Compositeness at LEP II (original) (raw)
Search for evidence of compositeness at LEP I
The European Physical Journal C-Particles and Fields, 1998
Abstract. Extensive searches for evidence of compositeness of quarks and leptons have been made in the complete set of ALEPH data from LEP running at the Z peak. These include searches for radiative and weak decays of excited fermions, produced either in pairs or singly, and a scalar partner of the Z. Coupling and branching ratio limits deduced from these searches are presented.
Search for compositeness with leptonic, hadronic and photonic final states at LEP II energies
A search for compositeness with leptonic, hadronic and photonic nal states has been made in data taken at LEP II by the DELPHI detector. The data analysed was accumulated at center-of-mass energies of 161 and 172 GeV and correspond to an integrated luminosity of about 20 pb ?1 . Single and double production of excited leptons were investigated, and new particles were allowed to decay radiatively or through weak decays. A possible anomalous behaviour of the e + e ? ! ( ) process due to excited electron exchange in the t-channel was studied. A search for excited quarks singly produced and decaying into a quark plus a photon or a gluon is also reported. No signal of compositeness was found. Preliminary limits with 95% con dence level were derived on the masses and couplings of the composite states.
Are there indications of compositeness of leptons and quarks in CERN LEP data?
2007
The "preon-trinity" model for the compositeness of leptons, quarks and heavy vector bosons predicts several new heavy leptons and quarks. Three of them can be produced in e + e − annihilations at CERN LEP energies, since they can be created out of a system of three preons and their antipreons, where three preons form a heavy lepton or quark, while the other three go into a normal lepton or quark. In fact, these new particles are predicted to be lighter than the top quark, while the top itself cannot be produced this way, due to its particular preon substructure. The empirical situation is analyzed, and the most likely masses are estimated.
Search for composite and exotic fermions at LEP 2
The European Physical Journal C, 1999
A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb −1 at an e + e − centre-of-mass energy of 183 GeV and about 20 pb −1 equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes 95% confidence level mass limits in the region between 70 GeV/c 2 and 90 GeV/c 2 , depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermion to its mass (λ/m f * ) as a function of the mass. (Accepted by E. Phys. J. C) ii
Physics Letters B, 2004
Elements of the spin density matrix for W bosons in e + e − → W + W − → qq ν events are measured from data recorded by the OPAL detector at LEP. This information is used to calculate polarised differential cross-sections and to search for CP-violating effects. Results are presented for W bosons produced in e + e − collisions with centre-of-mass energies between 183 GeV and 209 GeV. The average fraction of W bosons that are longitudinally polarised is found to be (23.9 ± 2.1 ± 1.1)% compared to a Standard Model prediction of (23.9 ± 0.1)%. All results are consistent with CP conservation.
Substructures from weak interactions in light of possible threshold signals at LEP and LHC
We present indications of possible substructures from weak interactions, by inspecting LEP and LHC date and inferring threshold effects due to the production of pairs of composite heavy gauge bosons W+-, Z and their hypothetical partners with different spin. Thus, we find possible evidence of scalar or pseudoscalar partners of the W+- and the Z, viz. at 53 and 57 GeV, respectively. Additionally, data may indicate excited states of the Z at 210 and 240 GeV.
Four families of composite quarks and leptons
Physics Letters B, 1982
Four families of composite quarks and ieptons, two standard and two non-standard, are found in a unique solution SU(3)HC X SU(6)L X SU(6)R of a restricted 't Hooft anomaly-matching program. Testable predictions emerge, such as prohibition of/~ ~ eT, zero charge asymmetry in e+e--+ r÷r -in contrast to e+e--+ #+/~-,and a rich new hadron spectrum masses around M W. A minimal set of spectator fermions contains color-singlet objects with fractional quark-like charges.
Leptonic signals for compositeness at hadron colliders
Nuclear Physics B, 1986
We consider composite models in which quarks and leptons have constttuents in common. Detaded amplitudes for subprocesses of the type quark + antiquark--, lepton + antilepton are constructed using the presumed similarity between QCD and compositeness/pre-color interactions. We demonstrate that sensitivity to composlteness scales, A, as high as 100 TeV to 300 TeV may be achievable at a supercollider with center-of-mass energy, ~/~ = 40 TeV For moderate values of A (£ 15-20 TeV) cross sections are several orders of magmtude larger than the background Drell-Yan estimate, reflecting the presence of the new underlying strong interaction. Furthermore, some models exhibit a resonant structure m lepton anti-lepton pair mass spectra, near Met;-A, corresponding to heavy preon-anttpreon composite states If A is m the SSC range, compositeness would probably dominate the cross sections of most processes and could readily be explored experimentally. Finally, at S~pS energies, ~ = 540 GeV, observation of lepton-antilepton pair mass spectra with no deviation from the standard-model Drdl-Yan prediction at Mr?= 150 GeV would place limits on A in the range 1.5 to 3 TeV.
Study of Z Boson Pair Production and Search for Physics beyond Standard Model at LEP-II
2002
The LEP collider at CERN, with its large data sample collected at energies that were never previously attained in e+e- collisions, is an ideal laboratory to test the predictions of the Standard Model (SM). One of the major areas to be explored at LEP is the self-interaction among the gauge bosons envisaged, due to the non-abelian nature of the SU(2)_LXU(1)_Y
Composite-model view of the events at LEP
Physics Letters B, 1994
We examine the phenomenological consistency of composite-model pictures for the ll-7y events at LEP: the picture with an extra boson and that with an excited lepton. It turns out that the former is inconsistent with the Bhabha scattering data, while the latter is consistent with the existing experimental data, as far as the excited lepton is lighter than 200 GeV.
Measurement of W polarisation at LEP
Physics Letters B, 2003
The three different helicity states of W bosons produced in the reaction e + e − → W + W − → νqq at LEP are studied using leptonic and hadronic W decays. Data at centre-of-mass energies √ s = 183 − 209 GeV are used to measure the polarisation of W bosons, and its dependence on the W boson production angle. The fraction of longitudinally polarised W bosons is measured to be 0.218 ± 0.027 ± 0.016 where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model expectation.
The reaction at LEP and constraints on anomalous quartic gauge boson couplings
Physics Letters B, 2002
The cross section of the process e + e − → Zγγ → qqγγ is measured with 215 pb −1 of data collected with the L3 detector during the final LEP run at centre-of-mass energies around 205 GeV and 207 GeV. No deviation from the Standard Model expectation is observed. The full data sample of 713 pb −1 , collected above the Z resonance, is used to constrain the coefficients of anomalous quartic gauge boson couplings to: −0.02 GeV −2 < a 0 /Λ 2 < 0.03 GeV −2 and −0.07 GeV −2 < a c /Λ 2 < 0.05 GeV −2 , at 95% confidence level.