1. Forward Tagger Calorimeter Prototype tests at Jlab: report CLAS12 Workshop February 22, 2012 A. Celentano

2. FT Prototype ● 3x3 PbWO 4 crystals (15 x 15 x 200 mm 3 ) + 7 stainless steel dummies. ● Each crystals is read using an APD glued to it. ● The signal from each APD is amplified by a trans-impedance amplifier. Signals, HV and LV are transported by a specific-designed motherboard. ● On top and above the crystals there's a copper covering (2 mm thickness) connected to an external cooling circuit, to keep the calorimeter at a constant temperature. ● The calorimeter is surronded by a 5-cm thick insulation material and inserted in a plastic black box. ● DAQ chain: each signal is splitted twice, one copy is sent to a FADC, the other one to a discriminator + TDC. DAQ is handled trough CODA. FT-Proto Characteristics:

3. FT Prototype First measurements we did with the prototype: test with cosmic rays in Genova (Oct.-Nov. 2011) Aim: ● Compare results from previous measurement of single elements in test-bench setup (APDs, Crystals). ● Verify the behavior of the whole system, at different temperatures. ● Get a first calibration point (at low energy). ● Validate Monte-Carlo simulations. -23 -14.5 -5.8 5.1 18 Light Yield, as a function of temperature, measured with cosmic rays. From simulations: the mean energy deposited by cosmics in each crystals is ~ 16 MeV. We used this measure as first energy calibration point for tests at JLab. Prototype, cosmic rays Test-bench (APD) Test-bench (PMT) Comparison between results from the FT-Proto and from test-bench setup, using different light sensors. The behavior of the prototype is consistent with results from its single channels.

4. FT Prototype : tests at Jlab with high-energy (~GeV) electrons Parasitic test of the FT-Proto during HD-ICE run (Dec. 2011-Feb. 2012): we installed the FT-proto below the photon tagger in Dec. 2011. Aim of the test: ● Measure of the energy resolution (at different energies), as a function of temperature and threshold ● Study of the time resolution of the system ● Study of the electron signals to develop analysis algorithm (charge integration, time from FADC) ● Validation of the GEMC simulations ● Measurement of electronic noise in a realistic condition Test setup: The prototype was installed below the photon tagger and aligned to electron trajectories. In front of it, we installed a plastic scintillator (to be used as stand-alone trigger) and a hodoscope prototype (one single tyle). First phase: stand-alone setup and DAQ. Parasitic test to check the proper alignment, configure DAQ parameters and see that everything was working fine. Second phase: FT-proto integrated into CLAS DAQ, to get also information from the tagger (thanks Eugene and Sergey!) Data were taken during normalization runs.

5. FT Prototype : tests at Jlab with high-energy (~GeV) electrons (3.356 GeV) (1.92 GeV) Since the beam energy changed during the test period, we did not moved the calorimeter along z: we took data at two different energies.

6. FT Prototype: simulation with GEMC A. Casale, R. De Vita 1.3 GeV1.9 GeV In first simulations we studied the energy resolution as a function of the incoming electron energy, including digitization effects and different thresholds on all channels. Electrons were generated in front of the calorimeter, always hitting the central crystal. The main contribution to the energy resolution is the energy leakage from the lateral sides of the prototype, due to its small dimensions. Thresholds effects become visible only at 20 MeV or more. Then we performed more realistic simulations, introducing the effect of E and T counter (electrons loose energy passing trough them, and multiple scattering can occurs). Results (+18 deg):

7. FT Prototype: simulation with GEMC A. Casale, R. De Vita 1.3 GeV electrons were used, hitting the central crystal. E and T counters are included in the simulation between the generation point and the calorimeter: they' modeled as a plastic tyle. Between the plastic tile and the calorimeter: air. e-e- Plastic tile (4x4x1 cm 3 ) FT-PROTO Deposited energy Reconstructed energy Relative difference Results: E R = 1.3 GeV is the real energy of the incoming electron. Digitization effects are negligible.

8. FT Prototype: standalone test First measurement were done in a standalone setup, with our own DAQ (CODA). ● We checked the behavior of the system and (roughly) the alignment of the calorimeter. ● We fixed some DAQ parameters (FADC widths, relative offsets) ● We measured the electronic noise in a real experimental hall! Event with an electron hitting the central crystal: signals acquired from FADC (1 LSB ~ 0.48 mV). The noise level is very small, we don't see any increase to what we measured in Genova in a test- bench setup. RMS ~ 8 LSB ~ 4 mV Central Crystal ns Signals are well defined: to calculate their area, at first, we decided just to sum over samples (no digital filtering).

