Beam-plug under M2 and HCAL shielding studies Robert Paluch, Burkhard Schmidt October 9,

Outline M2 beam plug – Description in the MC doesn’t correspond to reality… – Reality differs also from production drawings, since the beam-plugs were further modified prior to installation on the request of the vacuum group. – The shielding of the real beam plug has been evaluated. Here only default configuration (high thresholds); for low energy part see Alessia’s talk. – Different materials have been looked at. Additional shielding behind HCAL – A feasibility study has started, taking into account what can be implemented with reasonable efforts. – A more realistic configuration has also been simulated. 2

Simulation results Simulation parameters and configuration: – Gauss version v42r2 – detector description dddb – detector condition sim vc-md100 – beam configuration file Beam3500GeV-md100-MC11-nu2-50ns.py – beam energy 7 TeV – luminosity per coll. bunch 2.47 x /cm 2 /s – total luminosity /cm 2 /s The average track multiplicities/cm 2 /s refer always to particles leaving up to 4 hits in a chamber, depending on their angle (no double counting of hits coming from the same track). Only changes in % are given in the following, and always with respect to the nominal (but wrong) beam-plug description. 3

Track multiplicities, default MC layout of the M2 beam-plug The track multiplicities vary by a factor three, depending on the chamber position. (The uncertainty on the values given is about 2%.) The chambers left and right from the beam-plug have the highest rates (effect of the magnet), as expected: – Left/right: top/bottom: corners: The chamber closer to HCAL have a 15% higher rate: – Front row chambers: back row chambers: A-sideC-side 4

Piece cut out Small Openings ~12cm ~3cm ~9cm M2 beam plug 5

Effect of corrections in M2 beam-plug 1.Use correct outer dimensions of M2 beam-plug (23mm less in x, 7mm less y)  Effect on left/right chambers clearly visible (up to 20%)  Effect stronger in front- than in back-row  Total increase about 7.1% 2.Add the openings on the side of the plug  Effect most clearly see in the chamber closest to the opening.  However, not clear whether it is statistically significant.  Total increase about 8.7% A-side 13%4%2%-2% 6% 9% 22% 16% -3%2%0%5% 14%6%7%8% 15% 10% 23% 13% -7%7%-5%1% Remember the uncertainty on the average track multiplicity is about 2% 6

M2 beam plug 7

Effect of corrections in M2 beam-plug 3.Add the openings in MF1, behind M2  They have only a minor effect  Total increase about 6.5% 4.Add the collar and the beam-pipe fixation  Again, the effect is only minor  Total increase about 6.7% 4%-1%9%-6% 9% 12% 22% 14% -11%-5%8%0% 15%-1%10%-6% 5% 10% 20% 12% -6%0%10%5%  Without considering the very low energy background, the effect of the openings in the M2 beam-plug and of the collar is minor.  The strongest effect comes from the outer dimensions of the beam-plug 8

Description of beam-plug and beam-pipe in the simulation It remains to be seen how relevant a proper description really is, and how important it will be to fill the openings for Run II. 9

Change material from steel to tungsten ‘ Correct’ geometry description (4.) has been used as reference Overall reduction: – Top/bottom: – Left/right: – Corners: – Front rows: – Back rows:  It is not understood at present why the effect on the front-row chambers is much larger than in the back-row -12%-32%-42%-15% -6% -18% -24% -23% -6%-28%-22%-23% 10

Additional shielding behind HCAL 11

HCAL layout 20cm 12

HCAL layout The last 16cm of HCAL (along z), where the PMTs and the CWs are housed, are easily accessible and can easily be equipped with additional shielding. The 20cm (along z) where the wavelength- shifting fibres are bundled, are rather difficult to access, due to the end plate. It should be possible to enlarge the area of shielding along x to two HCAL cells (26cm), hence covering all of M2R1 along x. In y no changes are envisaged. 13

Shielding behind HCAL PID TDR versionRealistic version 14

Simulation results Comparison of tungsten shielding behind HCAL, as assumed for the TDR (used as reference) with a realistic version – Overall change small: Top/bottom: ; Left/right: Corners: Front rows: ; Back rows: Comparison of realistic tungsten shielding behind HCAL, with no add. shielding – Overall reduction: Top/bottom: ; Left/right: Corners: Front rows: ; Back rows:  Huge gain in the left/right chambers with the highest rate 14%9% 6% -11% -3% 13% 8% 4%-2%2%-10% -25%-2%-5%-20% -51% -40% -27% -33% -20%-7%-22%-38% 15

Additional shielding behind HCAL and tungsten beam-plug under M2 16

Simulation results Comparison of realistic tungsten shielding behind HCAL, with no add. shielding – Overall reduction: Top/bottom: ; Left/right: Corners: Front rows: ; Back rows: Comparison of realistic tungsten shielding behind HCAL and a tungsten plug under M2, with no add. shielding – Overall reduction: Top/bottom: ; Left/right: Corners: Front rows: ; Back rows:  Huge reduction in all chambers -25%-2%-5%-20% -51% -40% -27% -33% -20%-7%-22%-38% -41%-31%-41%-35% -50% -49% -40%-29%-30%-40% 17

Additional shielding behind HCAL and tungsten beam-plug under M2 and tungsten beam-plug under HCAL 18

Simulation results Comparison of realistic tungsten shielding behind HCAL and a tungsten plug under M2, with no add. shielding – Overall reduction: Top/bottom: ; Left/right: Corners: Front rows: ; Back rows: Comparison of realistic tungsten shielding behind HCAL and a tungsten plug under M2 and under HCAL, with no add. shielding – Overall reduction: Top/bottom: ; Left/right: Corners: Front rows: ; Back rows:  Again, huge reduction in all chambers -56%-45%-54%-46% -58% -60% -64% -37%-49%-51% -41%-31%-41%-35% -50% -49% -40%-29%-30%-40% 19

Conclusions Effect of openings in M2 beam-plug is minor compared to the right outer dimensions of the plug. However, it would be good to close the openings for Run II with steel plates. (Effect, also using tungsten will also be simulated.) We will also simulate the effect of thin plate in front of M2R1 to understand better the differences between front and back rows. A reduction of 55% can be obtained with a tungsten plug under M2 and HCAL, and additional realistic W-shielding behind HCAL. The effect on M2R2 with such a shielding is also significant, but not on M3R1/R2 20 Region M2 plug tungsten M2+add.shield tungsten M2+HCAL plug + add.shield (W) M2R1-22%-43%-55% M2R2-6%-12%-24% M3R1-4%-5%-4% M3R2-1%6%2%