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UK SM Physics Meeting Preliminary studies on the sensitivity to high x gluon's

UK SM Physics Meeting Preliminary studies on the sensitivity to high x gluon's. Ivan Hollins 30/11/05. Outline. 1) Summary physics processes 2) Expected event numbers for different kinematic ranges 3) Event kinematics 4) Pdf differences 5) Sensitivity to pdf differences 6) Conclusions

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UK SM Physics Meeting Preliminary studies on the sensitivity to high x gluon's

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  1. UK SM Physics MeetingPreliminary studies on the sensitivity to high x gluon's Ivan Hollins 30/11/05

  2. Outline • 1) Summary physics processes • 2) Expected event numbers for different kinematic ranges • 3) Event kinematics • 4) Pdf differences • 5) Sensitivity to pdf differences • 6) Conclusions • 7) Further work

  3. (1) Physics Processes - -jet • Use -jet events to probe the gluon • Aim to use this probe to discriminate between pdf sets Compton Annihilation

  4. (2) Event numbers for different Q2 and x values – 100pb-1 : |jet| < 4.9 , || < 3.2

  5. xa yd xb yc (3) Event Kinematics • Solving the Kinematics • Using pdfs for xa and xb can build up an expected event profile • For each point in yc, yd space can calculate the relative probability of an event from a gluon and any other parton pdf. • Plots p7, p8 are for Compton process only

  6. Probability map of Event distributions in  Q = 150 GeV • Compton process only • Agrees with event shapes as produced by Pythia • -jet occur preferentially in the same  region

  7. Q = 50 GeV • At increased Q the event shape contracts Q = 150 GeV • At high Q most, if not all the events should be observable in the detector Q = 350 GeV

  8.  distribution of -jet • Aim to extend pervious plots to include information about the xa / xb in the event • As Q increases will increase xa / xb used in the scatter, but where will these events appear? • Analysis • Use 4-vectors as given by Pythia • Plot  for  and jet together with value of xa and xb from the Truth • xa and xb is plotted for each jet and . This gives 4 entries per event.

  9. distributions for events with  and jet • PT > 50, 150, 350 GeV. • Each plot shows xa and xb associated with an event twice. Once for jet and once for . • Events typically combine one high x and one low x parton. • At increasing energy events become narrower in  • Sensitivity to high x events comes at high energies and high .

  10. PT > 50 GeV

  11. PT > 150 GeV

  12. PT > 350 GeV

  13. (4) Difference in pdf sets • Evolution of CTEQ sets at Q = 104 • Variations most noticeable between Fermi2002_100 and others x > 0.1. Should be most noticeable. • Other differences noticeable x > 0.2 (Zeus2005) and other x>0.3

  14. Cteq61 – all error sets 20 x 2 • 20 eigenvector parameterising the errors in Cteq61 • Biggest contribution for the error comes from eigenvector 15 – sets 29 and 30.

  15. (5) Observable differences in pdf sets • Use 4-vectors as given by Pythia • Basic kinematic cuts • PT > 110, 330 GeV • Comparing visible  ranges • Pdf sets used • Cteq61 – central value and error set 29 / 30 • MRST2004nlo • Zeus2005_ZJ • Plots are for photon distributions only • ~700k events in each ~ 700pb-1 (110GeV) and ~ 70fb-1 (330 GeV) • Plots look only at the shape, no comparison made to absolute numbers

  16.  - distributions for Zeus2005_ZJ and Fermi2002. PT > 330 GeV

  17.  - distributions for Zeus2005_ZJ and Cteq61. PT > 330 GeV

  18.  - distributions for MRST2004 and Cteq61. PT > 330 GeV

  19.  - distributions for Cteq61e29 and Cteq61e30. PT > 330 GeV

  20.  - distributions for Zeus2005_ZJ and Fermi2002. PT > 110 GeV

  21. - distributions for Zeus2005_ZJ and Cteq61. PT > 110 GeV

  22.  - distributions for MRST2004 and Cteq61. PT > 110 GeV

  23.  - distributions for Cteq61e29 and Cteq61e30. PT > 110 GeV

  24. Summary of Pdf Differences () • Differences are for the range || < 3.2 for both  and jet • Increasing PT / Q gives access to the tail of the  distribution and sensitivity to high x

  25. (6) Summary • There will be a reasonable event numbers in Q2 ranges up to ~400 GeV • High x events are kinematically accessible by looking at high  • Difference in pdf’s are most apparent at high x and manifest themselves most predominately in the  distributions - noticeably an excess / reduction at high . • Differences of in the central – edge  distributions of 2 - 6% (110GeV) and 3 -15% (330GeV) are typical.

  26. Further work • Understand differences in pdf sets and select “appropriate” sets for further studies • Introduce more realistic cuts on  and jet. • || < 3.2 for  , || < 4.9 for jet, angle between - jet • Improve kinematic cuts to preferentially select out high x events • Extend analysis to include atlfast event simulation

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