in large and in TeV^{-1} extra dimensions and the
compositeness-inspired four-fermion contact interactions. The availability of
both beams polarized in many cases plays an essential role in enhancing the
identification sensitivity.Comment: 21 pages, LaTex, 11 figures. One author was missing from the previous
version. The authors list has been completed, no other change
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