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AnDY @ IP2 Analysis

AnDY @ IP2 Analysis. Analysis scheme and algorithms MC Geant3 Fast Simulator Analysis of run-11 data and comparison to MC Calibrations Di-leptons Magnet and tracking. Akio Ogawa BNL 2012 Mar 30. Getting to DY. DY : ~7 x 10 -5 mb @ 500GeV. Hadronic : ~30mb. 10 6.

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AnDY @ IP2 Analysis

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  1. AnDY @ IP2Analysis • Analysis scheme and algorithms • MC • Geant3 • Fast Simulator • Analysis of run-11 data and comparison to MC • Calibrations • Di-leptons • Magnet and tracking Akio Ogawa BNL 2012 Mar 30

  2. Getting to DY DY : ~7 x 10-5 mb @ 500GeV Hadronic : ~30mb 106 Lepton daughters from γ* Detecting e+/e- at forward rapidity in ECal Reduce Hadron & Photon Backgrounds using ECal, HCal, Pre-shower detectors Magnetic field & tracking allow for charge sign discrimination as well as backgrounds suppression & measurements

  3. Event reconstruction in ECal/HCal • ECal – matrix of lead glass cells of two types: (3.8cm)2 x 45cm and (4.0cm)2 x 40cm • HCal – matrix of lead-scintillating fiber cells: (10cm)2 x 117cm lead cells with 47 x 47 matrix of 1-mm fibers in each cell) • Analysis scheme: • Clustering • - define a cluster (find a high tower, add adjacent cells with the energy deposition above a threshold); • - cluster categorization (for ECal): is the cluster likely contains 1g or 2g? • Output: cluster energy E, x,y-coordinates • (“center of gravity” position of the cluster), and • cluster type. An example of HCal event from jet trigger

  4. Event reconstruction (2) 2) Shower shape analysis (for ECal) – fit each cluster to the experimentally obtained and parametrized shower shape • - 1g-clusters are fitted with three parameters: • photon energy E and coordinates x,y • -2g-clusters are fitted with six parameters: • “center of mass” coordinates xp,yp of the two • photons, polar angle q of the line that connects • the two photons, distance between the photons dgg, • energy sharing zgg = (E1 - E2)/(E1 + E2), and total • energy Egg = E1 + E2 • Output: photon energies and coordinates. Resolution of single photons (electrons) in the calorimeter made from the same lead glass was measured before: sE /E ≈ 0.12/√E + 0.01 (in the energy range ~2-26 GeV) and sx ≈ 1.5 mm (at 26 GeV) Shower shape function:

  5. GEANT Models of AnDY Run-11 Run-13 PYTHIA + GEANT simulations for run11 data comparison Single particle studies for background rejection ⇒ Fast simulation

  6. Single particle GEANT studyPreshower 2 : hadron/photon rejection GEANT simulation of 2nd pre-shower detector made of 0.5cm thick plastic scintillation counter placed after 1cm Pb converter. Responses for 30GeV electrons, charged pion and photons are simulated. A cut of energy deposit in the 2nd pre-shower above 5MeV will retain 98% of electrons, while rejecting 85% of pions and 39% of photons. Retain 98% electrons Reject 85% hadrons Reject 39% photons More examples in backup slides

  7. Fast Simulatior ~1012 p+p events ~1.5k CPU years & 100Tbyte ⇒ full PYTHIA + GEANT not practical • Fast Simulator based on single particle GEANT studies • Parameterize GEANT response of ECal and use parameterized response in fast simulator applied to full PYTHIA events • Estimate rejection factors from GEANT for hadron calorimeter and pre-shower detector (both critical to h±/e± discrimination) • Explicit treatment in fast simulator to estimate path lengths through key elements (beam pipe and pre-shower), to simulate photon conversion to e+e- pair • Estimate effects from cluster merging in ECal (d < εdcell / use ε=1 for estimates) • Estimate/simulate ECal cluster energy and position resolutions. σE=15%/√E and σx(y)=0.1dcell, used to date for π0→γγ rejection. • Multiple scattering at beam pipe and GEMs & GEANT tracking codes for charged particles through magnetic field

  8. QCD Background Estimate from Fast Simulatior • ECal doesn’t measure full hadronic energy • ECal π0 reconstruction removes photons (including conversion e+/e-) • Preshower-1 charge particle veto reduces neutrals • Preshower-2 (after Pb Converter) reduces hadrons and photons • HCal reduces hadronic backgrounds

