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Particle identification by energy loss measurement in the NA61 (SHINE) experiment

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Particle identification by energy loss measurement in the NA61 (SHINE)experiment

Magdalena Posiadala

University of Warsaw

- Energy loss measurements in NA61 experiment at CERN
- Energy loss parametrisation
- Methods of Particle Identification in NA61 in the region of interest for the T2K.
- Energy loss measurement in the region below 1GeV/c
- Two methods of approach to analysis:
- Method 1 – fits done using TMinuit package
- Method 2- using probability functions

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

Max 72 points

Max 90 points

TPCs are filled with mixtures of Ar+ CO2(90:10) for VTPCs and (95:5) for MTPCs

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- The optimization of the parameters required for the determination of energy loss in the TPCs was performed using the method developed by NA49. (For details see Eur. Phys. J , C45 (2006) 343)
- Corrections for the following effects were applied during thecalibration of the NA61 data:
- signal loss due to threshold cuts; corrections were obtained using Monte Carlo calculations for gas mixture used in NA61,
- time dependence of the TPC gas pressure,
- residual time dependence of the measurements (day/night),
- charge absorption during the drift,
- differences in the TPC sector gain factors,
- differences in the amplification of the preamplifiers and edge effects at sectors boundaries.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

Preliminary distributions of corrected dE/dx values forpositively (white) and negatively (yellow) charged particles with momentum chosen around 5 and 15 GeV/c.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

1 island-> vtpc

2 island –> mtpc+vtpc

Estimated resolution of dE/dx measurements of 4-5% can be achieved for particles passing through both the vertex and the main TPC chambers.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

N>10

N>30

N>40

N>50

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

tracks with high dE/dx errors are rejected

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- In NA61 (SHINE) experiment particle identification is possible using ionization measurements in active volume of the TPCs and time-of-flight measurements in ToF counters.
- For ToF-F measurements see next presentation of Sebastien Murphy.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

Comparison of

NA61 data with T2K simulation

- JNUBEAM

JNUBEAM –simulation of the T2K beam

NA61, 2C data, N>30

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

dE/dx info

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

Energy loss measurementin the region below 1GeV/c

in %

In T2K bins

ptot: 200MeV/bin x 50 bins till10GeV/c

:

20 rad/bin x 20bins

till 0.4 rad

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

p (GeV/c)

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

Statistics below 1GeV/c -2C Data

in %

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Preliminary plot ofthe reconstructed dE/dx values versus momenta (p<1.2 GeV) for positively charged particles, together with the Bethe-Bloch curves for positrons,pions, kaons, protons and deuterons.
- of dE/dx vs dE/dx

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- For whole tracks we can calculate theoretical energy loss dE/dxteor using track total momentum and applied parametrisation functions.
- In this way we get theoretical distribution of energy loss in momentum bins (see example plot on the right).
- Smearing with Gaussian function

Example ->

dE/dx data

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- The theoretical distributions of energy loss are smeared with Gaussian function following this rules:
- Mean = dE/dxtheor calculated for each track
- Sigma = dE/dx for the each track; from NA61 data

After Gaussian smearing

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Having theoretical energy loss distributions smeared for each of the particle hypotheses I start to extract raw particle yields using 2 methods:
- Method 1-> Making fits using TMinuit Package in Root
- Method 2 ->Calculating probability functions for 4 particles hypotheses
- For more details look at the example in the next few slides.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Preliminary plot of the reconstructed dE/dx values versus momentum (p<1.2 GeV) for positively charged particles, together with the Bethe-Bloch curves for positrons, pions, and only kaons in selectedmomentum range.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- We have theoretical smeared with Gaussian energy loss distributions (right) and NA61 data (left)

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 1 -> uses 2 function for minimization
- Theoretical distribution of energy loss is fitted to data
- Calculation of the fit parameters ,,,

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 1
- TMinuit fits
- Results

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 2->Probability functions; for each of the bin i assuming particle hypotheses I calculate probability function defined as:

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 2-> Multiply probability functions by distribution of the energy loss for the data in selected momentum slice to obtain colourful plots at the bottom picture;corresponding to particle species.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 1
- TMinuit fits

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 2
- Probability functions

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

protons are seen

(yellow line)

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 1
- TMinuit fits

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 2
- Probability functions

Almost the same number of positrons and kaons, which is

of course not true.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 1
- TMinuit fits

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 1
- TMinuit fits

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 1
- TMinuit fits

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 1
- TMinuit fits

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- Method 2
- Probability functions

Method 2 at this stage of studies works well only for momentum slices where theoretical lines do not cross completely !!!

Needs further improvements (/K ratio parameterised by function)

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- The resolution dE/dx strongly depends on number of points per track. For tracks passing through all TPCs the resolution at the level of 4 - 5% .
- NA61 data cover acceptance in p, variables for the T2K experiment.
- Important dE/dx analysis below 1 GeV/c region.

- Method 1 –>making fits using TMinuit package
- Method 2 with probability functions still needs improvement->approaching towards max log-likelihood.

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009

- On the right relative error vs energy loss distribution is presented.
- Next step is to smear theoretical lines with Gaussians that have error equal to relative error of dedx and see how it influences the presented results

"Neutrino physics at accelerators", JINR, Dubna 27-30.01.2009