1. Backward EMC Task Force Report – Elba 20111 Backward EMC Task Force Dave Aston, Gianluigi Cibinetto, Steve Robertson, Achille Stocchi, Bill Wisniewski

2. Backward EMC Task Force Report – Elba 20112 Thanks The Task Force would like to thank the members of the DGWG who have labored long and hard to produce results for the effect on physics of the Backward EMC, as well as members of the EMC group who have presented to us the Backward EMC detector concept and measurements.

3. Backward EMC Task Force Report – Elba 20113 Physics Impact DGWG studies: pick key modes –Study two final states, B  K ( * ) νν and B  τν, in detector layouts with and without Backward EMC use in the analysis. –Use the B recoil technique. On one side, fully (partially) reconstruct one B in a hadronic (semi-leptonic) final state. Look for the signal signature (e.g., K ( * ) without any additional charged or neutral particles –Build E extra from the sum of extra neutrals seen in the Backward EMC. –Figure of merit: relative change of the significance: ∆( Significance )/ Significance = [S/√(S+B) (BEMC) – S/√(S+B)(no BEMC)] S/√(S+B)(no BEMC)

4. Backward EMC Task Force Report – Elba 20114 Physics Impact DGWG studies: –Results on ∆( Significance )/ Significance : Semi-leptonic analysis: Hadronic analysis: –~ 6% significance improvement B+ τ+νB+ τ+ν (6.08 ± 0.11 -0.69)% B +  K + νν (5.75 ± 0.98 -0.64)% B 0  K 0 νν (6.00 ± 0.42 -0.63)% B +  K* + νν (6.95 ± 0.16 -0.66)% B 0  K* 0 νν (9.07 ± 0.41 -0.68)% B 0  K* 0 νν (7.3 ± 1.8 -0.5)% B +  K* +( K S π + )νν (6.2 ± 2.1 -0.5)% B +  K* +( K + π 0 )νν (5.9 ± 2.5 -0.5)% B+ τ+νB+ τ+ν ~3-5% depends on τ decay mode

5. Backward EMC Task Force Report – Elba 20115 Physics Impact –But, there is a price to pay for this. The space occupied by the BEMC could be filled with an extended drift chamber. From FastSIM: Single particle momentum resolution in the lengthened DCH improves by ~30% in the backward region. dE/dx improvement with a lengthened DCH by +.4 σ at 2.5GeV and θ=150 o. For two final states considered, B  π + π - and B  D* - K +, efficiency increases with a 20cm longer chamber in the backward direction is of the order of ~.5% (for efficiencies in the range ~65-80%). –Comment: There is some loss of tracking capability with consequent small effects on overall efficiencies in some modes. The benefits in signature modes are at a level significant enough that these keys measurements are likely to be completed sooner. A preliminary study has been done where a π 0 formed from one fully contained BEMC shower and another EMC shower, though without backgrounds. Efficiency gains in the studied channels are ~4%, but needs more work. The potential PID improvement provided by the BEMC needs to be evaluated.

6. Backward EMC Task Force Report – Elba 20116 What we asked the proponents We asked the proponents to talk about: –The design of the detector location of the photodetectors, calibration scheme, cable plant expectations Radiation hardness issues for the photodetectors & alternate readout schemes. Readout boards, locations, susceptibility to rad damage if known. Prototype measurements to show the device’s potential performance. PID capabilities of the calorimeter: TOF Considerations for a design that does not capture the beam pipe. –Costs, duration of detector construction, manpower needed. –R&D that will be done. The proponents provided a comprehensive response containing the items requested. Task Force comments follow.

7. Backward EMC Task Force Report – Elba 20117 Comments The CALICE-program-inspired detector uses logarithmic spirals and truncated wedge strips in 24 lead/scintillator layers read out with WLS fibers (Y11) located in a groove machined into the strip and coupled to photosensors (MPPC, SiPM, …). This leads to a design that prefers to be built as a monolith. However, this 1152 strip detector would capture the beam pipe. Splitting the detector into two parts would increase the channel count by about 160 channels. –Some integration effort is needed here, but a first reaction is that splitting the device is likely to be necessary. Detailed engineering by the integration group is needed. In general, this is a very complicated area with many systems interacting in a small space. The photodetectors are expected to be located at the outer diameter of the strips, probably reducing the local radiation level. The performance of potential BEMC photosensors was presented in great detail. Alternative devices have been thought about (APDs, pixelated PMs). –The detectors are small, but this cuts into higher physics occupancy space. A detailed assessment of the local radiation environment is important here.The sensitivity of the readout devices to radiation needs to be understood more coherently. Above all, it would be good to have an order of magnitude headroom for these devices (robust safety margin).

8. Backward EMC Task Force Report – Elba 20118 Comments The cable plant is not overly large and should fit with a redesign of the backward plug and its support. –This redesign is probably needed for the DCH in any case. If the photodetectors are not rad hard enough, clear fibers can be taken out as in IFR to photosensors in safer environments. However, increasing the count of cables/fibers leaving the detector may exceed the carrying capacity of this region. Readout boards will be located between the plug and BEMC. The calibration boards are planned to be located at the OD of the BEMC. –The proposal is to use boards designed for other experiments. This will save on costs. However, in the case of the calibration boards, this pushes to a geometric solution that is not optimal. There is no data on the performance of this readout in the SuperB BEMC radiation environment.

9. Backward EMC Task Force Report – Elba 20119 Comments Particle ID issues: dE/dx measurement was discussed but not fleshed out. TOF calculations have been done. The studies emphasized the momentum regime over 1GeV, where at 100ps resolution 3 σ K-π separation is possible. –The primary benefit is more likely to be at lower momenta, filling the dE/dx ID hole. TOF resolution should be measured using the BEMC prototype, when it is constructed. These studies can be performed with cosmic rays. The task force believes that TOF capability is a very desirable feature for a device outboard of the backward end of the DCH to have. Performance measurements were presented. Many are from CALICE experience. Others are for BEMC specific devices and setups. In particular, there were many measurements of homogeneity. –A lot of work has been done, but a full set of measurements that pertain to the BEMC specific design are needed.

10. Backward EMC Task Force Report – Elba 201110 Comments A preliminary cost estimate was presented. The M&S adds up to about $450k. Detector assembly time was estimated at less than 4 months. –These estimates seem reasonable. –The task force feels that if a substantial increase (~50%) of this cost were necessary to insure good TOF capability, it would be a worthwhile investment Materials for the prototype are in hand. However, manpower is very thin. The goal has been to have a prototype in the test beam in mid-2011. –The proposed prototype should be able to provide a coherent performance measurement set. It is key to have this in hand for the TDR. It has not be available for the task force’s consideration. –It is likely to be an insurmountable challenge to have a well understood detector with fleshed out credible design in time for the TDR. It will need to be determined if a solid realistic plan and schedule for completion of design is sufficient. –If sufficient additional manpower can not be recruited to this task, construction of this detector might be deferred to be an upgrade of SuperB.

11. Backward EMC Task Force Report – Elba 201111 Recommendations The detector team should complete prototyping and beam tests expeditiously to provide a coherent set of measurements of the performance of the proposed detector, as well as investigate the time of flight capability of the device. The detector team has significant hurdles to overcome in order to develop a viable Backward EMC, and should add additional people in order to succeed. A Backward EMC provides an opportunity to enhance the physics capabilities of SuperB in select key decay modes. The Task Force feels that space should be maintained behind the DCH for such a device.