1. Studies for Delayed Photon 10/9/8 1 Delayed Photons in the exclusive  +Met final state Dave Toback for the Delayed Photon Group* Texas A&M University *Apologies for not showing this to all members before showing it…

2. Studies for Delayed Photon 10/9/8 2  +Met excess The delayed photon excess is very exciting Lots of things for the authors to do before we can publish this Need to rule out prosaic explanations for excess at high times Try to get more evidence that we understand production Try to explain why excess doesn’t look asymmetric in CES Z Need to explain why there is no excess in  +jet+met Same with sideband

3. Studies for Delayed Photon 10/9/8 3 W  e   fake +Met Hypothesis An ensemble of Photon candidates that are more likely to fly across the detector will have a different timing distribution than photons coming from the usual Z and  distribution Picking “wrong vertex” produces Z=100cm

4. Studies for Delayed Photon 10/9/8 4 The Wrong Vertex Assumption Right vertex “Wrong” vertex Wrong distribution created from reconstructed W  e events (good track) Good model for physics that is produced in the same way W  e  events are produced W  e   fake +Met has a different production –Photon fake rate is Z and  dependent –Different timing distribution (under study with MC) –Sensitive to true Z distribution

5. Studies for Delayed Photon 10/9/8 5 Geometric effects in real data Lots of examples of this type of effect Look at real electrons and pick ones where we get the wrong vertex well separated from the true vertex Can calculate Et from right vertex and wrong vertex Case where Et correctly calculated>40 GeV, but incorrectly calculated (from wrong vertex)<40 GeV –Shifted by 700 ps –Huge asymmetry in events in [2,7] compared to [-7,-2]

6. Studies for Delayed Photon 10/9/8 6 Beam profile We know the MC’s don’t have the correct beam profile implemented We don’t have any good studies about the beam profile (in Z or time) at |Z|>>80 cm. Are things linear out there still? Satellites certainly aren’t linear-type behavior…. Mean Vertex time vs. Z also makes a difference

7. Studies for Delayed Photon 10/9/8 7 e   acceptance A Toy MC with a simple Z distribution with a Gaussian shape, a mean of 100 cm and an RMS produces a timing distribution centered at 2 ns

8. Studies for Delayed Photon 10/9/8 8 Putting it all together Toy MC Simulation with admixture of fake e  g where production is different the normal Z=0 beta* Looks about the same to me… Allowing smaller Z would just put more events under the right-vertex distribution so that’s ok too… Real MC in progress

9. Studies for Delayed Photon 10/9/8 9 More studies needed Fake rate of e   as a function of Z and  Understand beam outside |Z|>60 cm Work on both is in progress

10. Studies for Delayed Photon 10/9/8 10 Another Hypothesis:  +jet   +met  +jet where the jet went down the beam pipe which is high eta production –Low eta wouldn’t have Met Biased towards high Z again Photon Jet that went down the beam pipe Z=100cm Note: Photon always at large Z, opposite side to vertex Sideband more likely to produce vertex? Would need to study Study acceptance vs. vert Z

11. Studies for Delayed Photon 10/9/8 11 Direct Evidence of Large Z prod ? Would like a direct handle on the photon to see if there is any evidence that these “photons” are not coming from the beam line or the usual Z distribution CES-CPR pointing capabilities CPR pads are 12.5cm in Z by 5 degrees in phi Full MC studies nearly finished Can test with data W’s Started thinking about LSHR CES and CPR to get impact parameter and Z Vert

12. Studies for Delayed Photon 10/9/8 12 Plug Timing Timing in the Plug calorimeter to see if there is any evidence this is beam-gas interactions that produced fake tracks PEM and PHA

13. Studies for Delayed Photon 10/9/8 13 Not sure what to make of this

14. Studies for Delayed Photon 10/9/8 14 The To-Do list 1.Finish testing the W  e   fake +met hypothesis: W events that produce fake photons are biased towards Large Z vert and large  (not well modeled by wrong vertex estimate)  shifted timing distribution and excess Photon fake rate as a function of  and Z Better beam understanding MC study in progress to see if small systematic uncertainties in Z distribution could produce this effect since W has a large cross section 2.Z  e  selected using kinematic quanties only. NO tracking information on either leg: e  mass only 3.Direct evidence that these photons come from Large Z 1.CES-CPR 2.LSHR 4.Test  +jet   +Met hypothesis 5.Check timing in plug for non-collision sources