9. FT Prototype: test with the photon tagger Data have been taken in 3 different experimental configurations: ● E=1.31 GeV, T=18 deg ● E=1.31 GeV, T=3 deg ● E=1.92 GeV, T=18 deg For each configuration, we took different runs with different thresholds on signals. Trigger configuration: The trigger is given by the tagger MasterOR, with T34, T35, T36. We chose this configuration after some initial studies, were all the T-counters were in the trigger, searching for T-counters in geometrical coincidence with the calorimeter.

10. E=1.31 GeV, T=18 deg: energy calibration To perform energy calibration, we decided to start with calibration constant calculated from cosmic rays measurement, then to introduce a correction: Correction: scale factor to equalize all the spectra at end-point. Central crystal is take as reference (we're interested at the relative energy resolution for events in which there's a dominant deposition in the central crystal). Correction ~ 20 % (same order of magnitude as the uncertainty on the cosmic calibration constants). No correction, energy calculated from cosmic rays constants.

11. E=1.31 GeV, T=18 deg: alignment The calorimeter is quite well aligned with electron trajectories Events with: ● Etot> 100 MeV ● At least one hit in T-35 (left and right) ● At least one hit in E-258 Charge center of gravity is defined (event by event) as: Calorimeter seen from the front

12. E=1.31 GeV, T=18 deg: energy resolution We used some cuts to select events with an electron hitting the central crystal of the calorimeter: with these events we calculated the relative energy resolution of the system. Set of cuts that we used: 1) E tot > 100, T-hit (35), E-hit (258). 2) E central > 600 MeV AND (1) 3) E i > 5 MeV AND (2) i:1..9 Cuts (1) and (2) are used to select “good” events, while cut (3) simulates the effect of an energy threshold applied to each channel. As above E r =1.31 GeV is the “real” energy of the incoming electron. The measured energy is lower due to the energy loss from the lateral sides of the calorimeter. There's no difference with and without threshold: the dominant effect is the energy leakage from the lateral side of the calorimeter.

13. E=1.31 GeV, T=3 deg We don't have cal. constants for T=3 deg: we need to interpolate cosmic rays results at differen T. OR: we use the same cal. constants as for T=18 deg, we correct them in the same way and see if there's an increase in the measured energy (due to the increase in LY) No correction Corrected cal. constants

14. E=1.31 GeV, T=3 deg: energy resolution Set of cuts that we used (as before): 1) E tot > 100, T-hit (35), E-hit (258). 2) E central > 600 MeV AND (1) 3) E i > 5 MeV AND (2) i:1..9 No differences from T=18 deg. But..

15. E=1.31 GeV, T=18 deg – T=3 deg comparison 1.15 1.1 1.05 1.16 1.1 1.14 1.06 Comparison between T=18 deg and T=3 deg (some cal. constants to avoid any bias). The increase in LY is reported for each crystal: values between 5% and 15%. From cosmic rays measurements in Genova: it was higher, ~ 30%

16. E=1.92 GeV, T=18 deg PRELIMINARY! Detector was calibrated repeating the same procedure discussed before. Corrections to cal. constants are the same as those with E=1.32 GeV, T=18 deg (Before was 2.6 %)

17. Conclusions References http://g3wiki.ge.infn.it/mediawiki-1.15.1/index.php/Test_at_JLabhttp://g3wiki.ge.infn.it/mediawiki-1.15.1/index.php/Test_at_JLab: results of Jlab tests. Page is updated while performing data analysis. We performed a parasitic test of the FT-prototype in HallB during HD-ICE run, installing the prototype under the photon tagger. We took data @ 2 beam energies: 2.282 GeV and 3.356 GeV (corresponding to 1.3 GeV and 1.9 GeV electrons on the FT-proto). Data analysis is still undergoing! ● We operated the FT-proto in a real experimental hall, without noticing any increase in the noise level of the signals (RMS ~ 4 mV ~ 8 MeV): validation of the design of amplifiers and of the signal distribution board! ● We measured the relative energy of the system @ 1.3 GeV ~ 2.7 %, in good agreement with GEMC simulations. ● No changes in the relative energy resolution are seen moving from T=18 deg to T=3 deg ● Analysis has to be completed: in particular, we need to study timing performances of the system (time from the tagger is used as reference!) and to look at the effect of the threshold. Thanks to all people from JLab for the great support they give us during the installation and operation of the FT-proto!

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