Changes between Version 1 and Version 2 of LowMassSMHiggs
 Timestamp:
 04/06/12 16:33:02 (8 years ago)
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LowMassSMHiggs
v1 v2 7 7 We want to investigate the following signatures: 8 8 9 WH  > ell+ + 2b<br />ZH > ell+ ell + 2b<br />tth >ell+ ell 4b9 WH > ell+ + 2b[[br]]ZH > ell+ ell + 2b[[br]]tth > ell+ ell 4b 10 10 11 11 <br /> We are now focusing on ttH 12 12 === II. Goal === 13 13 14 The project is to investigate the significance that can be achieved in the search for a Higgs produced in association with top quark pair <br />considering the '''dileptonic channel'''.<br />The main background is %$ t \bar t $% + 2 jets.<br /><br />The significance can be studied in different scenarios, for example<br />one can start to fill the following table14 The project is to investigate the significance that can be achieved in the search for a Higgs produced in association with top quark pair[[br]]considering the '''dileptonic channel'''.[[br]]The main background is $ t \bar t $ + 2 jets.[[br]][[br]]The significance can be studied in different scenarios, for example[[br]]one can start to fill the following table 15 15 16 16  Statistical significance  "thin" TF  "Broad TF"  … … 18 18  events with no ISR  S_3  S_4  19 19 20 <br />By estimating S_1,S_2 ... we will provide a reasonable estimate <br />of the maximum significance that can be reached at the LHC, and will<br />also show what are the most important factors controlling this maximum significance.20 <br />By estimating S_1,S_2 ... we will provide a reasonable estimate[[br]]of the maximum significance that can be reached at the LHC, and will[[br]]also show what are the most important factors controlling this maximum significance. 21 21 22 22 The strategy is to organize the work into a validation procedure (first step) and a pheno study (second step). 23 23 === III. Validation procedure === 24 24 25 Idea: apply MEM to reconstruct the mass of the Higgs or reconstruct the fraction of signal <br />events <strong>UNDER CONTROLLED CONDITIONS.</strong><br /><br />"under controlled conditions" means that the events in the prepared samples follow EXACTLY the probability <br />distribution function that is used to evaluate the matrix element weights.<br /><br />In this way, one can set up the calculation of the weights and check that <br />NO BIAS is observed in the final result, and hence validate the whole procedure in the absence of systematic errors. <br />The procedure for the calculation of the weights should be the same as the one used later on for the second step <br />(i.e. one should consider a finite resolution on jet energies, correct for ISR if necessary, ...)<br /><br />Only the samples of events are prepared in an artificial way so that we control exactly how the events are distributed in phasespace.<br />In particular: <br /> the energy of the finalstate partons are smeared exaclty according to the shape of the transfer functions<br /> the effect of ISR (if taken into account) is to boost the events in the transverse plan, according to a known distribution in pT25 Idea: apply MEM to reconstruct the mass of the Higgs or reconstruct the fraction of signal[[br]]events **g>UNDER CONTROLLED CONDITIONS.**[[br]][[br]]"under controlled conditions" means that the events in the prepared samples follow EXACTLY the probability [[br]]distribution function that is used to evaluate the matrix element weights.[[br]][[br]]In this way, one can set up the calculation of the weights and check that [[br]]NO BIAS is observed in the final result, and hence validate the whole procedure in the absence of systematic errors. [[br]]The procedure for the calculation of the weights should be the same as the one used later on for the second step [[br]](i.e. one should consider a finite resolution on jet energies, correct for ISR if necessary, ...)[[br]][[br]]Only the samples of events are prepared in an artificial way so that we control exactly how the events are distributed in phasespace.[[br]]In particular: [[br]] the energy of the finalstate partons are smeared exaclty according to the shape of the transfer functions[[br]]  the effect of ISR (if taken into account) is to boost the events in the transverse plan, according to a known distribution in pT 26 26 27 27 The idea is that once this procedure is validated, it can be used in a reliable way for the pheno study. 