EM Probes in STARA Look into the Future

Thomas Ullrich, STAR/BNL

International Workshop onElectromagnetic Probes of

Hot and Dense MatterECT, Trento

June 10, 2005

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Current STAR Layout and EM Capabilities

Detectors used for EM Probe Detection: TPC: tracking pT > 0.2 GeV/c, PID via dE/dx for pT < 0.7-1 GeV/c (-1.3 < < 1.3) BEMC & EMC: e/ PID best for p > 1.5 GeV/c, trigger (0 < < 2) ToF: electron PID ( PMD: detection, p > 20 MeV/c (2.3 < < 3.7) FPD: e,PID for p > 10 GeV, xF > 0.4, small pT (3.4 < < 4)

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Current EM CapabilitiesEMC+BEMC:

not optimized for low pT EM probes large coverage and efficiency for

high-pT electrons (p > 1.5 GeV/c) open charm, , Z (s = 500 GeV) high-E photons high-pT 0, -jet, jet-jet

ToF Patch: good electron PID for pT < 3 GeV/c in conjunction with TPC

successfully used for non-photonic single electrons (open charm) acceptance of present “prototype” too small for e+e physics

PMD: photon detection down to 20 MeV/c

DCC studies multiplicity and rapidity distributions in forward region

FPD: only for low-pT, high-p, xF > 0.4 physics (only p+p, d+Au. or peripheral

Au+Au) 0, open charm, J/ (), at high xF

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Electron PID with MRPC TOF/TPC and EMC

EMC1. use TPC for p and dE/dx2. use Tower E p/E3. use SMD shape to reject hadrons4. e/h discrimination power ~ 105

5. works for pT > 1.5 GeV/c

ToF1. use TPC and ToF PID

2. works for pT < 3 GeV/c

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and 0 Studies Using the TPC Only

STAR reconstructs 0, from conversions in material inside the TPC

Material budget crucial Sweet spot: ~6% radiation

length from vertex to TPC eff(0) ~ eff(e)4

PRC 70 (2004) 044902 130 GeV Au+Au Inclusive from 0 to 2.5 GeV/c E/E = 2% Fraction of contribution

to inclusive yield decreases in most central events

Large systematic uncertainties ~40% normalization complex interplay of corelated

und un-correlated uncertainties

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Same Idea: Photonic Single Electron Background Subtraction

Works well for photonic background rejection in single electron studies:

1. Combine candidate electron with opposite sign tracks anywhere in TPC

2. Reject tagged track when m < mcut

~ 0.1 – 0.15 MeV/c2

Rejection Efficiency: conversion and 0 Dalitz decay

reconstruction efficiency ~60% Invariant Mass Square

Rejected

Signal

Opening Angle

conversion and 0 Dalitz decay reconstruction efficiency :~60% at pT>1.0 GeV/c

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Studies on EM Probes in STAR

PMD:

62 GeV Au+Au Centrality dependence of dN/dy

(nucl-ex/0502008)

FPD:

Forward 0 production in 200 GeV p+p

(PRL 92 (2004) 171801)

Excellent (e,)-h

separation

Other studies: -HBT using TPC and EMC/TPC ( a la WA98)

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The Next Step: Upgrades

Barrel Electromagnetic Calorimeter (EMC) Current ¾ barrel will be instrumented to full azimuthal coverage,

-1 < < 1, for next RHIC run

Barrel Time of Flight (TOF) Current prototype patches to be upgraded to full azimuth, -1 < < 1. Project is in President’s budget.

Forward Meson Spectrometer (FMS) Full azimuthal EM Calorimetry 2.5 < < 4.0 Possibility of charm measurements in this region Proposal submitted to NSF

Data acquisition upgrade (DAQ1000) Upgrade TPC readout an order of magnitude, ~double effective

Luminosity

Heavy Flavor Tracker (HFT) High precision (<10 um) measurements for displaced vertices

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Time-of-Flight: MRPC /K separation up to 1.6 GeV/c p/K separation up to 3 GeV/c Thus cover wider range of

(p,K pT

Full ToF: -1 < < 1, 2

Relevant for EM Probes: ToF and HFT

Heavy Flavor Tracker (HFT)Two layers

1.6 cm radius4.8 cm radius

24 ladders2 cm by 20 cmMIMOSA Active Pixel Sensor (CMOS)

Precise (<10 m) , thin and low power

50 m thick chip - air cooling0.36% radiation lengthPower budget 100 mW/cm2

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Time-of-Flight: MRPC ToF + EMC

complement one another

ToF + TPC Electron PID p < 3 GeV/c Exactly where needed for J/Y Low mass dileptons spectra vector mesons allows us to trigger on J/

ToF used as fine granular veto

ToF PID of K, , p allows D meson

measurements up to higher pT

Relevant for EM Probes: ToF and HFT

Heavy Flavor Tracker (HFT)SVT + HFT

Clean D meson sample (v2 !)Test statistical modelsPythiap-p 200 GeV

Au-Au Statistical recombination*

D+/D0 0.33 0.455

Ds+/D0 0.20 0.393

c+/D0 0.14 0.173

J//D0 0.0003 0.0004 (No suppr.)

Disentangle b,c contributions to non-photonic singel electron spectrabb through B J/ + X (?)

