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The Solenoid Vertex Spectrometer - A Simulation Study

14 Jun 2018-
TL;DR: In this article, the authors examined the particle detection characteristics of a large solenoid magnet and spark chamber system by means of Monte Carlo simulation and concluded that it can measure most particles of 2 GeV/c or less very well, improve overall acceptances dramatically, fill in dead regions of decay distributions, and present no obvious difficulty for the pattern recognition of tracks.
Abstract: This study examines the particle detection characteristics of a large solenoid magnet and spark chamber system by means of Monte Carlo simulation. Such a device would serve as a vertex spectrometer in a two magnet system. The nominal parameters are: a 25 kG axial field, a 2 meter diameter and a 3 meter length. The solenoid magnet can surround the target and measure the low momentum, large angle particles and a second magnet downstream, with a conventional gap and field would measure the fast secondaries. The axial field solenoid has ideal azimuthal symmetry and is well suited for rotating the transverse momentum vector of slow particles in hadron interactions. A detailed study of the acceptance, momentum resolution and pattern recognition properties of the solenoid system are presented. The overall conclusions are that it can measure most particles of 2 GeV/c or less very well, improve overall acceptances dramatically, fill in dead regions of decay distributions, make high invariant mass studies feasible (8 to 16 GeV/c beams) and present no obvious difficulty for the pattern recognition of tracks. A fast track recognition algorithm is presented and no major computing needs are anticipated for the magnetic field inside the solenoid.

Summary (3 min read)

I. INTRODUCTION

  • This report examines the feasibility of using a larger aperture high field solenoid magnet as a vertex spectrometer.
  • Other individuals have persued these tasks and their work is not covered by this report.
  • Fast particles would be transmitted through to a downstream magnet and the second magnet would be a conventional dipole magnet with a magnetic field perpendicular to the beam.
  • The solenoid B field (along the Z axis) rotates the PT (transverse momentum) component of a charged particle inside it.
  • By using a spectrometer model and tracking Monte Carlo events through it the questions of acceptance resolution, etc. are easily answered.

Kp

  • The faster secondary particles are passed through to the downstream magnet and are only rotated by the BZ field.
  • They will not be deflected into or away from the dipole magnet aperture.

2. Model Results

  • The "lost" pions in the above extreme decays have typical lab momentum of 250 to 1500 MeV/c and lab production angles of 3' to 30' for apertures II and III.
  • Even if these particles make it into the entrance of a large aperture magnet, the low momentum means they will be swept into the magnet walls.

(i) Beam plug A0

  • It is assumed that the r+ beam trajectory must have a rtplug" through the gap magnet, This dead region is here defined as a &A6 cone centered on each beam track.
  • This f'plug" was assumed to be located at the entrance of the gap magnet.
  • The one 7r-track was assumed to be always separable from the beam cone.
  • In the high mass study this beam plug constraint was removed.
  • The second gap length, from the magnet to the last spark chamber was fixed at 4 meters for the Al study and 3 meters for the high mass events.

Solenoid geometry

  • The solenoid's purpose is to analyze the "low" momentum particles.
  • It is this spectrum which determines the solenoid losses.
  • The authors have defined a l'lossl' here as the case when the particle does not get through all chambers.
  • It follows that at lower beam values, and higher masses, the solenoid.

5. Plug Losses

  • The 30 mrad beam plug causes a 21% acceptance loss.
  • If there was no plug, the solenoid-large magnet system would have an acceptance increase of 17%.
  • That is, almost all of the t'plugtl losses are measurable events.
  • This is not quite the case for the no-solenoid system.
  • About half the events with a very fast track also have a slow track which then is missed.

6. No-Solenoid System

  • The conclusion is that without the solenoid, and even with a large magnet, at 8 GeV/c the three-pion acceptance is very small (about 5%).
  • With the small magnet it is essentially zero.

C. Real Field Versus Box Field

  • Given the usual Monte Carlo events generated at the target, it is very easy to integrate the pions through the solenoid by two different procedures and then compare the results.
  • Procedure A is the ideal box field approximation the authors have been using.
  • Thus even though the A@ variations may be extremely large by comparison with conventional spectrometer, the solenoid would still have good mass resolution.
  • A word of caution, however, since this example idealizes the situation.
  • The above defined variable R ijk is called the 3-spark search parameter.

