Pb-Scintillator sampling calorimeter 1 < h < 2 21 Radiation Lengths

1.  f STAR Beam-Beam Counters monitor both L and  polarization components via forward charged hadron production. Sectors 2-6 (“lower” half) relatively shielded by tunnel floor eLLUPPER - eLLLOWER The Endcap Electromagnetic Calorimeter (EEMC) at STAR Physics Goals and Motivation Where is the proton’s spin? SMC QCD-analysis: g-jet coinc.rare J = ½ = ½ DS + DG + Lzq + Lzg The EMC/SMC result shows that the quarks only carry a fraction of the proton’s spin. • Pb-Scintillator sampling calorimeter • 1 < h < 2 • 21 Radiation Lengths • 720 Projective Towers give EM energy • High-tower and Jet Patch triggers • Pre/postshower layers for e/h discrimination • Fine-grained shower-maximum detector • provides for p0/g discrimination p0 Jets and p0s The spin program at STAR is designed to study several different channels to measure DG. p0 We would prefer Heavy flavorrare • Dominant reaction mechanism • Experimentally clean reaction mechanism • Large aLL • But jet and p0 rates are sufficient to give significant DG constraints from 2005 data Measure Know from DIS pQCD “DG” • 12 sectors, matched to TPC sectors • 2 SMD planes (U,V) per 30° sector • 288 0.5 cm wide scintillating strips per plane p0 Reconstruction Algorithms Example p0 candidates in the EEMC The SMD in both calorimeters allows for reconstruction of high pTp0's which decay within a single or neighboring towers. Both calorimeters use a fixed-size cluster algorithm to determine the centroid and energy deposition of an electromagnetic shower within the SMD. One begins by finding seed strips in each SMD plane and associating them into “clusters”. Pairs of U,V (or Eta,Phi) clusters are associated into “points”. In the barrel, a cluster may be split into two if certain energy conditions are met. Once clusters have been found, the energy of nearby towers is then shared between nearby points according to the relative energy deposited in the SMD. In the barrel, points are rejected if a charged particle tracked by the TPC extrapolates to the point. In both algorithms, all points within a sector (module) are paired and two-body decay kinematics computed. The TPC is used to obtain the event vertex.. 8 GeV candidate Digamma invariant mass pT > 4.0 GeV Digamma invariant mass pT > 5.5 GeV 14 GeV candidate Cluster-based algorithms have difficulties at larger pT where the p0’s begin to overlap, degrading resolution. Algorithms which fit the SMD profiles, such as those used in the STAR Forward Pion Detector, are under development. BHT1 triggers BHT2 triggers Relative luminosities were observed online to vary with z-vertex at the few % level, comparable with our statistical precision. EHT2 triggers spectrum for day 174 New scalars for 2005 provide vertex-dependent relative luminosity measurements. R3=(L++ + L--)/(L+- + L-+) ~-2.5 m ~+2.5 m Calculations provided by Jaeger, Stratmann and Vogelsang. (CTEQ6, KPP and 4 versions of GRSV polarized pdfs). ALL(p0) Inclusive p0 Production in Polarized pp Collisions Using the STAR Endcap and Barrel Electromagnetic Calorimeters Jason C. Webb for the STAR Collaboration The STAR Experiment (Solenoidal Tracker At RHIC) STAR Detector • Large solid angle • Not hermetic • Tracking in 5kG field • EM Calorimetry • “Slow” DAQ (100Hz) • Sophisticated triggers EEMC Ready to be mounted on STAR Installation of a BEMC module Top Interaction Vertex Left * Right Bottom BBC West 3.3<|h|< 5.0 BBC East The Barrel Electromagnetic Calorimeter (BEMC) at STAR • Pb-Scintillator sampling calorimeter • -1 < h < 1 • 21 Radiation Lengths • 120 modules, with 40 towers per module • 4800 Projective Towers give EM energy • High-tower and Jet Patch triggers • Preshower layer for e/h discrimination • Fine-grained gaseous shower-maximum detector • provides for p0/g discrimination ` Systematic Error Concerns Which Require Ongoing Analysis BBC East-West time difference provides vertex information at trigger level with roughly 30cm resolution. Offline analyses use z-vertex as determined by the TPC. 2cm/ch This reflects a difference in the longitudinal width of bunches, a spin-dependent background, or a spin-dependent acceptance of the BBC's... (or some combination of these effects). +150cm -150cm Online monitoring of trigger rates in the endcap showed a large f-asymmetry during 2005. The plot at the right shows one of the worst runs. Offline analysis determined that the source is beam background. For 2006, several tons of shielding have been loaded into the tunnels to suppress this. ``` Projections and Outlook Test sensitivity to the background by computing the difference in eLL vs pT for pi0 production for the “upper” and “lower” half of the endcap, At right we show the expected statistical precision for ALL(p0) in the endcap. We expect similar statistics from the barrel analysis. In 2005, STAR sampled 3pb-1 of longitudinally polarized pp collisions at sqrt(s) = 200 GeV and average polarizations of around 45%. For 2006 we have proposed a run to accumulate 20pb-1 of longitudinally polarized pp collisions, with an expected polarization of 50%. Alone, these factors provide an increase FOM by a factor of 10. Better shielding, and a “fast” vertex detector promise an additional factor of 2.5, yielding a FOM 25 times higher in 2006 than 2005. Finally, the barrel SMD will be complete in 2006, doubling its fiducial volume available for p0 analysis. (N++ - R N+-)/(N++ + RN+-) Demonstrates a 2%, spin dependent background contamination... several tons of shielding loaded into tunnels during shutdown will improve for 2006. For 2005 analysis, need better treatment of backgrounds. Preliminary analysis of EHT2 triggers Z [cm]