# Changes between Version 1 and Version 2 of LightPseudo

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Timestamp:
04/06/12 16:33:03 (8 years ago)
Comment:

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Unmodified
 v1 == %$h \rightarrow A^0A^0 \rightarrow b\overline{b} \tau^+\tau^-$% in VBF at LHC (Les Houches Project)  == == $h \rightarrow A^0A^0 \rightarrow b\overline{b} \tau^+\tau^-$ in VBF at LHC (Les Houches Project)  == === Hypothesis === We assume SM-like weak vector boson fusion production of %$h$% with a xsec of order 2 to 4 pb depending on the mass. NLO corrections are available but have been shown to be small (typically of order 5 to 10% at most). We assume that %$Br(h\rightarrow A^0 A^0)=1$%. It is a simplifying hypothesis, often justified from the theoretical point of view (%$A^0$% is much heavier than light fermions). Anyway, if it's not true, all signal xsec should simply be scaled by this Br. We assume SM-like weak vector boson fusion production of $h$ with a xsec of order 2 to 4 pb depending on the mass. NLO corrections are available but have been shown to be small (typically of order 5 to 10% at most). We assume that $Br(h\rightarrow A^0 A^0)=1$. It is a simplifying hypothesis, often justified from the theoretical point of view ($A^0$ is much heavier than light fermions). Anyway, if it's not true, all signal xsec should simply be scaled by this Br. We also assume that %$A^0$% is a Higgs like scalar coupling to the mass, so that We also assume that $A^0$ is a Higgs like scalar coupling to the mass, so that Numerically, this gives %$Br(A^0\rightarrow \tau^+\tau^-)=8\%$% and %$Br(A^0\rightarrow b\overline{b})=92\%$% if one takes %$m_b=3.5$% Gev which is a reasonable value at the scale %$m_{A^0}$%. These BR could be modified if the coupling of %$A^0$% to charm is sizable, but this is not the case with SM like couplings or in large %$\tan(\beta)$% type II models like MSSM. Numerically, this gives $Br(A^0\rightarrow \tau^+\tau^-)=8\$ and $Br(A^0\rightarrow b\overline{b})=92\$ if one takes $m_b=3.5$ Gev which is a reasonable value at the scale $m_{A^0}$. These BR could be modified if the coupling of $A^0$ to charm is sizable, but this is not the case with SM like couplings or in large $\tan(\beta)$ type II models like MSSM. The total BR for the decay chain %$h \rightarrow A^0A^0 \rightarrow b\overline{b} \tau^+\tau^-$% is thus 2 * 8% * 92%=15%, and the typical xsec is thus ranging from 300 to 450 fb. The total BR for the decay chain $h \rightarrow A^0A^0 \rightarrow b\overline{b} \tau^+\tau^-$ is thus 2 * 8% * 92%=15%, and the typical xsec is thus ranging from 300 to 450 fb. === Benchmark point === For the LH project, we take %$m_{A^0}$% at 50 Gev and %$m_{h}$% at 120 Gev. The mass of the %$h$% is light enough to have a good production xsec and to avoid to consider its decays into WW or ZZ. The mass of the %$A^0$% is light enough to open the decay %$h\rightarrow A^0 A^0$% but heavy enough to give a good pT and a good separation for b's and tau's. For the LH project, we take $m_{A^0}$ at 50 Gev and $m_{h}$ at 120 Gev. The mass of the $h$ is light enough to have a good production xsec and to avoid to consider its decays into WW or ZZ. The mass of the $A^0$ is light enough to open the decay $h\rightarrow A^0 A^0$ but heavy enough to give a good pT and a good separation for b's and tau's. === Monte Carlo production === ==== Methodology ==== Signal and backgrounds are generated separately using MG/ME v4.1. The PDF is CTEQ6L1 and the renormalization and factorization scales are set to 120 Gev. All the following generation cuts are applied. Jet means non b jets and leptons means e, %$\mu$% and %$\tau$%. Signal and backgrounds are generated separately using MG/ME v4.1. The PDF is CTEQ6L1 and the renormalization and factorization scales are set to 120 Gev. All the following generation cuts are applied. Jet means non b jets and leptons means e, $\mu$ and $\tau$. * Minimal pT of 20 Gev for the jets and 10 Gev for leptons and b's ==== Considered backgrounds ==== ===== Irreducible: QCD %$2\tau 2b 2j$% background ===== ===== Irreducible: QCD $2\tau 2b 2j$ background ===== 44k events with tau's decayed into leptons only The cross section '''after tau decay''' into leptons is 1fb. There is '''no cut''' on the tau decay products. Plots before tau decay are [http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/PROC1/Events/run_01_plots.html here]. ===== Nearly irreducible QCD %$2e 2b 2j$% and %$2mu 2b 2j$% background ===== ===== Nearly irreducible QCD $2e 2b 2j$ and $2mu 2b 2j$ background ===== Irreducible if no tau tag and no missing Et cut. Cross section is 8.7fb (for each) with cuts on leptons same as cuts on tau's for signal. Should be small (see [http://arxiv.org/pdf/hep-ph/0702119 this paper]) and anyway impossible to simulate completely. ===== QCD %$2b 4j$% background for jets faking tau's ===== ===== QCD $2b 4j$ background for jets faking tau's ===== Not considered here since tau's are decaying into leptons. ===== 2ta4j without b's (mistagging) ===== Probably not necessary. CMS TDR I gives a b mistagging probability around %$10^{-2}$% for gluons and light quark jets (for a tagging efficiency of 0.5) and %$10^{-1}$% for c jets. The cross sections of 2ta4j and 2ta2c2j with the strong VBF cuts are probably to small to give sizable contribution after double mistag. Probably not necessary. CMS TDR I gives a b mistagging probability around $10^{-2}$ for gluons and light quark jets (for a tagging efficiency of 0.5) and $10^{-1}$ for c jets. The cross sections of 2ta4j and 2ta2c2j with the strong VBF cuts are probably to small to give sizable contribution after double mistag. ==== Summary of the situation... ==== === References === A good generic reference for VBF is the corresponding section in [http://arxiv.org/abs/hep-ph/0503172 Djouadi]. It gives different references for experimental analysis of %$h\rightarrow \tau^+\tau^-$% in VBF which could be considered as a good starting point (but ATLAS related!). A good generic reference for VBF is the corresponding section in [http://arxiv.org/abs/hep-ph/0503172 Djouadi]. It gives different references for experimental analysis of $h\rightarrow \tau^+\tau^-$ in VBF which could be considered as a good starting point (but ATLAS related!). ==== Les Houches 02 proceeding: ==== === Why is it interesting ? === Theoretical point of view: if %$m_{A^0}>2 m_b$%, most of NMSSM signal with only tau's and mu's decays are suppressed. Theoretical point of view: if $m_{A^0}>2 m_b$, most of NMSSM signal with only tau's and mu's decays are suppressed. Pheno point of view: signal xsec similar to (or even better than) SM one for VBF with h in tau's which has been shown to be a quite interesting channel (4.5 sigmas in each tau's leptonic mode, 6 sigmas for the combined analysis after 30 fb-1). Jet veto cannot be applied straightforward but a "non b jet" veto is an interesting new concept (check if it is new!). The additional double b tag could maybe compensate the less effective background rejection without decreasing too much the signal (25%).