Changes between Version 46 and Version 47 of Reweight


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Timestamp:
Apr 5, 2016, 12:43:35 PM (9 years ago)
Author:
Olivier Mattelaer
Comment:

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  • Reweight

    v46 v47  
    4343   $$\mathcal{W}_V^{new} = \frac{V^{new}}{V^{old}} * \mathcal{W}_V^{old} $$
    4444   $$\mathcal{W}_R^{new} = \frac{R^{new}}{R^{old}} * \mathcal{W}_R^{old} $$
    45  with the final weight computed by recombining these weights according to the prescription given before. This method of reweighting is called "'''NLO_basic'''".
    46 
    47 
    48  In MadGraph5_aMC@NLO, we have implemented a second NLO accurate method of re-weighting. This method dubbed "'''NLO_VT'''" is expected to have a smaller statistical uncertainty than the basic one. One potential problem of the "NLO_basic" method is related to the procedure adopted in the computation of the virtual contribution (see sect.2.4.3 http://arxiv.org/pdf/1405.0301.pdf). This speed optimisation method can easily statistical error associated to a sub-sample of events. To estimate such effect we propose this second reweighting  method --which should be less sensitive to such effects--. The difference between those two methods should be seen as a systematics.
     45 with the final weight computed by recombining these weights according to the prescription given before. In MadGraph5_aMC@NLO, we have not implemented this re-weighting.
     46
     47One potential problem of this method is related to the procedure adopted in the computation of the virtual contribution (see sect.2.4.3 http://arxiv.org/pdf/1405.0301.pdf). This speed optimisation method can easily increased the statistical error associated to a sub-sample of events. To limit such effect we proposed (and implemented) a second reweighting  method. The difference between those two methods should be seen as a systematics.
    4948For this re-weighting, $\mathcal{W}_B$ is split in two pieces :$\mathcal{W}_{BC}$, $\mathcal{W}_{BB}$. $\mathcal{W}_{BC}$ is the part, proportional to the Born, related to the one of the counterterms, while $\mathcal{W}_{BB}$ includes all of the other contributions (the Born itself and the approximate virtual).
    5049 The reweighting is then carried out as follows:
    … …  
    5655 
    5756 '''This method will be released in a future version of MadGraph5_aMC@NLO''' and can currently be provided on request. Since it is based on a dedicated decomposition, the NLO sample must be generated in a specific way for the Les Houches event file to contain the necessary information (see below).
     57
     58
     59
     60 '''Loop Improved:'''[[BR]][[BR]]
     61 As the NLO re-weighting this method use the NLO decomposition but applies the following re-weighting procedure
     62   $$\mathcal{W}_B^{new} = \frac{B^{new}}{B^{old}} * \mathcal{W}_B^{old} $$
     63   $$\mathcal{W}_V^{new} = \frac{B^{new}}{B^{old}} * \mathcal{W}_V^{old} $$
     64   $$\mathcal{W}_R^{new} = \frac{R^{new}}{R^{old}} * \mathcal{W}_R^{old} $$
     65 with the final weight computed by recombining these weights according to the prescription given in the NLO descriptions.
     66
     67 This method is mainly intended for case where the virtual can not be computed as in the case of loop-induced production. It might be more accurate than a simple LO/kamikaze re-weighting but this point was never proven for any processes.
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