28 28 29 The subsection below gives the <strong> work plan</strong>for the validation procedure29 The subsection below gives the**g> work plan** for the validation procedure 30 30 ===== A. Reconstruction of m_H (signal events only) ===== 31 31 ====== 1. Parton level + infinite resolution (DONE) ====== 32 32 33 Reconstruction of the mass of the Higgs using a pure sample of partonlevel signal events, and considering a narrow transfer function <br />for jet energies <br /><br />This is done (Priscilla): there is no bias in the reconstructed mass of the Higgs >OK33 Reconstruction of the mass of the Higgs using a pure sample of partonlevel signal events, and considering a narrow transfer function[[br]]for jet energies [[br]][[br]]This is done (Priscilla): there is no bias in the reconstructed mass of the Higgs > OK 34 34 35 35 ====== 2. Parton level + finite resolution (DONE) ====== 36 36 37 generation of a partonlevel event sample (no showering), smearing of the partons energies according to a "broad" transfer <br />function, reconstruction of the mass of the Higgs with the same TF that has been used to smear the parton energies.\\<br /><br />Things to keep in mind:38 * when we smear the energy of the partons, we are forced to apply some cuts on jet energies <br />>one should include the acceptance term in the likelihood.39 * to save some time, we are now considering only the gluongluon initiated process (for this <br />sanity check phase, it is ok). But then we should also consider '''only''' the gluongluon initiated process<br />when generating the partonlevel events. Otherwise we may introduce a bias.40 * one should also check the convergence for the evalutation of the matrix element weights in the regime where <br />the resolution on bjet energies is much worse than the width of the Higgs.<br />This is a delicate point, because the Higgs decay process %$ H \rightarrow b \bar b$% is overconstrained.<br />By default madweight consider 2 integration channels:37 generation of a partonlevel event sample (no showering), smearing of the partons energies according to a "broad" transfer[[br]]function, reconstruction of the mass of the Higgs with the same TF that has been used to smear the parton energies.\\[[br]][[br]]Things to keep in mind: 38 * when we smear the energy of the partons, we are forced to apply some cuts on jet energies[[br]]> one should include the acceptance term in the likelihood. 39 * to save some time, we are now considering only the gluongluon initiated process (for this[[br]]sanity check phase, it is ok). But then we should also consider '''only''' the gluongluon initiated process[[br]]when generating the partonlevel events. Otherwise we may introduce a bias. 40 * one should also check the convergence for the evalutation of the matrix element weights in the regime where[[br]]the resolution on bjet energies is much worse than the width of the Higgs.[[br]]This is a delicate point, because the Higgs decay process $ H \rightarrow b \bar b$ is overconstrained.[[br]] By default madweight consider 2 integration channels: 41 41 1. in channel 1, the invariant mass of the Higgs is mapped onto one variable of integration, 42 1. in channel 2, the energies of the bquarks originating from the Higgs are mapped onto 2 variables of integration, <br />but the invariant mass of the Higgs is not.42 1. in channel 2, the energies of the bquarks originating from the Higgs are mapped onto 2 variables of integration,[[br]] but the invariant mass of the Higgs is not. 43 43 44 44 When the width of the Higgs is orders of magnitude smaller than the resolution in jet energies, we expect that channel 1 is the most appropriate. This is indeed the case. But I also observed that running with \textbf{only} channel 1 makes a big difference: when I compare the values of the weights calculated with the onechannel integrator and with the twochannel integrator, the weights are systematically underestimated in the second case. The difference is quite sizable when we look at the likelihood: the difference is roughtly 4 units of $Log(L)$. So I would suggest to run MadWeight with only one channel of integration (the first one). This can be done by copying the files main_code_one_channel.f and data_one_channel.inc (available in the drop box) in the MW_P1_gg_bbxbmu+vmbxmuvmx. … … 63 63 === IV. Pheno study === 64 64 65 <br />  Redo the analysis, but with samples of events that are as realistic as possible. <br /><br /> Evaluate all the systematic uncertainties.65 <br />  Redo the analysis, but with samples of events that are as realistic as possible.[[br]][[br]]  Evaluate all the systematic uncertainties. 66 66 === V. Inputs of the analysis === 67 67 68 <br /> <br />We will do the analysis for the LHC at '''14 TeV'''.<br />There are several input parameters that need to be fixed right now.<br /><br />Even during the validation procedure, it will be very useful if we <br />consider realistic values the parameters associated with the <br />finalstate cuts, the reconstruction efficiencies, <br />the btaggings and the energy resolution.