1. Turtle ray interactions with the EMC Tim West University of Manchester

2. Outline What are turtle rays? What are turtle rays? About the simulated data About the simulated data Low energy ring results Low energy ring results High energy ring results High energy ring results Future plans Future plans

3. What are turtle rays? Coulomb and Bremsstrahlung related processes cause e − and e + in the beam to move off axis. Coulomb and Bremsstrahlung related processes cause e − and e + in the beam to move off axis. These ‘turtle rays’ then interact with material around the detector; the support structure, magnets and beam pipe itself. These ‘turtle rays’ then interact with material around the detector; the support structure, magnets and beam pipe itself. This interaction can produce an EM shower which is then picked up in the Calorimeter. This interaction can produce an EM shower which is then picked up in the Calorimeter. This shower can then add energy to digis produced by collisions. This shower can then add energy to digis produced by collisions.

4. About the simulated data Results presented here were produced from Monte Carlo data simulated in January of this year. Results presented here were produced from Monte Carlo data simulated in January of this year. The number of entries in plots may include events which produce no hits in the EMC. The number of entries in plots may include events which produce no hits in the EMC. LER results are for 2000 events per ntuple; HER results tend to for slightly less due to batch jobs timing out. LER results are for 2000 events per ntuple; HER results tend to for slightly less due to batch jobs timing out. Concentrate on the turtle rays produced in Coulomb scatters as these cause the most background. Concentrate on the turtle rays produced in Coulomb scatters as these cause the most background.

5. LER results Of 2000 events, only 278 produce the 2049 digi hits. Of 2000 events, only 278 produce the 2049 digi hits. Small number of hits in the endcap are concentrated in the inner rings. Small number of hits in the endcap are concentrated in the inner rings. Forward region of barrel has more hits that backward region. Forward region of barrel has more hits that backward region. No large variation over phi. No large variation over phi. Primary PEP hits are concentrated around the skew quad and quadrupole-2 magnets at front and rear ends. Primary PEP hits are concentrated around the skew quad and quadrupole-2 magnets at front and rear ends. Large peak at 556cm – has a 0.5mm spread. Large peak at 556cm – has a 0.5mm spread.

6. HER results

7. HER results (continued) Of the 1279 events, 676 produce 7016 digis in the EMC. Of the 1279 events, 676 produce 7016 digis in the EMC. A further 201 digis come from 80 events which have no pep hit; there are another 131 events with no pep hit or emc digis. A further 201 digis come from 80 events which have no pep hit; there are another 131 events with no pep hit or emc digis. Large excess of digi hits in the eastern quadrant of the detector. Large excess of digi hits in the eastern quadrant of the detector. Slight excess of digis in the top quadrant for pep hits further from the IP. Slight excess of digis in the top quadrant for pep hits further from the IP. Peak in hits in endcap – pep hits further from the IP produce very few hits in the barrel. Peak in hits in endcap – pep hits further from the IP produce very few hits in the barrel.

8. HER results (continued) Moving the pep hit closer to the IP increases proportion of hits in the barrel (excess in rear portion). Moving the pep hit closer to the IP increases proportion of hits in the barrel (excess in rear portion). Digi multiplicity increases rapidly as the pep hit moves towards the IP, peaking in the region of the septum. Digi multiplicity increases rapidly as the pep hit moves towards the IP, peaking in the region of the septum. PEP region (cm) N EMC N PEP N EMC /N PEP z<-4705172562.5 -470<z<-35014102177.1 -350<z508919126.6 Septum14283540.8

9. HER results – the septum Classify septum pep hits as those between 240cm and 285cm upstream of IP. Classify septum pep hits as those between 240cm and 285cm upstream of IP. Fairly small number of hits on the septum – very high digi multiplicity though. Fairly small number of hits on the septum – very high digi multiplicity though. Very few hits in the endcap – large excess towards the rear portion of the barrel. Very few hits in the endcap – large excess towards the rear portion of the barrel. Septum hits produce around 30% of the digis in the rear portion of the barrel. Septum hits produce around 30% of the digis in the rear portion of the barrel.

10. HER results (continued) These results are for zone 2 scattering events (26-42m upstream of IP). These results are for zone 2 scattering events (26-42m upstream of IP). Zones 3 (42-66m) and 4 (66m upwards) do not appear to show any hits in the region of the septum. We also see: Zones 3 (42-66m) and 4 (66m upwards) do not appear to show any hits in the region of the septum. We also see: o Much lower digi multiplicity (average ~1.5 for both). o Large excess in the endcap. o Slight excess in the rearmost part of the barrel. Have only had a preliminary look at zone 3 and 4; not looked at zone 1 (4-26m upstream) at all – these are on my to-do list. Have only had a preliminary look at zone 3 and 4; not looked at zone 1 (4-26m upstream) at all – these are on my to-do list.

11. HER results (continued) None of these events cause a trigger to fire. None of these events cause a trigger to fire. Average cluster energy is 37/41/44MeV for zone 2/3/4; number of clusters decreases as zone number increases. Average cluster energy is 37/41/44MeV for zone 2/3/4; number of clusters decreases as zone number increases. Very few clusters over 100MeV (16/486 over all zones). Very few clusters over 100MeV (16/486 over all zones). Around a third of the digis are on the default digi list. Around a third of the digis are on the default digi list. Average default digi energy is under 10MeV. Average default digi energy is under 10MeV.

12. Future plans o Look at HER zone 0, 1, 3 and 4 turtle rays more closely. o Look at LER zones 0, 1, 2, 3 and 4 turtle rays - results here are for zone 5 (62-2196m upstream). o Look for similarities with single beam data.

13. Zone 1 HER coulomb Pep hit z/cm N EMC N PEP N EMC /N PEP z<-470 56 (517) 20 (256) 2.8 (2.5) -470<z<-350 252 (1410) 35 (217) 7.2 (7.1) -350<z 19497 (5089) 693 (191) 28.1 (26.6) Septum 1752 (1428) 48 (35) 36.5 (40.8) No triggers No triggers Similar digi/cluster energy distribution. Similar digi/cluster energy distribution.

14. Zone 1 HER coulomb

15. Zone 2 HER coulomb

16. Zone 3 HER coulomb

17. Zone 4 HER coulomb

18. Zone 1 Zone 2