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### A New Surprising Result!

Today is the start of the Hadron Collider Physics conference, which is being held in Paris this year, hosted by IN2P3. If you understood the post from the organisers last week, you would have learnt that a collaboration requested an extra talk to present a new surprising result.

I’m here to tell you that that collaboration was LHCb and, yes we do have a new surprising result:

The first evidence of CP violation in the charm system.
$$\Delta A_{CP} = −0.82 \pm 0.21 (stat) \pm 0.11 (sys) \%$$

This is pretty exciting as the current Standard Model prediction of this effect is 1‰ or less.

Congratulations to everybody involved in the measurement. I know that the team has been working flat out for past few months double testing and triple testing their analysis in preparation for the public release. Unfortunately there is never any rest for the weary as both the LHCb collaboration and theorists have a lot of work ahead of them in the upcoming months. We experimentalists need to include the rest of the 2011 data and there are plans to perform a completely independent measurement of the same quantity using a different analysis strategy. The theorists need to go back and see whether the Standard Model can accommodate such a large amount of CP violation in the charm system or whether the observation needs a new physics explanation.

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### 5 Responses to “A New Surprising Result!”

1. nsetzer says:

Certainly exciting! When do you anticipate the paper being released?

• Anna Phan says:

Dear Nick,

The conference note should be released on Friday and the paper should be out in the first week of December.

Cheers,
Anna

2. [...] CP-violation in charm. Welcome New Physics? Or not?“, Quantum Diaries. 3. Anna Phan, “A New Surprising Result!“, Quantum Diaries. 4. Sean Carroll, “New Physics at LHC? An Anomaly in CP [...]

3. ben-hqet says:

Can the SM account for this? According to a paper in Phys Lett B 222 (1989)501 (look at the date, this is called “making a prediction” in science) YES. It says that in the absence of large SU(3) breaking in these decays one should expect order 1 CP asymmetries. The authors then retract a bit and state that “This is of course very unlikely; the preferred explanation … is that SU (3) violating effects are large in this decay.” (This discussion is in the next to last paragraph in that paper). So now we know, the preferred explanation is half-way, there is some SU(3) breaking and some enhancement of the amplitude that leads to large CP violation (the one the authors call 2F+G).

• Anna Phan says:

Dear Ben,

The simple answer is yes, the Standard Model could account for this much CP violation in the charm system. The question is what mechanism exactly… The paper you mention could be the solution, there are people looking into further into issue in light of the result. I haven’t noticed a flood of papers on the arXiv yet, but I’m sure it’ll happen eventually. The calculations in the charm sector are quite tricky.

Cheers,
Anna