1. Polarization effects in slepton production at hadron colliders
Benjamin Fuks
in collaboration with G. Bozzi and M. Klasen
Preprint submitted to arXiv : hep-ph/
November 22, 2004

2. Table of contents Introduction Cross sections Spin asymmetry
Conclusions
November 22, 2004

3. Introduction SUSY : MSSM : High energy extension to Standard Model
Only non trivial extension of the Poincaré group
Symmetry between fermionic and bosonic degrees of freedom
Solving the hierarchy problem
Stabilization of the Higgs mass
Explanation of gauge coupling unification
MSSM :
1 generator  one SUSY particle for each SM elementary particle
Renormalizability
B, L and R-parity conservation
November 22, 2004

4. Introduction Phenomenology :
None of these partners has been discovered yet
 SUSY must be broken
 Masses of the superpartners at a higher scale.
Hierarchy of scales must be maintained
 Supersymmetry breaking is soft
 Superpartner masses are no larger than a few TeV
 Interest for hadron colliders (RHIC, Tevatron, LHC)
 Exploration of the TeV mass range
November 22, 2004

5. Introduction Purposes of this work :
Processes studied : and (production of scalar leptons)
Unpolarised cross sections well known :
LO : S.Dawson, E.Eichten and C.Quigg, PRD 31 (1985) 1581
LO : H.Baer, C.Chen, F.Paige and X.Tata, PRD 49 (1994) 3283
NLO : H.Baer, B.W.Harris and M.H.Reno, PRD 57 (1998) 5871
NLO : W.Beenakker, M.Klasen, M.Krämer, T.Plehn, M.Spira and P.M.Zerwas, PRL 83 (1999) 3780
Polarised cross sections
Old paper for old colliders : P.Chiappetta, J.Soffer and P.Taxil, PLB 162 (1985) 192
No mixing (important, especially for the lightest slepton : )
Discrimination between new physics signal and SM background
 Spin asymmetries in longitudinally polarized hadron colliders
November 22, 2004

6. Table of contents Introduction Cross sections Spin asymmetry
Conclusions
November 22, 2004

7. Cross sections + Feynman Diagrams : Electroweak couplings : fermions
sfermions : multiplication by Sj1Si1* and Sj2Si2*
 Introduction of the mixing matrix :
November 22, 2004

8. Cross sections Unpolarised partonic cross section
Remark : and are supposed degenerate in mass
Unpolarised hadronic cross section
Parton Distribution Function : GRV98LO
M.Glück, E.Reya and A.Vogt, EPJ C5 (1998) 461
November 22, 2004

9. Hadronic cross sections
and supposed degenerate in mass  no mixing here
LHC : visible in the entire mass range
Tevatron : visible in a restricted mass range
RHIC : difficult !
Background : σ ~10 nb
 3 to 6 orders of magnitude higher
November 22, 2004

10. Table of contents Introduction Cross sections Spin asymmetry
Conclusions
November 22, 2004

11. Spin asymmetry Cross sections
and
and (no photon contribution here)
Introduction of the mixing angle θ Mass eigenstates and
Polarised PDF used : GRSV2000LO (standard and valence)
M. Glück, E. Reya, M. Stratmann and W. Vogelsang, PRD 63 (2001)
The lightest slepton
November 22, 2004

12. Spin Asymmetry, RHIC RHIC : = 500 GeV  SUSY scenario with light
 Maybe it will be visible
GMSB scenario based on SPS 7
 is the NLSP (after the gravitino)
Parameters :
Λ is varying (default : 40 TeV)
Mmes = 80 TeV
Nmes = 3
tan β = 15
µ > 0
November 22, 2004

13. } Spin Asymmetry, RHIC  Constraints on SUSY param. ? 30%
Only a small area of interest :
Invisible cross section
Mass exclusion domain (LEP)
Physical constraints on SUSY parameters
Large PDF uncertainties (large Bjorken-x)
Sensitive to the mixing
 Constraints on SUSY param. ?
Background : AL = – 0.1 … – 0.04
(after invariant mass cut at ≈ 52 GeV)
 Discrimination SUSY/SM }
30%
November 22, 2004

14. Spin Asymmetry, Tevatron
SUSY scenario based on SPS 1a’
 Standard choice
is the NLSP (after the neutralino), but slow decay
Parameters :
M1/2 = 250 GeV
M0 = 70 GeV (100 GeV for SPS 1a)
A0 varying (default : −300 GeV; -100 GeV for SPS 1a)
tan β = 10
µ > 0
November 22, 2004

15. Spin Asymmetry, Tevatron
Physical constraints on SUSY parameters
 cos(θ) is going from 0.21 to 0.30
Small PDF dependence (well known Bjorken-x range)
Sensitive to the mixing
 Constraints on SUSY param. ?
Background : AL = – 0.09 … – 0.08
(after invariant mass cut)
 Discrimination SUSY/SM }
5-6%
November 22, 2004

16. Spin Asymmetry, LHC SUSY scenario based on SPS 4 LHC : = 14 TeV
 We can reach heavy masses
 SPS 4 allows heavy
Parameters :
M1/2 = 400 GeV ( higher masses)
M0 = 300 GeV ( higher masses)
A0 varying (default : 0 GeV)
tan β = 50 (large  large splitting)
µ > 0
November 22, 2004

17. } } Spin Asymmetry, LHC  Constraints on SUSY param. ? 20%
Physical constraints on SUSY parameters
 cos(θ) is going from 0.29 to 0.40
Large PDF uncertainties (small Bjorken-x)
Sensitive to the mixing
 Constraints on SUSY param. ?
Background : AL = – … – (after invariant mass cut)
Discrimination SUSY/SM }
20% }
10%
November 22, 2004

18. Table of contents Introduction Cross sections Spin asymmetry
Conclusions
November 22, 2004

19. Conclusions Spin asymmetry measurements :
Differentiation of SM/SUSY processes for all 3 colliders.
More severe constraints on SUSY parameters ?
Tevatron : small PDF uncertainties  certainly
LHC, RHIC : large PDF uncertainties  more difficult
Outlook :
Better constraints on PDFs can help (HERA, RHIC,…)
NLO calculations
November 22, 2004