Investigating the Production of W and Z bosons at LHCb Stephanie Donleavy

Will look at: Numbers of bosons produced W and Z production and decay mechanisms Compare to theory

Mainly b physics but many Ws and Zs produced as well. At an integrated luminosity of 500 pb -1: –1.5 x 10 6 W + s, 9.4 x 10 5 W - s –1.2 x 10 5 Z 0 s (In the LHCb acceptance) At LHCb

Bosons produced at different angles depending on method of production: E.g. ➢ q + q -> forward ➢ q + q -> transverse In LHCb boson seen is mostly produced by q + q interactions

Principle decay modes: I will investigate muon channels

Histogrammed parameters: –Pseudorapidity –Rapidity –Angular Distributions –Transverse mass –Invariant mass Plotted for each boson and compared to theory. Theory paper used: Parton Distributions and the LHC : W and Z production. The European Physical Journal C, 14, (2000), A.D.Martin, R.G.Roberts, W.J.Stirling, R.S.Thorne Use mcfm-5.1 to generate data – A Monte Carlo for FeMto barn processes

Rapidity Theory Rapidity Distributions for Ws Rapidity: It is a measure of a particle's angle wrt the beam axis

Rapidity Results (Y-axes are just number of particles)

PDF sets - motivations In regions where the PDF is most accurate the most precise test of the standard model can be made In regions without accurate PDF sets, data input to theory to improve knowledge and prediction capability PDF sets used : cteq6m and mrst2001

Comparing different sets Different PDF sets have different errors for different regions of rapidity Due to different theoretical assumptions Program made to plot: pseudorapidity of lepton and / or neutrino rapidity of boson or lepton

The following graph was produced of rapidity to look at PDF errors in different regions Errors greater at central rapidities

Plots of Percentage error Percentage errors are much lower in central regions of rapidity Ratios mean that some unknowns cancel out so overall error is much less

Comparing MRST and CTEQ Plots were made of pull using the following definition: Overall Plot shown below: Width is not equal to 1 so separate plots were made for each process to analyse problem. Errors were found not to be independent.

Conclusions from PDF Sets PDF Sets found to be mostly within ~8% of each other's predictions. Main differences occurred in ratio plots at high values of rapidity / pseudorapidity - where there is a lack of data and theoretical assumptions are made. CTEQ errors generally larger than MRST – assumption of u-d sea ratio Plots made of Pull vs Pseudorapidity for each process:

Further Plans: For continuation to thesis, ~2.5 fb -1 of data expected Use LHCb code Look at selection of W/Z candidates Understand trigger and background

EXTRA PLOTS

Angular distribution: Theta is the angle of the lepton's direction with respect to the boost direction in the rest frame of the W.

Acceptances 13.9Z0Z0 24.1W-W- 27.6W+W+ Boson LHCb acceptance is in Pseudorapidity Acceptance (%) Cross- section (nb) / / / Acceptance cuts are made on lepton From generator using cteq6m