Summary of the L0 Trigger Performance

 

This page summarises the L0 trigger performance on the data produced with the successive Brunel versions. It contains information on the L0 thresholds used, the minimum bias exclusive rates, the results of the monitoring of the various sub-triggers, and the L0 efficiencies (normalised to offline selected events) for all the physics B-decay channels available.

Go to the requested Brunel version:

v13r1  |  v14r0  |  v14r2  |  v16r4  |  v17r3  |  v17r4  | 

 

Brunel v13r1 - Database v248r4 - SICBMC v254r3 and v254r4
(Summer production 2002)

In these samples the L0 thresholds were as follows:

L0 Thresholds (GeV) e γ h ∑ ET π0L π0G μ ∑ ETμμ
  2.40 3.99 3.18 5.00 4.10 4.60 0.46 4.01

The pile-up veto decision was taken with a cut on the height of the second peak at 2.

These settings translated into a minimum bias retention of 6.718%,
hence a L0 output rate of 0.06718 x 14.842 x 1000 = 997.09 kHz, assuming a L0 input rate of 14.842 MHz.

The exclusive rates on minimum bias (M.B.) events are:

M.B. Exclusive L0 Rates (kHz) e μ h μμ γ e+μ h+μ h+e h+μ+e π0L π0G π0L+G
Sum = 997.1 48.4 165.9 585.7 20.5 7.7 4.2 52.8 55.2 10.7 18.4 18.1 9.5

The L0 efficiency (normalised to the offline selected events) was calculated for some available physics channels:

L0 Efficiencies (%) true single int. all interactions
Bd → π+ π- 58.9 -
Bs0 → Ds-(K+ K- π-) K+ 42.0 37.7
Bs0 → J/Ψ(μ+ μ-) φ(K+ K-) 86.7 80.8

The table below summarises the L0 performance (as of 6/11/2002) for each of the sub-triggers for a variety of physics channels. Also shown are the percentage of events that pass L0 and the percentage of events vetoed by the pile-up veto.

L0 Performance % veto % pass e acc. γ acc. h acc. π0L acc. π0G acc. π0L+G acc. μ acc. ∑μ acc. # events
Minimum bias 18.31 6.72 0.80 0.18 4.75 0.89 0.86 1.26 1.58 0.30 50 k
Bd0 → D+ D- 41.57 26.67 3.55 0.48 19.46 4.02 3.57 5.36 7.28 2.09 55.5 k
Bd → D0(K+ K-) K*0(K+ π-) 41.70 29.61 3.83 0.53 22.36 4.47 4.15 6.04 7.57 2.12 19.5 k
Bd → J/Ψ(e+e-) KS(π+ π-) 41.68 30.99 15.03 0.68 17.25 9.47 9.14 12.39 6.36 1.72 24.5 k
Bd → J/Ψ(μ+μ-) KS(π+ π-) 41.44 54.38 3.41 0.65 16.39 3.72 3.25 4.80 37.07 25.19 20 k
Bd → K* γ 42.04 33.06 9.57 4.46 19.74 12.33 11.64 15.02 6.75 1.93 47.5 k
Bd → π+ π- 41.50 34.07 4.50 0.57 28.04 5.44 5.07 7.20 6.58 1.89 65 k
Bd → π+ π- π0 41.17 33.05 6.69 1.72 24.68 8.00 7.20 9.99 6.33 1.82 20.5 k
Bd0 → ρ0(π+ π-) π0 41.36 32.70 8.71 3.21 21.25 11.48 10.54 14.06 6.32 1.71 20 k
Bs0 → Ds+ Ds- 42.05 26.34 3.50 0.53 19.07 3.78 3.55 5.07 7.42 2.05 20.5 k
Bs0 → Ds-(K+ K- π-) K+ 41.59 30.14 3.90 0.57 23.07 4.23 3.86 5.64 7.49 2.15 22.5 k
Bs0 → J/Ψ(μ+ μ-) φ(K+ K-) 41.52 52.88 3.05 0.47 15.37 3.37 2.97 4.48 36.99 23.67 21978

 

Brunel v14r0 - Database v248r4 - SICBMC v254r3 and v254r4

In these samples the L0 thresholds were as in the Brunel v13r1 production.

The L0 performance is (8/11/2002):

L0 Performance % veto % pass e acc. γ acc. h acc. π0L acc. π0G acc. π0L+G acc. μ acc. ∑μ acc. # events
Bs0 → J/Ψ(μ+ μ-) φ(K+ K-) 40.74 53.83 2.90 0.60 15.31 3.38 3.20 4.46 37.16 25.08 8 k

 

Brunel v14r2 - Database v248r4 - SICBMC v254r3 and v254r4

In the samples produced with Brunel v14r2 the L0 thresholds were as in version v13r1.

