Romania-Bulgaria Cross-border Cooperation Programme 2007-2013: Status of implementation
Status of the cross section analysis in e ! e
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Transcript of Status of the cross section analysis in e ! e
Status of the cross Status of the cross section analysis in section analysis in
ee!! e e
Yelena ProkYelena Prok
PrimEx Collaboration PrimEx Collaboration MeetingMeeting
March 18, 2006March 18, 2006
OutlineOutlineEvent SelectionKinematic and Geometric CutsComparison with Simple SimulationBinning and AcceptanceObtaining the YieldWhat remains to be done
Dedicated Compton RunsDedicated Compton Runs40 (good) runs with the 5 % r.l. 12C target Target density=2.193 g/cm3
Target thickness=380 £ 2.54 cm Atomic mass= 12 Atomic number=6
2.1<Ebeam<3.1 and 4.9<Ebeam<5.5 GeV
4 (good) runs with the 5 % r.l. 9Be target Target density=1.848 g/cm3
Target thickness=70.6 £ 2.54 cm Atomic mass=9 Atomic number=4 4.9<Ebeam<5.5 GeV
Event ReconstructionEvent Reconstruction Skim files were created from raw datafiles at least 2 clusters, energy sum of 2 clusters >0.5 GeV,
central hole (3.8 cm) is cut out
Standard PrimEx reconstruction program used, with the following parameters
Clustering algorithm: combination of “island” + 5x5 algorithm
Using Double Arm Compton Calibration Constants Z=731.9 cm (survey) Coordinate reconstruction (method 3, alignment
correction, depth correction) Non-linearity correction in energy reconstruction
Event SelectionEvent Selection
To select candidates for a given event, look at the time difference distribution between the tagger and HYCAL (bit 9), then take all photons in a defined time window. Here, time window of § 6 ns is used.
Data SelectionData SelectionElasticity cut:|(eElasticity cut:|(e11+e+e22)/ebeam-1|<0.1)/ebeam-1|<0.1
4.9<Ebeam<5.5 GeV 2.1<Ebeam<3.1GeV
Data SelectionData SelectionCluster Separation:Cluster Separation:
4.9<Ebeam<5.5 GeV 2.1<Ebeam<3.1 GeVsep>18 cm sep > 25 cm
Data SelectionData SelectionGeometric Cuts (1)Geometric Cuts (1)
4.9<E<5.5 2.1<E<3.1
Fiducial region clearly contaminated by pair production is cut outMost likely, not all of the contamination is removed by this cut
Data SelectionData SelectionGeometric Cuts (2)Geometric Cuts (2)
Due to the potential problems with cluster reconstructionin proximity to the central hole, a region of 6x6 cm is cut out
Particle 1More
energetic of the two
Particle 2, less energetic
Data SelectionData Selection A simulation using GEANT 3 was performed with
the incident photons in the energy ranges of 2.1 <E< 3.1 and 4.9<E<5.5 GeV and target parameters of the experiment. No radiative losses were included. The purpose of this simulation is to determine detector acceptance, check the experimental kinematic distributions and to determine a set of appropriate cuts for data selection.
For compatibility, the experimental and simulated data are arranged into pairs of particles, so that the first particle of the pair is always most energetic
Comparison with SimulationComparison with SimulationCluster SeparationCluster Separation
cm cm
4.9<E<5.5 2.1<E<3.1
Comparison with SimulationComparison with SimulationGeometryGeometry
4.9<E<5.5 GeV 2.1<E<3.1 GeV
Comparison with SimulationComparison with Simulation11 vs vs 22 (deg) (deg)
4.9<E<5.5 GeV 2.1<E<3.1 GeV
Data Binning and AcceptanceData Binning and Acceptance• Data is binned consistently with the
photon flux binning in tagger TChannels• A simulation was done for the energy
range of every bin• Same cuts were applied to the simulated
and experimental data• Expected cross section and geometric
acceptance determined for every energy bin
Bin # tchannels E min (GeV) Emax(GeV) Acceptance(%)
1 1+2 5.45 5.5 6.29
2 3+4 5.39 5.45 6.45
3 5+6 5.32 5.39 6.61
4 7+8 5.27 5.32 6.71
5 9+10 5.22 5.27 6.83
6 11+12 5.17 5.22 6.95
7 13+14 5.12 5.17 7.08
8 15+16 5.07 5.12 7.18
9 17+18 5.01 5.07 7.3
10 19+20 4.95 5.01 7.4
11 21 4.89 4.95 7.5
30 59+60 3.0 3.13 6.81
32 63+64 2.8 2.9 5.84
34 67+68 2.61 2.7 4.89
35 69+70 2.52 2.63 4.40
36 71+72 2.44 2.53 3.81
38 75+76 2.30 2.37 2.80
39 77+78 2.22 2.31 2.33
Counting pairsCounting pairs• Summary of cuts: -Minimum cluster energy = 1 GeV -Cluster separation > 18 (25) cm -Central Area § 6 cm is cut out -Area mostly affected by pair- production contamination is cut out -Elasticity cut: |(e1+e2)/Ebeam-1| <0.1
• All events that passed the cuts above are used to fill the following histograms:
e1+e2-Ecompton vs bin #
Ebeam-Ecompton vs bin #
1 -2 vs bin #
e1+e2-ebeam vs bin #
Counting pairsCounting pairs
Each type of histogram is fitted with a gauss+gauss and gauss+polynomial functions
Ebeam-Ecomp
e1+e2-Ecomp
e1+e1-Ebeam
Acceptance Corrected Normalized YieldAcceptance Corrected Normalized Yield(per atom)(per atom)
Acceptance corrected normalized yield NCNY:
NCNY=C/L/A C=counts under the first gaussian
function L=*th*NA* th=target thickness =target density NA=Avogadro’s Number =atomic mass A=geometric acceptance obtained
from simulation
Detection efficiency and reconstruction efficiency are not known and set to 1
12C target
Acceptance Corrected Normalized YieldAcceptance Corrected Normalized Yield (per electron) (per electron)
12C target
Acceptance Corrected Normalized Acceptance Corrected Normalized Yield (per electronYield (per electron))
9Be, 5% r.l. target
Run 4875
Yield Stability vs Run Number Yield Stability vs Run Number (for (for 1212C target)C target)
Bin 35Problem with flux
Bin 1 Bin 2
Bin 3 Bin 4
Bin 5 Bin 6
Bin 7 Bin 8
Bin 9 Bin 10
Bin 11
Bin 30 Bin 32
Bin 34
Bin 36 Bin 38
Bin 39
VETO EffectVETO Effect
Requiring that one of the clusters is charged and the other one is neutral throws away ~10-20% of the data that passed the rest of the cuts
4.9<E<5.5
2.1<E<3.1
VETO effect (cont)VETO effect (cont)
No VETO cut1 neutal, 1 charged cluster
Background reduced: ~ 40 %Signal reduced:~ 20 %
Angular DistributionsAngular Distributions
DATA vs DATA vs GEANTGEANT 2.1<E<3.14.9<E<5.5
fast
slow
fast
slow
e- e-
Summary and OutlookSummary and OutlookWhat has been done First look at the total cross
section in e! e with 12C and 9Be targets
Results are on average 5-15% below the expectation (at least, partially, this is due to the assumption that the detection and reconstruction efficiencies are 100 %.)
Results show no obvious time dependence
What needs to be done Check of systematic
effects in data analysis Compton generator for
primsim Full simulation which will
allow more realistic comparison with data, and evaluation of detection and reconstruction efficiencies
Better understanding of the backgrounds (more simulations)
Trigger Efficiency not completely understood
Radiative Corrections