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

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

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

Frascati – Wednesday, 14 th November 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%

Frascati – Wednesday, 14 th November 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.

Frascati – Wednesday, 14 th November 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.

Frascati – Wednesday, 14 th November 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

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

Frascati – Wednesday, 14 th November 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)

Frascati – Wednesday, 14 th November 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

Frascati – Wednesday, 14 th November 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 14 TeV 92-93Single diffractive Double diffractive9.8 Non diffractive55.2

Frascati – Wednesday, 14 th November 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 ALL INELASTIC

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

Frascati – Wednesday, 14 th November 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 )

Frascati – Wednesday, 14 th November 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.

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

Frascati – Wednesday, 14 th November 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.

Frascati – Wednesday, 14 th November backup

Frascati – Wednesday, 14 th November 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

Frascati – Wednesday, 14 th November 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

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

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