Dear all,
Just to add something to the foreseen precision in alphaQCD(MZ).
Current uncertainties are the level of 1%, and it is difficult to
improve on that for instance with LHC data only.
On the other hand, at the proposed LHeC, you can get much
better precision:
https://indico.cern.ch/getFile.py/access?contribId=11&sessionId=3&resId=0&materialId=slides&confId=244768
(Slide 24)
Accuracies of 1 per mille are thus foreseen at an LHeC. NNLO
calculations are required, but these are also progressing at an
impressive pace recently.
Without an LHeC, it seems difficult to improve substantially
on the current alphaQCD uncertainties.
Best,
Juan
------------------------------------------
Dr. Juan Rojo
Physics Department, TH Unit
Case C01600, CERN
CH-1211 Geneva 23 Switzerland
Phone: (+41) 2276 77943
Webpage: http://cern.ch/juan.rojo
E-mail: [log in to unmask]
[log in to unmask]
Skype: juanrojochacon
------------------------------------------
On 4/19/13 9:28 AM, Ashutosh Kotwal wrote:
> hi Ayres and Sven,
> I hear you - but we are talking more than 20 years in the future.
>
> I am amazed at the progress in theory of higher order calculations over the past 20 years. No way do I see this "precision theory frontier" slowing down over the next 20 years.
>
> I am at the Instrumentation Frontier Snowmass workshop in Boulder and they talk of "grand challenges". To me, the discussion below also suggests a "grand challenge" in EWPO.
>
> regards,
> Ashutosh
>
>
> On Apr 18, 2013, at 10:26 AM, Ayres Freitas <[log in to unmask]> wrote:
>
>> Hi Michael,
>>
>> I second Sven's comments. I think going beyond GigaZ will be extremely challenging, both in terms the uncertainty of input parameters (mtop, alpha(mz), alpha_s), as well as higher-order calculations. Concerning the latter, we would need (at least) complete NNNLO, which is not completely inconceivable, but will require a hugh amount of effort, and I'm not sure if placing so much effort there is the best way to advance our field (and I am writing this as someone who at least partially makes a living from these calculations). See attachment for some more quantitative, but rough estimates of uncertainties from higher-order corrections that I made recently.
>>
>> Best,
>> Ayres
>>
>>
>> On Thu, 18 Apr 2013, Sven Heinemeyer wrote:
>>
>>> Hi Michael,
>>>
>>>> The question for you is, how much would the extra factor of 10 at the Z pole (or the
>>>> extra factor of 100 beyond Giga-Z) buy you in terms of the physics? My quick impression
>>>> is that it is not easy to convert the extra luminosity into physics. GF and MZ must be
>>>> improved, and NNLO electroweak becomes relevant. The uncertainty in alpha(mZ) also
>>>> needs improvement, and I do not see a way to do that.
>>> When we make GigaZ predictions for sin2eff, MW etc. we already use
>>> a very optimistic assumption on delta(Delta alpha_had) = 5 x 10^-5,
>>> resulting in an uncertainty of 1.8 x 10^-5 in sin2eff, i.e. even
>>> larger than the anticipated GigaZ uncertainty, see p. 7 of my talk
>>> at the BNL meeting a few weeks back:
>>> http://www.ifca.unican.es/users/heinemey/uni/talks/2013/SnowmassBNLEWPO.pdf
>>>
>>> On the next page I give an estimate of intrinsic uncertainties, i.e. due
>>> to missing higher-order corrections. Also here in the future the
>>> GigaZ result can be matched only "so-so", and even less so in the MSSM,
>>> which is the *only* model so far in which these quantities have been evaluated to a precision roughly as in the SM, it is much worse in any other model.
>>>
>>> Of course in the future many things are possible. But our expectations
>>> now (which are not wild guesses ;-) would not profit from another
>>> factor of 10 improvement.
>>>
>>> Cheers,
>>> Sven
>>>
>>>
>>> *******************************************************************************
>>> Sven Heinemeyer (IFCA (CSIC-UC), Santander, Spain) > The future is not set!
>>> phone: ++34/942/20-1536, fax: -0935 > There is NO FATE but
>>> email: Sven.Heinemeyer(at)cern.ch > what we make for
>>> WWW : sven-heinemeyer.de > ourselves!
>>> skype: sven.heinemeyer > (Kyle Reese, T2)
>>>
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