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Study of Misalignments in Muon Systems: Barrel and Endcap Analysis

This report summarizes findings from the Muon Week meeting on November 15, focusing on the misalignments in the Muon Systems (MS) and Inner Detector (ID). The study, based on v35 processing of Z skimmed data, was initiated due to the observed Afb effect and finds systematic eta-dependent issues affecting CB momentum. The study identifies significant misalignments impacting both Barrel and Endcap configurations through detailed comparisons, yielding insights crucial for future calibrations and corrections.

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Study of Misalignments in Muon Systems: Barrel and Endcap Analysis

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  1. Misalignment studiesMS z misalignments Barrel and Endcap Peter Kluit, Muon week meeting 15 November Summary of results 5/15 october Based on the v35 processing of the Z skimmed data

  2. Focussing on MS misalignments • Study was initiated by so-called Afb effect • CB momentum suffered from systematic eta dependent effects • Traced down to misalignment in z of MS and ID • Here below it is pinned down to misalignments in the Muon system • Using muons from Z events in ZMUMU v35 (release 17) processing. • Will be done in three ways: • Comparison of MS-MS parameters: z0-z0 • B) Comparison of MS-ID z0 parameter • Z0 of ID is consistent and precise to better than 0.1 mm apart from ONE global z shift • C) comparing theta ID and SA • Try to understand and model the Endcap structure: Barrel is more simple.

  3. Looking at z0 SA – z0 SAfor MS Barrel-Barrel events Select eta1<0 and eta2 >0 events and plot plot dz = z(eta>0) – z(eta<0) So Barrel A and C are not consistent at 2 mm level

  4. z0 SA – z0 SAfor MS Barrel-Endcap events plot dz = z(EC) – z(Barrel) both in eta >0 or both in <0 So Barrel and Endcap are not consistent at a few mm level - It is known that B-E overlap are not consistent - See also slide 9 that demonstrate this wrt z0 of ID

  5. Looking at z0 SA – z0 SAA simplified model for the Endcap R (sign) Inspired by the linear trend in slide 4 CSC region might be more complicated z • A possible deformation would look like this • Keeps the z distance between A-C approx. constant • not only a z shift of endcap A or C: can be added • has feature that dz vs eta is linear for Endcap AA or CC events • Can be tested and refined selecting Endcap-Endcap events: • - Events A-C (z distance between AC) and AA or CC events

  6. Looking at z0 SA – z0 SAMS Endcap A-C Recall slide MCP Plotted eta in EC A Means that EC distance is correct at ~2 mm level

  7. z0 SA – z0 SAMS Endcap AA Plotted delta eta of the two muons in EC A So: dz/deta = -6 mm/ unit rapidity By ‘definition’ through 0 Or 9 mm/1.5 rap Quite unexpected…

  8. z0 SA – z0 SAMS Endcap CC Plotted delta eta of the two muons in EC A So: dz/deta = -4.4 mm/ unit rapidity By ‘definition’ through 0 Or 6.6 mm/1.5 rap Quite unexpected… A and C seem to behave similarly

  9. A telescope model for the Endcap • Basically the same as the one on slide 5 • There are however NO z(R) shifts • There are rotations + small shifts (~1 mm). theta’ = theta + dtheta This generates a z0’: z0’ = z0 +/- 7000*dtheta/sin2(theta) Value of dtheta = 30 μrad (A side) and 50 μrad (C) This value is compatible with Survey and alignment constraints Interpretation: telescope effect in Endcap i.e. small rotations (dR/dz) that are phi sector dependent This is consistent with the observed sector dependence

  10. z0 ID – z0 SA at primary vertex before/after correction for dtheta Tighted MS track selection to three station tracks with NO EE chambers and NO Barrel-Endcap Flattened: After Before

  11. z0 SA – z0 SA correctedMS Endcap AA Plotted delta eta of the two muons in EC A Now flat!

  12. z0 SA – z0 SA correctedMS Endcap CC Plotted delta eta of the two muons in EC C Now flat!

  13. z0 SA – z0 SA correctedMS Endcap A-C Plotted eta in EC A Means that EC distance is correct at ~2 mm level After correction results more compatible with 0 Conclusion: Model in slide 9 seems to do the job

  14. z0 ID –z0 SA correctedEndcap: eta Sector projections Interpretation: dtheta is sector dependent and small misalignments cause q splitting

  15. z0 ID –z0 SA correctedEndcap: eta Sector projections

  16. z0 ID –z0 SABarrel: eta Sector projections Different interpretation for the Barrel: Here we have z shifts that are sector dependent The charge splitting could be due to misalignment in position and/or angle

  17. z0 ID –z0 SABarrel: eta Sector projections

  18. Endcap: q* (z0 ID –z0 SA) and q*(theta ID- theta SA) corrected Very similar shapes in dz and dtheta plots: implies that structure comes from dtheta MS endcap misalignments: in agreement with the model

  19. Endcap: q* (z0 ID –z0 SA) and q*(theta ID- theta SA) corrected Very similar shapes in dz and dtheta plots: implies that structure comes from dtheta MS endcap misalignments: in agreement with the model

  20. Barrel: q* (z0 ID –z0 SA) and q*(theta ID- theta SA) corrected Very similar shapes in dz and dtheta plots: implies that structure comes from MS Barrel z/theta misalignments.

  21. Barrel: q* (z0 ID –z0 SA) and q*(theta ID- theta SA) corrected Very similar shapes in dz and dtheta plots: implies that structure comes from MS Barrel z/theta misalignments.

  22. Conclusions • - An Interpretation for the Endcap is proposed: telescope effect in Endcap i.e. small rotations (dR/dz) that are phi sector dependent. Plus small shifts of the Endcap (~1 mm). • Correcting for the Endcap Model gives dtheta values of 30 and 50 microrad • These values are in agreement with constraints from Survey and the optical alignment. • The distributions in Endcap A and C are after correction flat • Detailed study of the sector dependent effects show that: • Endcap dtheta correction is sector dependent • Endcap q*misalignments in MS are observed in z0 and theta (wrt ID) -> misalignment within one sector • Everything compatible with dtheta << 50 microrad

  23. Conclusions • - The results in the Barrel can be interpreted as a set of sector dependent z shifts • This is in agreement with constraints from Survey and the optical alignment. • Looking into more detail at q*dz and q*dtheta (appended) plots structures are observed indicating misalignments in z/theta inside a sector. • Note that also clear MS effects within one sector are observed. • This is further confirmed by very high statistics studies performed by Phillipp Fleischmann. • What we learned from this: • can improve the alignment • using a z0 constraint might help a lot • Pierre-Francois Giraud is implementing this for the Barrel • For the Endcap Christoph and Ben and I look into this

  24. theta ID –theta SA correctedEndcap: eta Sector projections Interpretation: the observed structures are probably too big to come from the MS

  25. theta ID –theta SA correctedEndcap: eta Sector projections Interpretation: the observed structures are too big to come from the MS

  26. theta ID – theta SABarrel: eta Sector projections Interpretation for the Barrel? Looks like a global dtheta vs phi structure

  27. theta ID – theta SABarrel: eta Sector projections Interpretation for the Barrel? Statistics?

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