STAR TU, simulation status N. Smirnov Physics Department, Yale University, STAR Collaboration Meeting, MIT, July, 2006

What does mean STAR TU ? Conserve / Improve TPC performance ( RHIC II Luminosity). High resolution Vertex Detector ( heavy quark Physics ). “special” tracking in EEMC “direction” ( pp  W  e+/- ). Tracking data for PMD ( |η| > 2.); pp, dA μ – detector (?)

Conserve / Improve TPC performance ( RHIC II Luminosity). Additional tracking / calibration detectors inside and outside of TPC – Pad or XY strip GEM Detectors is a good choice : »Required 3d- precision » low mass, »fast. –Solves TPC space charge distortions correction problem {“charge” value / number of hits as a F ( t, φ, z); model (can/should be different for pp and AA); correction on “track level”} – and part of tracking (large surface to be covered, R~35 cm). Together with other “fast” detectors, help to solve the “Event pile-up” problem. TPC its own improvements; IFC shielding; “gap” between sectors; OFC gas leak  membrane HV, CF4 gas mixture  smaller diffusion, faster drift (new FEE, on-line cluster finding/reconstruction). Gas amplification calibration TPC MWPC data: number of tracks in drift volume, tracking for |η| > 1.

High resolution Vertex Detector ( heavy quark Physics ). Today (HFT) proposal relays on: -- perfect TPC space charge distortions correction (not in a simulation), -- perfect SSD performance ( does not work still, and …), -- perfect alignment, -- factor X improvement in APS read-out speed (X = 2 ?, 2 ms / frame), -- primary vertex is a “key factor”, -- D reconstruction efficiency and background – two different simulation steps, -- APS simulation (N of hits / frame and their position) is not a “realistic” one -- unknown beam-beam background conditions for small R. R&D “step” to demonstrate “hit – track” matching was not done, but in a schedule. It is too optimistic (my opinion) Natural limitations: high multiplicity events to get a primary vertex with “needed” precision ( multi-loop approach can help ?) Conclusion: needs a high precision, fast “pointer” ( SVT was a “candidate”, but...) The best: 3 points in space to be “independent” from TPC data.

A lot of simulation results have been presented during last STAR Upgrade meeting (December 1-2,2005) Some conclusions: - fast, high precision, low mass tracking detectors in front and behind TPC ( GEM) can be crucial to help with TPC “space charge distortions correction”. - HFT with 4 ms read-out time will work in a combination with TPC+SSD+(GEM) up to L=1x10 27, but not a RHIC II Detector. - IT has to provide a high quality “search corridor” for HFT to “help” with occupancy, primary vertex reconstruction, PP, dA, ….; - three double layers Si strip detector (MIT proposal) is not the best solution. - tracking detector in front of EEMC is useless for W  e+/- + X study because TPC end-cap material budget. - IT has to solve this problem: high Pt particle reconstruction in EEMC acceptance. Three possible variants for IT (personal opinion) - 3 or 4 double layers of Si strip detectors; first and last – with 90 deg strip direction rotation, and to use pad detectors ( with 2x2 mm 2 size) instead of stereo ones for 2 intermediate layers (Gerrit’s idea). - microTPC with fast, low diffusion gas mixture and MicroPattern read-out (no gating grid) - Two layers of Pixel Hybrid Detectors with pad size 50 x 425 μm 2

Variant with Si Pixel Det., SPD + Si strip + GEM (III) TPC “IN field-cage” “safety” Kapton foil GEM with X-Y read out SSD Si strip, 4x4 cm2 two layers, X and Z SPD (Hybrid Pixel) Two layers with 90 deg rotation HFT SPD – Design Parameters (ALICE) Two barrel layers; R1 = 6.4 cm, R2 = 7.6 cm. Pixel Cell: 50(rφ) x 425 (z) μm 2, (90 deg rot. second layer) Pixel ASIC thickness: <=150 μm. Si sensor ladder thickness: <=200 μm. “Bumps” technology. Cooling: water / C6F14/ [C3F8 (evaporative)] Material budget (each layer): 0.9%X 0 ( Si – 0.37, Cooling – 0.3, Bus – 0.17, Support – 0.1 )

