MeRHIC Interaction Region & Detector Integration

1. MeRHIC Interaction Region & Detector Integration Joanne Beebe-Wang Brookhaven National Laboratory EIC Collaboration Meeting, Stony Brook, NY, USA January 10, 2010

2. Outline 1. MeRHIC detector design requirements, concepts, status 2. MeRHIC IR design challenges 3. MeRHIC IR design 4. RHIC IR modifications for MeRHIC 5. Synchrotron radiation control in IR 6. Study on synchrotron radiation in IR 7. Summary and status

3. Detector Requirements from Physics • ep-physics • the same detector needs to cover inclusive (ep -> e’X), semi-inclusive (ep -> e’hadron(s)X) and exclusive (ep -> e’pp) reactions • large acceptance absolutely crucial (both mid and forward-rapidity) • particle identification is crucial • e, p, K, p, n over wide momentum range and scattering angle • excellent secondary vertex resolution (charm) • particle detection to very low scattering angle • around 1o in e and p/A direction  in contradiction to strong focusing quads close to IP • small systematic uncertainty (~1%/~3%) for e/p polarization measurements • very small systematic uncertainty (~1%) for luminosity measurement • eA-physics • requirements very similar to ep • challenge to tag the struck nucleus in exclusive and diffractive reactions. • difference in occupancy must be taken into account E.C. Aschenauer

4. First Ideas for a Detector Concept • Dipoles needed to have good forward momentum resolution • Solenoid no magnetic field @ r ~ 0 • DIRC, RICH hadron identification  p, K, p • high-threshold Cerenkov  fast trigger for scattered lepton • radiation length very critical  low lepton energies Solenoid (4T) Dipole 3Tm Dipole 3Tm FPD FED // // ZDC E.C. Aschenauer

5. MeRHIC IR Design Challenges 1. Merging and separating the electron beam with RHIC ion beams; 2. Matching the lattice of IR to the lattices of designed electron transport line and existing RHIC rings; 3. Providing large range of tunable ion beam energy for a fixed electron energy (80-250 GeV proton for a fixed 4GeV electron); 4. Confirming with the technical limitations of magnets and power supplies; 5. In accordance to the detector design and physics measurements; 6. Minimizing the detector background due to synchrotron radiations; 7. Confirming with space and geometrical conditions based on the installed RHIC hardware and existing tunnel; 8. Incorporating vacuum devices required by the further operation.

6. MeRHIC Interaction Region Design • Synchrotron radiation shielding not shown • Allows p and heavy ion decay product tagging proton energy range 80-250 GeV

7. RHIC IR Modifications for MeRHIC • Removal of both DX magnets • Removal of two D0 magnets at the sector 1 side • Move existing instrumentations to other locations • Separate pipes for blue and yellow beam • Add 6 DB dipole magnets (warm, two are used to replace two removed D0s) • length=3.6m, field=1.3T, pole width=14cm, pole gap=10cm • 6. Add two DS dipole magnets (warm) • length=3.0m, field=1.2T, pole width=60cm, pole gap=8cm • 7. Add two DW dipole magnets (warm) to blue line • length=3.6m, field=0.1T, pole width=8cm, pole gap=8cm • Add two spin rotators to the blue line (Same spec as PHENIX & STAR) • 9. Add 6m Beryllium pipe (OD=3in) to Blue line • 10. Add 20m long absorbers/masks with water cooling for Synchrotron Radiation • Heat load requirement = 10W/cm • 20m long complicated shape of Aluminum beam lines to accommodate the absorbers, masks, vacuum pumps, water cooling (similar design as NSLS-II)

8. Synchrotron Radiation Control in IR 1. Horizontal hard and soft bend on both side of the detector; 2. The forward radiation from the up stream hard bend is completely masked. No hard radiation passes through the detector; 3. The forward radiation from the up stream soft bend pass through the detector. 4. The secondary backward radiation induced by the forward radiation generated in down stream bends is largely masked from the detector; 5. Total length of absorbers = 20m (including both up & down stream)

9. Vacuum Chamber with Integrated Absorber/Mask

10. Sources of the Radiation Background in Detector 1. Forward synchrotron radiation generated upstream of the detector. • The rate is analytically calculated by employing electromagnetic theory. 2. Direct backward radiation caused by the photons hitting beam pipe downstream of the detector. • The rate from soft bend is obtained by applying the kinematic Born approximation deduced from scattering dynamics. Then diffuse scattering cross section is calculated as a function of the surface properties of the vacuum system. The rate from hard bend is estimated by simulation. 3. Indirect secondary radiation caused by hard photons hitting vacuum systems, masks, collimators, absorbers or any other elements in the interaction region. • The rate is estimated by computer simulations.

11. Forward Synchrotron Radiation The photon spectrum of forward synchrotron radiation: P = synchrotron radiation power EC = critical photon energy S-function defined as: K5/3(z) = the modified Bessel function of the second kind.

12. Secondary Radiation due to Hard Photons 1. Some hard photons produced in the strong dipole magnets could have energies up to 80 keV. 2. Even though these photons are masked from the detector opening, they could undergo multiple scattering through photon-matter interactions and cause increased background in the detector. 3. It was noticed from the simulation of secondary radiation with photon energies of 1-70 keV in the eRHIC interaction region that spectrum of backward radiation peaked around 8 keV, which is close to the K-shell energies of iron (7.11 keV) and copper (8.98 keV). 4. The secondary radiation is dominated by the values of the shell energies in the photoelectric coefficients. The radiation background in the MeRHIC detector is minimized with proper knowledge of the photon energy distribution and selection of suitable materials.

13. Photoelectric absorption Coefficients

14. Coherent Scattering Coefficients

15. Compton Scattering Coefficients

16. Choice of Materials SR absorbers/masks for IR and electron arcs: Glidcop (Copper based) Secondary photon energy: 9keV IR beam lines and Electron beam lines: Aluminum Complicated shape to accommodate absorbers/masks, vacuum pumps, water cooling… Secondary photon energy: 1keV Experimental beam pipe (EBP): Beryllium Secondary photon energy: 0.1keV

17. Secondary Radiation due to Soft Photons stainless steel chamber with some what “jagged” surface structure (h=0.5) stainless steel chamber with extremely “regular” surface structure (h=1.0)

18. Summary and Status 1. The physics requirements for the detector and the design concepts are developed. 2. The GEANT simulation study based on the current MeRHIC detector and IR design is in progress. (Anders Kirleis’s talk) 3. The current MeRHIC IR design successfully integrates the detector into the existing RHIC environment. The design meets all the challenges identified. 4. The study on synchrotron radiation background in IR and in detector is carrying out. 5. The related engineering challenges haven been identified and solutions developed by experts. (Joe Tuozzolo’s talk)