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

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Presentation on theme: "Determining Spin in Hadron Colliders Itay Yavin In collaboration with Lian-Tao Wang Harvard University."— Presentation transcript:

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

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. L NSM 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/ We are also not the first to think about spin determination: A. Barr hep-ph/ , hep-ph/ P. Meade and M. Reece, hep-ph/

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

5 Rules for spin correlations CircularLongitudinal Circular LH, RH(RH)(LH)

6 When do particles get polarized? To understand how a particle might get polarized consider its rest frame 1) Production through Z 0 : Z0Z0 2) Decay through massive gauge-boson Z’Z’ RH long. dominate RHLH circ. dominate

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

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

9 Designed to simulate hadronic emissions with special emphasis on gluon interference. HERWIG 1 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 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 Coming soon: Tedious but done.

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

13 Comparison of theory with MC TheoryMC

14 Observing the Lepton Farther study required

15 KKSS Do we need to tell apart Jet far from Jet near ?

16 M 1 = We performed an initial scan of the parameters M 1 and M 2 keeping all the other parameters (m q, , tan  ) fixed

17 Why is it a good channel? 1.Very sharp contrast between SUSY and KK signal. 2.Results in only few jets so combinatorics is not terrible. 3.2 of the jets can (in principle) be set apart from the rest by reconstructing the W. 4.The signal is still strong even when averaged over J near and J far. 5.Assume no sleptons in the spectrum so fairly generic. 6.Standard model background?

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

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

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? J near - J far J far - J W

22 J near - J W J W1 – J W2 Jets seem well separated, but farther study is certainly necessary


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