Year Period CIP veto eff., % ToF veto eff., % Total veto eff., % 0304 e+p RH 99.79 ± 0.03 99.30± 0.25 99.09± 0.25
LH 99.56 ± 0.07 99.30± 0.25 98.86± 0.26 2005 e−p RH 99.44 ± 0.07 99.09± 0.09 98.54± 0.11 LH 99.49 ± 0.04 99.44± 0.04 98.93± 0.06
Table 6.4: Veto efficiencies.
6.8.4 Trigger Efficiency
TheLAr electron 1 TE and timing conditions are the core of the high Q2 NC trigger used in this analysis. It is required that the trigger is fully efficient for the selected data. The regions in which this is not the case are excluded as indicated on the figure 6.31.
The efficiency of the veto conditions, which are introduced in the trigger to reject non-ep background, does not depend on the epphysics process. The small inefficien-cies observed due to these requirements are corrected for.
An uncorrelated systematic uncertainty of 0.5% is attributed to the trigger efficiency.
/ deg ϕe
-150 -100 -50 0 50 100 150
/ cm LArz
-200 -150 -100 -50 0 50
100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100 99 100 100 100 95 99 100
100 100 100 100 100 100 100 100 100 100 100 100 100 100 97 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 95 100
100 99 100 100 100 100 100 100 100 100 100 100 100 100 96 100
100 100 99 100 100 100 99 100 99 100 100 100 99 100 100 100
100 100 99 100 100 100 98 100 85 100 100 100 98 100 100 100
100 100 98 100 100 100 99 100 98 100 99 100 98 100 100 100
100 100 100 99 100 100 97 100 100 100 100 100 92 99 95 89
100 100 100 100 100 100 99 100 100 100 100 100 90 99 88 75
100 100 100 100 100 100 99 100 100 100 100 100 84 99 87 65
99 100 99 100 99 100 100 99 100 100 100 100 99 100 86 100
99 100 99 100 100 100 100 100 100 100 100 100 99 100 77 99
100 100 99 100 100 100 100 100 100 99 100 100 98 100 87 100
100 100 99 100 100 100 100 100 100 100 100 100 92 100 82 99
100 100 98 100 100 100 100 100 100 100 100 100 92 100 80 100
100 100 100 100 100 100 100 100 100 100 99 100 97 100 89 88
100 100 100 100 100 100 100 100 100 100 100 100 99 100 100 87
100 99 100 100 100 100 100 100 100 100 100 100 100 100 100 84
99 99 99 100 100 100 99 100 98 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 98 99 100 100 100 100 100 100
100 100 98 100 100 100 100 100 96 98 100 100 100 100 100 100
100 100 100 100 91 100 100 100 99 100 100 99 100 100 100 100
/ deg ϕe
-150 -100 -50 0 50 100 150
/ cm LArz
-200 -150 -100 -50 0 50
(a)
/ deg ϕe
-150 -100 -50 0 50 100 150
/ cm LArz
-200 -150 -100 -50 0 50
100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100 100 100 100 100 97 99 100
100 100 100 100 100 100 100 100 100 100 100 100 100 100 99 99
100 100 100 100 100 100 100 100 100 100 100 100 100 100 96 99
100 100 100 100 100 100 100 100 100 100 100 100 100 100 98 99
100 100 100 100 100 100 99 100 99 100 100 100 99 100 100 100
100 100 100 100 100 100 98 100 94 100 100 100 99 100 100 100
100 100 99 100 100 100 100 100 95 100 100 100 99 100 100 100
100 100 100 100 100 100 99 100 100 100 100 100 93 100 93 91
100 100 100 100 100 100 99 100 100 100 100 100 85 100 87 76
100 100 99 100 100 100 98 100 100 100 100 100 84 100 85 65
99 100 88 100 100 100 100 100 100 100 100 100 98 100 86 99
98 100 89 100 100 100 100 100 100 100 100 100 99 100 82 100
100 100 94 100 100 100 100 100 100 100 100 100 98 100 76 99
86 100 98 100 100 100 100 100 100 100 100 100 94 100 72 100
70 100 99 100 100 100 100 100 100 100 100 100 96 100 87 100
94 100 99 100 100 100 100 100 100 100 100 100 99 100 86 90
100 100 100 100 100 100 100 100 100 100 100 100 100 100 85 92
100 100 100 100 100 100 100 100 100 100 100 100 100 100 86 84
100 100 100 100 100 100 100 100 98 100 100 100 100 100 100 100
100 100 100 100 100 99 100 100 99 97 100 100 100 100 100 100
100 100 100 100 100 99 100 100 96 99 100 100 94 100 100 100
100 100 100 100 100 100 100 100 99 100 100 100 97 100 100 100
/ deg ϕe
-150 -100 -50 0 50 100 150
/ cm LArz
-200 -150 -100 -50 0 50
(b)
Figure 6.31: Trigger efficiency in the z −ϕ plane of the electron impact position, shown for the 2003-04 e+p (a) and for the 2005 e−p (b) data taking periods. The hatched areas indicate regions which are excluded because of low trigger efficiency.