Variant I – 4 Double Si strip/Pad 1 st – 2x2 cm 2 (X/Z); 2 nd – 4x4 cm 2 (X/Pad); 3 rd – 4x4 cm 2 (X/Pad); 4 th – 4x4 cm 2 (X/Z) TPC in field cage GEM Detectors SSD Si Strip HRVD

Simulation / Reconstruction approach Stand – along routines (FORTRAN) on the basis of personal experience and knowledge from previous experiments and R&D activities Special for fast (but reliable) test / checking different detector SetUps including PiD (dE/dX, Ch.Det., RICH, TRD) and secondary Vertexes finding/reconstruction. GEANT-3 (GSTAR) Detector response simulation – 4 variants: -- GEANT hits, but not GSTAR variants (sometimes) -- Gaussian smearing -- “intermediate” scale simulation ( to save a compute time) -- “full” scale simulation ( check Hans Bichsel web page) Two variants of a “helix fit” Keep all needed “pointers” for evaluation / control

One particle (π+) /event. Hits in a fit - only IT detectors (primary vertex – OFF); 100% efficiency, perfect alignment. dZ, cm dX, cm Pt, GeV/c Matching performance: IT track crossing position – 2 nd HFT layer hit (Local CS). Variant III Here it will be presented the simplest, “first step” simulation results: “one π/event”, GEANT hits with Gaussian smearing

Matching performance: track crossing point – HFT L2 hit position (LCS) SSD, Vertex in FIT; All hits Lines – Sp.Ch. effect Set Up Variant: TPC + GEM + SSD + 1 double SiStrip + 2 Si Pixel; ITH SSD + 2 Si Pixel; All hits SSD + 1 Si Pixel; All hits GEM + SSD + 2 Si Pixel; ITH GEM + SSD + 1 Si Pixel; ITH GEM + SSD + 3 double Si strip/pad ( MIT proposal), ITH GEM + SSD + 2 double Si strip/pad + 2 Si strip XZ ( MIT proposal)mod, ITH “ITH” – only IT hits are in Fit, “All hits” -- + TPC hits. dZ dX σ of Gauss fit, cm Vertex OFF

Matching performance: track crossing point – HFT L2 hit position (LCS) SSD, Vertex in FIT; All hits Lines – Sp.Ch. effect Set Up Variant: TPC + GEM + SSD + 1 double SiStrip + 2 Si Pixel; ITH SSD + 2 Si Pixel; All hits SSD + 1 Si Pixel; All hits GEM + SSD + 2 Si Pixel; ITH GEM + SSD + 1 Si Pixel; ITH GEM + SSD + 3 double Si strip/pad ( MIT proposal), ITH GEM + SSD + 2 double Si strip/pad + 2 Si strip XZ ( MIT proposal)mod, ITH “ITH” – only IT hits are in Fit, “All hits” -- + TPC hits. dZ dX σ of Gauss fit, cm Vertex OFF

Variant “3Si2” – 3 Double Si strip/Pad 1st – 2x2 cm 2 (X/Z); 2nd – 4x4 cm 2 (X/Pad); 3rd – 4x4 cm 2 (X/Pad) Variant “Pixel” - 1 or 2 (with 90 deg rotation) layers of SPD (ALICE, LHCB, PHENIX ) “Special Variant” for detector response simulation; TPC, GEM, SSD – gaussian smearing SPD, Si-strip / pad – “intermediate”, q with noise, but no FEE, no cross-talk,… APS – Yes/No but realistic read-out and background hits simulation / reconstruction ( 640x640 pads, 30x30 μm 2 size, 4 read-out ports, 50 MHz read-out frequency  2. ms read-out time )

Si detectors, number hits (Central HJ) PIXEL 3Si2 R pos cm Det. Size cm 2 Strip/pad cm 2 N hits (8, 3) (7, 2) (18, 7) (20, 7) (17, 4) ( max, aver) N “destroyed” hits because occupancy ~0.3% ~ 15% Number of tracks that “contributed” in reconstructed hit 3Si2 PIXEL

