1. Proposal for a test with the pure low-energy e beam @Desy Pasquale Migliozzi INFN Napoli

2. Outline Why low energy electron beams? Past exposures at PS The electron beam at Desy Proposed strategy Manpower involved and possible schedule

3. Why low energy e beams?  e DIS  e QE e CC  CC Dalitz e  CC  from  0   e (GeV)4.5 200.71.06.9 f(E e <10GeV)(%)90.290.638.399.899.276.2 f(E e <20GeV)(%)99.199.561.899.999.896.6 f(E e <30GeV)(%)99.799.976.610099.999.6  m 2 =0.0025 eV 2 e in the beam  8‰

4. Past exposures From a hadronic machine Very difficult to obtain a pure electron beam Serious environmental background At the PS the electron beam is a fraction (ranging from 50% @1GeV to 10% @10GeV) of a mixed beam containing e/  /  Impossible to exploit the eID efficiency and the energy measurement

5. Electron beam at Desy (contact person Norbert Meyners) A bremsstrahlung beam is generated by a carbon fiber in the circulating beam of the electron synchrotron DESY II. The photons are converted to electron/positron pairs with a metal plate. Then the beam is spread out into a horizontal fan with a dipole magnet. Like a slice the final beam is cut out of this fan with a collimators.

6. Details The carbon fiber has a thickness of 6-10 µm diameter. The photon beam leaves the DESY II vacuum chamber through a 0.5 mm Al window and then it has to pass through the DESY III vacuum chamber via two 0.5 mm Aluminium windows. There are different conversion targets availableconversion targets (Cu wire, Al and Cu plates of different thickness from 1 mm to 10 mm). The beam shutter and the shielding wall follow the variable collimator behind the magnet. Inside test beam area it's possible to put a second lead collimatorlead collimator with different holes. The geometric arrangement is such that for beam 21 and 22 a bend of 32 mrad and for 24 of 80.6 mrad and a second of 32 mrad backward is needed to get the beam through the center of the collimator. The magnet currents, the choice of the target and the collimator hole size is under control of the user. The accelerator control room handles the fiber target.

7. conversion targets lead collimator

8. Expected rates RatesTarget Energy3mm Cu1mm Cu 1 GeV33 %22 % 2 GeV50 %33 % 3 GeV100 %66 % 5 GeV50 %33 % 6 GeV25 %16 % In table you can find a rough estimate of the rates. The rates are influenced by a lot of parameters. In practice the maximum rate around 1 kHz (3 GeV, 3mm Cu convert, Collimator ca. 5mm x 5mm, DESY II maximum energy at 7 GeV, no beam extraction, no DESY III ramp). Highest rates at 2.9 GeV The rates in the table are too large, but …

9. > Particle rate > Is it possible to go down to a > rate of a few Hz? Yes! By closing the collimator and/or choosing the thinnest target. And it should be possible to request a special operation mode of DESYII for your experiment with a lower current. (=> Michiko) I think that T24 with its two magnets would allow to reduce the rate by mis-steering the second one without acting on the machine. This possibility did come to my mind after I had received your mail the first time.

10. > Beam control > is it possible to stop the beam > at any time the user wants? If so, how long does > it take? Yes! Closing the beam shutter takes some seconds! A faster switch off might be possible by acting directly on the machine (=> Michiko).

11. > Beam spot > For special measurements we need to collect one > particle per hundred centimeter squared. > Therefore, the question is: what is the maximum > beam spot achievable? ~10cm wide, maybe 15cm, Heigth? ~some cm

12. > Finally, for our exposure we need to build > lead-emulsion bricks in a dark room. Do you know > where there is a dark room at Desy we can use > for our emulsion handling? Our photographer still has a dark room of about 2.5m x 4.5m which she could offer for a week. Another solution would be to prepare an existing room. Already two bigger rooms came to my mind. By the way I have no idea about the space you need in the beam and in the dark room.

13. > Do you have a rough idea of how many photons there > are in the electron beam? In the electron beam should be nearly zero. Because of the bend the original photons are block by the collimator, but I never did tried to measure the photon content.

15. > Concerning the schedule of our test, we would > like to have it in october. Till when we can > send our application? We do not have a deadline. We work with the principle: "First come, first served."

16. Which kind of exposure? The present electron ID algorithm combines MCS measurement before showering starts Counting of tracks associated to the shower From an experimental point the two measurements have opposite requirements For MCS a several tracks (1-10) per mm 2 are affordable For track counting no overlap among shower 1 (or less than) electron per cm 2

17. Proposal 3 energies (1, 3, 6 GeV) with a high density to validate the MCS algorithm 3 energies (1, 3, 6 GeV) with a low density to study (with small statistics) the MCS and track counting at the same time Once the data and MC agree one could use the latter to increase the statistics This exposure could also be used to study vertex location for  ->e QE events

18. PROBLEM!!! The major problem with this exposure is the transportation of the material from CERN to DESY (12-14 hours by train) All operations related to the emulsions (refreshing, development) and the brick assembly should be performed at CERN

19. Possible schedule In july in parallel with the TB at CERN perform a reharsal of the exposure at DESY Trasport emulsions from CERN to DESY and viceversa to measure the integrated background In october we perform the final exposure First we setup the beam with electronic detectors As soon as it is ready we ask for bricks to people at CERN

20. Possible setup Electron beam Brick CS doublet to distinguish beam electrons

21. Manpower and time schedule NB Here we discuss only the manpower to perform the exposure successfully. The sharing of the scanning of this exposure is another business Contact person with Desy (P. Migliozzi) Study of the beam characteristics before the exposure (D. Autiero) Refreshing and development (G. Rosa) Material procurement to be discussed within the Emulsion WG Alignment with cosmics at Desy Brick assembly (BAM team) MC studies to optimize the exposure (Y. Caffari, A.Marotta) Mechanics (we plan to use the Bern table) Manpower for the testbeam (D. Autiero, Y. Caffari, M. De Serio, F.Di Capua, L. Esposito, A. Marotta, P. Migliozzi,V. Tioukov, xxx)