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-------- Forwarded Message -------- From: Mikhail Dubinin <dubinin at theory.sinp.msu.ru> To: Alexander Kryukov <kryukov at theory.sinp.msu.ru> Cc: comphep-devel <comphep-devel at theory.sinp.msu.ru> Subject: Re: [Comphep-devel] [Fwd: [Comphep-common] uncertainty on 2l invariant mass distributions of ZZ production] Date: Mon, 2 Jun 2008 18:04:01 +0400 (MSD) Dear Pedro, (1) yes, CompHEP includes Z^*-Z^, Z-gamma^* and gamma^*-gamma^* interferences since it calculates complete set of twelve 2 -> 4 diagrams. See recent detalization for pp -> 4 muons on the page https://twiki.cern.ch/twiki/bin/view/CMS/Regularization ( and also https://twiki.cern.ch/twiki/bin/view/CMS/CompHEPInterface ) (2) main sources of uncertainties are in PDF's, especially at small invariant masses. The PDF factorization scale at m_Z, usually taken in this case, is an approximation. One can also try to take not CTEQ*L (leadind log QCD evolution in PDF's) but other choices to feel the QCD uncertainties. I remember that Alexander Sherstnev studied recently pp->ZZ case together with Florida group. Probably he can give you refernces to his detailed publications. Best wishes Mikhail Dubinin On Mon, 2 Jun 2008, Alexander Kryukov wrote: > Hi, > > I get the mail (see below). > > -- A.K> > > -------- Forwarded Message -------- > From: Pedro Ribeiro <ribeiro at lip.pt> > To: comphep-common at theory.sinp.msu.ru > Cc: Michele Gallinaro <michgall at lip.pt>, Malgorzata Kazana > <kazana at lip.pt> > Subject: [Comphep-common] uncertainty on 2l invariant mass distributions > of ZZ production > Date: Mon, 02 Jun 2008 11:57:50 +0100 > > Dear CompHEP team > > > We are studying UED signal in 4 lepton final state for which the main > background is ZZ->4l. We have been using ZZ->4l samples produced with > Comphep. > > In order to discriminate signal from background we have been looking at > the distribution of dilepton invariant mass, which has a triangular > shape and a endpoint between 20-60 GeV (depending on the model) for the > signal due to the presence of a "neutralino" like particle. As expected, > the same distribution for the ZZ background shows a peak at the Z mass. > > We wish to use the Z peak of the dilepton invariant mass distribution to > normalize the distribution when data is available. Then we would rely on > the shape as given my MC to extrapolate the event yield in our signal > region which is located at lower mass scale (10-60GeV) . > > Two questions: > > - Does compHep includes interference between Z and virtual gamma ? > > - Which are the most relevant sources of uncertainty in the shape of > dilepton invariant mass distribution between 10 and 60 GeV, that is, > which parameters in CompHEP should we vary to get a estimate of the > uncertainty ? > > Best Regards > > Pedro > > > _______________________________________________ > Comphep-common mailing list > Comphep-common at theory.sinp.msu.ru > http://theory.sinp.msu.ru/mailman/listinfo/comphep-common > -- шБ _______________________________________________ Comphep-devel mailing list Comphep-devel at theory.sinp.msu.ru http://theory.sinp.msu.ru/mailman/listinfo/comphep-devel -- Alexander Kryukov <kryukov at theory.sinp.msu.ru> SINP MSU, Moscow