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Determining Spin in Hadron Colliders

Determining Spin in Hadron Colliders. Harvard University. Itay Yavin. In collaboration with Lian-Tao Wang. The road ahead. Introduction Simple decays, developing some tools. HERWIG – simulating spin correlations Where shall spin be found Conclusions. Introduction.

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Determining Spin in Hadron Colliders

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  1. Determining Spin in Hadron Colliders Harvard University Itay Yavin In collaboration with Lian-Tao Wang

  2. The road ahead • Introduction • Simple decays, developing some tools. • HERWIG – simulating spin correlations • Where shall spin be found • Conclusions

  3. Introduction The LHC is about to go on-line very soon and discerning new physics is not going to be easy. • Resonances • End points • Edges • Lepton, jets • what have you. LNSM for a recent accessment of the challanges in correctly interpreting the data, see: N.Arkani-Hamed, G.L.Kane, J.Thaler and L.T.Wang, arXiv:hep-ph/0512190 We are also not the first to think about spin determination: A. Barrhep-ph/0405052 , hep-ph/05111115 P. Meade and M. Reece, hep-ph/0601124

  4. Observable Observable Observable Observable Unobservable Unobservable Spin??? Cascades In this talk I will concentrate on measuring the spin through cascade decays.

  5. Circular Longitudinal LH, RH (RH) (LH) Longitudinal Circular Rules for spin correlations

  6. 1) Production through Z0: Z0 RH LH circ. dominate 2) Decay through massive gauge-boson RH Z’ RH long. dominate When do particles get polarized? To understand how a particle might get polarized consider its rest frame

  7. LH a) LH RH different LH b) RH RH LH Both must be chiral vertices 3) Decay through a Majoranna fermion 4) Decay through a Dirac fermion – must involve chiral interactions

  8. Monte-Carlo Simulators There are many available: Pythia, HERWIG, ISAWIG, MadGraph, CompHEP Approximations with MC simulators: (not with MadGraph and CompHEP) The spin information in the propagator’s numerator is lost: Narrow width approximation: SPINCORRELATIONS IN MONTE CARLO SIMULATIONS, Peter Richardson, JHEP 0111:029,2001and references therein

  9. HERWIG1 Designed to simulate hadronic emissions with special emphasis on gluon interference. Utilizes a spin-correlations algorithms: [1] G. Marchesini, B.R. Webber, G. Abbiendi, I.G. Knowles, M. H. Seymour and L. Stanco, HERWIG: a Monte Carlo event generator for simulating hadron emission reactions with interfering gluons. Version 5.1 - april 1991, Comput. Phys. Commun. 67 (1992) 465.

  10. Massive Gauge-Bosons In order to implement spin-correlations for massive gauge-bosons in HERWIG, we need to write the polarization in terms of massive spinors: And massive spinors can be expressed in terms of mass-less spinors as usual and implemented into Herwig.

  11. Implemented diagrams + permutations Tedious but done. Coming soon:

  12. Where shall spin be found? We will assume for the moment that no leptonic partners are light enough to be produced. Vs. Vs.

  13. Comparison of theory with MC Theory MC

  14. Farther study required Observing the Lepton

  15. Do we need to tell apart Jetfar from Jetnear? KK SS

  16. 100 120 160 M1=180 We performed an initial scan of the parameters M1 and M2 keeping all the other parameters (mq, m, tanb) fixed

  17. Why is it a good channel? • Very sharp contrast between SUSY and KK signal. • Results in only few jets so combinatorics is not terrible. • 2 of the jets can (in principle) be set apart from the rest by reconstructing the W. • The signal is still strong even when averaged over Jnear and Jfar. • Assume no sleptons in the spectrum so fairly generic. • Standard model background?

  18. Using Sleptons A. Barr originally considered, Process 2 Process 1 • Two problems: • You don’t know which lepton is which. • There is an equivalent chain starting with an anti-squark having all the arrows opposite which tends to wash out correlations

  19. SS KK We can solve the second problem by considering instead: Information about the charge is kept in the leptons.

  20. Conclusions • The tools to investigate the possibility of measuring spin are available. • The channels we considered seem promising, but farther study (background, cuts, smearing etc.) is warranted. • Spin determination through production channels (ala’ A. Barr) might prove to be a cleaner signal. • Global studies combining different methods to cover the full parameter regions are needed. • Gluon partner’s spin? Seems pretty hard!!!

  21. Jet Overlap How close the jets are to each other? Jfar - JW Jnear - Jfar

  22. Jnear - JW JW1 – JW2 Jets seem well separated, but farther study is certainly necessary

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