  9. Calibration of ECal Based on p0gg reconstruction: association of the p0peak seen in the di-photon invariant mass distribution with the high tower in the detector, scaling the gain to put the peak at the known p0 mass, and iterate procedure until convergence. Di-photon mass distributions in both ECal modules before (top) and after (bottom) calibration Energy spectra in ECal from PYTHIA+GEANT and calibrated data (normalized by total number of events) Sorted by HT mass distributions in the cells of 7x7 module (Left) of ECal after seven iterations ECal calibration in run-11 was defined at the level of ~5%. There is a reasonable agreement between data and simulations. 9

  10. Calibration of HCal • Relative gains for individual cells are determined from cosmic-ray muons • Absolute energy scale - based on p0gg reconstruction • Require: (1) 1-tower clusters; (2) E>1.8 GeV; (3) |x|>50 cm to avoid ECal shadow; (4) >1 clusters to form pairs; (5) Epair>5 GeV; and (6) zpair<0.5. • Apply to 20M minimum-bias events from run-11 data • Apply to 20M PYTHIA events subjected to BBC charge sum trigger emulation (no vertex cut) • Data and simulations are both absolutely normalized, so PYTHIA is expected to provide a good basis for QCD backgrounds to DY. • HCal clusters are subjected to event selections to suppress hadronic response: (1) single-tower clusters; (2) x,y location of the cluster is outside of ECal shadow. • The selected clusters are converted into four momenta of incident particles, assuming they are produced at the event vertex and they are photons, using a scaling factor to convert cluster energy into incident total relativistic energy. • Invariant mass is computed from inclusively pairing all such clusters for the event. 10

  11. HCal : cell by cell calibration usingp0 peaks Relative gains for HCal cells were adjusted using p0ggreconstruction • The detector associated with the mass is • hit by the leading photon of the pair. • Used vertex z from the BBC time • difference. The difference between the • maximum TAC values was scaled • by 0.25 cm/ch. • Require: (1) HCal cluster has 1 or 2 towers • (identified as “electromagnetic”) and energy • deposition > 0.25 GeV, bounded by cells • with energy deposition < 0.06 GeV; • (2) E(HighTower)/E(cluster) >0.7; • (3) 24.8 < |xcl| < 54.0 cm and -17.4 < ycl < • 11.6 cm (excludes ECal shadow on HCal); • (4) 3 < Epair < 15 GeV. The HCal modules in run-11 have been calibrated to ~5%. Corrections for hadron showers are expected to be small, but need to be measured. Cell-by-cell pair mass distribution for HCal (Left) module

  12. BBC and ZDC calibration • Peaks from a single minimum-ionizing particle passing through the detector were used to calibrate Beam-Beam Counter arrays (left) • Absolute calibration of ZDC was done with the ~100 GeV neutron flux produced at 0 in sNN=200 GeV Au+Au collisions (right) ZDC summed charge distributions from Au+Au collisions Charge distributions for Blue-facing BBC for minimum bias events

  13. Vertex z from Beam-Beam Counters z-position of collision vertex is important for background suppression to access DY production through the matching of ECal and HCal clusters that require a line from the primary vertex and the matching to the pre-shower, as well as for tracking. zvertex is proportional to the time difference of the earliest hits in BBC-Yellow and BBC-Blue arrays. TAC difference was calibrated using two methods: 1) single beam background (left); 2) neutral pion reconstruction in ECal (right). The two methods give calibration constants that disagree Mid-h detector for additional constrains on z-vertex

  14. Dileptons from Run 11 Data versus Simulation • Compare run-11 mass distribution to model used to make background estimates for DY • Large-mass background found to be well-represented by fast-simulator model in both magnitude and shape

  15. PHOBOS split-dipole magnet • The plan is to reuse the split-dipole magnet at IP2 designed, built and operated by the PHOBOS collaboration. • PHOBOS provided their field map and geometry files for GEANT for simulation studies. • The magnetic field calculation by Wuzheng Meng that opens the gap between the poles of the split dipole from 15.7cm to to 31.4 cm • Split-dipole magnet is planned for installation in RHIC run13 after modifications and to be used in RHIC run14. Interaction Point Vertical component of B versus x,z at y=0 from modified PHOBOS split-dipole magnet