A. Andronic et al., PLB 571,36 (2003).

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Low Mass Dileptons: What STAR Can Do

Upgraded detectors:

Full TOF+TPC SVT+HFT (-Vertex detector)

Electrons PID Reject electrons not from primary vertex

( conversion + Dalitz)

NIM Article in preparation:Studies on Particle Identification with TPC and ToF

γ conversion and π0 , η Dalitz decay background How can μVertex detector deal with γ conversion subtraction?

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STAR not hadron blind a low level of hadron contamination crucialStudy in 62.4 GeV Au+Au

Hadron contamination increases for pT > 1.5 GeV/c (eff = const.) need to accept slightly lower efficiency at intermediate pT

This is the pT range where EMC because effective Hadron Rejection Power ~ 10-5 for pT < 1 GeV/c

Def: (hadron contamination) (e/h) / (electron efficiency)

Low-pT Electron PID with ToF

Evaluated through dE/dx fits

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Low-Mass Dileptons: Background Rejection

Dalitz decay background/event: ~5∙10-6/25MeV (ω) ~5∙10-7/25MeV (Φ)Total background/event : ~10-4/25MeV (ω) ~2∙10-5/25MeV (Φ)

1 M PYTHIAEvents

Require TPC+SVT+μVertex (HFT):~98% electrons from gamma conversion rejectedDalitz decays become dominant sources!!!

Background inv. mass spectrum Conversion Electrons only

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What one wants …

R. Rapp, hep-ph/0010101

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Vector Mesons Rate Estimate

(pp) 1|/ dydn 15.0 02.0Assume:

5107)(BR ee 4103)(BR eeFrom PDG:

MeV15 MeV8Au)(Au 300|/ dydn

TOF match+PID eff ≈ 80% TPC+SVT+μVertex eff ≈ 60% (?)

Au+Au #events for ω

with 3σ signal

#events for Φ with 3σ signal

TOF+TPC 7M 2M

TOF+TPC+SVT+ μVertex (HFT)

800K

(350K)

150K

(50K)

Preliminary estimates:

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b Quark Measurements with HFTB mesons accessible using semileptonic decay electronsIssue: nonphotonic electrons will be measured, but what is the real fraction of

these from B? Highly model dependentUsing displaced vertex tag is the most promising method

pT ~ 15 GeV/c:

(Au+Au) ~ 20b/Gev 10 nb-1 yields 200k bb pairs

Non-photonic electrons in d+Au

Tagging in Au+Au (w/ HFT)

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DAQ Upgrades (1000 Hz)

Current limit from TPC front-end electronics is 100 Hz Limits size of datasets

~100M events/nominal RHIC run

Affects available luminosity Deadtime scales linearly with rate 50 Hz = 50% dead, i.e. 50% drop in luminosity available to rare

triggers: usual compromise

Proposal to replace TPC electronics with ALICE chips to increase maximum rate by order of magnitude

Rate of events to disk increased though timely processing of events on disk is an issue

Removes deadtime: effective doubling of RHIC luminosity

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Summary STAR has proven capabilities for EM probes and heavy flavor measurements

at RHIC PMD: Photon multiplicity FPD: forward and electron detection - high xF physics Electron identification using three detector systems (TPC, TOF, EMC) from 1 to >10 GeV/c Direct reconstruction of charmed mesons

Shortcoming in PID, vertexing, and acceptance

STAR has a clear path for improving its capabilities in the near future Completion and extension of calorimetric coverage Extension of TOF coverage to full azimuth for electrons and combinatoric background

rejection in direct reconstruction Upgrade of Data Acquisition to increase effective luminosity and untriggered data

samples Installation of the heavy flavor tracker for displaced vertices for heavy flavor physics

and photonic electron rejection

Low Mass Vector Mesons and Thermal Dileptons Will Become Part of STAR’s Program

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Argonne National Laboratory Institute of High Energy Physics - Beijing University of Bern University of Birmingham Brookhaven National Laboratory California Institute of Technology University of California, Berkeley University of California - Davis University of California - Los Angeles Carnegie Mellon University Creighton University Nuclear Physics Inst., Academy of Sciences Laboratory of High Energy Physics - Dubna Particle Physics Laboratory - Dubna University of Frankfurt Institute of Physics. Bhubaneswar Indian Institute of Technology. Mumbai Indiana University Cyclotron Facility Institut de Recherches Subatomiques de

Strasbourg University of Jammu Kent State University Institute of Modern Physics. Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer PhysicsMichigan State University Moscow Engineering Physics Institute

City College of New York NIKHEF Ohio State University

Panjab University Pennsylvania State University

Institute of High Energy Physics - Protvino Purdue UniversityPusan University

University of Rajasthan Rice University

Instituto de Fisica da Universidade de Sao Paulo

University of Science and Technology of China - USTC

Shanghai Institue of Applied Physics - SINAP SUBATECH

Texas A&M University University of Texas - Austin

Tsinghua University Valparaiso University

Variable Energy Cyclotron Centre. Kolkata Warsaw University of Technology

University of Washington Wayne State University

Institute of Particle Physics Yale University

University of Zagreb

545 Collaborators from 51 Institutionsin 12 countries

STAR Collaboration