Low mass dimuon acceptance

Shiuan-Hal Shiu

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Contents Introduction

The result of varying M1 current

The result of varying M2 current

Dump/Target separation

Conclusion

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The location of M1 and M2

Configuration file

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WantOriginal

Why varying the magnet current

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Why varying the magnet current

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In low mass region the dimuon events have small opening angle

Use the E906 Fast Monte Carlo simulation for study configuration data.

The configuration file is “fe198v5.dat”.

By changing the entry “current and step to scale” we can adjust the M1 or M2 current.

Fix M2 current and vary M1 current

The input to the simulation is decided by Ykick*input/2000 and

the tracking plane from #2 to #13 will affected

by this factor.

The input to the simulation is decided by Ykick*input/2000 and

the tracking plane from #2 to #13 will affected

by this factor.6

The top diagram is the mass distribution of generated dimuon pairs.

The middle diagram is the mass distribution of accepted dimuon pairs.

The bottom diagram “Acceptance” as a function of dimuon mass. 7

The mass range of generated dimuon pairs is from 0.2Gev to 15Gev

Green line is the acceptance value with the original M1 current setting.

By increasing the current we find that the peak of acceptance is shifting to high mass end.

Reducing the M1 current can increase the acceptance in the low-mass region.8

Fix the M1 current, and change the M2 current (Ykick).

Fix M1 current and vary M2 current

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M2*1.5 M2*1 M2*0.5

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M2*1.5 M2*1 M2*0.5

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M2*1.5 M2*1 M2*0.5

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Dump/Target separationM1*1

Cuts conditionsPurple: all events

Green: xF>0 and M>4.5 GeV and pz>20 GeV

Blue: Green and |ytrack|>2.25 in at z=0 (zdump)

Red: Blue and |ytrack|<10.0 in at z=-60 (zstart)

Target

Target

Dump

Dump

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Dump/Target separation

M1*1 M1*0.5 M1*0.1

Target retrace and dump

retrace can be separated

Target retrace and dump

retrace can be separated

Target retrace and dump

retrace can not be separated

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Dump/Target separationM1*0.5

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2

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Dump/Target separationM1*0.1

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Reducing the M1 current will lead the z resolution bad.16

Change the target location

The target original location is at -70 to -50. We change it to -150 to -130.

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Change the target location

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2

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M1*0.5

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Change the target location

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2

3

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M1*0.1

Changing target location can not improve the z resolution.19

Cuts conditionsPurple: all events

Green: xF>0 and M>4.5 GeV and pz>20 GeV

Blue: Green and |ytrack|>2.25 in at z=0 (zdump)

Red: Blue and |ytrack|<10.0 in at z=-60 (zstart)

Moving the cut condition at zdump to Station 1 and change the value.

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Original Changed

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Original Changed

Try |ytrack|>8 in at z=238 (before station1)22

M1*0.5

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4

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M1*0.1

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Changing cut condition can not improve the z resolution.24

Check the relations of retrace mass and retrace z Left diagram is using

the original cut condition.

The mass cut is “>4.5Gev” here.

After applied the cut(mass >4.5 Gev) , we can see that the events are almost spread in the region which less than z=0.25

Check the relations of retrace mass and retrace z

M1*0.1

M1*0.5 Left diagram is using the original cut condition but mass cut is “<4.5Gev”.

After applied the cut , we can see that the events are still scattered throughout the x axis.

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Momentum Difference(X) (M1*0.5)

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Momentum Difference(Y) (M1*0.5)

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Momentum Difference(Z) (M1*0.5)

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Pt/Pz(positive) (M1*0.5)

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Pt/Pz(negative) (M1*0.5)

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Opening angle of muon pairs

fe198v5m101mrtr.le.4.5zrtr.le.0

fe198v5m101mrtr.le.4.5zrtr.ge.0

fe198v5m101_dumpmrtr.le.4.5zrtr.le.0

fe198v5m101_dumpmrtr.le.4.5zrtr.ge.0

Momentum Difference(X) (M1*0.1)

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Momentum Difference(Y) (M1*0.1)

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Momentum Difference(Z) (M1*0.1)

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Pt/Pz(positive) (M1*0.1)

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Pt/Pz(negative) (M1*0.1)

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Opening angle of muon pairs

fe198v5m101mrtr.le.4.5zrtr.le.0

fe198v5m101mrtr.le.4.5zrtr.ge.0

fe198v5m101_dumpmrtr.le.4.5zrtr.le.0

fe198v5m101_dumpmrtr.le.4.5zrtr.ge.0

Conclusion

Reducing the M1 current can increase the acceptance of low mass dimuons.

Adjusting the M2 current does not change the acceptance significantly.

Howerer, decreasing M2 current can enlarge the acceptance.

After reducing the M1 current, the z resolution is become bad.

Changing target location and cut condition can not improve the Dump/Target resolution.

Low mass events are affected by the multiple scattering seriously.

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backup

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Theta y distribution of positive muon at zstart

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Theta y distribution of positive muon at zstart

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Theta y distribution of negative muon at zstart

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Theta y distribution of negative muon at zstart

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Momentum distribution of positive muon at zstart

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Momentum distribution of positive muon at zstart

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Momentum distribution of negative muon at zstart

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Momentum distribution of negative muon at zstart

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X distribution of positive muon at zstart

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X distribution of positive muon at zstart

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X distribution of negative muon at zstart

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X distribution of negative muon at zstart

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Theta x distribution of positive muon at zstart

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Theta x distribution of positive muon at zstart

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Theta x distribution of negative muon at zstart

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Theta x distribution of negative muon at zstart

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Xf distribution of muon at zstart

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Xf distribution of muon at zstart

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X1 distribution of muon at zstart

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X1 distribution of muon at zstart

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X2 distribution of muon at zstart

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X2 distribution of muon at zstart

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Total momentum distribution of muon at zstart

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Total momentum distribution of muon at zstart

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Station 1 Chamber RatesOccasionally a muon showers in the

absorber If this happens in the center of the

absorber, no effect is seen as shower is also absorbed

If this happens in the last few inches of the absorber, shower can create extremely large rates in Station 1 (of low momentum particles)

Solution is to have an absorber-free region at the end of the field volume and use field as a sweeper

In Solid Iron magnet, there is no absorber-free sweeper region! (Can we find a wide gap sweeper magnet?)

Requires GEANT MC to see magnitude of effect

Absorber and B Field

Sta. 1

Absorber and B Field

Absorber and B Field

B Field only

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