Pt(h) / Pt(e) (finder 0)
0 0.5 1 1.5 2
0 50 100
Pt(h) / Pt(e) (finder 0)
0 0.5 1 1.5 2
0 50 100
Pt(h) / Pt(e) (finder 1)
0 0.5 1 1.5 2
0 10 20
Pt(h) / Pt(e) (finder 1)
0 0.5 1 1.5 2
0 10 20
Pt(h) / Pt(e) (finder 5)
0 0.5 1 1.5 2
0 5 10 15
Pt(h) / Pt(e) (finder 5)
0 0.5 1 1.5 2
0 5 10 15
Pt(h) / Pt(e) (finder 6)
0 0.5 1 1.5 2
0 5 10
Pt(h) / Pt(e) (finder 6)
0 0.5 1 1.5 2
0 5 10
Pt(h) / Pt(e) (finder 7)
0 0.5 1 1.5 2
0 50 100
Pt(h) / Pt(e) (finder 7)
0 0.5 1 1.5 2
0 50 100
Pt(h) / Pt(e) (finder 8)
0 0.5 1 1.5 2
0 20 40 60
Pt(h) / Pt(e) (finder 8)
0 0.5 1 1.5 2
0 20 40 60
Figure 6.32: Distribution of pT balance for events found by the background finders 0-8 (points). The line corresponds to genuine NC events from MC (see text).
muon events are two isolated muon tracks in the instrumented iron, the liquid argon calorimeter and the central tracking detector which are “back-to-back”
in polar and azimuthal angle, and with a timing difference of a few nsbetween the tracks measured in the central jet chamber.
• Beam-halo particles are produced in collisions of stray protons in the tails of the transverse beam profile with the beam-pipe walls. The produced hadronic component is absorbed quickly, so that mainly muons are observed in beam-halo events in the H1 detector. The experimental signature of beam-beam-halo events is a muon track in the backward iron endcap, the liquid argon calorimeter and the forward iron endcap, parallel to the beam-pipe.
• Beam-gas events originate from collisions of the proton beam with residual gas molecules in the beam-pipe. As a result of the high proton beam energy, the particles produced in beam-gas interactions are strongly boosted in the forward direction. The experimental signature of beam-gas events are many low pT
tracks isotropically distributed in azimuth.
The majority of the beam-halo, beam-gas and cosmic muon background may be suppressed by algorithms (“non-ep background finders” [98]) that reject the non-ep background on the basis of topological criteria, exploiting information about tracks and clusters in different sub-detectors that are characteristic for beam-halo, beam-gas and cosmic muon events.
Finder Algorithm Description
0 HALAR Longitudinal energy pattern in the LAr calorimeter.
1 HAMULAR Longitudinal energy pattern in the LAr calorimeter with energy deposit inside the backward iron endcup.
5 COSMUMU Two opposite muon tracks matching in directions.
6 COSMULAR At least one muon with 90% energy deposited in a matching LAr cluster.
7 COSTALAR Two opposite clusters in the Tail Catcher with 85%
energy deposited in matching LAr clusters.
8 COSTRACK Two CJC tracks with opposite directions in space.
Table 6.5: Background finding algorithms [98] for halo-muons and cosmic muons.
Distribution of the pT balance for events found by different background finding algo-rithms are shown in 6.32. The NC events, as expected, have PTh/PTe '1. Therefore an event is rejected if it is found:
• by one of the finders 5, 6 forPTh/PTe <0.5,
• by finder 7 for PTh/PTe <0.1,
• by finder 0 and 1 or by two finders out of 5-7 for PTh/PTe >0.1.
Distribution of the pT balance for events found by pair of the background finders as described above are shown in figure 6.33.
Figures 6.32 and 6.33 demonstrate that the background finders allow for an efficient rejection of the non-epbackground while keeping all epNC events shown by the line.
After applying the background finders the selected sample is essentially free from non-epbackground events. This was also confirmed by visual scanning of events with Q2 >5 000 GeV2.
Pt(h) / Pt(e) (f0 + f1)
0 0.5 1 1.5 2
0 2 4 6
Pt(h) / Pt(e) (f0 + f1)
0 0.5 1 1.5 2
0 2 4 6
Pt(h) / Pt(e) (f5 + f6)
0 0.5 1 1.5 2
0 2 4 6
Pt(h) / Pt(e) (f5 + f6)
0 0.5 1 1.5 2
0 2 4 6
Pt(h) / Pt(e) (f5 + f7)
0 0.5 1 1.5 2
0 2 4 6
Pt(h) / Pt(e) (f5 + f7)
0 0.5 1 1.5 2
0 2 4 6
Pt(h) / Pt(e) (f6 + f7)
0 0.5 1 1.5 2
0 5 10
Pt(h) / Pt(e) (f6 + f7)
0 0.5 1 1.5 2
0 5 10
Figure 6.33: Distribution ofpT balance for events found by background finders which are rejected by a pair of background finders (see text). The line corresponds to genuine NC events from MC.
