1. Report on the collider session: part 1
EuroGDR meeting 27/11/2004

2. A. M. Magnan
SUSY particles searches with R-parity violation at DØ, Tevatron. (λ121 coupling)
Introduction
Analysis
Results
Comparison with other experiments
Conclusion and prospects
EuroGDR meeting 27/11/2004

3. Final state with λ121 coupling
i) Production: Rp conserved  pair of Charginos-Neutralinos, mainly Z* f W* f
Production of a pair of
ii) Decay: Rp violated with λ121 coupling  Decay of the neutralinos into leptons. eμ ee
Final state: eeee, eeeμ, or eeμμ
iii) Detector not fully efficient  we search for ee+X, X = e or μ
EuroGDR meeting 27/11/2004

4. Present preliminary limits: more luminosity (310 pb-1) and better selection cuts
tanβ = 5, A0 = 0
Theoretical x-sect
σ95 experimental limit
m0 = 100 GeV
m0 = 250 GeV
m0 = 500 GeV
μ < 0
Not yet approuved
249 GeV
μ > 0
Not yet approuved
271 GeV
EuroGDR meeting 27/11/2004

5. J.F. Grivaz: The LSP mass limit at LEP
There is no absolute neutralino-LSP mass limit from LEP
(ee vanishes for a pure photino and heavy selectrons)
Indirect limits have been
obtained under the assumption
of gaugino mass universality
For large slepton masses:
~ m/2 (52 GeV) at large tan,
somewhat lower otherwise
For low slepton masses, scalar
mass universality is also needed
(The limit is set in the “corridor”)
And finally Higgs searches are
used at low tan …
The impact of stau mixing has recently been investigated: no loophole
EuroGDR meeting 27/11/2004

6. Focus-Point studies at LHC
U. De Sanctis, T. Lari, C. Troncon
University of Milan and INFN
ATLAS Collaboration
Focus-Point studies at LHC
EuroGDR meeting 27/11/2004

7. mSUGRA and DM SUSY spectrum computed with ISAJET 7.69
In most of mSUGRA
parameter space the
predicted relic density
is too large.
In the Focus-Point region
(large m0) the lightest
neutralino has a significant
Higgsino component, and
the relic density is reduced
by s-channel annihilation
in the early universe.
SUSY spectrum computed with ISAJET 7.69
Relic density computed with Micromegas 1.3.0
Focus Point
Coannihilation
(very narrow)
Selected for a detailed study with ATLAS simulation.
EuroGDR meeting 27/11/2004

8. Dilepton mass distributions
The c02 edge can be measured (constrain
on neutralino mixing matrix from the shape?)
The c03 edge hardly visible even after three
years at design luminosity.
At generator level
ATLAS ~ ~
c02 → c01 l+l-
Experimental, flavour subtracted ~ ~
c03 → c01 l+l-
ATLAS 20 40 60
Mll (GeV)
300 fb-1
No SM background
Cuts: Meff > 750 GeV, ETmiss > 100 GeV,
1 jet with pT > 100 GeV
Leptons with pT > 10 GeV 20 40 60 80
Mll (GeV)
EuroGDR meeting 27/11/2004

9. Conclusions
Part of the Focus-Point region is accessible by the LHC experiments. A test
point was studied with the ATLAS detector fast simulation. A number of mass
constrains can be measured: m(c02)-m(c01), m(g)-m(c±) and m(g)-m(c0).
A scan of mSUGRA focuspoint space has been performed with ISAJET to study how the SUSY mass spectrum varies and select points for more detailed studies.
The gluino gets heavier as one moves along the band in the m0-m1/2 plane. The LHC reach to observe gluino pair production should be about m1/2 ~ 900 GeV. Gaugino production may be used to extend this reach, assuming it can be isolated from the SM background.
The neutralino spectrum is sensitive to position both along and trasversal to the band.
The squarks are accessible for low top masses and/or high tanb - this would allow to get m0 (and confirm that sfermions are there…)
The Focus-Point is under active study by the ATLAS collaboration. All results are preliminary and more are coming.
EuroGDR meeting 27/11/2004

10. EuroGDR meeting 27/11/2004

11. EuroGDR meeting 27/11/2004

12. EuroGDR meeting 27/11/2004

13. Polarization effects in slepton production at hadron colliders
Giuseppe Bozzi
Euro-GDR 2004
Frascati - November 25, 2004
in collaboration with B. Fuks and M. Klasen
Preprint submitted to arXiv : hep-ph/
EuroGDR meeting 27/11/2004

14. Introduction Purposes of this work :
Processes studied : and
Unpolarised cross sections well known (both LO and NLO):
- 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
(NLO enhances LO by ~ 35% at Tevatron and ~20% at LHC --> extended discovery reach)
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
Verify and extend previous polarized calculations, including mixing effects relevant for third generation sleptons
EuroGDR meeting 27/11/2004

15. Conclusions and outlook
Spin asymmetry measurements :
Differentiation of SM/SUSY processes for all 3 colliders.
More severe constraints on SUSY parameters ?
Tevatron : small PDF uncertainties --> reliable
LHC, RHIC : large PDF uncertainties --> more difficult
Outlook :
Better constraints on PDFs (from HERA, RHIC,…) are welcome!
Higher order calculations
EuroGDR meeting 27/11/2004