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LumiCalo background subtraction

LumiCalo background subtraction. Trigger. e +. adc2. adc3. adc1. adc4. adc0. adc12. adc11. adc13. adc9. adc5. adc10. adc14. IP. adc8. adc6. adc7. e -. adc18. adc16. adc19. adc15. adc17. trg(i) = (discriminated) OR of the 5 sectors in the i-th module. trg(i). threshold.

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LumiCalo background subtraction

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  1. LumiCalo background subtraction P. Valente, 28-29 April 2008

  2. Trigger e+ adc2 adc3 adc1 adc4 adc0 adc12 adc11 adc13 adc9 adc5 adc10 adc14 IP adc8 adc6 adc7 e- adc18 adc16 adc19 adc15 adc17 trg(i) = (discriminated) OR of the 5 sectors in the i-th module trg(i) threshold P. Valente, 28-29 April 2008

  3. Trigger trg(0) trg(3) IP trg(2) trg(0) AND trg(1) trg(1) OR T1 trg(2) AND trg(3) P. Valente, 28-29 April 2008

  4. Trigger words trg0=10 trg1=11 • We found some hardware problem, since there should be • no singles • no “wrong” doubles doubles trg0 AND trg1 AND trg2= 10+11+12=33 singles triples trg0 AND trg1= 10+11=21 P. Valente, 28-29 April 2008 “wrong” doubles (10+12, 11+12, 11+13)

  5. trg2 AND trg3 trg0 AND trg1 After having fixed trigger hardware configuration… …everything looks fine No singles No “wrong” doubles trg1 AND trg2 AND trg3 trg0 AND trg1 AND trg2 P. Valente, 28-29 April 2008

  6. Background We can have energy deposits over threshold in another module, in addition to the couple of triggering modules: this gives us the “triples” We expect a similar level of events with no Bhabha, but with two “spurious” deposits, giving a fake coincidence P. Valente, 28-29 April 2008

  7. Background Bhabha peak Si=0,…,4 (ADCi – <PED>i) • Indeed not all the triggering events look like Bhabha events… • …but it seems difficult to reject effectively background introducing a cut on energy • Additional difficulties: • dependence on sector calibration • dependence on threshold background P. Valente, 28-29 April 2008

  8. Background topology imax(1) = sector with most energy imax(2) = 2nd most energetic sector Diagonals=back-to-back sectors + neighbor 100+100 bunches 1+1 bunches P. Valente, 28-29 April 2008

  9. Background topology 9 14 Excess of events with most energy in sectors 9 and 14 Probably due to background… P. Valente, 28-29 April 2008

  10. Background topology Cross check looking at runs with only 1 beam run 1392, e- 350 mA, 100 bunch run 1394, e+290 mA, 100 bunch P. Valente, 28-29 April 2008

  11. Background topology adc2 adc3 adc1 adc4 adc0 adc12 adc11 adc13 adc9 adc5 adc10 adc14 IP adc8 adc6 adc7 adc18 adc16 adc19 adc15 adc17 Excluded from trigger the 2 most external sectors [the most affected by background] in all 4 the calorimeter modules Since April 2nd, 2008 P. Valente, 28-29 April 2008

  12. Background topology 96.3% 79.0% The fraction of triples is greatly reduced: 21.0%  3.7% … P. Valente, 28-29 April 2008

  13. Background topology 43% 21% … and of course, the out-of-time events are greatly reduced too 6% 2% P. Valente, 28-29 April 2008

  14. Time • Let’s give a look at the time information: • Time of single sectors is not always available [~50% of events] because the minimum threshold of the SDS discriminator is too high [and cannot be further lowered…] • We can use the time of analog sum of the five sectors in each of the 4 modules adc15 … adc19 t(1) threshold adc(21) Passive splitter tdc15 … tdc19 P. Valente, 28-29 April 2008 SDS threshold

  15. Trigger time n=3 n=2 n=1 Since we have a multi-hit TDC, we can have more than 1 hit for the 4 modules + 2 coincidences t(0)…t(3) t(4)=time of 0 AND 1 t(5)=time of 2 AND 3 Choose the largest time [the one closest to the COMMON STOP] P. Valente, 28-29 April 2008

  16. Trigger time t(4)=time of 0 AND 1 t(5)=time of 2 AND 3 Select triggering combinations: 0 AND 1 = t(4)>3600 counts 2 AND 3 = t(5)>3600 counts P. Valente, 28-29 April 2008

  17. Trigger time Assume that in-time events are true Bhabha’s… trigger narrow wide …and “later” coincidences are due to background wide narrow P. Valente, 28-29 April 2008

  18. Trigger time If we plot Dt=t trigger module 0 – t trigger module 1 we observe a narrow peak, s~2 counts, To select “in-time” coincidences, we can apply a 3-s cut: [–6,6] counts Then, by weighting the narrow peak [12.5 ns] with respect to the wide time interval [~80 ns], we can extract the background rate: 12.5/80×Nwide-narrow/Nwide×rtrigger Side consideration: The flat distribution (“wide”) is not symmetric with respect to the narrow peak because of different length of the digital signals put in coincidence… P. Valente, 28-29 April 2008

  19. Trigger time In order to reduce the fraction of background events, we have reduced the digital signal length, thus reducing the “wide” interval [also making the signals “symmetric”, all ~25 ns] Since April 9th, 2008 P. Valente, 28-29 April 2008

  20. Out-of-time events P. Valente, 28-29 April 2008

  21. Out-of-time events We have assumed that in-time events are true Bhabha’s, while out-of-time coincidences, belonging to the “wide” distribution in Dt, are due to spurious events In order to validate this hypothesis, we put the beam out of collision [by shifting the RF phase of 180 degrees] in collision out of collision P. Valente, 28-29 April 2008

  22. Online filter  - Use side-band to estimate background contribution under peak P. Valente, 28-29 April 2008

  23. Online filter correction • Take data on “trash” [without storing raw files] • Run filter on data buffer • Accumulate 1000 events… [Dt ~3 seconds at 300 Hz] • Evaluate in-time events, subtracting side-band • Do this for 0•1 coincidence as well as 2•3 coincidence • Weight T2 rate with these corrections… [T2 rate=1000/Dt] • Store every 1000 events on bhabha.stat • Synchronize every 15 seconds with general information in DAFNE, including T1FREE rate • Display on web… P. Valente, 28-29 April 2008

  24. Online filter • Since the out-of-time method seems quite robust, we have introduced a level-3 filter, counting only triggers “in-time”. Summarizing: • T1FREE= rate of T1 triggers • [not vetoed by the DAQ busy NOR by the DAFNE injection hardware signal] • T2 = rate of T2 triggers [fixed dead-time of 4 ms] • T2FARM= T2 triggers with • t(0 AND 1)>3600 counts • N[abs(t(0)-t(1))<6 counts] - N[sideband] • + • t(2 AND 3)>3600 counts • N[abs(t(2)-t(3))<6 counts] - N[sideband] P. Valente, 28-29 April 2008

  25. Online filter Since April 21st, 2008 During injections T1FREE is jumping up… … while T2FARM is going down due to injection veto in DAQ P. Valente, 28-29 April 2008

  26. Online filter Background contribution is – quite obviously – lower at lower currents Smoothing due to statistical fluctuations [1000 events integrated by T2FARM] P. Valente, 28-29 April 2008

  27. Bad e+ injections Good e+ injection Bad e+ injections P. Valente, 28-29 April 2008

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