Dear Xiaochao, Happy New Year! > Thank you very much for your reply. You have raised many important questions. I will try to answer some > of them below, and for some questions we will need more time for simulations. I have numbered your > questions for easy references. Thanks. I worry about the question what threshold of photon registration would be for main version of preshower? The significant amount of energy for few hundred MeV shower should be absorbed in lead of preshower. Do you have a simulation for low energy photons? >- Answer: We can also reserve a gap of 30-40mm between preshower and shower detectors. But due to our new >idea on the Preshower design, the preshower WLS fibers may not need to be bended within this space anymore. >One relevant question that was not clear to me: Will the shower WLS fibers be bended and turned around at the front >of the shower, which might require about 5cm of space? In later part of this email you mentioned mirrors for the >fibers. Is that relevant to this? What do you mean by a new design? I have always used in calorimeter the WLS fiber with a mirror at the opposite end from the photomultiplier. In this case we exclude any bended fibers in front of calorimeter, save 5cm of space, reduce irradiation of fibers and also exclude light loss in loop. Reflectance of mirrors is 80-85% and consistently over time. We use fiber with mirrors in the COMPASS hadron calorimeter and don't seen a noticeable change of light yield during 12 years of exploitation. >Ib) Also length of light guide, 100mm in slide, can be reduce on 30-40mm, if shower WLS fibers collect in four optical >connectors. In this case 100x100mm**2 module and 50x50mm**2 module will uses the same connectors and the >same equipments can be use for assemble. > >- Answer: Both are possible. We are talking to a local company who claimed they can make plastic "plates" with a >lateral size of about 10x10cm and with 100 holes to connect the WLS and the clear fibers. The quote is about >$175/module. In fact, if IHEP can make similar connecting plates with lower price, it will probably be our preferred >option due to reduced cost and more integrity. Can IHEP make these fiber connectors? I discussed the possibility of production of optical connectors in our workshop. Could you send me a technical discription and/or drawing of connectors? >Ic) Would you examine to build two independent detectors, preshower and calorimeter with independent support >structure, like in LHCb? > >Id) In this case, lead converter can build from few large pieces, that will simple and cheap. All read out fibers can be >easy send to the side of detector, also LHCb expirience can be use. > >Ie) Also in LHCb preshower detector consist of two layers of scintillator pads separeted by lead plate. First layer of >scintillator pads placed in front of lead convertor use for photons/electrons separation. Do you need photons/electrons >separation? > >- Answer to 1c, 1d and 1e Thanks to your question now we are considering a different design for the Preshower that >will cost less and be simpler. Although the exact geometry has not been set, we think we can make the preshower in >"fan shapes", with the 2pi azimuthal angle divided into 30 or more segments. Each fan section consist of plates of Pb >and Scintillators. In this case we will need two Preshower detectors: the large angle PReshower will have inner and >outer radius of 80 and 140 cm, respectively, with one Pb layer followed by one scintillator layer; the forward angle >Preshower will have inner and outer radius of 100 and 261 cm, respectively, with one Scitillator layer followed by one >Pb layer followed by another scintillator layer. You can see that our forward angle Preshower design has adopted >your suggestion on the additional Scintillator pad, but for the large angle the additional photon rejection is not >necessary. The exact size of the pad will need to come from further simulation since it depends on how many >segments we need to divided the full 2pi into. > >- Readout of the Scintillator pads in the preshower will still follow the same method as before, using imbeded WLS >fibers. The larger fan-shape size of the pads will require more fibers to be used, but might make it easier for bending >the WLS fibers within, and the fiber can go out from the outer radius, then be connected to clear fibers for transporting >to PMTs. > >- For the scintillator pad we are studying the possibility of using 10cm or 12cm as you questioned (simulation is >underway). Meanwhile, the additional Scintillator layer will probably need to be less than 1cm thick. > >- Can you comment on both the fan-shape and the thickness of all Pb and scintillator layers for our new design? Also, >if we go with the fan-shape, will 20cm scintillators still be issue for your production? > >- How will the cost change for the Preshower part based on the new design? ??? I don't have a picture with new design. >If) Can you reduce a thickness scintillator in preshower from 20mm to 12mm or 10mm? The fact is that 20mm >scitillator with size 10x10cm**2 can't be produce by the injection molded technique in IHEP. I discussed this question >with Sergey Chernichenko, he is head of scintillators subdivision. But it's possible for 12mm and exactly for 10mm >thickness. As I understand for preshower will be need 25-30 photoelectrons for MIP, I think that this light yield can be >achieved with 10mm scintillator. > >- Answer: please see above; > >II. Support modules: >First electromagnetic calorimeter in COMPASS has similar size 3x4 m**2 and total weight of calorimeter modules is >24t. The mechanical platform, chariot and light isolated cassette was designed and produced in Protvino workshop. >ECAL1 calorimeter can move in three direction along vertical and horizontal and also along beam axes. >I send you two photos with ECAL1 cassette and chariot. I have all working drawings and I can send you if it's need. > >-Answer: At the moment we are working with engineers at both JLab and Argonne National Lab on the support >structure. What I see the main difference between our EC and COMPASS is on the experimental swapping. The >supporting structure must allow quick re-arrangement of all green blocks of Fig.7a into red blocks of Fig.7a and blue >blocks of Fig.7b, and vice versa. So supporting all directly from the floor/bottom is not preferred. If you have any >suggestions for how to design the support structure, we would like to hear them. > >- Can you tell me that, based on the mechnical strength of the module, how many modules can we stack on top of >each other without inter-module support? At least 50 blocks with 38x38mm size. We tested the light yield and the light attenuation for this weight. >III. Calorimeter module. >I will consider design and cost estimate for Shower 18X0 Shashyk, as shown in your slide 7, page 2. Some >assumption: >1) we will build a straight Shashlyk, due to large impact angles. It's correct? > >- Answer: yes, if "straight" means the WLS fibers in the shashlyk are along straight lines. > >2) the cost of preshower will not included; > >3) the all materials and press mold will be produced and buys in Russia and/or IHEP. Of course WLS fibers, optical >connectors and also diamond cutter and mill will be better to buy in USA or Europe. > >-Answer: We will buy WLS fibers and have them shipped to you. For optical connectors, as mentioned above, we >have quotes from a local company which is about $175/module for one plate to connect 100 WLS fibers with 100 >clear fibers. The same company will look into making the connectors between the clear fibers and the PMTs (We will >use 28-mm-diameter PMTs). But if IHEP has relevant expertise for making fiber connectors, that would be an option >too. We have not looked into diamond cutters but will do so. Could you send me a drawing? I send to you a photo with COMPASS modules included PMT housing. The plastic tube fix to right flange of Shashlyk module (see fig.1b in your report). The PMTs are placed inside tube. It's simple and cheap solution and can be modify and adopt for your calorimeter. >- On a different note, does IHEP have any expertise in fiber fusing between WLS and clear fibers? That would be >option for the Preshower. Fusing fibers was developed in IHEP during LHC preparation and can be restore, but it's not simple technic. >So I don't add: preshower price, optical connectors, WLS fibers and mirrors on fibers, overheads cost in IHEP, >transportation cost, assemble and production tools. > >- Answer/Question: Can you explain what "mirrors on fibers" refer to? It's a mirror at the opposite end from the photomultiplier. I am sorry for delay, really Russian Chistmas holyday was ended only this Monday. Best regards, Vladimir.