Status of the IHEP Studies for the ATLAS and CMS Very Forward Detectors

1. Status of the IHEP Studies for the ATLAS and CMS Very Forward Detectors I.Azhgirey, I.Baishev and I.Kurochkin IHEP, Protvino

2. Secondary Halo of Momentum Cleaningat FP420 Part I - I.Baishev, was presented on 28-29.09.2006 at FP420 simulation meeting.

3. Momentum cleaning removes the off-momentum protons ( p < p0 , d = 1–p/p0 > 0 ) to protect the arcs. The horizontal dispersionDxat the primary momentum collimator TCP is larger than in the arcs. Off-momentum orbits have a horizontal offset -Dx(s)·d with respect to the beam orbit. The off-momentum orbit touches the edgexTCPof the primary collimator when dcut -xTCP / Dx . Scattering in the TCP converts the primary halo to the secondary halo oscillating around the orbit of dcut Note that the secondary halo of the betatron cleaning (IR7) oscillates around the beam orbit (d=0) Momentum Cleaning Orbit of IR5 IR1 from TCP

4. Simulation: the tool and some technical details STRUCT code - beam losses in the proton synchrotrons Electromagnetic and nuclear scattering of high energy protons in “targets” (collimators etc.) Inelastic scattering - diffractive and non-diffractive production of protons with p < 0.7p0 Multi-turn tracking of the scattered protons through the accelerator lattice element by element until their absorption in the collimators or their loss at the apertures of other elements. The MAD output (elements sequence, lengths and k-values for “thick lense”, not the lattice functions) is used as the input lattice/optics. The lattice functions are reproduced very well. Here STRUCT was used to simulate the process of momentum cleaning starting from the impact of the primary halo at the primary momentum collimator. 20000 protons were tracked in each of these preliminary runs (nominal collision optics Beam1 and Beam2). The hits (x,x’,y,y’,p) at 420m downstream of IP1 and IP5 were recorded for every pass through these planes.

5. At the primary momentum collimator ( mx = my = 0 ) TCP Beam1 : Dx = 2.20m, dcut = 1.78×10-3 TCP Beam2 : Dx = 2.46m, dcut = 1.57×10-3 At FP420 ( fp1 – 420m downstream of IP1 , fp5 – 420m downstream of IP5) fp1 Beam 1 : Dx = 1.53m, mx = 49.25, my = 45.07 fp1 Beam 2 : Dx = 1.99m, mx = 17.87, my = 16.36 fp5 Beam 1 : Dx = 1.48m, mx = 16.99, my = 15.36 fp5 Beam 2 : Dx = 1.94m, mx = 50.11, my = 45.97 m – phase advance between FP420 and TCP in units of 2p. For the betatronic oscillations initiated by scattering in TCP : xb ~ sin mx , yb ~ sinmy Lattice and Optics Nominal Collision Optics Version 6.5 Beam 1 and Beam 2 Chromaticity correction – ON Beam crossing schemes – ON Betatron collimators in IR7 at n1 = 6 , n2 = 7 , nA = 10 (H,V) Tertiary collimators in IR1, IR2, IR5 and IR8 at n3 = 8.3 Momentum collimators in IR3 at n1 = 15, n2 = 18 , nA = 10 (V) , nA = 20 (H)

6. Off-momentum orbits in the dispersion suppressors IR1 IR5 from IP

7. Horizontal distribution of hits At FP420 the maxima of the halo horizontal density must be at x0 -Dx(420m)·dcut The horizontal (vertical) shape of the halo depends in particular on the phase advances mx ( my) For the betatronic oscillations initiated by scattering in TCP : xb ~ sin mx , yb~ sin my fp1 fp5

8. x-y map of hits Beam 1 : dcut= 1.78×10-3 Beam 2 : dcut= 1.57×10-3 sinmx = 0.999 sinmy = 0.431 Dx = 1.53m sinmx = -0.729 sinmy = 0.758 Dx = 1.99m ←fp1→ sx= 0.259mm sy = 0.156mm sx = 0.238mm sy = 0.161mm ←fp5→ sinmx = -0.063 sinmy = 0.790 Dx = 1.48m sinmx = 0.642 sinmy = -0.193 Dx = 1.94m

9. Secondary Halo of Momentum Cleaningat FP420 Part II – I.Baishev, final statistics for halo calculations.

10. Higher statistics : 2×106 events fp1

11. Higher statistics : 2×106 events fp5

12. Secondary Halo at ATLAS Lumi Part III – I.Baishev.

13. Roman pots at ~240 m downstream of IP1 ATLAS Lumi High b* Collision Optics Version 6.5 Beam 1 b* = 2625 m in IP1, b* = 1535 m in IP5 Chromaticity correction – ON Beam crossing schemes – OFF 43 bunches per beam 1010 protons per bunch Normalized emittance eN = 1.0 mm×mrad Betatron collimators in IR7 at n1 = 6 , n2 = 7 , nA = 10 (H,V) Momentum collimators in IR3 at n1 = 21, n2 = 25 , nA = 10 (V) , nA = 28 (H) Tertiary collimators - OPEN

14. Betatron Cleaning Secondary and tertiary halo. Vertical distribution of hits x-y map of hits with |y|>7sy

15. Momentum Cleaning Secondary and tertiary halo. Vertical distribution of hits x-y map of hits with |y|>7sy

16. Beam-Gas scattering Beam-gas scattering in the arcs and DS. Vertical distribution of hits x-y map of hits with y>|7|sy

17. Vertical distributions .

18. Local Beam-Gas at ATLAS Lumi Part IV – I.Azhgirey, I.Baishev and I.Kurochkin.

19. Model for Local Beam-Gas Interactions • Calculations: MARS/IHEP Code, v.106 • Model: Long SS1 from MQM.B7L to MQM.B7R (538 m) • Machine elements: VC, magnets, absorbers, vacuum and cryogenic equipment around beam • Magnetic optics for β* = 2.6 km and L = 1029 cm-1s-1 • Particle source is located along the trajectory of 7 TeV proton in the lattice (for Beam 1) • Detecting plane placed at 242.43 m from IP1

20. Residual Gas Density Estimations Residual gas density was reduced proportionally to beam current reduction (compare to case with Nb=43 bunches and np=1.15 p/bunch after machine conditioning, see A.Rossi, LHC-PR-783,p.9) only for cold sections of SS1. Gas distribution was averaged over the straight section.

21. Simulations • Results are preliminary. • Absolute normalization: • 3 inelastic beam-gas interactions in one half of the SS1 per one second for our gas density estimations and beam intensity(compare to 8000 p-p interactions in IP at L = 1029). • 1st stage: standard approach – • background was collected from TAS to object.

22. Local vs Distant Beam-Gas Background Vertical distribution of the local beam-gas generated background (blue, all charged hadrons) compare to distant one (red, 7 TeV protons).

23. Local Beam-Gas Background at 242 m Horyzontal and vertical distributions of the beam-gas generated background particles at 242 m from IP1. Solid – charged hadrons (E > 14.5 MeV), red – electrons (E > 100 MeV), blue – muons (E > 20 MeV).

24. Local Beam-Gas Background at 242 m

25. Local Beam-Gas Background at 242 m 2nd stage source: beam-gas from behind IP1 (left part of the SS1)

26. Local Beam-Gas Background at 242 m

27. Plans • To finalize LSS5 model for nominal optics. • To calculate local beam-gas in LSS5. • To start calculate radiation environment in LSS5 and around. • To calculate distant beam-gas for nominal optics. • Request to detectors: • Specification of functionals to be calculated (correct location, energy thresholds, format). • Clarification of the final LHC design (CMS – forward region).