List of models

From Wiki Les Houches 09

Revision as of 12:47, 23 June 2009 by Agashe (Talk | contribs)
Jump to: navigation, search

This is a list of models producing boosted W and Z bosons (with x-section estimates), ranked by other objects in the event.

Pairs (WW/WZ/ZZ):

  • Warped/(partially) composite Standard Model (SM): this framework can address both the Planck-weak and flavor hierarchy problems of the SM. Here W', Z', graviton', t', b' denote Kaluza-Klein (KK) W, Z, graviton, top and bottom in warped extra dimensional picture or composite W,Z, graviton,

top and bottom in the 4D picture of partial compositeness of SM. There's also a particle called "radion" (fluctuation of size of extra dimension) which is like Higgs' (i.e., couplings similar to SM Higgs). Very rough cross-sections (they vary a bit depending on details of the model) for the processes below are:

(1). W' (2 TeV) -> WZ, WH: ~O(10) fb each

(see reference for precise cross-sections and other details. The process W' -> t bbar - giving boosted t and b - can also give similar reach for W'. Interestingly, the gluon' -> t tbar - with gluon' mass beinig similar to W' - can be a siginificant background to this channel since highly boosted t can fake b: techniques similar to the ones used to identify highly boosted tops can now be applied to veto the top faking b.)

(2). Z' (2 TeV) -> WW, ZH: ~O(10) fb each

(see reference for precise cross-sections and other details. The process Z' -> t tbar also has similar rate, but it can be swamped by gluon' -> t tbar if the Z' and gluon' have similar mass.)

(3) graviton' (2 TeV) -> WW, ZZ, HH: ~O(10) fb each

(see references, and for precise cross-sections and other details.)

(4). Higgs' -> WW, ZZ, HH

(see reference for more details. Also, see Seung+Mugetalk)

Model file for CalcHEP implementation of RS radion (with radion mass larger than ~400 GeV) is linked in the following link:

(5). t', b' -> t/b + W/Z/H

The composite/KK partners of fermions have typically masses similar to W'/Z' and hence are constrained to be ~2 TeV (in turn, based on masses of W'/Z' required to satisfy precision tests). DIRECT constraints on masses of these fermions can be weaker. In this case, even single production of these fermionic partners might be very small (pair production is even smaller).

However, in certain (well-motivated) models the partners of top, bottom (in the generalized sense, i.e., including extended symmetries/representations for fermions) can be lighter than W'/Z', possibly ~500 GeV. Hence, production (both pair and single, perhaps in association with other SM particles) can be significant. The fermionic partners can decay into t/b + W/Z/H, with W/Z being boosted (even for fermionic partners being ~500 GeV).

(see references and for more details. Also, see Seung+Mugetalk.)

[A few comments are in order:

(a) It turns out that W/Z in all channels above are dominantly LONGITUDINAL. All the above decay patterns follow automatically from overlaps of profiles in extra dimension: light SM fermions are localized near the Planck brane and photon, gluon and transverse W/Z have flat profiles, whereas all KK's, Higgs (including longitudinal W/Z) and top quark are localized near the TeV brane. In the 4D picture, the light fermions are mostly elementary and Higgs and top are mostly composite, whereas photon, gluon and transverse W/Z are sort of in-between.

(b) Masses below 2 TeV for W'/Z' are strongly disfavored by lower-energy precision tests, whereas graviton' mass is expected to be of similar size to W'/Z' and hence is also constrained to be above ~2 TeV. Radion mass can vary from ~100 GeV to ~2 TeV.

(c) Finally, one can lower the UV brane scale to below Planck scale, of course at the expense of not explaining the full Planck-weak hierarchy. Such a modified framework - dubbed "little RS": see reference - leads to larger couplings to light fermions than the framework which explains the Planck-weak hierarchy, whereas couplings to top/W/Z/H are reduced. Hence, production cross-section for W'/Z' via q qbar annihilation is enhanced and so are the decays to cleaner channels such as dileptons.]

  • W,Z from Heavy neutrinos pair production from Z' in the U(1)_B-L model Basso LH09 talk

Heavy neutrino pair production: up to ~100fb, decaying in (see reference for more details):

- WW+2leptons (up to ~25fb);

- WZ+1leptons + MET (up to ~25fb);

- ZZ+MET (up to ~6fb);

- WH+1leptons + MET (up to ~25fb);

- ZH+MET (up to ~12fb);

- HH+MET (up to ~6fb);

  • W,Z from Heavy KK fermions: for pair production of B' at 500 GeV, sigma ~ 1pb @10 TeV. See Muge's talk for details
Personal tools