<br />In such a way, the significance that we will obtain<br />at the end of the validation procedure will not be completely unrealistic,<br />and this will give us some insights to jump into the second part<br />(e.g. if we find that the significance is extremely low for a given <br />signature even under ideal conditions, it may not be worth to push <br />the analysis further for this signature.)68 <br />[[br]]We will do the analysis for the LHC at '''14 TeV'''.[[br]]There are several input parameters that need to be fixed right now.[[br]][[br]]Even during the validation procedure, it will be very useful if we [[br]]consider realistic values the parameters associated with the [[br]]finalstate cuts, the reconstruction efficiencies, [[br]]the btaggings and the energy resolution.[[br]]In such a way, the significance that we will obtain[[br]]at the end of the validation procedure will not be completely unrealistic,[[br]]and this will give us some insights to jump into the second part[[br]](e.g. if we find that the significance is extremely low for a given [[br]]signature even under ideal conditions, it may not be worth to push [[br]]the analysis further for this signature.) 69 69 70 70 For the theoretical parameters, we can stick to the default param_card.dat file on the web. 71 71 ===== A. Cuts ===== 72 72 73 <br />We need to agree on a set of cuts to be applied on the jets and on the leptons. <br />I think a resonable set of cuts are (see http://arxiv.org/pdf/1106.0902.pdf)73 <br />We need to agree on a set of cuts to be applied on the jets and on the leptons.[[br]]I think a resonable set of cuts are (see http://arxiv.org/pdf/1106.0902.pdf) 74 74 75 pT(jets) > 30 GeV, eta(jet)<2.4 delta R (p_i,p_j) >0.3 with p_i, p_j =jet or lepton75 pT(jets) > 30 GeV, eta(jet)<2.4 delta R (p_i,p_j) > 0.3 with p_i, p_j =jet or lepton 76 76 77 pT(e) > 20 GeV, eta(e)<2.5, pT(mu)> 30 GeV, eta(mu)<2.577 pT(e) > 20 GeV, eta(e)<2.5, pT(mu)> 30 GeV, eta(mu)< 2.5 78 78 79 <br /> <br /><em>Partonlevel cuts vs reconstructedlevel cuts</em>:<br /><br />In the validation procedure, partonlevel cuts are different from reconstructedlevel cuts<br />because:<br />  partonlevel events are boosted in the transverse plan (if ISR is taken into account) <br />  finalstate parton energies are smeared according to the shape of the transfer function<br /><br />So one need to apply looser cuts at the partonlevel, and then apply the correct set of cuts <br />at the "reconstructed level".79 <br />[[br]]<em>Partonlevel cuts vs reconstructedlevel cuts</em>:[[br]][[br]]In the validation procedure, partonlevel cuts are different from reconstructedlevel cuts[[br]]because:[[br]]  partonlevel events are boosted in the transverse plan (if ISR is taken into account) [[br]]  finalstate parton energies are smeared according to the shape of the transfer function[[br]][[br]]So one need to apply looser cuts at the partonlevel, and then apply the correct set of cuts [[br]]at the "reconstructed level". 80 80 ===== B. Transfer function ===== 81 81 82 <br />For the parametrization of the transfer functions, <br />we can stick to the usual asumptions: a superposition<br />of two Gaussian distributions for the energy of the jets, <br />a delta function for all other visible quantities.82 <br />For the parametrization of the transfer functions,[[br]]we can stick to the usual asumptions: a superposition[[br]]of two Gaussian distributions for the energy of the jets, [[br]]a delta function for all other visible quantities. 83 83 84 84 The parametrization of the TF for jet energies is given by … … 86 86 87 87 88 with %$ \delta=E_pE_j $% (partonlevel energy minus reconstructed energy).It would be good to choose values for the parameters<br /> The parameters %$p_i$% can be assumed to depend linearly on the '''partonlevel''' energy (%$ p_i=a_1+b_i*E_p $%).88 with $ \delta=E_pE_j $ (partonlevel energy minus reconstructed energy).It would be good to choose values for the parameters[[br]] The parameters $p_i$ can be assumed to depend linearly on the '''partonlevel''' energy ($ p_i=a_1+b_i*E_p $). 89 89 90 90   '''a_i'''  '''b_i'''  … … 95 95  p_5  XXXX  XXXX  96 96 97 It would be good to choose values for the parameters %$a_i, b_i$% in the TF that capture the typical resolution of the <br />CMS detector. Olivier, do you think you could get these values ?97 It would be good to choose values for the parameters $a_i, b_i$ in the TF that capture the typical resolution of the [[br]]CMS detector. Olivier, do you think you could get these values ? 98 98 99 99 ANSWER from Olivier: