SuperB General Meeting XI IR Summary M. Sullivan SuperB General Meeting XI Frascati, Italy December 1-5, 2009

Several excellent presentations IR update SR background rates QD0 update IR Interface Issues Thin Be beam pipe SVT backgrounds Rapid access to Central Region Solenoid Compensation Polarization Measurement

Present IR Design Stable since October

Improvement details Old New QD0 HER/LER HER/LER QF1 R inside (mm) 24.0/31.5 22.5/32.5 R outside (mm) 28.0/35.5 28.5/38.5 Length (m) 0.40 0.40 Dist to IP (m) 0.58 0.60 Gradient (T/cm) -1.192/-0.522 -1.025/-0.611 Field at inside radius (T) 2.80/1.61 2.31/1.99 Maximum y (m) (sqrt) 1970(44)/2193(47) 1550(39)/2566(51) QF1 R inside (mm) 50.0 50.0 R outside (mm) 56.0 60.0 Length (m) 0.30 0.30 Dist to IP (m) 1.60 1.80 Gradient (T/cm) 0.726/0.399 0.640/0.358 Field at inside radius (T) 3.48/1.92 3.20/1.79 Maximum x (m) (sqrt) 580(24)/200(14) 799(28)/486(22)

Beam sizes at the face of QD0 65 mm dia. 45 mm dia.

SR Incident photons/crossing LER HER 748 215 1600 5300 4.4E4 1E4 1.3E6 1.1E5 7.5E5 1.8E7

Estimate of the photon rate incident on the detector beam pipe LER HER 0.24 0.07 10 13 111 13 8 9 968 105 Backscattering SA and absorption rate (3% reflected)

QD0 update Baseline QD0 is getting reviewed by engineers We also have a new proposed design for QD0 from BINP It uses vanadium permendur iron and a Panofsky style quadrupole winding

QD0 Cross-section

New QD0 design option The iron yokes mean the maximum B field in the magnet iron can not exceed 2T The initial suggested design used cold beam pipes (80K) which we can not do because of SR fans from the last soft bend but we can try to increase the space for these magnets so a warm bore works The magnetic field gradients have to be the same value for the LER and HER and the aperture is square There are several advantages to being able to use this design and work has started on developing an IR design using these magnets

Siberian Style QD0

First approximation design Backed up QD0 to make more space in front to add PM slices to the HER (toward getting the magnetic fields equal) and to increase the space between the beams (to fit in a warm bore) Moved QD0 back 10 cm (face is 70 cm from the IP) Added 5 more 2 cm long PM slices to the HER Still not enough to get the fields equal Added another smaller defocusing quad to the HER behind the twin magnets This quad has no partner and uses all of the space between the beams for an iron yoke to absorb the stray field on the nearby LER side Also moved QF1 farther back 20 cm (now at 1.8-2.1m from the IP). This lowers the magnet strengths as well.

Not a complete success The QD0 parameters look ok But the QF1 parameters don’t work yet. The two field strengths for the QF1s are very different and the HER maximum field strength is much too high (well over 2 T) We will try again following somewhat more the design choice of SuperKEKB where the magnets are offset in Z as much as possible The advantage of being able to offset in z is that we can decouple the beam energy ratio and are able to adjust the beam energy of each ring separately over limited ranges

SR rates for super-ferric case with offset QD0s LER HER 8.9E5 3.3E7 5.1E4 3.9E7 1.1E5 7E8 Some of these numbers are too high Apologies. This is the basic design picture. Beampipe geometry is the same.

Summary of super-ferric design An interesting option that needs to be pursued It holds the possibility of decoupling the beam energies from each other The first attempt was not a complete success, but there is room to try several different paths to see if we can come up with a solution that works

A List of Topics at the Interface Physics Beampipe Inside radius is currently 10 mm As thin a Be wall as possible Looking at 1 mm Be + 4 um Au Trapped HOM power Beampipe junction is +/-36 cm from the IP PEP-II junction was +/-2.4 m from the IP Angle of Acceptance 300 mrad is currently assumed by machine people Cryostat may end up close to that boundary SVT e+e- pair production background Presently the background is manageable Under Study

A first attempt to locally increase the magnetic field in the beam pipe in order to lower the SVT background 1.4T NdFe Rin=12.5 mm Rout=17.5 mm Zin=15 cm Zout=25 cm from K. Bertsche

SVT background This idea of using small PM slices around the beam pipe might be a useful method of diverting e+e- pairs from a specific section of the beam pipe (say just under the electronics) A much more detailed study would be needed using the GEANT4 detector model before we can see if this actually does help to lower the backgrounds

