Tevatron Photon Measurements Summary of photon results Inclusive

Tevatron Photon Measurements • Summary of photon results – Inclusive photon production • cross section at 1800 Ge. V • cross section at 630 Ge. V – Exclusive photon production • gamma plus gamma • gamma plus charm 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 1

Tevatron Photons 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 2

Photon Measurements • Background Evaluation: – CDF • Lateral shower shape goodness of fit (best below 35 Ge. V) • Conversion rate in the coil – D 0 • “Early” energy deposition in the electromagnetic calorimeter 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 3

Background Subtraction CDF • Goodness of lateral shower fit (p 0 broad) • Count conversions in coil 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 4

1800 Ge. V Cross Section D 0 • Fit E 1 = energy in first calorimeter section • two background components (b, c) • photons (a) 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 5

1800 Ge. V Cross Section CDF pp 0 mass D 0 result 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 6

1800 Ge. V Cross Section D 0 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 7

CDF 630 Ge. V Cross Section 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 8

630 Ge. V Cross Section CDF • Goodness of lateral shape • Conversion rate Independent methods with different strengths Simple “efficiency” 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 9

Photon Scaling Good agreement with UA 2 results 29/4/00 Some systematic differences with theory (the usual Kt shape) Robert Blair (ANL) DIS 2000 Liverpool 10

Jet Scaling • Taking different renormalizations scales in theory for 630 vs 1800 Ge. V produces good quantitative agreement between D 0 data and NLO QCD • Mangano proposes an O(3 Ge. V) non-perturbative shift in jet energy (losses out of cone, underlying event, intrinsic k. T) Could be different for D 0 data. Ratio of Scale Invariant Cross Sections sd(630)/sd(1800) vs x. T 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 11

Photon Scaling 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 12

Diphotons Resummed results are in good agreement with data This rightfully serves as a measure of soft emission effects 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 13

Photon Plus Muon (c, b) CDF 1760 events mu pt > 4 Ge. V |eta|<1. 0 12<gamma pt<40 Ge. V Et (cone. 4)<2 Ge. V 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 14

Photon Plus Muon NLO calculation by Berger, Bailey and Gordon 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 15

Conclusions • Soft physics (Kt/soft emissions) play a role in many of the photon measurements – Understanding these would help • Luminosity (Run. II) will help – All photon measurements will benefit significantly from more events 29/4/00 Robert Blair (ANL) DIS 2000 Liverpool 16