1. Francesco Noferini Centro Studi e Ricerche “Enrico Fermi”, Roma Bologna University & INFN Frascati Wednesday, 14 th November 2007 TOF contribution to the Minimum Bias Trigger of pp collisions Terzo Convegno Nazionale sulla Fisica di ALICE

2. Frascati – Wednesday, 14 th November 2007 2 Summary TOF geometry Trigger with the TOF PYTHIA pp collisions – fully reconstructed events Efficiency for the trigger Efficiency for beam-gas/halo events

3. Frascati – Wednesday, 14 th November 2007 3 TOF geometry Holes for the PHOS 18 SuperModules

4. Frascati – Wednesday, 14 th November 2007 4 TOF geometry (II) The TOF detector is composed by: 18 Super Modules (18 sectors in  )  1600 MRPC x 96 channels Granularity: 2.5x3.5 cm 2 at  3.7 m from the primary vertex; Total sensitivity area  150 m 2 Time resolution, σ < 100 ps High efficiency, ε > 99%

5. Frascati – Wednesday, 14 th November 2007 5 The TOF trigger Based on a very fast detector (L0); Large area; |  | <1; High segmentation; FPGA Flexibility allows to search for different topology and to change the trigger selection on the fly. Status: Magnetic and radiation test for all the electronic components: done.

6. Frascati – Wednesday, 14 th November 2007 6 Trigger with the TOF Ultra Peripheral AA collisions (L0) pp MB (L0) High multiplicity (L0) Jets in pp collisions (L1) Cosmics (commissioning, μ physics) (L0); AliTOFTrigger class: read the TOFdigit information and return the mask with the TOF trigger response.

7. Frascati – Wednesday, 14 th November 2007 7 Granularity for the TOF trigger 2 MRPC = 2 x 96 ch 2 x ½-MRPC.OR. of 96 ch MaxiPad (MP) 2 x ½-MRPC.OR. of 96 ch MaxiPad (MP) TOF pad (~ 10 cm 2 ) 1000 cm 2

8. Frascati – Wednesday, 14 th November 2007 8 To Alice CTP 72 cables, L=60 m, 25 pairs (LVDS) Crate 1 Crate 2 LTM CTTM LTM 1638 strips, 157248 pads................... Crate 72 LTM Stratix II Trigger decision, VME 36 x 25 Stratix II 25x36 input Stratix II 25x36 input TO CTP Piggy back

9. Frascati – Wednesday, 14 th November 2007 9 The L0 MB TOF trigger When the number of MP signals is greater than a given threshold the trigger is set ON. An independent trigger signal for each bunch crossing (time of the clock = 25 ns) can be asserted MP-0001 MP-0864 … Front MP-0865 MP-1728 … Back Counter  thr. LUP (Look Up table)

10. Frascati – Wednesday, 14 th November 2007 10 Background from the detector noise The choice for the MB threshold depends on the background expected for the detector noise. Measured rate Safety rate The Fake Trigger Rate is expected to be of the order of 1 Hz for a threshold of 4. Please note: if Single pad rate = 5 Hz/pad  FTR ( TH = 3) as low as 60 Hz, compared With few tens of kHz of MB genuine trigger

11. Frascati – Wednesday, 14 th November 2007 11 Comparison with ITS-VZERO trigger MB1 = GLOB.FO.OR. VZERO.OR MB2 = GLOB.FO.AND. VZERO.OR MB3 = GLOB.FO.AND. VZERO.AND.AND. notBG ISUBSubprocess nameCross Section (mb) @ 14 TeV 92-93Single diffractive14.3 94Double diffractive9.8 Non diffractive55.2

12. Frascati – Wednesday, 14 th November 2007 12 Results vs. TOF threshold Comparison between TOF (N thr = 4 MP) and MB3. The TOF gain for different processes:  1.5% for Minimum Bias (All Inelastic) ~8% for single diffractive ~12% for double diffractive. 3 3 3 ALL INELASTIC

13. Frascati – Wednesday, 14 th November 2007 13 Efficiency vs. N tracks (18 SM)

14. Frascati – Wednesday, 14 th November 2007 14 beam-gas/halo results Expected contamination to the MB pp interaction dur to beam-gas interactions. For N thr = 4 it reduces to 2.5% (N thr )

15. Frascati – Wednesday, 14 th November 2007 15 Some considerations The simulations above are performed in the pessimistic case: the background is a factor 5 higher than the one measured in the laboratory. Should the background be at the expected level (5 Hz/pad ~ 0.5 Hz/cm 2 ). In this case the threshold for MB triggering can be lowered to MP = 3 (FTR = 60 Hz). Other configurations can allow to low the threshold.

16. Frascati – Wednesday, 14 th November 2007 16 An example TOF.AND. ITS (N thr < 4)

17. Frascati – Wednesday, 14 th November 2007 17 Conclusions TOF trigger performances for pp MB events was presented; TOF trigger provides a fast (L0) and flexible signal (programmable on the fly) for each pp bunch crossing; Fake trigger from electronics noise is under control; The gain wrt the current MB setup was shown and it is relevant in the region of low multiplicity; The beam-gas effect was shown.

18. Frascati – Wednesday, 14 th November 2007 18 backup

19. Frascati – Wednesday, 14 th November 2007 19 Detector utilizzati nel trigger ITS OR di 1200 canali Soglia > 100 σ rispetto al fondo Integrazione su 100 ns (4 bunch crossing) VZERO 2 set di contatori a scintillazione 4 finestre temporali (BBA, BBC, BGA, BGC) Segnale di veto per interazioni beam-gas

20. Frascati – Wednesday, 14 th November 2007 20 Some EVENT DISPLAYs TOFsw = ppMB TOF trigger response MB1sw = response for MB1 ITS-VZERO configuration MB2sw = response for MB2 ITS-VZERO configuration MB3sw = response for MB3 ITS-VZERO configuration Red Line = primary track with a digit on the TOF Black Line = track which gives a digit on the TOF through a secondary track TOF TRD TPC ITS VZERO

21. Frascati – Wednesday, 14 th November 2007 21 Efficiency wrt the MB-TOF threshold (18 SM) Gain from TOF for MB3 = 3.5 % SD +6.5% DD +14%

22. Frascati – Wednesday, 14 th November 2007 22 Efficiency wrt the type of the process (18 SM) - old version (no time digit cut)