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November 7, 2005

Staring at the Tea Leaves

LEP closed down in 2000, to make way for the LHC. There were, towards the end, intriguing hints that there was, perhaps, a bit of a bump in the number of b-jet events, indicating the possibility of a Higgs. Arguments were made that the LEP run should be extended. But, in the end, LEP was shut down on schedule, and the consensus was that it had established a lower limit of m h>115m_h \gt 115 GeV.

Still, people continue to pore over the data and, recently, Dermisek and Gunion have challenged the above consensus. The limit seems to be rather neatly evaded in the NMSSM1. Rather than the dominant decay being hbb¯h\to b\overline{b}, one expects the dominant decay mode to be haah\to a a, where aa is a CP-odd boson of mass, m a3040m_a\sim 30-40 GeV. The aa subsequently decays, abb¯a\to b\overline{b}. The upshot is that, rather than a big excess of two b-jet events, from ZhZbb¯Z h\to Z b\overline{b}, we expect smaller excesses of both two b-jet and four b-jet events (from ZhZaaZbb¯bb¯Z h\to Z a a \to Z b\overline{b}b\overline{b}). That, according to Dermisek and Gunion, is what’s seen in the LEP data, and is consistent with m h105m_h\sim 105 GeV.

If correct, that’s very bad news for direct detection of the Higgs at the LHC. [As I emphasize to Sean, below we’ll see other stuff, just not a Higgs.]

Update (12/7/2005):

John Gunion chimes in below, with an update to their analysis. In the new “best-fit”, the mass of the aa is below 2m b2m_b, so it decays predominantly into τ +τ \tau^+\tau^-, instead of bb¯b\overline{b} (even worse for detection at the LHC). Their estimate for the Higgs mass is slightly lowered, to m h100m_h\sim 100 GeV.

1 In the NMSSM, the μ\mu parameter is replaces by a singlet field, SS, which develops an expectation value. The augmented Higgs sector (H,H˜,SH,\tilde{H},S) includes the light pseudoscalar, aa, above.

Posted by distler at November 7, 2005 11:50 PM

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Re: Staring at the Tea Leaves

I presume, being no expert, that these points in the NMSSM parameter space would predict plenty of other observable particles, even if “the Higgs” were inaccessible. That wouldn’t be such a disaster; much preferable to finding the Higgs and nothing else.

Posted by: Sean on November 8, 2005 8:30 AM | Permalink | Reply to this


Oh yeah. If there’s (conventional) low-energy supersymmetry, we’ll know it.

I was talking, specifically, about Higgs detection. A light Higgs is hard to see at the LHC. And, if I understand correctly, a light Higgs with this particular decay mode is durn near impossible.

Posted by: Jacques Distler on November 8, 2005 9:44 AM | Permalink | PGP Sig | Reply to this

Re: Staring at the Tea Leaves

The paper has been revised. The scenario preferred by the full LEP analysis is one
for which the light CP-odd Higgs boson (a) has mass below 2 times the b quark mass. The CP-even SM-like Higgs (h) will then decay primarily via h->aa ->4 tau and secondarily via h->bb. The latter alone is sufficient to explain the Z+b-jets excess in the LEP data. Such an h will be particularly hard to detect at hadron colliders such as the LHC but will be easily seen at an electron positron collider.

Posted by: J. Gunion on December 7, 2005 12:58 AM | Permalink | Reply to this


Thanks for the update, John!

And, for the rest of you, this is a nice example of the trackback system in action. John arrived here by following the link from the trackback page for his paper.

Posted by: Jacques Distler on December 7, 2005 1:36 AM | Permalink | PGP Sig | Reply to this

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