Transcript G. De Lellis

Pure  exposure for e/ separation
Giovanni De Lellis
University of Naples
• Physics motivation
• Available data from past TB exposures
• Planning for a new exposure
Physics motivation
• Goal: measure P(e)
• Background to  decays from 1-prong 
interactions (pt cut is 100 MeV)
• Loss of efficiency (i.e. primary pion identified
as electron: tau  charm or 2ry int)
Current algorithm
• Basic principle: rate of energy loss is
different for electrons
and
hadrons
z

E ( z )  E0 e
E ( z )  E0
X0
X 0  5.6mm
int  170mm
• Classify the tracks in different categories:
– Stopping with shower  electrons
– Stopping without shower  2 analysis
– Punch through  2 analysis
χ2 analysis to measure energy variation
: separator
1mm
~ 2mrad
In the experiment, the incident momentum is unknown,
so E0 is treated as a free parameter to minimize chi-square.
Data from May 2001 TB (Toshito, Nagoya)
χ2 for punch through
Not interacting
Data and pure  MC
agreement
Data from May 2001 TB (Toshito, Nagoya)
χ2 for stopped tracks
Mixture of electron
interacted 
Data and MC
agreement
e-identification: shower + negative 2
(May 2001 TB- Toshito, Nagoya)
According to MC
Efficiency 88% mis-id Prob. 6% @2GeV/c
Efficiency 91% mis-id Prob. 4% @4GeV/c
Comparison with Cerenkov detector
Installed in the upstream
of ECC to monitor e/ ratio.
e/ ratio
2GeV/c
4GeV/c
ECC
1.42±0.17
0.41±0.05
cherenkov
1.46±0.11
0.32±0.03
Consistent
Open questions and possible improvements
•Significant impurity in the beam  use MC to evaluate
efficiencies
•Mis-identification probability still high for background
requirements (try to improve measurements since the
feasibility of the method has already been proved)
•Pure beam needed during the exposure
•Accurate measurements while analysing the data
Electron contamination in the T9 beam
(PS-CERN)
We performed an exposure
for the Multiple scattering
measurement in 2000
(accepted for publication
on NIM A) after reducing
the electron contamination
with material before the last
focusing magnet
PS beam parameters
e/(e+)
beam flux
Target
thickness
and Z
Beam
momentum
At 1 GeV e/ running over 2050% (T7-T9)
•impossible to get low intensity and high purity electron beam
•difficult (but possible) to get low momentum pure pion beam
Pure “low” momentum pion beam
• Lead plate before focusing magnet (as already
done in Nov 2000 at T9 with about 4 X0  permill contamination)
• Scintillator counters to monitor the beam flux
• Beam monitoring (geometry) using multi-wire
chambers
• Electron contamination monitored by Cerenkov
Pion identification study
• Refreshing of the emulsion sheets
• High density (~103/cm2) and high purity  beam exposure
to study  identification efficiency (2 part) and purity with
high statistics
• No other reference tracks needed in the brick
• Perform the exposure at different  momenta (2-10 GeV)
• Different pion momenta can be exposed at different angles
(~3 energies per brick)
• Classification of tracks as passing through and stopping 
2 analysis
Problems with this exposure
• Unavoidable µ contamination (a few %, energy-dependent)
• Muons are passing through the effect will be to change
the ratio of the two categories in the analysis (increase
punch through w.r.t. stopping without shower)  artificial
improvement of the e/ separation
• Reduce as much as possible the contamination (energy
focusing magnet)
• Possible to control the contamination (Cerenkov)
• Correct the numbers: we need a contamination knowledge
at the level of 1% or less
Complementary part of the algorithm:
cascade shower analysis at low density
•
•
•
•
•
Low density exposure
Open a cone (250mrad) around the leading track
Count segments inside the cone  energy
Electron detection efficiency ~ 95% (Toshito)
Contamination of  ~ 2 events at most (14
electrons detected at 2 and 4 GeV in May 2001
exposure-Toshito)
• Performances can be improved with low
background conditions
Shower analysis on pion beam
• Refreshing of the emulsion sheets
• Low density (~1/cm2) and high purity pion beam
exposure to study  mis-identification with the shower
analysis method
• Reference tracks needed (inclined muon beam)
• Perform the exposure at different  momenta (1-10 GeV)
• Different momenta cannot be exposed in the same brick
• Define a cone and apply shower analysis
• Muon contamination is not a problem in this case
Test beam planning and organization
•
•
•
•
•
•
•
•
TB period (July 9-21)
TB design (G. De Lellis)
Monte Carlo studies (G. De Rosa and V. Tioukov)
Electronic detector (I. Kreslo)
Beam parameter tuning (G. De Lellis and I. Kreslo)
Refreshing (G. Rosa)
Brick assembling (BAM)
Brick exposure (M. Cozzi, G. De Lellis, G. De Rosa,
I. Kreslo, L. Scotto, V. Tioukov, …)