Changes between Initial Version and Version 1 of LightPseudo

Timestamp:

Mar 20, 2012, 4:18:02 PM (12 years ago)

Author:

trac

Comment:

--

LightPseudo

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+
+
+== %$ 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$% is much heavier than light fermions). Anyway, if it's not true, all signal xsec should simply be scaled by this Br.
+
+We also assume that %$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)$% type II models like MSSM.
+
+The total BR for the decay chain %$ 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$% but heavy enough to give a good pT and a good separation for b's and tau's.
+
+=== Monte Carlo production ===
+
+==== Methodology ====
+
+Signal and backgrounds are generated separately using MG/ME v4.1. The PDF is CTEQ6L1 and the renormalization and factorization scales are set to 120 Gev. All the following generation cuts are applied. Jet means non b jets and leptons means e, %$\mu$% and %$\tau$%.
+
+   * Minimal pT of 20 Gev for the jets and 10 Gev for leptons and b's
+   * Maximum rapidity of 5 for jets and 2.5 for leptons and b's
+   * Minimal deltaR>0.3 for all objects
+   * Maximal invariant mass of 80 Gev for the tau's pair (to avoid the Z peak)
+   * Minimal invariant mass of 700 Gev for the two jets (VBF cut)
+   * Delta eta >4 for the two jets (VBF cut)
+
+==== Signal ====
+
+100k events with tau's decayed into leptons only: [http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/Decay/signal_out.lhe.gz Events]
+
+The cross section '''after tau decay''' into leptons is 9.5fb. There is '''no cut''' on the tau decay products. Plots before tau decay are [http://madgraph.hep.uiuc.edu/MadGraphData/mherquet@fyma.ucl.ac.be/PROC4/Events/run_06_plots.html here].
+
+If you need to split LHEF files, please use Software.SplitEvents
+
+==== Considered backgrounds ====
+
+===== Irreducible: QCD %$2\tau 2b 2j$% background =====
+
+44k events with tau's decayed into leptons only
+[http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/Decay/bkg_2tau2b2j_out_out.lhe.gz Events]
+
+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 =====
+
+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.
+
+A 25k events '''muon''' sample: [http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/PROC7/Events/bkg_2mu2b2j_1.lhe.gz Events]  
+
+Another 26k events '''muon''' sample
+[http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/PROC7/Events/bkg_2mu2b2j_2.lhe.gz Events]
+
+I propose to use one of these two '''muon samples''' as an electron sample (just need to switch the PDG code in the LHEF file since the kinematic is the same).
+
+Some [http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/PROC7/Events/run_02_plots.html Plots] for the whole 50k sample.
+
+===== Reducible tt + 2j with t>Wb and both W going to e, mu or tau and tau going to e or mu  =====
+
+
+A 100k event sample with W's in e or mu (xsec=2300fb): [http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/Decay/run_03_unweighted_events_out.lhe.gz Events]
+
+A 50k event sample with W+ in tau's (and tau+ in e or mu) and W- in e or mu (xsec=404fb):
+[http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/Decay/run_04_1_unweighted_events_out.lhe.gz Events]
+
+A 50k event sample with W- in tau's (and tau- in e or mu) and W+ in e or mu (xsec=404fb):
+[http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/Decay/run_04_2_unweighted_events_out.lhe.gz Events]
+
+A 50k event sample with W- and W+ in tau's (and tau's in e or mu) (xsec=70fb): [http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/Decay/run_04_3_unweighted_events_out.lhe.gz Events], another one [http://madgraph.phys.ucl.ac.be/MadGraphData/mherquet@fyma.ucl.ac.be/Decay/run_04_4_unweighted_events_out.lhe.gz Events] 
+
+Without any cut on leptonic final state, the total xsec is 3200 fb! But the kinematic is '''very''' different for both leptons pairs and b pairs, large invariant masses and large deltaR are typically preferred. Also, there is a lot (half of it if I'm right) of mismatched pairs e-mu (instead of e-e or mu-mu) which should be easy to remove. The amount of Et is also typically much higher (neutrinos are coming from W's), so a max Et cut should also be rather efficient. So there is maybe a hope...
+
+==== Not considered backgrounds ====
+
+===== QED (i.e. alpha_EW^4) backgrounds =====
+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 =====
+
+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. 
+
+==== Summary of the situation... ====
+A 10fb signal with a 1fb irreducible bkg, two 9fb nearly irreducible background which could be efficiently cut by a mass window on leptons and a delta R cut on b's. A huge 3.2 pb tt background with very different kinematic but same final state...
+
+=== 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!).
+
+==== Les Houches 02 proceeding: ====
+[http://arxiv.org/abs/hep-ph/0203056 Azuleos]
+
+==== ATLAS notes ====
+[http://doc.cern.ch//archive/electronic/cern/others/atlnot/Note/phys/phys-2002-018.pdf phys-2002-018]
+[http://doc.cern.ch//archive/electronic/cern/others/atlnot/Note/phys/phys-2003-004.pdf phys-2002-004]
+
+==== Parton level Papers: ====
+
+   *  [attachment:e014037.pdf PRD59 014037]
+
+   *  [attachment:e093005.pdf PRD61 093005]
+
+PLB454 297
+
+==== CMS  ====
+
+To be checked: Physics TDR and Notes
+
+=== 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.
+
+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%). 
+
+=== Final Version of our paper ===
+
+   * [attachment:VBF_hAA2b2ta.pdf pdf]: Our contribution to Les Houches Proceedings
+ 
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