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L0-trigger and new generator (lhcb-trig)

From: dyk@mail.cern.ch
Date: 2/4/00
Time: 8:13:31 PM
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Since the TP days we have changed quite a few items concerning the
L0-trigger rates. In this mail I would like to quickly review the TP
situation, and then give the situation from SICB v220 onward.
- TP situation.
  . We generated only hard-scattering processes, assuming a total cross 
    section of 80 mb.
  . We used the 3x3 code for electron and hadron triggers.
  . The bandwidth of 1 MHz of L0-YES was subdivided as follows:
    Average number of interactions/crossing=cross-section*luminosity/rate,
    where luminosity=2*10**32, and the rate of filled bunch crossings
    per second is 30 MHz. This gives 0.533 interactions/crossing.
    #interaction Probablity/interaction rate(MHz)
         0         0.587                 17.6 (+10 due to empty bunches)
         1         0.313                 9.39
        >1         0.100                 3.00
    Hence we need a L0-mbias-retention of: 1/(9.39+3)=8.1% to get a 
    1 MHz L0-accept rate.
    (However, the L0-mbias-retention fraction was usually quoted as
     a fraction of events which were accepted by the pile-up veto.
     The pile-up veto accepted 95% of single and 20% of multiple
     interaction crossings, hence: 1/(0.95*9.39+0.2*3)=10.5%. 
     The h/mu/e then took: 6/2/1% of this 10.5% leaving the 
     remaining 1.5% for single-photon, mumu, LHC-halo-muons etc.
     I suspect that the pile-up veto loss of 5% (or maybe more for
     B-channels) has not been taking into account for the final
     trigger acceptance in the TP.)
     The pt/Et thresholds used for the TP were:
      parameter (rmucut = 1.0,    !   L0 muon Pt cut
     >           relcut = 2.34,   !   L0 electron Pt cut
     >           rgacut = 4.0,    !   L0 gamma Pt cut
     >           rhacut = 2.4,    !   L0 hadron Pt cut
- Situation since SICB v220:
  . We generate hard-scattering+diffractive(single and double)+elastic
    processes. The total cross section is 102.4 mb. This is evtyp=61. 
    The cross section of 102.4 mb is coherent with respect to the one 
    adopted at the TP time: the main difference is that we model the 
    inelastic events taking into account all the effects and the 80 mb 
    are now shared in the following (more realistic) way:
    - sigma(hard scattering) 55 mb
    - sigma(diffractive)     25 mb
    and in addition we have  22.4 mb of elastic events.
    (Evtyp=51 is the hard-scattering only part)
  . We moved to the 2x2 algorithm for the calorimeters. (Bank T2X2).
    Note that the "energy-scale" is slightly changed due to this move.
    (We did NOT yet move to the new pile-up code, which has two passes to
     to recognise two pile-up events with very different multiplicity)
  . We started producing tapes with pile-up events according to the
    expected luminosity: DST1=no pile-up.
                         DST2=1.56*10**32 and 2*10**32 (see note 1)
    DST2 tapes are produced assuming a falling luminosity during a fill
    with a lifetime of 10 hours and a fill time of 7 hours, requiering
    the AVERAGE luminosity to be 2.10**32 (or 1.56*10**32 see note 1).
    DST3 tapes try to simulate "worst conditions", hence a flat luminosity
    of 5.10**32. (Which will hopefully last for minutes rather than hours
    during the real experiment).
    Note 1: For the data produced with v220 the total-cross-section*L was 
            assumed to be 80 mb * 2.10**32, but since the correct 
            total-cross-section is 102.4, (80mb+24.4mb elastic) this 
            effectively means that L=1.56*10**32 for these tapes.