  16. Tracking with split-dipole & GEM Charged Particle 3rd 1st & 2nd GEM Straight Tracking Dz/2

  17. Charge sign separation from fast simulator • Prior experience with ECal shows (x,y) position localization to ~1/10 cell size, or ~4mm. • A single tracking station provides space point of resolution better than 0.2mm  robust zvertex and robust ECal/PS association even without magnet • Fast Simulator includes tracking through magnetic field and multiple scattering • Straight tracking from GEM back to vertex • Charge sign discrimination can determine if hadronic backgrounds are suppressed • Smaller z-vertex distributions at RHIC is important

  18. Summary • Analysis codes for calorimeters (clustering & shower shape fitting) is ready • GEANT models used for • Run11 data & MC comparison • Single particle studies for basis of Fast Simulator • Fast Simulator is used for • background rejection studies for DY • Run11 di-lepton backgrounds comparison to PYTHIA • Run11 analysis • Ecal and HCal are calibrated to ~5% • Data & MC (GEANT and Fast Simulator) comparison OK • First di-lepton signals • Magnetic field and GEM tracking are important • (tracking algorithm is under development)

  19. Backup

  20. Management and responsibilities • ANDY analysis coding is an adaptation of coding developed by the collaboration • members for other forward calorimetry projects at BNL, IHEP, JLab. • Reconstruction algorithms are checked against PYTHIA/GEANT simulations • to assure that detector responses and mass distributions are real and understood. • Analysis of ANDY data is the responsibility of individual members of the collaboration. • Detector mapping and calibration files are shared among those doing the analysis. • Physics results from ANDY will require documentation of the analysis and archiving • of all coding used for the analysis.

  21. Single particle GEANT studyPreshower 1 : photon rejection GEANT simulation of a pre-shower detector made of 0.5cm thick plastic scintillation counter. Responses for 30GeV electrons and photons are simulated. A cut of 0.5MeV < dE < 1.5MeV will retain 86% of electrons, while rejecting 98% photons including ones converted to e+e- pairs in beam pipe and preshower detector itself. Retain 86% electrons (and charged hadrons) Reject 98% photons

  22. Single particle GEANT study ECAL hadron response ½ hadrons leave MIP in ECAL Remaining ½ leave a fraction of evergy in Ecal, thus “mismeasure” hadron energy. With falling energy spectra of hadrons, ~1/100 suppression of hadron just due to response in ECAL GEANT simulation of EMcal response to E>15 GeV π± from PYTHIA 6.222 incident on (3.8cm)2x45cm lead glass calorimeter. GEANT response not so different from 57-GeV pion test beam data from CDF [hep-ex/0608081]

  23. Single particle GEANT studyECAL hadron response : MC Uncertainty GEANT simulation with hadronic interaction package GEISHA (black) and GCALOR(red) of energy deposited in an EMcal built from 3.8 cm × 3.8 cm × 45 cm lead glass bars. Charged pions with E=30 GeV are used in this simulation. The fraction of the incident pion energy deposited in the EMcal is f.

  24. Single particle GEANT studyHcal : hadron rejection GEANT simulation for energy deposit in an EMcal and Hcal for 30GeV electrons and charged pions. A 3x3 cluster sum of deposited energy forms the ratio R=DE(EMcal)/(DE(EMcal)+DE(Hcal)) shown in top plot. With R>0.9 cut, EMcal+Hcal can reject 82% of hadrons while retaining 99% of electrons. The bottom plot shows distribution of f for hadrons that survive R>0.9 cut. Retain 99% electrons (and photons) Reject 82% charged hadrons

  25. Single particle GEANT studyHcal : hadron rejection GEANT simulation for energy deposit in an EMcal and Hcal for 30GeV charged pions. The top plot shows the distribution of f in EMcal 3x3 clusters around the high tower. The bottom plot shows the ratio R=DE(EMcal)/(DE(EMcal)+DE(Hcal)). Blue shaded area is for hadrons surviving cut f>0.7. Red shaded area is hadrons which can be identified using Hcal by R>0.94 cut. This gives 40% hadron rejection for hadrons with f>0.7. Retain 99% electrons (and photons) Reject 40% charged hadrons which left >70% of energy in ECal

  26. Open Bottom Background Estimate from Fast Simulation

  27. Multiple scattering smearing of 50GeV tracks at each tracking station from GEANT simulation Fast Simulator including multiple scatterings and GEANT tracking code through magnetic field

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