1. Pure  exposure for e/ separation
Giovanni De Lellis
University of Naples
Physics motivation
Available data from past TB exposures
Planning for a new exposure

2. 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)

3. Current algorithm
Basic principle: rate of energy loss is different for electrons and hadrons
Classify the tracks in different categories:
Stopping with shower  electrons
Stopping without shower  2 analysis
Punch through  2 analysis

4. 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.

5. Data from May 2001 TB (Toshito, Nagoya)
χ2 for punch through
Not interacting
Data and pure  MC
agreement

6. χ2 for stopped tracks Data and MC agreement
Data from May 2001 TB (Toshito, Nagoya)
χ2 for stopped tracks
Mixture of electron
interacted 
Data and MC
agreement

7. e-identification: shower + negative 2 (May 2001 TB- Toshito, Nagoya)
According to MC
Efficiency 88% mis-id Prob.
Efficiency 91% mis-id Prob.
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

8. 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

9. 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

10. 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

11. Pure “low” momentum pion beam
Lead plate before focusing magnet (as already done in Nov 2000 at T9 with about 4 X0  per-mill contamination)
Scintillator counters to monitor the beam flux
Beam monitoring (geometry) using multi-wire chambers
Electron contamination monitored by Cerenkov

12. 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

13. 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

14. 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

15. 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

16. 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, …)