Gluino Stransverse Mass

1. Gluino Stransverse Mass Yeong Gyun Kim (Sejong U. & KAIST) In collaboration with W.S.Cho, K.Choi, C.B.Park (KAIST)

2. Contents • SUSY at the LHC • Stransverse mass • Gluino stransverse mass • Conclusion

3. SUSY at the LHC

4. We are entering exciting period in particle physics. The LHC is about to explore for the first time the TeV energy scale. The origin of EWSB ? The nature of dark matter ? Supersymmetry ? Extra dimensions ?

5. LHC (the Large Hadron Collider) : 2008 ~ a proton + proton collider at 14 TeV c.m energy in the 26.6 km tunnel 1033 cm-2 s-1 ~ 10 fb-1/yr (low luminosity) 1034 cm-2 s-1 ~ 100 fb-1/yr (high luminosity)

6. ATALS and CMS : Two general purpose detectors at the LHC ATLAS CMS

7. Weak scale supersymmetry -Provide a solution for the naturalness problem -Complies with gauge coupling unification -Lightest Supersymmetric Particles (LSP) a natural candidate for non-baryonic Dark Matter

8. Dominated by the production of gluinos and squarks, unless they are too heavy • Squark and gluino • production rates • determined by • strong interaction, and • the squark and gluino masses, • -do not depend on • the details of model (Baer etal. 1995) • General features for SUSY at the LHC ~50 pb for m_gluino~500 GeV ~ 1 pb for m_gluino~1000 GeV

9. The gluinos and squarks cascade down, generally in several steps, to the final states including multi-jets (and/or leptons) and undetected two LSPs

10. Characteristic signals of SUSY with Rp • Invisible LSPs Missing Transverse Energy • Decays of squarks and gluinos Large multiplicity of hadronic jets and/or • Decays of sleptons and gauginos Isolated leptons

11. Effective mass • (Multi-jet plus missing ET signature is generic in most of R parity conserving models) An excess of events with large Meff could be the initial discovery of“supersymmetry”(Model with new colored particles decaying into neutral stable particle) A mSUGRA point with m0=100 GeV, m1/2=300 GeV , A0=300 GeV, tanb=2.1 Signal (open circles) SM background (histogram) With 10 fb-1 (Hinchliffe etal. 1997)

12. LHC (5-sigma) Reach for mSUGRA The LHC reach in the jet plus MET channel extend to squark and gluino masses larger than 2 TeV with 300 fb-1 ~1.5 TeV with 1 fb-1 (one month at low luminosity) ~1 TeV with 100 pb-1 (a few days at low luminosity)

13. Measurement of SUSY masses • Precise measurement of SUSY particle masses •  Reconstruction of the SUSY theory • (SUSY breaking mechanism) • SUSY events always contain two invisible LSPs •  No masses can be reconstructed directly • One promising approach  Identify particular decay chain and measure kinematic endpoints using visible particles (functions of sparticle masses)

14. When a long decay chain can be identified, various combinations of masses can be measured in a model independent way

15. Stransverse Mass

16. For the decay, ( ) • Stransverse Mass (Lester and Summers, 1999) Massive particles pair produced Each decays to one observed and one unobserved particle. For example,

17. ( : total MET vector in the event ) However, not knowing the form of the MET vector splitting, The best we can say is that : with minimization over all possible splitting of total MET momentum

18. MT2 distribution for LHC point 5, with 30 fb-1, (Lester and Summers, 1999) With m_chi=121.5 GeV MT2 (max) vs. m_chi

19. Right handed squark mass from the MT2 m_qR ~ 520 GeV, mLSP ~96 GeV SPS1a point, with 30 fb-1

20. At an unconstrained minimum, we have with • Unconstrained minimum of mT

21. Solution of mT2 (the balanced solution) mT2 : the minimum of mT(1) subject to the two constraints mT(1) = mT(2) , and pTX(1) +pTX(2) = pTmiss

