Splitting tracks at the TPC Central membrane for fixed target data samples. New 2024 Alignment.

The plots are addressing issue observed by M. Labonte for 31GeV_fixedTarget_2019 sample and confirmed by Gene for all fixedTarget samples.

The plots of Y versus X of the last hit on global and primary tracks near the TPC Central Membrane (|z| < 3 cm) obtained with the embedding MuDst (/star/data105/embedding/production_31GeV_fixedTarget_2019/Kminus_100_20230701/P21id.SL21d/2019/190/*/*MuDst.root) show the claimed behavior:

• There is obvious φ dependence of the last point on track at the Central Membrane, especially at 3-4 o'clock and 9-10 o'clock.
• There are bumps around Z = 0 with factors from 3 (global) to 5 (primary) pointing to splitted tracks at the Central Membrane.

Old Alignment	Y versus X at |Z| < 3cm
global tracks	primary tracks
Old Alignment	Z of the last hit
global tracks	primary tracks

The same plots at the TPC Central membrane for fixed target data samples with new (2024) Alignment

With 2024 Alignment :

• There is no obvious φ dependence.
• The bumps around Z = 0 are reduced from 3-5 to 1.5 for both global and primary tracks.
• There some structures in sectors 11/23 for 13p5GeV_fixedTarget_2020, 19p5GeV_fixedTarget_2020, 7p35GeV_fixedTarget_2020, and in sectors 4/16 and 10/22 for 26p5GeV_fixedTarget_2020. I believe that these structures are related to dead RDOs and have nothing to do with alignment.
• The splitting of tracks at the Central Membrane has reduced by a factor of 2-3 with new aligmnet but it is still there. My guess is that this is related to timing. This problem will be addressed later.

Alignment 2024	Y versus X at |Z| < 3cm
global tracks	primary tracks
Alignment 2024	Z of the last hit
global tracks	primary tracks