Based on these default settings the L0 performance is (14/11/2002):

L0 Performance % veto % pass e acc. γ acc. h acc. π0L acc. π0G acc. π0L+G acc. μ acc. ∑μ acc. # events
Minimum bias 15.55 7.51 0.84 0.17 5.38 1.00 0.88 1.38 1.82 0.30 94 k
Bd → J/Ψ(μ+μ-) KS(π+ π-) 36.63 56.54 3.47 0.48 17.21 4.16 3.54 5.31 40.69 26.00 10 k
Bd → K* γ 36.55 36.21 10.68 4.76 21.68 13.63 12.66 16.57 7.46 2.00 52 k
Bd → K* π0 36.59 34.85 9.40 3.26 22.26 12.11 11.17 14.86 7.49 1.90 42 k
Bd → π+ π- 36.40 37.15 5.04 0.69 30.84 6.25 5.79 8.21 7.23 1.98 50 k
Bs0 → Ds+ Ds- 37.48 28.92 3.80 0.56 21.16 3.95 3.75 5.33 8.43 2.10 20.5 k
Bs0 → Ds-(K+ K- π-) K+ 36.98 32.90 4.05 0.60 25.27 4.77 4.42 6.50 8.39 2.28 22 k
Bs0 → Ds-(K+ K- π-) π+ 36.52 32.21 4.51 0.62 25.01 4.72 4.58 6.49 7.90 2.09 22 k
Bs0 → J/Ψ(e+ e-) φ(K+ K-) 37.13 33.44 15.61 1.00 18.14 11.02 10.11 13.83 7.67 2.01 119 k
Bs0 → J/Ψ(μ+ μ-) φ(K+ K-) 36.60 56.23 3.22 0.60 17.41 3.85 3.43 5.05 40.30 24.93 21.5 k

But these default thresholds now gave a minimum bias retention of 7.5% (~ 1114 kHz), to be compared to 6.7% (~ 997 kHz) in Brunel v13r1!
And the pile-up veto now only vetoes 15.6% compared to 18.3% in v13r1.

The sources of differences were investigated (19/11/2002):
For the purpose of a comparison between the Brunel versions v13r1 and v14r2, the same set of L0 default thresholds (listed above) was used. The sources of differences can potentially be 2-fold:

  • changes that affect the L0 hadron/electron/... distributions?
  • only the pile-up veto?
    ... or both?

    The ET distributions for the hadron, electron, etc. triggers were all compared; they were found to be the same (apart from inevitable statistical fluctuations, mainly in the tails).So this cannot be the reason.

    The behaviour of the pile-up veto was also studied in some detail, looking at the percentage of (true) single interaction and multiple interaction events that pass it:

    veto pass (%) only single int. mult. interactions
    Brunel v14r2 92.7 66.0
    Brunel v13r1 91.2 60.8

    It is clear from these numbers that the pile-up veto is now letting pass a further 5% of multiple interaction events. Also there is a somewhat smaller increase in veto-accepted true single events.

    It is also possible to see what is then the origin of the extra L0 bandwidth ... the exclusive rates on minimum bias (M.B.) compare as follows:

    M.B. Exclusive L0 Rates (kHz) e μ h μμ γ e+μ h+μ h+e h+μ+e π0L π0G π0L+G Sum
    Brunel v14r2 51.2 188.8 662.8 19.9 7.3 5.1 67.3 58.9 9.5 18.8 17.0 7.1 1113.7
    Brunel v13r1 48.4 165.9 585.7 20.5 7.7 4.2 52.8 55.2 10.7 18.4 18.1 9.5 997.1

    The hadron trigger is what is triggering the bulk of extra events (mainly multiple interactions) that are passing the pile-up veto. Also the muon trigger, to a lesser extent. The reason why the veto is vetoeing less events is related to changes in the veto code, and in particular in the new digitization of the VELO.

    If one retunes L0 back to an output rate of 1 MHz, the new thresholds become

    L0 Thresholds (GeV) e γ h ∑ ET π0L π0G μ ∑ ETμμ
      2.46 4.00 3.32 5.00 4.10 4.60 0.55 4.34

    With these new retuned thresholds one obtains a minimum bias retention of 6.75%, hence a L0 output rate of approx. 1002 kHz, assuming a L0 input rate of 14.842 MHz.

    The exclusive rates on minimum bias events now compare as

    M.B. Exclusive L0 Rates (kHz) e μ h μμ γ e+μ h+μ h+e h+μ+e π0L π0G π0L+G Sum
    Brunel v14r2 - retuned 51.8 171.5 582.5 18.0 8.1 5.2 57.2 52.7 7.3 20.4 20.0 7.6 1002.4
    Brunel v13r1 48.4 165.9 585.7 20.5 7.7 4.2 52.8 55.2 10.7 18.4 18.1 9.5 997.1

    They are seen to be very similar to the exclusive rates in Brunel v13r1. This is expected, and reflect the fact that the bandwidth division was kept identical in the two Brunel versions.

