Difference: ScentificProgramme (2 vs. 3)

Revision 32005-10-28 - Main.DenisPerretGallix

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META TOPICPARENT name="WebHome"

Scientific Goals of Feynman@Home

ALERT! in preparation

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<		For the LHC as well as for the linear collider program, the computation of higher precision and high multiplicity processes
>
>		For the LHC as well as for the linear collider program, the computation of higher precision and high multiplicity processes
 has become a must.

For QCD, next-to-leading order computations mitigate scale uncertainties, provide a first estimate of the observable normalization and include additional sub-processes that may change observable distribution shapes. Resummation techniques can be checked and improved.

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 But most importantly many QCD processes contribute to the background to Higgs or “new” physics searches; If the background is large, it has to be known precisely (st least better than signal/background ratio), otherwise extracting the signal will become intractable. Such a precision can only be obtained by including NLO calculations.

An experimenter’s wish list has been presented a few years ago, in the frameworks of the Tevatron Run II, it still apply to the LHC energy. One can see that the multiplicity is quite high, from 6 to 8 still keeping the boson undecayed. Performing these calculations at tree level is already a substantial effort, at NLO it is a challenge. 

<--
Experimeter's Wish list (K. Ellis, J. Campbell)
-->
Experimeter's Wish list (K. Ellis, J. Campbell)

Due to these extreme difficulties, the “les Houches 2005” the wish list was less ambitious. But it still requires computing power Feynman_at_Home could provide:

  1. 2 --> 4 processes
    • pp --> V V jet,
    • pp --> V V V

  1. 2 --> 4 processes
    • pp --> 4 jets
    • pp --> t t-bar b b-bar
    • pp --> t t-bar + 2 jets,
    • pp --> t t-bar H + jet
    • pp --> V + 3 jets
    • pp --> V V + 2 jets
    • pp --> V V V + jet
Changed:
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<		New Physics models (MSSM, extra-dimensions) generate many more particles and therefore many more diagrams translating into a large memory size and computing time increase.
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>		"New Physics" models (MSSM, extra-dimensions) generate many more particles and therefore many more diagrams translating into large memory size and computing time increases.
  For example: e+e- nu-e nu-e-bar b b-bar b b-bar goes from 5720 diagrams in the SM to 19508 in MSSM. So the signal is also more and more complex even at tree level.
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 Today achievement for one loop amplitudes processes are presented in “Les Houches 2005” as ‘state of the art for amplitudes, although only a few results are available for 2--> 3 and 2-->4 are considered as frontier calculations (see. Gudrun Heinrich).

  1. Status NLO 2 --> 3 (LHC)
    • pp --> 3 jets
    • pp --> V jj (V = γ;Z;W)
    • pp --> γγj
    • pp --> V bb-bar
    • pp --> tt-barH; b_b-barH
    • pp --> tt-bar j
  2. Status NLO 2 --> 3 (ILC)
    • e+e- --> 4jets
    • e+e- --> νν-barH
    • e+e- --> e+e-H
    • e+e- --> ννγ
    • e+e- --> tt-bar H
    • e+e- --> ZHH
    • γγ --> t t-bar H
  3. Status NLO 2 -> 4
    • e+e --> 4 fermions : in progress

A lot of effort is directed toward theoretical issues, but often process cannot be computed because they involve too much computing although most if not all theoretical issues a well under control. The Feynman_at_Home collaboration will be active in both sectors: Theory and computing.

-- DenisPerretGallix - 26 Oct 2005

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