22. Example 1 of extreme momentum configuration Squark pair produced at rest Each squark decays into a quark and a LSP on TR. plane Two sets of squark decay products are parallel to each other , With the two constraints the balanced solution is obtained when ,

23. gives All possible splitting Therefore, we have • Example 2 of extreme momentum configuration Squark pair produced at rest Each squark decays into a quark and a LSP on TR. plane Two quarks are back to back each other ,

24. Well matched with MC result Therefore, (occurs at theta=0)

25. Some remarks on the effect of squark boost In general, squark pair is produced with non-zero pT The mT2 solution is invariant under the back-to-back boost of mother squarks

26. The balanced solution of squark stransverse mass with

27. Gluino stransverse Mass

28. The Gaugino Code (Choi, Nilles 2007) ask K. Choi Three distinct mass patterns emerge from many SUSY breaking scenarios mSUGRA pattern M1 : M2 : M3 ~ 1 : 2 : 7 Anomaly pattern M1 : M2 : M3 ~ 3.3 : 1 : 9 Mirage pattern M1 : M2 : M3 ~ 1 : 1.3 : 2.5 (for alpha=1)

29. Gluino stransverse mass A new observable, which is an application of mT2 variable to the process Gluinos are pair produced in proton-proton collision Each gluino decays into two quarks and one LSP through three body decay (off-shell squark) or two body cascade decay (on-shell squark)

30. : transverse mass and momentum of qq system : trial mass and transverse momentum of the LSP • For each gluino decay, • the following transverse can be constructed • With two such gluino decays in each event, • the gluino stransverse mass is defined as (minimization over all possible splittings of the observed MET)

31. Therefore, if the LSP mass is known, one can determine the gluino mass from the endpoint measurement of the gluino stransverse Mass distribution. • However, the LSP mass might not be known in advance and then, can be considered as a function of the trial LSP mass , satisfying • From the definition of the gluino stransverse mass

32. Possible mqq values for three body decays of the gluino :

33. Example 1 of extreme momentum configuration Gluino pair produced at rest Each gluino decays into two quarks moving in the same direction and one LSP moving in opposite direction Two sets of squark decay products are parallel to each other The balanced solution is given by

34. Example 2 of extreme momentum configuration Gluino pair produced at rest Each gluino decays into a quark and a LSP on TR. plane Two quarks are back to back each other, while LSP is at rest , , give All possible splitting Therefore, we have

35. Two sets of decay products have the same mqq and are parallel to each other Gluino stransverse mass

36. ) (  The maximum of mT2 occurs when mqq= mqq (max)  The maximum of mT2 occurs when mqq= 0 • The gluino stransverse mass has a very interesting property  mT2 = m_gluino for all mqq This result implies that (This conclusion holds also for more general cases where mqq1 is different from mqq2)

37. If the function could be constructed from • experimental data, which would identify the crossing point, • one will be able to determine the gluino mass and • the LSP mass simultaneoulsy. • A numerical example and a few TeV masses for sfermions

38. Experimental feasibility An example (a point in mAMSB) with a few TeV sfermion masses (gluino undergoes three body decay) We have generated a MC sample of SUSY events, which corresponds to 300 fb-1 by PYTHIA The generated events further processed with PGS detector simulation, which approximates an ATLAS or CMS-like detector

39. Experimental selection cuts • At least 4 jets with • Missing transverse energy • Transverse sphericity • No b-jets and no-leptons • The four jets are divided into two groups of dijets by the hemisphere method GeV

40. The gluino stransverse mass distribution with the trial LSP mass mx = 90 GeV Fitting with a linear function with a linear background, We get the endpoints mT2 (max) = The blue histogram : SM background

41. as a function of the trial LSP mass • for the benchmark point Fitting the data points with the above two theoretical curves, we obtain The true values are

42. Conclusions We introduced a new observable, gluino stransverse mass We showed that the gluino stransverse mass can be utilized to measure the gluino mass and the LSP mass separately.

44. Unbalanced Solution of mT2