    At this point, a study of the L0 bandwidth division was performed on the new data. The new L0 thresholds reflect the change (25/11/2002):

    L0 Thresholds (GeV) e γ h ∑ ET π0L π0G μ ∑ ETμμ
      2.85 3.00 3.23 5.00 4.10 4.60 0.92 2.50

    The L0 efficiencies (normalised to the offline selected events) were calculated for some available physics channels (9/12/2002):

    L0 Efficiencies (%) true single int. all interactions
    Bd → π+ π- 65.3 55.2
    Bs → K+ K- 60.1 50.9

    The L0 performance becomes (13/12/2002)

    L0 Performance % veto % pass e acc. γ acc. h acc. π0L acc. π0G acc. π0L+G acc. μ acc. ∑μ acc. # events
    Minimum bias 15.55 6.76 0.52 0.42 5.19 1.00 0.88 1.38 0.92 0.53 94 k
    Bd → K+ π- 36.98 35.79 3.25 1.66 29.56 5.91 5.44 7.74 5.24 3.91 62.5 k
    Bd → K* γ 36.55 35.58 8.18 7.44 21.14 13.63 12.66 16.57 4.99 3.67 52 k
    Bd → π+ π- 36.48 36.29 3.42 1.65 30.23 6.22 5.78 8.19 5.02 3.66 62.5 k
    Bs0 → Ds+ Ds- 37.48 27.60 2.40 1.40 20.56 3.95 3.75 5.33 5.67 4.06 20.5 k
    Bs0 → Ds-(K+ K- π-) π+ 36.52 31.07 2.94 1.54 24.50 4.72 4.58 6.49 5.30 3.90 22 k
    Bs0 → J/Ψ(μ+ μ-) φ(K+ K-) 36.61 59.42 2.11 1.45 16.89 3.90 3.45 5.10 37.20 40.30 22 k
    Bs → K+ K- 36.79 36.81 3.27 1.59 30.30 5.92 5.44 7.71 5.69 4.40 65 k

    The L0 efficiency (normalised to the offline selected events) was calculated for all the B-physics decay channels used in the LHCb performance studies presented to the LHCC (13/1/2003):

    L0 Efficiencies (%) true single int. all interactions
    Bd → K+ π- - -
    Bd → K* γ 77.4 62.7
    Bd → π+ π- 65.2 55.1
    Bs0 → Ds-(K+ K- π-) K+ 46.9 41.3
    Bs0 → Ds-(K+ K- π-) π+ 46.0 42.9
    Bs0 → J/Ψ(e+ e-) φ(K+ K-) 53.5 44.4
    Bs0 → J/Ψ(μ+ μ-) φ(K+ K-) 91.8 90.3
    Bs → K+ K- - -

     

    Brunel v16r4 - Database v253r0 - SICBMC v259r1
    (Christmas 2002 production)

    The L0 performance of these data was checked (21-22/1/2003) with the following thresholds that correspond to the latest tuning as used to produce the LHCb trigger performance results presented end of January at the LHCC meeting.

    Note that the pile-up veto decision was taken (for the first time) with a cut on the height of the second peak at 3 (not at 2 as in the past)!

    L0 Thresholds (GeV) e γ h ∑ ET π0L π0G μ ∑ ETμμ
      2.60 3.00 3.52 5.00 4.85 4.90 1.23 1.42

    The data from Brunel v16r4 and v14r2 were analysed with DaVinci v7r2 and v6r1, respectively; but it was cross-checked that identical results are obtained for a given setting with both DaVinci versions.

    Here is how the new data compared to the Summer production data for minimum bias events (with the above set of thresholds and veto cut):
     
    L0 Performance % veto % pass e acc. γ acc. h acc. π0L acc. π0G acc. π0L+G acc. μ acc. ∑μ acc. # events
    Brunel v16r4 8.04 5.59 0.83 0.45 3.80 0.52 0.42 0.65 0.81 1.06 50 k
    Brunel v14r2 7.71 6.77 0.87 0.53 4.95 0.70 0.93 1.20 0.84 1.07 107 k

    One can observe a non-negligible decrease in the L0 output rate, from the nominal ~6.7% (~1MHz) to ~5.6%. The effect comes clearly from quantities related to the calorimeter measurements.

    The comparisons for the ET distributions of the various triggers can be found here.

    Explanation by Olivier Callot (mail from the 22/1/2003):
    " A side effect of the new use of the time information in the digitisation, starting from Brunel v16r4 (Christmas production) is that the HCAL energy, now restricted to the energy deposited in the 25 ns window, is lower than before, and thus the energy calibration of Hcal is incorrect ... A fix is expected in the coming days ... The same change of digitisation was also implemented for Ecal (and Prs and SPD) but the effect is smaller due to the different time structure of electromagnetic and hadronic showers. "

    Both the Ecal and the Hcal were recalibrated to "bring things back to normal".

