Report on the Activities of WORKING GROUP I Collider Physics

1. Report on the Activities of WORKING GROUP I Collider Physics Coordinators: Sunanda Banerjee Rohini M. Godbole Sreerup Raychaudhuri

2. Working Group Talks • Gobinda Majumdar • Issues In The Construction Of Detectors For ILC • Satyaki Bhattacharyya • Photon Detection Efficiency In The Measurement • Of • Ben Allanach • Dark Matter Constraints on the Parameter space of the MSSM and mSUGRA

3. D E F I N E D P R O B L E M S • Z-boson decay to a photon + graviton • Light charged Higgs in the NMSSM with and without CP-violation • SUSY Studies at LHC in the light of Dark Matter Constraints • Observing the Higgs through its decay into a tau and a muon • CP-violating observables in Higgs decays at the LHC • Benchmark points for little Higgs models with T-parity

4. 1.

6. 2. Light charged Higgs in the NMSSM with & without CP-violation D.P.Roy, D.Choudhury, R.Godbole, D.Miller, S.P.Das, S.Kraml, S.K.Rai • LEP Bound of 114 GeV forces the MSSM pseudoscalar to be • heavy and hence the charged Higgs to be heavier than the top quark • Can be relaxed in • NMSSM • CP-violating MSSM • Possible to have a light pseudoscalar and a light charged Higgs • of mass 120 – 160 GeV in the regime

7. at LHC • Final state is 2j + 4b • Reconstruction of t gets rid of QCD backgrounds • Channel is shown to work PROPOSAL : Carefully study region in NMSSM parameter space where this scenario dominates, e.g. vacuum stability. Extend for NMSSM with CP-violation.

8. 3. SUSY dark matterB. Allanach, SP Das, RM Godbole, M Guchait, S Kraml, D P Roy • In stau coannihilation scenario, stau-LSP mass difference is 10 GeV or smaller • New feature in LHC cascade decays: soft taus • Need to investigate whether soft tau signal can be dectected at LHC

9. SPS3 inspired scenario: m0=80, m1/2=400, A0=0, tb=10, sgn(m)=+ Not most favorable point but ok to start with

10. pt of t´s from neutralino2 chain • Taus from neutralino2 decay into stau+tau are no problem; ptmean=147 GeV • Taus from stau decay into LSP are very soft; ptmean=19 GeV • Very unlikely to get mtt endpoint. • Add. info from mll or nt2→nt1+h may help to contrain stau mass

11. pt of t´s from chargino1 chainchargino1→stau+neutrino→tau+neutrino+LSP • Tau is again soft; ptmax,mean = 26 GeV • Rapidity distribution within the tracker range

12. Stop coannihlation • Stop-LSP mass difference ~20-30 GeV. • Gluino will decay into stop+top; 50% same-sign top quarks → same-sign leptons due to Majorana nature of gluino [hep-ph/0512284] • Intend more detailed study for coannihilation region; c+LSP as well as 3/4-body stop decay modes.

13. Summary of Problem # 3 • Stau coannihilation scenario: • stau-LSP mass difference 10 GeV or smaller • new feature in LHC cascade decays: soft taus • Study how signal can be extracted • Stop coannihilation scenario: • stop-LSP mass difference ~20-30 GeV • Gluino will decay into stop+top; 50% same-sign top quarks → same-sign leptons because gluino is Majorana [hep-ph/0512284] • More detailed study in small DM region, incl c+LSP and 3-body stop decay modes

14. 4. Detection of Higgs through its tau-muon decay D. Zeppenfeld, R. Vaidya, M.Guchait, S.D. Rindani, D.Miller No details are available, but it was reported that it does not seem to be feasible to detect the Higgs boson through this decay channel.

15. 5. CP Observables Coordinators: D. Miller & D. Choudhury Aim: To find Higgs sector observables at the LHC which are zero in models where CP is conserved but may be non-zero if CP is violated. Production and decay • Scalar nature of the Higgs ) there can be no correlations between production and decay. • e.g. • Need at least 3 directions to construct CP odd observable • e.g. (need not be particle momenta – may also be polarization vectors) no correlation These requirements severely limit the possible channels at the LHC

16. must rely on vertices MSSM • Most general HVV vertex contains • CP-even terms (i.e. ) • CP-odd terms (i.e. ) • However, in the MSSM, these CP-odd terms are absent at all orders! In principle, observables like are CP-violating observables, but we cannot distinguish the two gluons in the experiment, so this is no use. We can here use rapidity to distinguish between the quark and anti-quark, but this is presumably too small to be any use (?)

17. So we really need a process which doesn’t use the initial state gluons or quarks but still has plenty of other particles in the production !associated production A possible asymmetry is As a first step, we could just look at Santosh has agreed to look into this using MADGRAPH

18. More General Models In principle, other models of new physics could contain AVV couplings, with a coefficient suppressed by MEW/. What is the sensitivity of the LHC to such couplings? (Are there already constraints from LEP?) Look at Higgs decays via Possible Asymmetry: David Miller, Margarete Mühlleitner & Rohini Godbole have agreed to look at this. Note that this is the crossing of the process which Rohini et al have already looked at for CP-violating observables.

19. 6. Little Higgs Model with T Parity M.Perelstein, S.K.Rai, R. Godbole, S.Kraml, N.Okada • Little Higgs models are viable theories of EWSB with a composite Higgs • LH with T Parity (a la R parity of the MSSM) passes electroweak precision tests without fine-tuning • New T-odd states: an extra set of SU(2)xU(1) gauge bosons, partners of (left-handed) quarks and leptons, a triplet Higgs field

20. LHT @ LHC: Phenomenology • Predominant production channel @ the LHC: pair-production of heavy quarks Q' • Lightest T-odd Particle (LTP) is stable; typically the “heavy photon” B' -> missing energy signal • Look for cascade decays: Q' -> (jets, leptons)+B' • This is just like the MSSM!

21. LHT or SUSY? • How can the LHC experiments distinguish between these models? Non-trivial -> interesting! • First step: identify benchmark points in LHT and SUSY with the same observable particle spectra for a fair comparison • LHT spectrum is not entirely flexible -> cannot be faked by the usual mSUGRA

22. LHT/SUSY Comparison: Benchmark Point(s) • In SUSY we need gaugino mass non-universality: M2/M1~4 at the weak scale • We found a good benchmark point with this property by “deforming” the SPS1a. • Substantial rate of dilepton cascade decays at this point will allow for a precise determination of the spectrum at the LHC • A more general scan of SUSY parameter space could also be useful

23. LHT/SUSY Comparison: Plan • The next step is to compute event rates and distributions at the benchmark point and look for good discriminating signatures • This will require simulation tools for the LHT model – implement this model in existing event generators?

24. Concluding Remarks • We have identified 5 problems which seem interesting and worth pursuing • Preliminary discussions have clarified the problems and indicated a plan of action for each • A contact person has been identified for each problem and he/she will be requested to provide a more detailed write-up for the WG report • All that remains is to do the work!