TPC track distortions Review of situation

TPC track distortionsReview of situation Alain Blondel, Silvia Borghi, Simone Giani, Simone Gilardoni and all the people that contributed with ideas or suggestions or comments during the analysis meetings and offline Thanks to Charles Pattison for the ntuple productions

Outlook • Two distortions effect • Electromagnetic effect induces a d0 shift dependent on z position (smaller effect, 10 mm) • Blondel’s effect (larger effect 30-40 mm) Silvia Borghi

y Track r>0 clockwise 1/r Fit circle center f 0 X O x d0 impact parameter Sxy=0 How d0 changes in case of distortions Definition of d0 - Silvia Borghi

First Effect Presented at analysis meeting on 29th April 2003 and studied in Dydak’s et al. HARP Memo 03-002, 30 June 2003 Silvia Borghi

A 29th April 2003 • We consider the following regions. • the forward part (region A and E) • the backward part (region C and B2) • We observe a different effect in these two regions. E 500 mm 285 mm 215 mm 500 mm C B2 C: -51°<<0 B2: 0<>35° E: 68°<<77° A: 0<<77° from end-cap Silvia Borghi

29th April 2003 MiniBoone at 8.9 GeV/c E C B2 Silvia Borghi

No feedback from collaboration until HARP Memo 03-001 6 June 2003 ¨ Therefore, during all of HARP data taking after 8 August 2001, the high voltage of the inner field cage was lowered by 1.6% than the corresponding high voltage of the outer field cage. [3] We thank L. Linssen for having brought the high voltage misalignment problem to our attention, and for ongoing calibration work to ascertain the precise size of misalignment ¨ Silvia Borghi

HARP Memo 03-002 30 June 2003 ¨ The effect is most prominent at small radius, where near the target position displacements of order 10 mm are expected. Positive tracks are systematically shifted to smaller momentum, negative tracks to higher momentum. ¨ ¨ ¨ (As already shown in my previous first plot) ¨ The effects of the magnetic and electric field inhomogeneities have the same overall effect on the distortion of track sagittas. Another distinct feature is the strong dependence of the displacements on the longitudinal position inside the active TPC volume, especially around the nominal target position. This suggests that the position and the length of the target plays an important rôle. The higher upstream the track, the less it will be affected. Therefore, tracks from thin targets will generally be less affected than tracks emerging at the downstream end of long targets. This may shed some light on observations on TPC track distortions reported recently [7]. ¨ F. Dydak, A. Krasnoperov, Yu. Nefedov Silvia Borghi

BUT … As you can see in the next plots the shift for positive particles is constant in the direction of negative d0, but for negative particles the shift is not always in the same direction of positive d0 and sometime the shift is equal to one of positive particles Silvia Borghi

Be thick (1 l) at 12 GeV/c C E Silvia Borghi

Be thin (2% l) at 8 GeV/c E C Silvia Borghi

Be thin (5% l) at 15 GeV/c with inverted B E C Silvia Borghi

Conclusions (on 29th April 2003) … In the forward region (region A or E) the d0 peak for positive particles is shifted to -10 mm and sometime the d0 peak for negative particles is shifted to 10 mm. If we consider the first part of TPC (region C and B2) this effect disappears and the d0 distribution is centered in 0. The shift for positive particles is the same also for inverted magnetic field. Silvia Borghi

On the same subject: CONCLUSIONS Memo 03-002 The problem of TPC track distortions due to magnetic and static electric field inhomo geneities has been adressed in a quantitative way. … The high voltage misalignment between the outer and inner field cages is identified as the likely primary cause of sagitta distortions of TPC tracks. The position and the length of the target plays an important rôle. ¨ ¨ Our state of the art knowledge: The Memo 03-002 could confirm the shift for positive particles, but it could not explain, yet, why sometimes the peak of negative particle is not shifted on the positive d0. The last plot shows that a more dominant effect of distortion exists. Silvia Borghi

Blondel’s Effect Already presented in analysis meetings in April 2003 Silvia Borghi

Where did we start? Ta thick at 3 GeV/c Negative blue Positive red Silvia Borghi

Ta thick at 3 GeV/c From C. Morone’s Thesis Silvia Borghi

Ta thick at 3 GeV/c E D C B D E A C B X A 1/ r - O Silvia Borghi

Ta thick at 3 GeV/c + - - - + + -+ 1/(charge * Pt) (1/MeV/c) Silvia Borghi

Miniboone at 8.9 GeV/c + - - - + + -+ Silvia Borghi

One possible explanation Distortions due to ExB effects are the cause of this effect. This effect may not be constant in time and in space. Silvia Borghi

Different settings Silvia Borghi

Summary of table • The banana effect does not depend in conclusive manner on • the target (al and k2k 1 lambda) • the interaction length of target • (k2k 1 lambda and k2k replica) • beam momentum (Be thin at 8 GeV/c and 12 GeV/c) • the data 2001 or 2002 (C and Al). Silvia Borghi

What happens if B is inverted? Be 5%l at 15 GeV/c B neg C 2%l at 3 GeV/c B pos Silvia Borghi

What happens if B is inverted? If the beam is positive the banana has the same position also when B is inverted. Compatible with ExB effect. Not yet explained: Why is the d0 peak at 0 always present? (demonstrates that this ExB effect is not constant) Why not in coincidence with understood spill time structure or run time structure? Silvia Borghi

Another possible explanation (additional or alternative) • Beam effects: • Rate • Size • Optics. Silvia Borghi

Does the banana depend on the beam? C 2%l at 3 GeV/c B pos no beam interruption between runs with banana and runs without banana First run: 9377-9381 Silvia Borghi

After ~7 runs: • On 15th October 2001 at 12.39: • vertical collimator settings: 53.8 • events per burst 60 • On 15th October 2001 at 17.56: • Beam expert has finished tuning the beam. • On 15th October 2001 at 18.13: • the vertical collimators to +- 52.0. • events per burst is ~80 ? ABRACADABRA Silvia Borghi

Does the banana depend on the beam? C 2%l at 3 GeV/c B pos no beam interruption between runs with banana and runs without banana First run: 9377-9381 First run: 9389-9449 Silvia Borghi

What happens? (preliminary) • In C setting (and also in a Be setting) the banana disappears when the beam spot size decreases. • The spot size alone does not create the banana, in fact in Be 2% lambda 15 GeV/c a smaller spot size shows the banana effect • We never observed the banana with negative beam. Silvia Borghi

Preliminary conclusions In these cases the spot size and the focusing of the beam seems to play a important role. The rate of T9 protons seems not to matter. Silvia Borghi

Space dependence of the banana effect • The banana is always present in all regions and no evident changes are noted. • The tracks belonging to the banana have no strong dependencies by • 0 • tan() • z0 Silvia Borghi

Conclusion • The banana effect does not depend in conclusive manner on • the target (al and k2k 1 lambda) • the interaction length of target • (k2k 1 lambda and k2k replica) • beam momentum (Be thin at 8 GeV/c and 12 GeV/c) • the data 2001 or 2002 (C and Al). • setting (C) • magnetic field polarity (Be at 15 GeV/c) • rate of protons in T9 (C) • on spill time during the same run • the spatial regions • the track parameters: 0, tan(), z0 Silvia Borghi

? Under investigation • Does the banana effect depend on • the beam spot size • the time: in which way • the ionization of the chamber that • creates a ExB effect • If we do not use the settings affect by the banana, which amount of data we lose • If we do not understand really this effect, how can we be sure that the effect (in a smaller way) is not present in the other settings • Why does the banana effect changes in time ? ? ? Silvia Borghi

TPC track distortions Review of situation