M. Sullivan International Review Committee November 12-13, 2007 SuperB IR Design M. Sullivan International Review Committee November 12-13, 2007

Outline Detector Considerations Accelerator Parameters IR Design Summary

Detector Considerations Reasonable angular acceptance ±300 mrad Small radius beam pipe 10 mm radius Thin beam pipe Minimum amount of material

Detector Considerations (2) Backgrounds under control SR Rates comparable to PEP-II Few hits per crossing on Be beam pipe Little or no hits on nearby beam pipes BGB -- coulomb Keep nearby upstream bending to a minimum Low vacuum pressure upstream of the detector Touschek Collimation

Detector Considerations (3) More backgrounds Luminosity backgrounds Beam lifetimes Radiative bhabhas Beam-beam Local HOM power Small diameter beam pipes trap higher frequencies Always get modes when two pipes merge to one PEP-II and KEKB experience can help the design

Accelerator parameters LER HER Energy (GeV) 4.0 7.0 Current (A) 3.95 2.17 No. bunches 3466 Bunch spacing (m) 0.63 Beat x* (mm) 20 20 Beta y* (mm) 0.2 0.2 Emittance x (nm-rad) 1.6 1.6 Emittance y (pm-rad) 4 4 Full crossing angle (mrad) 34 These parameters constrain or define the IR design

Start with Pantaleo’s FF Conceptual Design

SR fans when the shared QD0s have no offsets HER QDO QDO LER QDO QDO

IR Design The crossing angle is ±17 mrad The beam pipe diameters are 20 mm at the outboard end of QD0 for both beams (same size as IP pipe) This leaves enough room (~10 mm) to place a permanent magnet quadrupole and get the required strength (Using Br = 14 kG) We have placed small bending magnets between QD0 and QF1 on the incoming beam lines to redirect the QF1 SR The septum QF1 magnets for the outgoing beams are tilted in order to let the strong outgoing SR fans escape The B0 magnets on the outgoing beams are C shaped in order to allow the SR fans to escape

IR design parameters Length Starts at Strength Comments L* 0.30 m 0.0 Drift QD0 0.46 m 0.30 m -820.6 kG/m Both HER and LER QD0H 0.29 m 0.76 m -820.6 kG/m HER only B00L 0.40 m -1.05 m -2.2 kG Incoming LER only B00H 0.40 m 1.05 m 1.5 kG Incoming HER only QF1L 0.40 m ±1.45 m 293.2 kG/m LER only QF1H 0.40 m ±1.45 m 589.1 kG/m HER only B0L 2.0 m ±2.05 m 0.3 kG LER only B0H 2.0 m ±2.05 m 0.526 kG HER only QD0 offset 6.00 mm Incoming HER QD0 offset 7.50 mm Incoming LER

SR Power Numbers The total power is similar to PEP-II SR power in QD0 (kW) for beam currents of 1.44A HER and 2.5A LER No QD0 offsets SuperB PEP-II 3A on 1.8A Incoming HER 41 4 49 Incoming LER 28 1 16 Outgoing HER 41 93 49 Outgoing LER 28 55 16 Total 138 153 130

Same scale as the picture on the previous slide

LER SR fans

HER SR fans

±1 meter

SR backgrounds We use a gaussian beam distribution with a second wider and lower gaussian simulating the “beam tails” The beam distribution parameters are the same as the ones used for PEP-II We allow particles out to 10 in x and 35 in y to generate SR Unlike in PEP-II the SR backgrounds in the SuperB are dominated by the particle distribution at large beam sigma, so we are more sensitive to the exact particle distribution out there

SR background numbers LER LER 7726 /xing > 10keV These numbers are for a 4A LER and a 2.2A HER 280 /xing > 10keV 107 /xing > 20 keV 331 /xing > 10keV 125 /xing > 20 keV HER HER Chamber slopes are steep enough to prevent scattered photons from hitting the detector beam pipe

More on SR The ~8000 photons striking the downstream mask tip from the LER have a shot at hitting the detector beam pipe If we assume a 10% reflection coefficient (we should be able to get it down to 3% or lower) then we have ~800 photons > 10 keV scattered out of the tip surface A solid angle calculation for the detector beam pipe (±4 cm) from this source point at 10 cm away gives 1.1% We then have ~8 photons/crossing > 10 keV hitting the detector beam pipe and ~0.14 photons/crossing >20 keV hitting the detector beam pipe

Radiative Bhabhas The outgoing beams are still significantly bent as they go through QD0 Therefore the off-energy beam particles from radiative bhabhas will get swept out Knowing this, we will have to build in shielding for the detector

HER radiative bhabhas

LER radiative bhabhas

Design with a new QD0 Under study is a new QD0 design where each beam has a separate magnetic field This allows each beam to be close to on-axis in this shared magnet Greatly reduces the total bending and hence the total SR produced Greatly reduces the radiative bhabha background for the detector

Possible QD0 Design

SR background An added constraint of the new design is to keep SR power very low on the cold bores of the QD0 magnets The beams are very close (6 mm) to the cold bore magnets The small emittances help and the lower beam currents help Ended up having to bend the incoming HEB a little to redirect the SR away from the QD0 inner bore and the detector beam pipe

Expanded Layout of the IR

SR power numbers again The total power is much lower SR power in QD0 (kW) for beam currents of 1.44A HER and 2.5A LER No QD0 offsets SuperB PEP-II New 3A on 1.8A QD0 Incoming HER 41 4 49 5.3 Incoming LER 28 1 16 1.5 Outgoing HER 41 93 49 0.9 Outgoing LER 28 55 16 1.5 Total 138 153 130 9.2

SR summary for new design The overall SR power coming out of the IP is much lower Keeping the SR off of the QD0 cold bores is an added constraint The lower beam emittances help The SR masking has to be fairly tight because the beam is close to the QD0 magnet A very preliminary design has a comparable background rate for the detector from SR The beam bending has been greatly reduced. The radiative bhabha background should be also greatly reduced if not eliminated Further optimization will improve the design

Touschek Background and Lifetime M. Boscolo preliminary results with the latest lattice (ex=2.8 nm; sz=5 mm; Ib = 1.5 mA) M. Boscolo Touschek lifetime with no collimators tTOU ≈ 12.5 min in agreement with evaluation from parameters scaling from CDR lattice trajectories of particle losses close to the IR particle losses at IR ≈ 4 KHz/ bunch essentially downstream the IR with a preliminary set of collimators inserted at: -86, -60, -47 m far from IP 20x lower with this preliminary collimators set lifetime reduced by 30% work in progress to optimize collimators for best longitudinal position along the ring and best trade-off between IR losses and lifetime

Summary We have an IR design that has acceptable SR backgrounds with a crossing angle of ±17 mrad and an energy asymmetry of 7x4 The QD0 shared magnet is super-conducting The QD0H magnets can be built with permanent magnet technology – does not rule out super-conducting but the space is small The strong bending of the offset outgoing beams in the shared QD0 produces a significant amount of SR power but the outgoing magnet apertures can be designed to let the SR escape. The bending of the outgoing beams also produces radiative bhabha background in the detector—we will need to shield the detector from this radiation source We are looking at a new design for a QD0 magnet where the beams are not bent. Preliminary studies are very encouraging. Close cooperation with the magnet designers will be needed to insure an optimal design.