FMS review, Sep FPD/FMS: calibrations and offline reconstruction Measurements of inclusive  0 production Reconstruction algorithm - clustering - shower shape function - fitting Calibration - cell-by-cell gains - energy dependent corrections - run dependent corrections and LED monitoring Run9 analysis

2 Measurements of  0 inclusive production with the FPD/FMS  Important physics results: cross-section is consistent with NLO pQCD calculations PRL 92, (2004) PRL 97, (2006) precision A N measurements allow for a quantitative comparison with theoretical models [PRL 101, (2008)] transverse spin asymmetries found at lower energies persist to √s=200 GeV

3 Measurements of  0 inclusive production (2)  Important physics results: azimuthal dependence appears to be as expected A N is comparable to prior measurements with the FPD   0 reconstruction is a powerful tool for detector calibrations and monitoring  Measurements of  0 A N at √s=500 GeV are planned (Run 11?)

4 Clustering - definitions Start with a cell with maximum energy deposition in the matrix, adding adjacent cells with non-zero energy Define cluster parameters: Require that cluster energy E c > 2 GeV Perform moment analysis to make an “educated guess” whether the cluster contains one or two photons provide information about size and orientation of the cluster

5 Clustering - categorization Simulations of  0  →  On the E c  max –E c plane, there are distinct event loci when the two photons make two different (1  ) clusters or a single (2  ) cluster, and the overlapping region => these parameters can be used to distinguish between one- and two-photon clusters FPD data type=1 1  clusters type=0 type=2 2  clusters

6 Shower shape function Transverse shower profile was measured in the detector of lead-glass cells (the same as used in the FPD and in the FMS inner matrix) with a 10 GeV electron beam, and fitted by the function: where d is a cell size and parameters are as follows: a 1 =0.8, a 2 =0.3, a 3 =-0.1 (a 1 +a 2 +a 3 =1), b 1 =0.8, b 2 =0.2, b 3 =7.6 For the “large” cells (outer matrix of the FMS) there was no dedicated studies of shower shape; the same function used given that ratio of Molière radius to the cell size is close to that for the “small” cells.

7 Fitting 1  -fit - three parameters: photon coordinates x and y, and energy 2  -fit - six parameters: pion coordinates x  and y , polar angle  of the line that connects the two photons in the detector local coordinate system, distance between the photons d , energy sharing z  =(E 1 -E 2 )/(E 1 +E 2 ), and summed energy of the two photons E=E 1 +E 2 Each cluster is fitted with the shower shape function: type=1 – only 1  -fit is tried type=2 – 2  -fit is tried, but required that  2 is less than a preset value type=0 – both fits are tried, decision made based on  2 Outcome of the reconstruction – list of photons with their coordinates and energies

8 Calibrations - overview Cell-by-cell gains – using   reconstruction g i = c i  b, b – “basic” gain [MeV/ADC count], the same for all cells in a module; c i – correction factor for each cell Software correction factors c i then used for “online” calibration on hardware level: - effective gains through LUT - adjusting HV for the PMTs  need to know gain curve for an individual channel; data were obtained for the FMS in Run9 Offline corrections: - energy dependent - run (time) dependent

9 Cell-by-cell correction factors The Pb-glass detectors of the FPD/FMS are calibrated by associating gaussian centroid of the  0 peak seen in the di- photon invariant mass spectrum with the "high-tower" in the module The absolute gain of the cell is scaled to put the  0 peak at its known position, and the procedure is iterated until convergence Run9, day= (200 GeV, “far” position) The calibration methodologies employed for the FPD have been successfully adapted to the FMS Run8, FMS, WS-sml-top

10 Energy dependent corrections Position of the  0 peak in the invariant mass distribution increased as a function of energy Dedicated MC study (with full Čerenkov light simulation) showed that there are three possible sources of this dependence: - missing energy due to longitudinal shower profile - transverse leakages - ADC granularity Run9, day= (200 GeV, “far” position)

11 Energy dependent corrections (2) Correction works well for the energy range where it was determined, but extrapolation does not work if we go below ~10 GeV or above ~65 GeV => Energy dependent corrections must be determined for the whole energy range, where physics results are to be obtained (especially critical for data at √s=500 GeV)

12 Energy dependent corrections (3) GEANT simulations and association analysis: comparison of generated quantities to reconstructed values Eliminating energy dependence in   mass peak position gives the correct neutral pion energy uncorrected corrected Calibration on   s gets mass peak for heavier mesons correct  →    fit by Gaussian+p3 μ=0.784 ± GeV/c 2 J/  →e + e - fit by Gaussian+Offset μ = ± GeV/c 2

13 Run dependent corrections FPD/FMS responses vary with time and beam conditions Run8, FMS Run6, FPD Up to ~10% variation; corrections were applied per module The detector was stable within a few percent; no corrections applied

14 LED monitoring system LED system: critical calibration tool Run9, FMS – variations with time in individual channels

15 Run9 - first data at √s=500 GeV    event reconstruction in the FPD: using matrix+preshower (no SMD data) 20 GeV < E total < 80 GeV fixed vertex (z=0), no minbias condition N  =2 FPD measures energy up to ~200 GeV ═> SMD information is required to reconstruct pions above ~60 GeV Example of 2-photon event when two clusters Significantly overlap in the matrix, but are clearly separated in the SMD

16 Run9 data analysis Energy dependence is much stronger than it was for the FPD in all previous runs (comparable to FMS in Run8) – not yet fully understood slopes of the corrections in the data and simulations ??? linear corrections do not work above ~65 GeV FPD, day= PYTHIA+GSTAR simulations