15. Studies for Delayed Photon 10/9/8 15 Conclusion Clearly the excess is an interesting thing and statistically significant Need to understand if this is something real or if it’s some forgotten but prosaic background before going public in any way –“Extraordinary claims require extraordinary evidence” – Carl Sagan Lots of tests to be done, –Work on things mentioned is in progress, but just starting… –“Roma non fu fatta in un giorno”

16. Studies for Delayed Photon 10/9/8 16 Back up slides

17. Studies for Delayed Photon 10/9/8 17 6: EMTiming behavior at High Lum Since we’re now in high luminosity we’ve been seeing funny behavior in the EMTiming system at very low levels. –Admem’s often read out zero –Fake rates go up –Overlaps are more likely when lots of min-bias collisions occurring at the same time –HADTDC showed noise at high rates

18. Studies for Delayed Photon 10/9/8 18 Collision or Not collision? Unlikely to be non-collision based –  should have seen in events without a vertex New source of physics? Anomalous  1 0 pair- production in GMSB SUSY (Toback & Wagner PRD 70, 114032 (2004)) –  If it were real then ~25% should have a jet and we would see this in  +met+jet –Rate W+Jet/Rate W = 0.25 Prosaic background? Obvious guess is that this is some SM collision that is poorly measured (and when it’s well measured it looks like something else)

19. Studies for Delayed Photon 10/9/8 19 Type of effect Seen before? Yes This effect dominates the PEM calibrations See CDFNote 7928 (2005) & Peter Wagner’s Thesis –CDF Note 8932, Appendix D (page 202) Need “ring corrections” to get the PEM calibrations right. When you look at W’s in the plug you get a mean offset by 0.5 ns because what “produced” the calibration sample wasn’t centered at vert Z =0 cm

20. Studies for Delayed Photon 10/9/8 20 Other places this shows up Opposite side makes a difference in wrong-vertex timing distribution vs. Z Would needs to be very large Z CDFNote 7960

21. Studies for Delayed Photon 10/9/8 21 Useful things to be working on… 1.MC study of  +jet to get rates 2.CES/CPR to see if there is evidence that the photons in the “excess region” point to non-beam line events Use what Z pointing we have

22. Studies for Delayed Photon 10/9/8 22 Work? A real MC would be needed, but if it’s  +jet the collisions with small vert Z would show up as  +jet and/or be symmetric in vert Z –Wrong-vertex timing distribution –If the photons were on the same side as the CES Z then high angle production would hit PEM and not be part of our sample

23. Studies for Delayed Photon 10/9/8 23 Gamma Met excess Low Z production  both go down the beam pipe? PEM Photon Jet that went down the beam pipe Z=0cm So… is either  +jet (low Z vert and low  ),  pem +jet (low vert and high  ) or  central CEM or PEM +met (high vert and high  ). Wouldn’t give g+met+jet I would guess, and g+jet would get swamped in SM background. Still need to think about this…

24. Studies for Delayed Photon 10/9/8 24 Study 3: MC acceptance Simple acceptance turn-on of an error function at 100 cm with a width of 10 cm would produce a timing distribution with a mean of 2ns. Can’t use current MC’s for rate and timing… next slides  +jet   +Met  +jet   +jet or  +jet+ met?

25. Studies for Delayed Photon 10/9/8 25 Toy MC Ran a toy MC to see if this could produce the effect –EMTsim Resolution 0.6 ns –Vertex Res 0.2 ns –Take into account time vs. Vert Z variation Does a nice job of reproducing expected right and wrong vertex distributions

26. Studies for Delayed Photon 10/9/8 26 What do we need to produce? The excess looks (to my eye) to be an Gaussian with a mean of 2 ns and an RMS of about 2 ns –(at least on the positive side) What Z distribution would produce this? –Take CES Z to be flat except required vertex on opposite side –Take into account t vs. Z and resolution

27. Studies for Delayed Photon 10/9/8 27 Do something simple A simple Z distribution with a Gaussian shape, a mean of 100 cm and an RMS of 10 cm does the trick