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Elina Fuchs, Silja C. Thewes, Georg Weiglein (DESY Hamburg, Germany)
521. WEH- Seminar: First Results from the LHC, Bad Honnef, December 2012.
The Standard Narrow-Width Approximation (sNWA)
Renormalisation: Higgs sectorand neutralino-/ chargino sector
A Generalised Narrow-Width Approximation (gNWA)
Example process:
Improved Predictions of Interference Effects for New Physics Searches.
gNWA @ 1-loop
Interference effect in the gNWA
Vertex corrections to
References
Higgs sector: [3] Correct on-shell properties of external, mixing Higgs bosons
Neutralino-/ chargino sector: on-shell [4-7]● 3 out of 6 neutralino-/ chargino masses on-shell● remaining 3: loop-corrected masses● choose most bino-, wino- and higgsino-like states
→ stable fixing of the 3 parameters● otherwise: huge counterterms and unphysically large mass shifts
Approximation of 1-loop prediction with interference termApproximation of 1-loop prediction with interference term
Motivation: on-shell approximation Factorisation: production x decay
Limitation of sNWA:Interference term
scenario-specificschemes
Sub-process with loop-correction in gNWA
Relevance of interference effects
Extended particle spectrum➔ typical cascade decays
Many-particle final states technically challenging Simplifying factorisation into production x decay Applications:
➔ MC generators➔ Experimental limits
Narrow width Both sub-processes
kinematically open No interference with
other processes
On-shell approximation of the interference term:
Full cross-section
3-/2-body decays FeynArts / FormCalc Higgs masses and widths with
FeynHiggs
Scenario
Conditions for NWA
Similar masses of h/ H
Gaugino hierarchy
Large High
➔ Loop corrections to enhanced varied as input Real parameters
➔ Only h-H mixing
Large negative interference term● neglected by sNWA● well approximated by gNWA to a few percent accuracy
Large negative interference term● neglected by sNWA● well approximated by gNWA to a few percent accuracy
If intermediate particles quasi mass-degenerate
➔ Breit-Wigner propagators overlap strongly If mixing non-vanishing
Compare NWA (dashed) vs. 3-body calculation (solid) for h/H separately Compare sNWA and gNWA with full 3-body decay
including interference term
Validation of the approximation
Technical aspects of the calculation
Vertex corrections to Approximated interference term based on R-method 2-loop corrected Higgs masses and widths from FeynHiggs
Combination
(S)fermions
Gauge and Higgs bosons, gauginos
Vertex contributionsof different MSSM sectors
Sizable vertex corrections: relevant for full processSizable vertex corrections: relevant for full process
Outlook
CP-violating mixing H-A production
CP-violating mixing H-A production
full 3-body decay at 1-loop➔ Estimation of accuracy➔ Validation of method
Comparison of several stable renormalisation schemes
➔ Estimation of contribution to theoretical uncertainty
full 3-body decay at 1-loop➔ Estimation of accuracy➔ Validation of method
Comparison of several stable renormalisation schemes
➔ Estimation of contribution to theoretical uncertainty
New processes Implications fornew physics searches
Improved predictions
Instead of full process:➔ On-shell production of
intermediate particle➔ Subsequent decay
Error [1] Iteratively
Choose stable scheme for given parametersChoose stable scheme for given parameters
[1] C. Uhlemann, Diploma thesis, Würzburg (2007)[2] A. Fowler, PhD thesis, Durham (2010)[3] M. Frank, T. Hahn, S. Heinemeyer, W. Hollik, H. Rzehak, G. Weiglein, JHEP 02 (2007) 047[4] A. Fowler, G. Weiglein, JHEP 1001 (2010) 108[5] A. Bharucha, A. Fowler, G. Moortgat-Pick, G. Weiglein, arXiv:1211:3134[6] A. Bharucha, S. Heinemeyer, F. v.d. Pahlen, C. Schappacher, Phys. Rev. D86 (2012) 075023[7] A. Chatterjee, M. Drees, S. Kulkarni, Q. Xu, Phy. Rev. D 85 (2012) 075013
[1] C. Uhlemann, Diploma thesis, Würzburg (2007)[2] A. Fowler, PhD thesis, Durham (2010)[3] M. Frank, T. Hahn, S. Heinemeyer, W. Hollik, H. Rzehak, G. Weiglein, JHEP 02 (2007) 047[4] A. Fowler, G. Weiglein, JHEP 1001 (2010) 108[5] A. Bharucha, A. Fowler, G. Moortgat-Pick, G. Weiglein, arXiv:1211:3134[6] A. Bharucha, S. Heinemeyer, F. v.d. Pahlen, C. Schappacher, Phys. Rev. D86 (2012) 075023[7] A. Chatterjee, M. Drees, S. Kulkarni, Q. Xu, Phy. Rev. D 85 (2012) 075013
Interference term
Matrix-element on-shell , but phase space Also phase space on-shell Additional approximation:
➔ Interference term as R-factors [2]
➔ Ingredients
➔ Universal integral
Identify gauginos
➔ Most bino-like:➔ Most wino-like:➔ Most higgsino-like:
Degeneracy problematic in some renormalisation schemes
Higgs production from decay of heavy neutralino
Breit-Wigner propagator
Modified theoretical predictions of due to interference and higher- order effects
➔ Modified limits on parameters
Modified theoretical predictions of due to interference and higher- order effects
➔ Modified limits on parameters