More Topics Angle of Acceptance (cont.) Magnetic Fields Presently assume that any detector hardware inside 300 mrad must be negotiated with machine (and vice versa) This is out to some radius – Machine will need some space down near the physics beampipe for a bellows and possibly a flange pair The SVT will want some space in this area as well Magnetic Fields The super-conducting quads will have an external field that might perturb the detector field The same may be true for the compensating solenoids We are looking at race track type of solenoids for QF1 and possibly QD0 if this is a better way to go. Presently settling out at about 20 cm

Still More Topics Polarization measurements Ken Moffeit has done a lot of nice work in defining a polarimetry system for measuring the beam polarization Cryostat supports and Rapid access The cryostats must be rigidly supported We also want rapid access to the SVT and PMs Presently working toward an access time of a couple of days Most currently liked notion is an idea from J. Seeman where we have strong supports to the floor that are on rails. This would allow us to support and slide the cryostats back and forth without touching the detector.

Location of Compton Polarimeter From Ken Moffeit’s presentation Location of Compton Polarimeter Unfortunately, the Compton detector would intercept multi-GeV gammas at a rate of multi-hundred MHz from the radiative bhabha process. This is where we will put our luminosity detector Option A: Near IP as beam electron leave IR. Laser light in Laser light out to analysis box Compton IP Compton Photon Detector Compton Electron Detector 4.18 GeV Spin Pros: Near IR. Beam direction same as that at IR. Easy to verify beam direction is within 7.5 mrad of beam direction at IR. A change in beam direction of 7.5 mrad between the IR and the Compton IP gives a spin projection at the Compton IP lower by 0.25%. Polarization measurement accurate even when beam is not at designed energy of 4.18 GeV for P. Cons: Backgrounds from beamstrahlung large. Horizontal beam size large ~900mm at Compton IP reducing Compton luminosity. Crossing angle with the beam may be as large as 50mrad resulting in lower Compton scattering rate. Compton Polarimeter must be downstream of IR if located near the IR. The Compton scattering will give backgrounds in physics detector if located upstream of IR.

Option B: Compton IP at location with pi spin rotation between Compton IP and IR From Ken Moffeit’s presentation e- e- Pros: Backgrounds small. Smaller Compton Crossing angle (~18mrad) due to more room for Compton IP. Horizontal beam size ~500 mm.. Cons: After n*pi spin rotations systematic error due to uncertainty in the orbit angle between IP and Compton IP. Uncertainty in electron beam orbit angle must be < 1 mrad. Compton IP may not be at magic angle for p spin rotation.

Compton IP near 180o spin rotation from spin direction at IR (orbit -0.358019 mrad from orbit at IR) From Ken Moffeit’s presentation Future iterations of SuperB machine optics may give longitudinal spin direction closer to 180o at the Compton IP from the spin direction at the IR.

From Ken Moffeit’s presentation This will have to be a special quadrupole Ken has produced a great deal of detailed work and has put it all together into this very nice presentation

Rapid Access Scenario Standard Plan View

Side view

Doors opened

Cryostats and SVT slid out of the detector We need to do more work to study the details, but the general concept looks OK

Solenoid Compensation We need to cancel the detector solenoidal field around the QD0 and QF1 quadrupoles Both the Italian design and the Siberian Panofsky design require minimal stray external fields In addition, in order to get the high luminosity, we need to minimize the coupling (beam twisting) from the detector (get the integrated B.dl as close to zero as we can) In order to do this we use anti-solenoids in the cryostats

Current solution from K. Bertsche’s talk

Field Profile from K. Bertsche’s talk

White Paper (CDR2) Work has started on getting a new write up for the interaction region section The IR design is completely different from the CDR design we wrote up almost 3 years ago

IR CDR2 (1)

IR CDR2 (2)

IR CDR2 (3)

Summary The Interaction Region design has held steady We have a new idea about how to make QD0 that we want to explore. QD0 has always been one of the most challenging aspects of the IR design. The new design has added constraints as well as many attractive features . We have a very well developed proposal for a polarimeter

Summary (2) Rapid access schemes are being investigated and are at least looking conceptually feasible. This would also the way you initially assemble things. Detector magnetic field compensation schemes are getting better Starting to look more carefully at the requirements of energy changes (including down to the charm threshold)

Conclusion We need to write up the present IR design. Our (by now) old CDR IR chapter is completely out-of-date. As always, there is still a lot of work to do but (so far – knock on wood – in this case, my head is good enough) it looks possible