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Perspectives of model-independent searching for Z’ boson at modern hadron colliders

Perspectives of model-independent searching for Z’ boson at modern hadron colliders. A.Gulov Dnipropetrovsk Univ. Perspectives of model-independent searching for Z’ boson at modern hadron colliders. Z’ boson as a scenario of ‘new physics’ beyond the SM What can be taken from the theory ?

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Perspectives of model-independent searching for Z’ boson at modern hadron colliders

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  1. Perspectives ofmodel-independent searchingfor Z’ bosonat modern hadron colliders A.Gulov Dnipropetrovsk Univ.

  2. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ boson as a scenario of ‘new physics’ beyond the SM • What can be taken from the theory? • What can be taken from previous experiments at high energies (LEP)? • What can be expected at modern hadron colliders (Tevatron, LHC)?

  3. Perspectives of model-independent searching for Z’ boson at modern hadron colliders Z’ is a new heavy neutral vector particle beyond the SM Popular in the theory: • It is predicted by lots of models designed for energies up to the Plank scale (GUTs, Extended gauge groups) Popular in HEP experiments: • It can easily arise in the annihilation of SM fermions as an intermediate off-shell or on-shell state • It can decay into the SM charged leptons preferable for precision measurements in experiments

  4. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ is predicted by lots of models designed for energies up to the Plank scale (GUTs, Extended gauge groups):

  5. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ is predicted by lots of models designed for energies up to the Plank scale (GUTs, Extended gauge groups):

  6. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Phenomenological (model independent) description of the Z’ boson: Some general parameterization of the Z’ couplings to the SM particles General theoretical reasons can be taken into account • How the generic Z’ boson can manifest itself in experiments? Z’ boson can be visible in one observable amplifying the signal, but it can be easily missed in another one. The optimal observables have to be found. Model-independent constraints from recent experiments can help to estimate the discovery potential of future experiments. The combined constraints from different experiments are also possible How signals of the Z’ boson can be separated from another possible ‘new physics’ (Gomel STU team @ NPQCD-2011).

  7. Only one Z’ at 1-10 TeV Below 1-10 TeV the Z’ is decoupled, and the theory is reduced to the SM (THDM) Perspectives of model-independent searching for Z’ boson at modern hadron colliders General theoretical assumptions which can be taken into account It is enough to parameterize: • Z’ interactions to the SM fermions • Z’ couplings to scalars (determine Z-Z’ mixing)

  8. Z’ interactions to the SM fermions Z-Z’ mixing related to the Z’ couplings to scalars Only one Z’ at 1-10 TeV Below 1-10 TeV the Z’ is decoupled, and the theory is reduced to the SM (THDM) Interactions of the renormalizable types (potential  current) Abelian Z’ (Z’ interactions to W,Z are due to the Z-Z’ mixing only) Perspectives of model-independent searching for Z’ boson at modern hadron colliders

  9. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • The contact couplings describe the phenomenology at low energies: These couplings were constrained by the LEP experiments • What is the number of unknown constants?

  10. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • 2 constants (a, v)  12 fermion species(charged lepton, neutrino, u-quark, d-quark  3 generations) = 24 parameters • + mixing angle = 25 parameters Phenomenology of contact couplings • + Z’ mass = 26 parameters Beyond the phenomenology of contact couplings Too many parameters!

  11. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • 2 constants (a, v)  electron, muon, u-quark, d-quark = 8 parameters • + mixing angle = 9 parameters Phenomenology of contact couplings • + Z’ mass = 10 parameters Beyond the phenomenology of contact couplings Too many parameters! Successful data fits need 1-2 parameters

  12. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Universality? Nobody knows… • Neglecting mixing angle? It is small, but it generally affects the Z couplings to the SM particles producing effects of the same order as Z’ states. Some theoretical motivation is necessary to reduce the number of unknown parameters. One of the general requirements on the Z’ couplings is the renormalizability of the theory including this particle

  13. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Renormalizability (in the form of RGE for scattering amplitudes) + • The parameterization of the Abelian Z’ couplings = • Relations between the Z’ couplings Due to the decoupling, we need no additional information about other new heavy particles The relations cover a huge number of Z’ models (model independence)

  14. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • The relations f * is the SU(2)-partner of f. T3f is the weak isospin. • The axial-vector coupling is universal. It also determines the Z-Z’ mixing angle. • There is only one independent vector coupling for each SU(2) doublet.

  15. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • 1 constant v  6 SM fermion doublets = 6 parameters • + universal a (determining also the mixing angle) = 7 parameters Phenomenology of contact couplings • + Z’ mass = 8 parameters Beyond the phenomenology of contact couplings Instead of 26 parameters!