B. Procedure and Results

  • The Monte Carlo simulation study used the following procedure.
  • (1) As described earlier in this report, a four-body event is generated in the target and the particles are traced through the solenoid.
  • The spark chamber intercepts are then defined as "sparks!' (3) The four sparks from each solenoid chamber are then collected and all possible combinations of the R.. 1Jk parameter are calculated (64 total for 4 sparks in each of 3 planes).
  • (4) Remembering which sparks really belonged to a track, one can then examine the resolution of the algorithm.
  • (5) No acceptance checks or measurement checks were made on the sparks or tracks in this chapter.

XY Plane Distribution of Sparks

  • The ease of recognizing tracks will depend strongly on the spatial distribution of the sparks in the three chambers.
  • To remove some of the very fast tracks, one can simply check the r value of the spark and disregard it if it lies within some small circle (e. g. , 5 -10 cm from the center line).
  • This reduces the number of combinations (i. e., computing time) and emphasizes the search for the slower tracks, which one is measuring in the solenoid.
  • If one wishes, a second pass search can then be made on the remaining and unassigned sparks.

Algorithm Results

  • Thus one can quickly disregard all R.. values, i. e., all spark 1Jk combinations, that are not near this signal.
  • Table VIII summarizes the percent of the signal as well as the noise to real track ratio for three different cuts on the R number.
  • The wider this cut, the more signal one gets but the higher the background ratio.
  • Because the proton tracks have such a low Pz, their sparks are well separated in the XY plane and so R.. 1Jk for the proton has a much better signal than for the pions. (4) A 50 kG solenoid does not seem to affect the signal very much (case 6). (5) A reduction of beam energy improves the signal somewhat.
  • Figure 21b shows what the R distribution looks like when the authors reject all sparks in the first chamber within 5 cm of the center line.

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Content maybe subject to copyright    Report

SLAC-152
UC-34
(EXP) (EXPI)
THE SOLENOID VERTEX SPECTROMETER -
A SIMULATION STUDY
GEORGE JURIS LUSTE*
STANFORD LINEAR ACCELERATOR CENTER
STANFORD UNIVERSITY
Stanford, California 94305
PREPARED FOR THE U. S. ATOMIC ENERGY
COMMISSION UNDER CONTRACT NO. AT(04-3)-515
June 1972
Printed in the United States of America. Available from National Technical
Information Service, U. S. Department of Commerce, 5285 Port Royal Road,
Springfield, Virginia 2215 1. Price: Printed Copy $3.00; Microfiche $0.95.
*
Presently at the University of Toronto, Toronto 5, Ontario, Canada.

ABSTRACT
This study examines the particle detection characteristics of a large sole-
noid magnet and spark chamber system by means of Monte Carlo simulation.
Such a device would serve as a vertex spectrometer in a two magnet system.
The nominal parameters are: a 25 kG axial field, a 2 meter diameter and
a 3 meter length.
The solenoid magnet can surround the target and measure
the low momentum, large angle particles and a second magnet downstream, with
a conventional gap and field would measure the fast secondaries. The axial field
solenoid has ideal azimuthal symmetry and is well suited for rotating the trans-
verse momentum vector of slow particles in hadron interactions.
A detailed study of the acceptance, momentum resolution and pattern
recognition properties of the solenoid system are presented. The overall con-
clusions are that it can measure most particles of 2 GeV/c or less very well,
improve overall acceptances dramatically, fill in dead regions of decay distri-
butions, make high invariant mass studies feasible (8 to 16 GeV/c beams) and
present no obvious difficulty for the pattern recognition of tracks. A fast track
recognition algorithm is presented and no major computing needs are anticipated
for the magnetic field inside the solenoid.
- ii -

