Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Progress With Jet Studies Dan Clements

Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Summary Errors on Inclusive Jet Cross-Section (study with NLOJET) Disagreement between JETRAD and NLOJET has been resolved. Work currently being written up for ATLAS note. Pseudo-Data Generation For ATLAS Data sets for the Inclusive Jet Cross-Section have been created and smeared for statistics and Jet Energy Scale, available at: Grids For NLO Jet Cross-Section Calculations Code currently under development and testing.

Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Grids For NLO Jet Cross-Section Calculations (1) Background: At a hadron-collider the cross-section for a hard 2-hadron scattering process is given by: Hadron momenta PDFs Parton Level Cross-Section, (the bit theorists worry about) Sum over parton types Parton momenta

Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Grids For NLO Jet Cross-Section Calculations (2) Problem: Generating NLO Cross-Sections takes a long time (~days). For PDF fitting need to create lots of cross-section predictions (for different PDFs) to compare with experimental data. Solution: Attempt to split the cross-section calculation into two pieces, so that the parton-level cross-section is calculated independently of the PDFs. Create a grid of weights in (x 1,x 2,Q 2 )

Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Grids For NLO Jet Cross-Section Calculations (3) NLOJET event generator Event with weight w i, x 1, x 2, Q 2 Fill Grid with weight w i, at point (x 1,x 2,Q 2 ) Step 1: Fill the Grid Grid of weights in (x 1,x 2,Q 2 ) PDFs defined at (x 1,x 2,Q 2 ) Jet Cross-Section Multiply and add over (x 1,x 2,Q 2 ) Step 2: Multiply grid by PDFs to generate Cross-Section

Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Grids For NLO Jet Cross-Section Calculations (4) Step 1 is slow, but step 2 is fast allowing for a variety of PDFs to be used to generate cross-sections quickly. Grid is finite and introduces errors into the calculation. Current Work: Using and developing code from Tancredi Carli to calculate grids for the Inclusive Jet Cross-Section. Finding an optimum grid size for cross-section calculations (i.e. accuracy vs computer memory). Modifying code to allow for efficient step1 production, error analysis and implementation of different PDFs.

Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Grids For NLO Jet Cross-Section Calculations (5) Progress Studies indicate that a (30×30×30) grid in (x 1,x 2,Q 2 ) can create inclusive jet cross-sections at ~0.5% accuracy. Step 1 generation takes a long time due to statistical errors from NLOJET. Code has been developed to perform step 1 on multiple nodes for efficient production. Variable histogram bins in pT implemented to reduce statistical errors in NLOJET. Error analysis on grids under development. Trial PDF fitting being carried out by Claire Gwenlan.

Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Grids For NLO Jet Cross-Section Calculations (6) LHAPDF interface to (step 2) created agreement with pure NLOJET (older version) good ~1% CTEQ6.1

Dan Clements – Jan 2006 Glasgow ATLAS physics meeting Grids For NLO Jet Cross-Section Calculations (6) CTEQ6.1