# $W' \rightarrow \tau \nu$ not Jacobian?

1. Aug 23, 2015

### ChrisVer

I don't understand why the $W' \rightarrow \tau \nu$ doesn't show a Jacobian peak whereas the $W' \rightarrow (e/\mu) \nu$ decay modes do....??
Is it because the $\tau$ decays even further (before measured) and gives additional Missing Transverse Energy? Is it the same for $W \rightarrow \tau \nu$ and $W \rightarrow (e/ \mu) \nu$?

2. Aug 23, 2015

### Staff: Mentor

If you reconstruct the τ, you'll get the same peak. If you take the decay products, your spectrum will look different because you are missing at least two neutrinos then. The spectrum then depends on the decay mechanism.

3. Aug 23, 2015

### ChrisVer

So for larger invariant masses reconstructions you will have a "Jacobian" shape, while for lower the spectrum will become flatter (because of the extra neutrino)?

4. Aug 23, 2015

### Staff: Mentor

What do you mean with "larger invariant masses reconstructions"?

Additional neutrinos smear out the spectrum. The remaining decay products and the initial neutrino don't have to be back to back any more.

5. Aug 23, 2015

### ChrisVer

#### Attached Files:

• ###### b1.jpg
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6. Aug 23, 2015

Staff Emeritus
Did you read the associated paper (CMS-PAS EXO-12-011)? If not, why not? If so, why didn't you point us to it and the part in the paper you didn't understand?

The red and the blue show Jacobians. The red and the blue in the plot right under that show peaks and a low mass non-resonant tail. The green shows no peak in the lower plot, just the non-resonant part, so of course it won't show a Jacobian in the upper part.

7. Aug 23, 2015

### ChrisVer

8. Aug 23, 2015

Staff Emeritus
9. Aug 24, 2015

### ChrisVer

yes, sorry, I misunderstood the "the plot right under that" + the context of the associated paper.

So it seemed to me and that's weird.
It seems that it's not true that we don't expect a Jacobian peak from the W'->tau nu, but whether we expect one or not depends on the $\theta_E$ of the W' (that's what the colored lines are for)...
$\theta_E$ is somewhat connected with how large/small the couplings to the two light and the heavy generations are and so the Universality of the model. If $\cot \theta_E = 1$ then the couplings to the generations are universal (NUGIM= SSM), whereas for other values the coupling to tau or to e/mu is enhanced.

and it seems that as the cotangent approaches 1 (SSM) we get the Jacobian shape...

10. Aug 24, 2015

### ohwilleke

While the post is tagged "A" so that most readers sophisticated enough to understand it would know, it does bear a mention that a W' is a hypothetical BSM particle that is being searched for at the LHC and elsewhere, and that this paper merely describes one version of this hypothetical particle, rather than an actually observed phenomena.

11. Aug 24, 2015

### ChrisVer

Yes, the $W^\prime$ is an hypothetical particle which is predicted by some BSM physics...
Such a BSM is the $SU_h(2) \times SU_l(2) \times U_Y(1)$, which breaks down to the SM... Since no BSM physics has been found, this is an hypothetical model...and the "prediction" figures are obtained from simulations (the plot under discussion states it in the upper left corner)..