Changes between Version 1 and Version 2 of LightPseudo
 Timestamp:
 04/06/12 16:33:03 (8 years ago)
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LightPseudo
v1 v2 1 1 2 2 3 == %$ h \rightarrow A^0A^0 \rightarrow b\overline{b} \tau^+\tau^$%in VBF at LHC (Les Houches Project) ==3 == $ h \rightarrow A^0A^0 \rightarrow b\overline{b} \tau^+\tau^$ in VBF at LHC (Les Houches Project) == 4 4 5 5 === Hypothesis === 6 6 7 We assume SMlike 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.7 We assume SMlike 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. 8 8 9 We also assume that %$A^0$%is a Higgs like scalar coupling to the mass, so that9 We also assume that $A^0$ is a Higgs like scalar coupling to the mass, so that 10 10 11 11 12 12 13 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.13 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. 14 14 15 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.15 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. 16 16 17 17 === Benchmark point === 18 18 19 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.19 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. 20 20 21 21 === Monte Carlo production === … … 23 23 ==== Methodology ==== 24 24 25 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 %$\tau$%.25 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 $\tau$. 26 26 27 27 * Minimal pT of 20 Gev for the jets and 10 Gev for leptons and b's … … 42 42 ==== Considered backgrounds ==== 43 43 44 ===== Irreducible: QCD %$2\tau 2b 2j$%background =====44 ===== Irreducible: QCD $2\tau 2b 2j$ background ===== 45 45 46 46 44k events with tau's decayed into leptons only … … 49 49 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]. 50 50 51 ===== Nearly irreducible QCD %$2e 2b 2j$% and %$2mu 2b 2j$%background =====51 ===== Nearly irreducible QCD $2e 2b 2j$ and $2mu 2b 2j$ background ===== 52 52 53 53 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. … … 82 82 Should be small (see [http://arxiv.org/pdf/hepph/0702119 this paper]) and anyway impossible to simulate completely. 83 83 84 ===== QCD %$2b 4j$%background for jets faking tau's =====84 ===== QCD $2b 4j$ background for jets faking tau's ===== 85 85 86 86 Not considered here since tau's are decaying into leptons. … … 88 88 ===== 2ta4j without b's (mistagging) ===== 89 89 90 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.90 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. 91 91 92 92 ==== Summary of the situation... ==== … … 95 95 === References === 96 96 97 A good generic reference for VBF is the corresponding section in [http://arxiv.org/abs/hepph/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!).97 A good generic reference for VBF is the corresponding section in [http://arxiv.org/abs/hepph/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!). 98 98 99 99 ==== Les Houches 02 proceeding: ==== … … 118 118 === Why is it interesting ? === 119 119 120 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.120 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. 121 121 122 122 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 fb1). 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%). … … 162 162 163 163 164