Selection of NC Events
This chapter presents the data selection applied for the inclusive neutral current cross section measurement. The run selection including the polarisation requirements and the luminosity measurement are explained and the data samples used in the analysis are introduced. Finally, the NC selection is summarised and the Monte Carlo simu-lation is compared to the data.
7.1 Run Selection
During data taking, events are collected in time intervals (up to two hours), called runs, with nominally stable accelerator and detector conditions. Depending on the overall detector performance, background situation, problems with readout and so on, the runs are classified as “good”, “medium” or “poor”. For this analysis only
“good” and “medium” runs are selected. Furthermore, for each run it is required that all important components are fully operational (supplied by high voltage, HV) and included in the readout. These components are the LAr calorimeter and the LAr trigger, the central drift chambers (CJC1 and CJC2) and the proportional chamber (CIP), the luminosity system and the ToF system 1. The information about the high voltage status of each hardware component during data taking is stored in a database every ten seconds. A run is rejected if any of the relevant detector components was
“off” for a large fraction of time. An event in the run is accepted only during time periods when the relevant (see above) HV settings were “on”. Correspondingly, the luminosity associated with the run is calculated only for these time periods. The luminosity measurement procedure was discussed in section 3.10.
Runs with luminosity less then 0.2 nb−1 are rejected to ensure a certain level of sta-bility during data taking.
7.1.1 Polarisation Selection
The technical aspects of the polarisation measurement were discussed in section 3.3.
The polarisation is taken as measured by the LPOL polarimeter. If there is no LPOL
1Some HV requirements are already included in the definition of a “good” or “medium” run.
Since a run can be classified as “medium” when CIP or ToF is off, or just only one of the central drift chambers is operational, explicit HV requirements are applied.
measurement available, then the TPOL is used. If neither polarimeter is operational at the time when an event is recorded, the event is rejected. This requirement was put in order to reduce the systematic error on the polarisation measurement. The luminosity is calculated only for the time periods when the polarisation measurement is available, in a similar manner as for the HV requirement.
Runs with polarisation −20% < Pe < 0% for 2003-04 e+p and 0% < Pe < 15% for 2005 e−p were excluded from the analysis. The fraction of luminosity for these runs is small compared to the main sample.
The luminosity weighted profiles of the measured e+ and e− polarisations are shown in figure 7.1.
Polarisation /%
-60 -40 -20 0 20 40 60
-1Luminosity /pb
0 0.5 1 1.5 2 2.5 3 3.5
e+p 2003-04
H1 Collaboration
(a)
Polarisation /%
-60 -40 -20 0 20 40 60
-1Luminosity /pb
0 1 2 3 4 5 6 7 8
e-p 2005
H1 Collaboration
(b)
Figure 7.1: The luminosity weighted polarisation profile for the 2003-04e+p (a) and the 2005 e−p (b) data.
Both 2003-04e+p and 2005 e−p data sets are subdivided into samples with positive (“RH”) and negative (“LH”) average longitudinal polarisations. The corresponding luminosities and average longitudinal lepton beam polarisations are given in table 7.1.
Data sample Luminosity Polarisation Time period
e+p RH 26.9 pb−1 (+33.6±0.6)% 17.10.03-01.04.04, 02.07.04-12.08.04 e+p LH 20.7 pb−1 (−40.2±1.1)% 03.04.04-19.06.04
e−p RH 29.6 pb−1 (+37.0±1.3)% 25.05.05-06.09.05
e−p LH 68.6 pb−1 (−27.0±1.8)% 03.02.05-18.05.05, 09.09.05-11.11.05 Table 7.1: Table of luminosities and luminosity weighted average longitudinal polar-isations, for the data sets presented in this analysis.
A global uncertainty of 1.3% and 2.0% on the luminosity measurement is assigned for e+p and e−p data respectively, of which 0.5% is common to both [119]. For the e+p data the uncertainty in the measurement of the lepton beam polarisation is taken to be 1.6% for the LPOL and 3.5% for the TPOL [120], yielding a total relative polar-isation uncertainty of 1.8% for RH data set and 2.7% for the LH data set. For the e−pdata a global uncertainty of 5% is considered [119].
The run selection criteria used in this analysis are summarised in table 7.2.
Run quality “good” or “medium”.
Runs with “problems” are excluded (see text).
High voltage on and
in read-out LAr and LAr trigger, CJC1 and CJC2, Lumi, CIP, ToF Run duration Lrun>0.2 nb−1
Polarisation Polarimeter measurements are available and Pe <−20% for 2003-04e+p LH
Pe >+15% for 2005 e−pRH
Table 7.2: Run selection requirements related to data taking conditions and opera-tional status of the detector systems.