1. Where do the protons go II? Mike Lamont LBOC 2 nd February 2016 Acknowledgements TOTEM in the first few slides

2. Total cross section 2

3. Cross sections 7 to 14 TeV 3 √selasticinelastictotalCOMPETE 725.4 ± 1.573.1± 1.398.6 ± 2.898 ± 5 827.1 ± 1.474.7 ± 1.7101.7 ± 2.9101 ± 5 1329.780.0109.7n/a 1430.280.9 ± 1.7 ± 2.2111.1111.5 ± 1.2 + 4.1 -2.1 7 and 8 TeV: TOTEM luminosity independent 14: extrapolation by ATLAS and CMS (inel)/TOTEM(el) 13: LPC scaling (inel) /TOTEM extrapolation (el) But good enough for government work

4. Inelastic includes diffractive 4 1 proton survives with momentum loss ξ 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 here that surviving protons get lost locally Non-diffractive processes: ~60 mb at 7-8 TeV

5. Elastic scattering 5

6. 6

7. 7 s: square of the center-of-mass energy √s = 13 TeV in 2015 Elastic Scattering A and B given by e.g TOTEM ~Elastic cross section

8. 8

9. Elastic scattering mean scattering angle 9 Slope parameter B (TOTEM 8 TeV value)~19.9 GeV -2 √s13000 GeV 0.05 GeV 2 rms scattering angle34.5 urad rms scattering angle – one plane24.4 urad Angular divergence at IP (80 cm, 3.5 um)25.1 urad What is the fate of the elastically scattered protons? Question 1: through what angle are protons scattered at the IP?

10. Angle through which protons are scattered at the IP Differential cross-section well described by Ae -Bt For the sake of this analysis cut off at t=0.53 – 4 orders of magnitude in differential cross-section – Integral of Ae -Bt out to t=0.53 very close to el. xsec Very few particles get scattered by these high angles 10 80 cm: minimum t accessible by RP at 5.5 sigma (say) in 2015: ~0.7 GeV 2 (~90 urad)

11. So… We have a distribution of angles at the IP characterized by the rms divergence Have the elastic cross section – and thus for a given luminosity the number of elastic events per second Have the differential cross-section for elastic scattering i.e. probability for scattering with a given angle Form a 2D Gaussian probability density function (pdf) for distribution of (x,x’) at IP (truncate at 6 sigma) Form a pdf for elastic scattering – truncate at t = 0.53 11

12. Toy Monte Carlo 1 In 1 second ~66,000 elastic collisions per 1.1e11 bunch with a luminosity of 5e33 cm -2 s -1 Take a 66,000 (x,x’) sample in 2-D Gaussian phase space For each particle, sample pdf, convert t to θ Randomize projection to get θ x Add scattered angle to x’ New distribution of angles/phase space 12 Vanishing small chance of multiple collisions Mean = 0.05 GeV^2 Mean = 24.2 urad

13. Phase space at IP 13 Remember - only looking at scattered particles, there’s another 1e11 out there

14. Phase space at IP 14

15. Toy Monte Carlo 2 Transport distributions to collimator (e.g vert) Number of particles outside n sigma? Apply one turn matrix a few times, remove and sum any lost particles (e.g. > 4 sigma) 15 “Lose” 400 – 500 particle/s above 4 sigma – Gaussian beam remember Gently populating tails ES will also gently clean non-Gaussian tails (to be quantified)

16. 90 m is a different story 16 10 minutes sample IP Roman Pot

17. 2.5 km! 17 An hour’s worth of ES

18. Emittance growth 18 Peak normalized emittance growth from elastic scattering in 2015 ~ 0.015 mm.mrad/hour See D.A. Edwards and M.J Syphers or A.W. Chao and M. Tigner

19. Loss rates during Stable Beams Luminosity – calculate losses based on inelastic cross- section at 6.5 TeV – Assume 80 mb for inelastic cross-section – Sum luminosity from ATLAS, CMS, LHCb Use SVD/losses at D,C,B, IR3 B1 & B2 to establish losses in collimation regions (see Belen) – (Or scaled 2012 calibration) Ignore for the moment: – residual gas; diffractive component Sum loss rates to get overall dN/dt Calculate lifetimes etc. 19

20. Beam losses from SVD analysis 20 Thanks to Belen, Mirko and Michal Wyszynski Sum components to get total losses Raw data SVD breakdown

21. Loss breakdown 2012 21 Before OCP After OCP Not SVD… Settings make a difference!

22. Loss breakdown 2015 22 Green: inelastic luminosity losses (ATLAS+CMS+LHCb) Pink: total number of elastically scattered protons – possibly not lost! Note high loss rate during 1 st hour… presumably tails – DA less than 5.5 sigma?

23. Cross-check losses versus BCT 23 After 8 hours Work in progress on the matrix Certainly some issues with B2

24. Single beam lifetimes 24 Fit to BCT data – sliding 10 minute window Lifetime from loss contribution from collimation and inelastic luminosity Note 1 st hour

25. Single beam lifetime breakdown 25

26. Luminous region (ATLAS) 26 OFFLINE data

27. Emittance from luminous region 27 Standard picture Emittances similar at t=0 as per 2012 Naively calculate corresponding emittances

28. Luminosity 28

29. Emittance from luminosity 29 -0.008 um/hour at t=0 -0.002 um/hour at t=22hr

30. Comparison of lumi and lumireg 30

31. Luminosity lifetime 31 Rolling 15 minute window Bit ratty because of the drifts

32. Luminosity lifetime breakdown 32 More-or-less makes sense Dominated by losses rather than emittance Emittance and F are both net positive bringing L(t) up

33. First hour v. BBTS 2012 33

34. First hour v. BBTS 2015 34 Hum…

35. Conclusions The majority of elastically scattered protons stay within the beam. Elastic scattering (ES) contributes to the emittance growth. Relatively high loss rate during 1 st hour of SB – Presumably tails – Cleaning effect of ES to be quantified – DA < 5.5 sigma? Losses later in the fill considerably down on 2012 – But still significant – If not ES then octupoles, Q’, e-cloud, beam-beam, WP? – If latter then diligent optimization in SB should be able to reduce these losses. The luminosity lifetime is brilliant! 35