     

    Brunel v17r3 - Database v254r1 - SICBMC v260r0
    (test production before the large production for the Trigger TDR)

    The same L0 thresholds and veto settings were used here as in the production with Brunel v16r4.

    Based on these default settings the L0 performance is (3/2/2003):

    L0 Performance % veto % pass e acc. γ acc. h acc. π0L acc. π0G acc. π0L+G acc. μ acc. ∑μ acc. # events
    Minimum bias - 6.71 0.96 0.56 5.10 0.53 0.49 0.70 0.68 0.89 44 k
    Bs0 → J/Ψ(μ+ μ-) φ(K+ K-) - 61.78 3.74 1.86 18.15 2.43 1.95 3.03 39.38 51.74 6.5 k

     

    Brunel v17r4 - Database v254r1 - SICBMC v260r2
    (large production for the Trigger TDR)

    The same L0 thresholds and veto settings were used here as in the production with Brunel v16r4.

    Based on these default settings the L0 performance is (3/2/2003):

    L0 Performance % veto % pass e acc. γ acc. h acc. π0L acc. π0G acc. π0L+G acc. μ acc. ∑μ acc. # events
    Minimum bias 8.08 7.14 0.95 0.57 5.51 0.65 0.50 0.80 0.71 0.88 200 k
    Bd → D0(K+ π-) K*0(K+ π-) 24.56 34.50 4.50 2.20 27.13 3.19 2.98 4.21 5.08 6.77 49 k
    Bd → D* π 24.73 35.93 4.98 2.29 28.95 3.25 3.21 4.39 4.66 6.26 49.5 k
    Bd → J/Ψ(e+e-) KS(π+ π-) 24.57 37.07 18.83 3.17 20.54 9.27 7.71 10.46 4.35 5.81 49.5 k
    Bd → J/Ψ(μ+μ-) KS(π+ π-) 24.54 63.95 4.21 2.20 19.35 2.94 2.60 3.70 41.23 53.70 49.5 k
    Bd → J/Ψ(μ+μ-) K*0(K+ π-) 25.00 62.99 3.99 2.02 19.07 2.74 2.38 3.49 40.25 52.58 50 k
    Bd → K+ π- 24.90 40.56 5.27 2.26 33.73 3.49 3.74 5.00 4.84 6.42 49 k
    Bd → K* γ 24.69 40.96 12.30 10.22 23.59 11.25 11.29 13.53 4.39 5.92 48 k
    Bd → φ(K+ K-) KS(π+ π-) 24.67 33.46 4.84 2.34 26.05 3.21 2.88 4.21 4.84 6.58 50 k
    Bd → μ+ μ- K*0(K+ π-) 24.56 61.20 4.10 2.15 20.24 2.89 2.44 3.63 37.78 49.30 50 k
    Bd → π+ π- 24.91 40.44 5.66 2.35 33.84 3.44 3.85 5.09 4.37 5.89 49 k
    Bd → π+ π- π0 24.69 38.94 8.58 5.48 28.09 7.15 6.81 8.81 4.26 5.75 105 k
    Bs0 → Ds-(K+ K- π-) K+ 24.90 35.12 4.58 2.16 27.70 3.08 2.99 4.16 5.07 6.85 137.5 k
    Bs0 → Ds-(K+ K- π-) π+ 24.55 34.88 4.80 2.17 27.73 3.19 3.07 4.31 4.73 6.35 200 k
    Bs0 → J/Ψ(μ+ μ-) η(γ γ) 24.75 64.07 6.93 4.80 17.61 4.97 4.82 6.37 40.69 53.23 50 k
    Bs0 → J/Ψ(e+ e-) φ(K+ K-) 24.81 36.54 18.44 3.17 19.79 9.47 8.02 10.65 4.30 5.85 48.5 k
    Bs0 → J/Ψ(μ+ μ-) φ(K+ K-) 24.48 62.52 4.03 2.07 18.65 2.82 2.43 3.52 40.14 52.07 50 k
    Bs0 → K+ K- 24.70 41.39 5.31 2.36 34.32 3.64 3.75 5.15 5.08 6.87 50 k
    Bs0 → K- π+ 24.61 40.84 5.37 2.26 34.05 3.37 3.65 4.91 4.78 6.43 51 k
    Bs0 → ηc(1S) φ(K+ K-) 24.88 29.96 4.16 2.02 22.18 2.99 2.48 3.71 5.05 6.67 49.5 k
    Bs0 → μ+ μ- 24.95 71.58 3.81 2.02 16.82 2.71 2.31 3.35 48.98 64.47 49 k