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Regina Caputo | USLHC | USA

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Exciting new physics from the Tevatron

I was going out to dinner last night with some of my colleagues and the topic of new physics results at the Tevatron (specifically DZero) came up. I’m always happy to hear about new physics happenings  because it’s too easy to get so caught up in your work that you don’t notice other work being done around you. I know a couple of other bloggers have already posted it, but I’m still excited about it. And maybe a little out of the loop since it’s my last week at CERN and I’ve been really focused on getting a functioning analysis together :).

So for those of you that haven’t heard/read… there’s some interesting stuff happening with CP violation at the Tevatron. Here’s some background:
The Tevatron produces copious amounts of particles called B mesons. B mesons (quark-antiquark b – d or s pairs) oscillate between themselves and their antiparticles (Something I’m happy to elaborate on if anyone is interested). This oscillation can violate CP (charge conjugation and parity symmetry) thus preferring one state in the matter/antimatter system vs. the other.  (This also happens in the kaon system, and was one of the first pieces of experimental evidence that CP was violated). According to the standard model, this asymmetry is supposed to be very small (on the order of 10-4) – so small the Tevatron experiments can not measure it accurately. However that’s not what they found…
There is evidence that the asymmetry is about 100x larger than expected or 3.2 sigma (or 3.2 standard deviations). Now that’s not enough away from the predicted value to claim discovery just yet (need 5 sigma to be really sure). But it’s a very interesting result. Here’s a link to the arXiv paper

The New York Times also published a nice article.  You know you’ve hit the big time, when the NYT has an article about it ;). Although I dislike it when physicists talk about finding faces or toes of god.



7 Responses to “Exciting new physics from the Tevatron”

  1. Paolo says:

    hi there, i’m interested.
    Assuming it turns out to be discovery what are current expectations about model that would fit best?, Fourth family of quarks?

  2. TimG says:

    Are you sure the mesons in question are b – anti-b pairs? I think I’ve read elsewhere that they’re b – anti-s or b -anti-d.

  3. Mark says:

    B mesons (quark-antiquark b pairs) oscillate between themselves and their antiparticles (Something I’m happy to elaborate on if anyone is interested).

    Please do so :)

  4. Regina says:

    @Paolo- Good question! Off the top of my head, I’m not sure. Flip would be a good guy to ask for implications of a high muon charge asymmetry – him being a theorist and all.

    @TimG – You’re totally right. Thanks for the catch! I was trying to say they had either a b or anti-b (its antiparticle partner) but it didn’t come out right :)

    @Mark – will do… maybe that will be my next post :)

  5. Flip Tanedo says:

    Hi everyone — a few thoughts:

    CP observables, such as D0′s semileptonic asymmetry result, provide a chance to indirectly observe new physics. Unfortunately, while these observables are great channels for looking for deviations from the Standard Model, they are not very good at discriminating between possible new models. In other words, they’re great for identifying that there should be new physics, but it’s much more difficult to extract details about the nature of the new physics.

    Also, I should remark that this result should be taken with a grain of salt. In addition from the CDF null results mentioned above, the D0 results seem a bit fishy since the deviation from the Standard Model is *too* large when taken at face value. These kinds of observables are well-constrained by self-consistency conditions, and the D0 mean value for this observable takes a bit of work to make it consistent. For more details for experts, see, e.g. the first section of [1005.4238]. So while the signal may indeed be 3 sigma, one should also have some healthy skepticism that there might be a systematic effect. (I’m *not* an expert on the experimental side, so don’t this as anything other than naive, uninformed speculation.)


  6. Regina says:

    @humble reader: Aaah let the debate begin! This is one of the most exciting aspects of science… having to back up your claim. I knew CDF would have an opinion about the D0 result. Thanks for posting the updates.

    Also Thanks Flip for some good theoretical perspective. And healthy skepticism is always appreciated :)


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