Tracks finding / reconstruction (Vertex OFF) ( TPC  SSD  Si…) PIXEL 1 2 3Si2 Eff: Ghost: Track DCA parameters DCA, XY, cm DCA, Rz, cm Red: all tracks 3Si2 variant Blue: good one, 3Si2 variant Black: all tracks PIXEL variant

Primary Vertex reconstruction TPC + SSD + PIXEL (1 or 2) PIXEL 1 PIXEL 2 DCA, xy, cm DCA, Rz, cm N of event

APS, number hits L = 2.x10**26, L1, 2 ms read-out time; Nmax hits / det event = 79 Naver = 42 L = 2.x10**27,  L1 (2.8 cm R) - ( 815, 314), L2 (4.6 cm) – (284, 135) (max, aver) (max, aver) N hits (L1) N detector Central HJ plus background One detector, reco hits X, cm Y, cm

Tracks finding / reconstruction (Vertex OFF) ( TPC  SSD  PIXEL (1 or 2)  APS) Luminosity PIXEL x10**26 Eff Ghost x10**27 Eff Ghost Very preliminary DCA track parameters to Primary vertex Detector combination DCA, xy, μm DCA, Rz, μm (sigma) APS only SSD + APS PIXEL 1 + APS SSD + PIXEL 2 + APS All hits 53 91

What is the reason for GEM D ? -- not to use TPC hits (can be strong distortions) for the “final” step – to match track with APS hits, and vertexes (both primary and secondary ) finding and reconstruction -- the best “tool” to struggle with TPC hits space charge distortions, as a scaller and high precision tracker. -- help with events pile-up problem -- may be the first step – use one CTB slat for fast, precision tracking detector behind TPC. Data from TPC before (in time) a trigger signal -- scaller data -- coordinate inform for particles in EEMC acceptance SSD two layers of Si strip ( if it will be any problem or timing will be a “stopper” point) in a combination with GEM D. Tracking in EEMC direction to study pp  W  e-/+ (next slide)

IT set up -- asymmetric (in Z); Two more layers of Si strip detectors ( one side, 4x8 cm2) to cover “EEMC direction”, for pp program. Sample of events, W  e(μ) + X pp, √s=500, PYTHIA η Pt, GeV/c “barrel” position; NOT “disk”

Track reconstruction performance. One π+ / event; HFT + IT + minimum 6 TPC hits; perfect alignment dPt/Pt30 % dPt/Pt η The reconstruction “chain” has to work well; TPC track  EEMC cluster  electron E  electron P (HELIX Radius)  matching hits from IT  constraint Refit  electron charge (+/-)

Points to be discussed SSD status / performance / future GEMD; fast, reliable gas detector, COMPAS experience, 10x10 cm2 active size, XY data with q- selection power and “scaler” data to solve TPC sp.ch. distortions corrections on a “track” level (?); man-power support (MIT, Yale); needs “some R&D” ( low mass construction approach, FEE); good progress with foil mass-production. Si one sided strip detector: does not need R&D, reliable and good tested technology, SSD substitution and EEMC direction (pp); man-power support (MIT) Si pixel detector: the best way (my opinion) to get in STAR very powerful and reliable Vertex Detector; mass-production is in a progress and a lot of such detectors will be installed in nearest future (ALICE, LHCB, PHENIX). It is crucial to be “in a line” and keep a control and get an experience (can LBL takes a care?) One layer will help a lot (special for 2. ms read-out variant); it means ~490 sensors (<2. M$), but man-power, experience, DAQ,… are very difficult points. Very crucial – to prepare and control a “global” mechanical structure for IT and HFT (together!!) as a one construction part. Alignment problem can be very difficult to get a high precision tracking data, and it should be flexible for different variants of IT setup(s). STAR tracking is a “not easy” problem, and needs (may be) nonstandard decisions. It should be a “one person supervision” approach, with high “KEAL” factor, like HHW did a job for TPC