.DST2 tapes for v222: (For v220 data I do not give the pt/Et threshold, since they are not so relevant at L=1.56*10**32, the first DST2 tapes of v222 have this low L too, hopefully to be fixed soon). The new number of interactions/crossing=0.683 (But note that on our tapes a fair fraction of the events is "empty", elastic, backward- single-diffractive, even hard-scatter with very low multiplicity) #interaction Probablity/interaction rate(MHz) 0 0.505 15.16 (+10 due to empty bunches) 1 0.345 10.35 >1 0.150 4.49 Hence we need a L0-mbias-retention of: 1/(10.35+4.49)=6.5% to get a 1 MHz L0-accept rate. I have retuned the pt/Et thresholds to get roughly the same division of bandwidth as for the TP. Eventually Clair's allocation of trigger rates (TP, section 12.3.5) has to be revived again to do this properly, now I just required h:mu:e:g:mumu=6:2:1:0.1:0.1, and 10% of the bandwidth is left for LHC-halo-muons and random-triggers and etc. I get the following rates for all the triggers: (rate=number of events which pass both the threshold cuts, and are not vetoed by the pile-up or "activity" veto (see note 3 below), devided by the total number of events on tape, each event enters only once): mu = 0.010355 (mu+(mu+e)+.... )/6.5%=23% e = 0.00419132 (e+(mu+e)+(h+e)+(mu+h+e))/6.5%=11% mu+e = 0.000493097 h = 0.0357495 (h+(h+mu)+... )/6.5%=64% h+mu = 0.00345168 h+e = 0.00221893 h+mu+e = 0.000493097 gamma = 0.000739645 /6.5%= 1% mumu = 0.000739645 /6.5%= 1% -------------------- Sum = 0.0584 %, hence leaving .7% for LHC-halo-muons etc. The pt/Et thresholds used for the above are: parameter (rmucut = 1.17, ! L0 muon Pt cut > relcut = 2.67, ! L0 electron Pt cut > rgacut = 4.43, ! L0 gamma Pt cut > rhacut = 2.65, ! L0 hadron Pt cut > rmmcut = 3.45, ! L0 sum pt mumu cut: Note 2 > etocut = 50., ! L0 min etot cut : Note 3 Hence: the cuts are very similar to the TP values as expected, maybe slightly higher (i.e. less efficient for B's?). Note 2: I introduced a mumu cut, which requires two muons to be reconstructed, and the sum of their pts>3.45 GeV. This trigger ignores the pile-up veto decision. Mainly for rare B-decays. Forced to be small=1% of L0. Note 3: I require some minimal "activity" in the spectrometer, for now etot(calorimeter)>50 GeV. Note that about 20 MHz of crossings will not have "hard-scattering" pp interactions, but for these events we do not want to have the muon trigger fire when it finds a LHC-halo-muon. The 10 MHz of empty bunches could be vetoed by the trigger supervisor. The source of this "activity" signature should be discussed, Etot, number of hits in pile-up veto, both, ??. This 50 GeV cut lost me one event in 10k B->pipi events, while 39% of the events on tape have Etot<50 GeV. The pile-up-veto finds more than 1 vertex in 12% of the events, or .12/(1-.39)=20% of the "active" events, which is roughly the same as in the TP days: (.05*9.39+.8*3)/(9.39+3)=23%. .DST3 tapes for v222 onward, i.e. 5*10**32 flat rate. Number of interactions/crossing=1.707 #interaction Probablity/interaction rate(MHz) 0 0.181 5.44 (+10 due to empty bunches) 1 0.310 9.3 >1 0.509 15.28 Hence we need a L0-mbias-retention of: 1/(9.3+15.28)=4.1% to get a 1 MHz L0-accept rate. No data available yet. Hence I have reweighed the DST2 tapes to get a mixture which looks like 5*10**32 (but low statistics). The corresponding pt/Et cuts are: The pt/Et thresholds used for the above are: parameter (rmucut =2.8 , ! L0 muon Pt cut > relcut =3.2 , ! L0 electron Pt cut > rhacut =3.4 , ! L0 hadron Pt cut > etocut = 50., ! L0 min etot cut (Photon and mumu did not have enough statistics to give a "tuned" cut) At 5*10**32, 26% of the events have Etot<50 GeV, while 18% are vetoed by the pile-up-veto, i.e. pile-up=.18/(1.-26)=24% of "active" events. Especially the increase in the muon threshold is somewhat surprising, maybe due to statistics(1000 events left after reweighing all the DST2 data), but clearly the muons have a much longer/flatter tail in their pt distribution. Maybe very large pT muons should be deappreciated? We will know the moment we get DST3 data.

Once the luminosity is in the PASS bank per event, I'll release a AXTRIGGER replacement which will return the level-0 decision according to the generated conditions automatically. Regards, Hans Dijkstra.

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