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Comprehensive Analysis of HERA Collider Data on Excited Fermions and SUSY Limits

This study presents a detailed analysis of the HERA collider experiments H1 and ZEUS, with a luminosity of approximately 200 pb–1 for e–p and 300 pb–1 for e+p at center-of-mass energy √s=319 GeV. It includes the search for excited fermions and limits on compositeness scale, showcasing the best collider constraints on high mass ν* and excited quark states. Additionally, we explore Rp-violating SUSY search results and quark radius limits, demonstrating an excellent agreement with Standard Model predictions up to the highest Q² values. No significant deviations were observed.

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Comprehensive Analysis of HERA Collider Data on Excited Fermions and SUSY Limits

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  1. HERA • ep Collider • Collider experiments H1 and ZEUS • Luminosity: ~200 pb–1 in e–p ~300 pb–1 in e+p √s = 319 GeV e± p 920 GeV 27.6 GeV

  2. Excited Fermions PLB 663, 382 (2008)‏ PLB 666,131 (2008)‏ PLB 678, 335 (2009)‏ • Full HERA statistics analysed and published • Best collider limits on compositeness scale f/Λfor high ν* masses • Best excited quark limits for fS=0 complementary to Tevatron assumption fS=f

  3. General Search • event topologies with particles with high pT > 20 GeV • e, μ, γ, ν and jets • search for deviations from SM in invariant mass, sum of pT • no significant deviation observed PLB 674, 257 (2009)

  4. Rp-violating SUSY • resonant production of single squarks • many different decay channels possible • branching fractions depend on SUSY parameters: M2, μ, tan β • search in many topologies • scan SUSY parameter space

  5. Quark Radius Quark form-factor (electron assumed to be point-like). If a quark has a finite size, the SM cross section is expected to decrease at higher Q2: Rq is a root-mean-square radius of the EW charge distribution in the quark. The same dependence expected for e-p and e+p. Excellent agreement with SM expectations up to highest Q2. ZEUS (94-07 data): Rq< 0.63 x 10-3 fm H1 (94-07 data): Rq< 0.74 x 10-3 fm @ 95% C.L.

  6. Contact Interactions (CI) LEP New interactions at higher scale (Λ >> √s) can be effectively described at lower energies as 4-fermion eeqq Contact Interactions (CI). Reminder: before W and Z0 were discovered, weak interactions (Λ≈MW) were described as 4-fermion CI with Fermi constant GF=g2/M2W. At HERA: CI modify the tree level eq → eq scattering amplitudes. HERA Tevatron where αand βare electron and quark helicities (L,R). + e-p sensitive to and e+p sensitive to and

  7. CI, General Models Also referred to as Compositeness Models. Couplings are related to the mass scale Λat which new interactions occur: gCI is a coupling strength of new interactions and ε= ±1. By convention g2CI = 4π. Different models assume different helicity structure of new interactions, given by set of couplings (4 for every q flavour). ZEUS CI analysis based on full NC sample of L=0.44 fb-1 . ZEUS (94-07 data): Λ> 3.8 - 8.9 TeV (95% C.L.)‏

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