1. Where did all the protons go? Mike Lamont LBOC 20 th January 2015

2. Total cross section Elastic: (27.1 +/- 1.4) mb; Inelastic: (74.7 +/- 1.7) mb. 2

3. 14 TeV Inelastic: – 80.9 ± 1.7 (TOTEM 7 TeV meas.) ± 2.2 (extr. to 14 TeV) mb (c/o of ATLAS/CMS) Elastic: – TOTEM's latest fit to the elastic cross-section gives 30.2 mb at 14 TeV. Total cross-section: – 111.1 mb plus/minus errors 3

4. Inelastic includes diffractive 4 1 proton survives with momentum loss . Some of these will either stay within the beam or get lost in the DS or IR3 Cross-sections for different momentum lost ranges can be evaluated Assume herein that all get lost locally Non-diffractive processes: ~60 mb at 7-8 TeV

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6. Elastic scattering 6

7. 7 Mean t? Straightforward integral

8. Elastic scattering mean scattering angle 8 Slope parameter b~19.9 GeV^-2 √s8000 GeV rms scattering angle – one plane39.6 microrad The elastically scattered protons stay within the beam. ~22.6 microrad at 14 TeV

9. Elastic scattering emittance growth 9 Initial ES growth rate: 1.2%/hour 27.1 mb

10. IBS Transverse emittance – Effective emittance from luminosity – Assume vertical ~ horizontal (not totally satisfactory…) dispersion, coupling… MD (Maria Kuhn) collimator diffusion measurements (G. Valentino et al) luminous region size Longitudinal emittance – From bunch length, RF voltage etc. Bunch current Trundle through fill – every hour ask MADX what the IBS growth rates are 10

11. ES and IBS 11 Fill27103192 ES1.2%/hour IBS3.6%/hour2.8%/hour Initial growth rate 5.8%/hour6.4%/hour ES&ISB/Total83%63% Majority of emittance growth explained by ES and IBS Additional source(s) post OPC… But growth rate not hugely different before and after OPC ES+IBS Emittance from lumi MADX pts Warning: derived emittance input into IBS calculation and H=V

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13. Luminous region 13 H V

14. Emittance growth rate not hugely different before and after OPC 14 2710 3363 Would not expect IBS and ES to be OPC dependent… It’s reproducible and quite moderate And it is not the major contributor to the luminosity lifetime

15. Calculate loss rates Luminosity – calculate losses based on inelastic cross- section at 4 TeV – 75 mbarn – ATLAS, CMS, LHCb Use “squeeze” calibration factor to establish other losses, principally IR7 – while recognizing some losses to IR3 (see below) Ignore for the moment: – residual gas; small diffractive component Sum loss rates to get overall dN/dt Calculate lifetimes etc. 15 Lifetime Analysis at High Intensity Colliders Applied to the LHC B. Salvachua, R.W. Aßmann, R. Bruce, F. Burkart, S. Redaelli, G. Valentino, D. Wollmann IPAC 2013

16. Loss breakdown 16 LumiColl B160%40% B253%47%

17. Loss breakdown 17

18. Cross-check 1/2 18 Note same factor used for both B1 and B2 – optimization possible Where’s the difference coming from?

19. Cross check 2/2 19 Good agreement Note low IR3 losses both beams

20. Loss breakdown 20 Most non-luminosity related losses into IR7 – confirmed by Belen (see below) Significant % of beam going into collimators both before and after OPC Situation clearly worse after OPC Cross checks with delivered luminosity BCT doesn’t lie (much)

21. Belen@LMC 21

22. Luminosity lifetime breakdown 22 Dominated by losses rather than emittance growth

23. So… Relatively gentle core emittance growth given by IBS and elastic scattering and a bit of something else(s) Calibrated proton losses at IR7 plus luminosity losses approximately equal to delta BCT Losses in IR7 are not ES Losses in IR7 are not (core) emittance growth But we were sticking a fair bit of beam into IR7 – worse after OPC, high Q’, higher bunch population, octupoles.. 23

24. Start of fill – a closer look 24 1.3 s running sum Adjust and Stable beams – first hour

25. Start of fill – a closer look 25

26. Losses versus intensity 26 Further optimization of octupoles and chromaticity might have been possible. But wait for the first 20 minutes to pass 2710: peak lumi 6.76e33 3192: peak lumi 6.66e33

27. Versus BBTS 27 “Beam-beam limit phenomenon is observed in degradation of luminosity lifetime and/or beam lifetime in hadron colliders.”

28. BCT! 28 1.5e10 p/s 1.95e9 p/s 8.5e9 p/s 2.8e9 p/s Reference: 7x10 33 x 75x10 -27 x 2 = 1.1e9 p/s

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30. FZ & YP 30 Dependence of diffusion due to long-range collisions on the beam current: (a) the change of action variance per turn as a function of the bunch population; (b) approximate diffusive aperture as a function of the bunch population; Nominal LHC – we were at 4 TeV, 50 ns, high bunch population, high HO beam-beam shift… (HL-LHC?)

31. For discussion… Collide – DA comes down – Anything out in the tails is going to get murdered Steady state – A lot of beam is being pushed out into the tails and onto the collimators – Exacerbated by high chromaticity, high bunch intensity and possibly octupoles – To get that many particles out there, the diffusive aperture would have to be pretty small… 31