1. 1 Stop pair production in photon-photon collision at ILC A.Bartl (Univ. of Vienna) W.Majerotto HEPHY (Vienna) K.Moenig DESY (Zeuthen) A.N.Skachkova, N.B.Skachkov JINR (Dubna)

2. 2 Experimental restrictions on the STOP mass “First Search for the Four Body Decay of the Scalar Top Quark” B.Olivier, U.Bassler, G.Bernardi, F.Machefert D0 Note 3820 13 Jan 2001

3. 3 Top σ = 16.5 fb STOP σ = 2.97 fb

4. 4 The subsequent decay channels are considered: The subsequent decay channels are considered: STOP STOP → b χ 1 + b χ 1 - → b b q q’ μ - ν μ χ 1 º χ 1 º STOP STOP → b χ 1 + b χ 1 - → b b q q’ μ - ν μ χ 1 º χ 1 º t t → b W + b W - → b b q q’ μˉ ν μ t t → b W + b W - → b b q q’ μˉ ν μ In order to simulate the STOP pair production, we assumed the following scenario for the MSSM model parameters: In order to simulate the STOP pair production, we assumed the following scenario for the MSSM model parameters: M ~g = M ~q M ~g = M ~q M ~q = 370 GeV (the mass of the light squarks is varied) M ~q = 370 GeV (the mass of the light squarks is varied) M ~t L = M ~t R = M ~b R = M ~q - 100 GeV (left and right squark masses) M ~t L = M ~t R = M ~b R = M ~q - 100 GeV (left and right squark masses) M ~l = M ~ν = M ~q + 10 GeV M ~l = M ~ν = M ~q + 10 GeV A t = A b = -500 GeV (top and bottom trilinear coupling) A t = A b = -500 GeV (top and bottom trilinear coupling) M A ° = 500 GeV (pseudoscalar higgs mass) M A ° = 500 GeV (pseudoscalar higgs mass) μ = - M ~g μ = - M ~g tanβ = 5 tanβ = 5 Our aim is: Our aim is: To find out physical variables (Energy, PT, angle and invariant mass distributions) most suitable for signal (stop) / background (top) separation To find out physical variables (Energy, PT, angle and invariant mass distributions) most suitable for signal (stop) / background (top) separation To estimate the corresponding values of cuts on these variables To estimate the corresponding values of cuts on these variables Corresponds to M stop = 167 GeV, χ1º M χ1º = 80 GeV 1+ M χ 1+ = 159 GeV

5. 5 M STOP dependence on M gluino and Tan β

6. 6 Cross-section σ dependencies

7. 7 General t hat = (Pγ - P stop ) 2 and M inv (stop+stop) = M inv (γγ) = √ (Pγ 1 + Pγ 2 ) 2 distributions t hat M inv Polarization : +- / -+ Polarization : ++/ --

8. 8 STOP Energy distributions Polarization : +- / -+ Polarization : ++/ --

9. 9 STOP P T distributions Polarization : +- / -+ Polarization : ++/ --

10. 10 STOP angle Θ distributions Polarization : +- / -+ Polarization : ++/ --

11. 11 PT of B quarks & charginos are slightly disbalanced STOP TOP

12. 12 Used cuts for jets The events with not clear distance separation The events with not clear distance separation of jets are dropped (cut efficiency = 0.7) of jets are dropped (cut efficiency = 0.7) The distance between parent quark and jet The distance between parent quark and jet R η,φ < 0.7 R η,φ < 0.7 (cut efficiency = 0.4, together with the cut above) (cut efficiency = 0.4, together with the cut above) These cuts work differently for TOP and STOP events (due to difference in kinematical distributions) These cuts work differently for TOP and STOP events (due to difference in kinematical distributions)

13. 13 Comparison of quark W distributions with the distributions of jet W E jet_W have lost 6 GeV PT jet have lost 6 GeV

14. 14 B jets need a tuning of tails B quarks B jets have small tails E B_jets gain 5 GeV due to tails PT B_jets gain 4 GeV due to tails

15. 15 Self compensation in invariant masses: B jets increase while W quark jets decrease M inv increase by 3 GeV due to B quark  B jet transition Finally M inv change from 57.8 GeV (quarks) to 60.0 GeV (jets), 2GeV transition Quark W  Jet W transition makes a loss of 2 GeV

16. 16 W mass reconstruction as M inv of 2 W jets STOP TOP Partonic level Level of jets Good for Signal / Background separation !

17. 17 Missing energy and detected energy distributions STOP TOP ν μ, ~χ1º Missing energy ( ν μ, ~χ1º, beam pipe) Energy detected in calorimeters Good for Signal / Background separation !

18. 18 Total scalar Σ PT variable STOP TOP Good for Signal / Background separation !

19. 19 Jet algorithm influence

20. 20 Most important is the Invariant mass of B jet & 2jets W STOP TOP Right edge of M inv ≈ 87 GeV χ1º M stop – M χ1º = 167 – 80 = 87 GeV M inv ( B jet & 2jets W ) = M Top χ1º M inv (STOP) = M χ1º + M inv (B jet, 2jet W ) = χ1º + = M χ1º + √ (P B + Pjet1 W +Pjet2 W ) 2 Reconstruction of M STOP (167 GeV): Reconstruction of M Top (175 GeV) : Good for Signal / Background separation !

21. 21 Invariant mass of B jet & Bbar jet STOP TOP

22. 22 Invariant mass of 4 jets STOP TOP Good for Signal / Background separation !

23. 23 Invariant mass of 4jets + μ STOP TOP Good for Signal / Background separation !

24. 24 Conclusion The main results: 1. A code that allows to take into account the polarizations of colliding photons is implemented into PYTHIA 6 code for crossection of STOP production in photon-photon collisions. An account of spectrum of energy of colliding photons is done by use of CIRCE 2. 2. A possibility of a good M STOP reconstruction from right-hand edge point of 3 jets ( Bjet + 2 jets W ) is demonstrated. It is shown also that the invariant mass of the final state objects ( jets, leptons ) and missing energy variable turns out to be most efficient for signal / background separation. 3. It is shown also that the invariant mass of the final state objects ( jets, leptons ) and missing energy variable turns out to be most efficient for signal / background separation. So, finally, So, finally, it is shown that it is shown that in a region of small values of stop mass ~ 167 GeV in a region of small values of stop mass ~ 167 GeV the channel the channel STOP STOP → b χ 1 + b χ 1 - → b b q q’ μ - ν μ χ 1 º χ 1 º STOP STOP → b χ 1 + b χ 1 - → b b q q’ μ - ν μ χ 1 º χ 1 º is very promising for STOP quark search! is very promising for STOP quark search!