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