physics:crosssection
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| - | ===== Calculation of the Cross Section ===== | + | ====== Calculation of the Cross Section ====== |
| + | ===== Introduction ===== | ||
| + | Note that the follwing numbers all depend on the settings of the Monte Carlo generator (Pythia, in this case), as none of the quantities has been measured to a high accuracy at the LHC energy. | ||
| ===== 1. b bbar Cross Section ===== | ===== 1. b bbar Cross Section ===== | ||
| Note that the numbers for the b bbar cross section differ quite a lot, depending on where you look them up. | Note that the numbers for the b bbar cross section differ quite a lot, depending on where you look them up. | ||
| Often, **500 microbarn** is quoted. However, for the DC06 production, **698 microbarn** was used, where the MC09 production uses **1040 microbarn** for 14 TeV and **699 microbarn** for 10 TeV. | Often, **500 microbarn** is quoted. However, for the DC06 production, **698 microbarn** was used, where the MC09 production uses **1040 microbarn** for 14 TeV and **699 microbarn** for 10 TeV. | ||
| + | |||
| + | ===== 2. Hadronization ===== | ||
| + | A b quark hadronizes with a certain probability into different sorts of B mesons. In **DC06**, these are: | ||
| + | * B+/B-: 40.5% | ||
| + | * B0/B0bar : 40.5% | ||
| + | * Bs0/Bs0bar: 10% | ||
| + | * b Baryons: 9% | ||
| + | |||
| + | In **MC09**, these are: | ||
| + | * B+/B-: 41% | ||
| + | * B0/B0bar : 41% | ||
| + | * Bs0/Bs0bar: 10.5% | ||
| + | * b Baryons: 7.5% | ||
| + | |||
| + | ===== 3. Factor of 2 ===== | ||
| + | As your b-quark as well as your bbar-quark may hadronize into your decay, you have to multiply the decay with a factor of 2. | ||
| + | |||
| + | ===== 4. Branching Fraction of your Decay ===== | ||
| + | The get the cross section for your decay, you have to know the branching fraction of the corresponding B-meson to the desired final states (which can be found in the PDG or the EvtGen decay table). | ||
| + | |||
| + | ===== 5. Acceptance / Efficiency ===== | ||
| + | Depending on what you want to calculate you also have to take into account the acceptance of the detector and the efficiency of the reconstruction. | ||
| + | The cut that is applied in Pythia to generate events that mostly decay in the LHCb detector (angular acceptance of 400mrad) is about 34.7% for B mesons and 43.2% for b bbar inclusive. | ||
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| + | ===== Summary ===== | ||
| + | The formula then is: | ||
| + | b bbar cross section * 2 * f_had * branching fraction * efficiency and acceptance. | ||
| + | |||
| + | The yield can the be calculated by multiplying it with the integrated luminosity. | ||
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| + | |||
| + | ===== Links ===== | ||
| + | The numbers used for DC06 production can be found [[https:// | ||
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physics/crosssection.1244536995.txt.gz · Last modified: 2009/06/09 10:43 by decianm
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