ACKNOWLEDGEMENTS
This publication would not have been possible without the encouragement
and direct aid of a number of people.
Leon Madansky first introduced me to the spectrometer ideas and problems
while on a sabbatical at SLAC. Together we explored some of the acceptance
kinematics of a dipole magnet and a solenoid magnet system.
This early
collaboration was an invaluable learning experience for the author and it was
at this suggestion that we first considered some simple solenoid kinematics
in December of 1968.
David Leith has provided the support and encouragement to make the study
comprehensive enough for a real spectrometer proposal. Without him, and
his desire to build a good spectrometer facility this study could not have taken
root.
His enthusiasm and advice along the way did much to sustain it.
A number of my fellow colleagues at SLAC have also provided useful
comments and advice during the course of this work.
They are Jim Loos,
Bob Carnegie, Kei Moriyasu, and Bill Johnson. John Matthews was kind
enough to read the original draft of this report.
Chuck Stoner and Dave Budenaers helped with some of the calculations
and computer programming.
. . .
- 111 -

I.
II.
III.
Iv.
V.
TABLE OF CONTENTS
Page
Introduction.
............................
The Solenoid
............................
Acceptance
.............................
A. Gap Magnet Acceptance Difficulties
..............
B.
Solenoid System Acceptance Studies.
.............
C.
Low Mass Acceptance (m( 7r7wr) < 1.5 GeV/c2)
........
D.
High Mass Acceptance
.....................
E. Conclusions
..........................
Track Resolution Inside the Solenoid.
...............
A. Momentum Resolution
.....................
B.
Solenoid Field Map
......................
C. Real Field Versus Box Field
.................
D.
Some d$ Comments
......................
Pattern Recognition
.........................
A. TheAlgorithm .........................
B.
Procedure and Results
....................
References. . . . . . . . . . . . . . . . . 0 . . . . 0 . . . . . . . . .
1
4
10
10
15
26
36
39
40
40
44
46
49
53
53
55
62
- iv -

LIST OF TABLES
I.
II.
III.
rv.
V.
VI.
VII.
VIII.
A1 region acceptances for (A) small gap magnet, (B) medium
gap magnet, and (C) large gap magnet plus solenoid spec-
trometer . Variations with beam momentum, magnetic field,
resolution, geometry, plug size, etc. are shown. The
losses are shown at the different spectrometer aperture
locations. . . 0 . . . . . . . . . . . . . . 0 . . . . 0 . . . . . .
A1 region acceptance comparisons of solenoid versus no
solenoid system . , . . . . . . . 0 . . . 0 . . . n . . 0 . . . 0 .
Higher 7rr7r mass acceptances with similar parameter
variations . . . . . . . . . . . . . . . D . . . D . . . . . . 0 . .
Higher mass losses inside the solenoid as a function
ofzposition . . . . . . O.....D..O..O . . . . . . . . .
Solenoid momentum resolution as a function of PT, PI,
AZ, B, and dx, dy, dz spark jitter . . . . . . . . . . . . . . . .
Ideal field versus field map comparison of particle
parameters . o . . . . . . D . . . . . . . . . . 0 . . . . 0 . . .
Solenoid Px and mass resolution as a function of A@ jitter . . .
Pattern recognition efficiency inside the solenoid (3 planes)
as a function of beam, plane separation and spark jitter. . . . .
Page
34
35
37
38
43
48
52
54
-v-

Citations
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Journal ArticleDOI
TL;DR: In this paper, the performance of cluster logic circuits used in the LASS Spectrometer is discussed and a K − p experiment (E-132) is used as an example to familiarize users with the properties of this device for forming multiplicity type triggers with any of the proportional chambers in LASS.
References
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Frequently Asked Questions (1)
Q1. What have the authors contributed in "The solenoid vertex spectrometer - a simulation study" ?

This study examines the particle detection characteristics of a large solenoid magnet and spark chamber system by means of Monte Carlo simulation. The solenoid magnet can surround the target and measure the low momentum, large angle particles and a second magnet downstream, with a conventional gap and field would measure the fast secondaries. The axial field solenoid has ideal azimuthal symmetry and is well suited for rotating the transverse momentum vector of slow particles in hadron interactions. A detailed study of the acceptance, momentum resolution and pattern recognition properties of the solenoid system are presented. The overall conclusions are that it can measure most particles of 2 GeV/c or less very well, improve overall acceptances dramatically, fill in dead regions of decay distributions, make high invariant mass studies feasible ( 8 to 16 GeV/c beams ) and present no obvious difficulty for the pattern recognition of tracks. A fast track recognition algorithm is presented and no major computing needs are anticipated for the magnetic field inside the solenoid.