  16. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • 1 constantv electron, muon, u(d)-quark = 3 parameters • + a (mixing angle) = 4 parameters Phenomenology of contact couplings • + Z’ mass = 5 parameters Beyond the phenomenology of contact couplings We can try to fit data

  17. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Constraints from the LEP data. • e+e-m+m-, t+t- a2,vevm,vea,vma special 1-param. observable, LEP2: 1s hint: a2 = 1.30  10-5 Constraint on Z-Z’ mixing from LEP1: 1s hint: a2 = 1.25  10-5 • e+e- e+e- a2,ve2,vea special 1-parameter observable: 2s hint: ve2 = 2.24  10-4 general 2-parameter fit at 95%CL: no hint: ve2<1.69  10-4

  18. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • The current knowledge about Z’ couplings • Max. likelihood value: a2 = 1.3  10-5 • 95% CL intervals: 0 < a2 < 3.61  10-4 4  10-5< ve2 < 1.69  10-4 0 < Vm,t,u,c,t2 < 4  10-4 (suppose from the observation of no signals in the hadronic channel)

  19. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ @ Tevatron and LHC Searching for the (narrow) resonance in the Drell-Yan process: pp or pp Z’  e+e- ,m+m-

  20. Perspectives of model-independent searching for Z’ boson at modern hadron colliders We can estimate: • Z’ width (total) • Partial Z’ widths (BRs) • Z’ production cross-section • Limits on the Z’ mass, discovery limits, …

  21. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Estimation Scheme #1 All the Z’ couplings are varied in their 95% CL intervals. This gives the widest intervals for predicted observables. The data outside of these predictions are excluded by LEP (not the Abelian Z’ boson, something else) “95% CL Scheme”

  22. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Estimation Scheme #2 The maximum-likelihood value is used for the axial-vector coupling. The other Z’ couplings are varied in their 95% CL intervals. This gives predictions under the assumption that the real hint of the Z’ boson has been observed by the LEP 2 data. These are our expectations concerning the Abelian Z’ boson. “Max. Likelihood (M.L.) Scheme”

  23. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ Width: calculation Can be calculated by the optical theorem: At the one-loop level (corresponding to Z’ decays into 2 particles): Estimated value of this quantity is practically independent of the Z’ mass

  24. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ Width: results (95%C.L. and M.L. schemes) M.L. 95%C.L.

  25. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ Partial Widths: results (M.L. scheme) m+m- e+e- qq

  26. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ @ Tevatron The Z’ production cross-section can be estimated (details will be given by A.Kozhushko@NPQCD2011) Our predictions can be compared with the Tevatron results and the model predictions The lower limit on the Z’ mass can be obtained

  27. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ @ Tevatron: D0 e+e- vs M.L. estimate D0 m+m- vs M.L. estimate

  28. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ @ Tevatron: CDF e+e- vs M.L. estimate

  29. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ @ Tevatron: The Z’ hint observed by the LEP 2 data can be the Abelian Z’ boson with the mass between 400 GeV and 1.15 TeV. It can be still hidden as the resonance in the Tevatron experiments. The popular set of model are completely covered by our model-independent bounds.

  30. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Z’ @ LHC The Z’ production cross-section can be estimated (details will be given by A.Kozhushko@NPQCD2011) Our predictions can be compared with the model predictions The discovery limit for the Abelian Z’ boson can be obtained (A.Tsytrinov@NPQCD2011)

  31. Perspectives of model-independent searching for Z’ boson at modern hadron colliders • Summary • The model-independent relations for the Z’ couplings exist. The number of unknown Z’ parameters can be significantly reduced • The Z’ width and the production cross-sections in proton-(anti)proton collisions can be estimated from the LEP2 constraints on the Z’ couplings. • The Z’ hint observed by the LEP 2 data can be the Abelian Z’ boson with the mass between 400 GeV and 1.15 TeV (by Tevatron results). We have good chances to discover it at modern hadron colliders. • We have new model-independent results which are complementary to the usual model-dependent schemes.

  32. Perspectives of model-independent searching for Z’ boson at modern hadron colliders Related publications and talks: • with V.Skalozub: Int. Journal of Modern Physics A 25, 5787–5815 (2010) • with A.Kozhushko: will be published in May, 2011 also A.Kozhushko@NPQCD-2011 • Dnipr. Natnl. Univ. team with Gomel State Techn. Univ. team: A.Tsytrinov @ NPQCD-2011

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