JUNE 1997PHOBOS Review Mark D. Baker PHOBOS Review Physics Simulations Mark D. Baker Physics PHOBOS design is sound. –( & PHOBOS Computing Project is on

JUNE 1997 PHOBOS Review Mark D. Baker

PHOBOS Review Physics Simulations

Mark D. Baker

• Physics PHOBOS design is sound.– ( & PHOBOS Computing Project is on track.)


PHOBOS Physics Goals

• Typical physics topics:– Look for Excess Entropy

• Source Size & Lifetime (HBT)

• Multiplicity distributions and fluctuations

– Look for collective phenomena (over large V)• Low transverse momentum

– Look for unusual medium effects• Phi mass and width

Study QCD confinement and vacuum


Detailed GEANT simulation


Types of Uncertainties

• Statistical (Poisson)– Unavoidable in event-by-event physics– Can be made negligible for distributions

• Instrumental – Fluctuations in non-ideal detector

• Landau fluctuations

• Secondary production, etc.

• Systematic


Event-by-Event Multiplicity

Instrumental uncertainty: N3

250


Event-by-event dN/d

5938trueN6122. avgN

.)(51.)(775881 inststatNmeas .)(51.)(775881 inststatNmeas

5938trueN


Measuring Multiplicity Corrections

• Spectrometer– Measure p distributions for primaries– Measure dE/dx distribution directly

• Vertex Detector– Measure dE/dx directly

• Multiplicity Detector:– Effective measurement of most secondaries:– Primaries: independent of Zvtx ,


Measurement of secondariesPHOBOS testbeam data (May ‘97)

Target Beam mom. Chg. # ev.

Empty 2-5 GeV/c - 600k

Thin Be 0.5-5 GeV/c +/- 900kThick Be 5 GeV/c - 230k

Thin Al 4 GeV/c - 50kThick Al 5 GeV/c - 220k

Thin Fe 5 GeV/c - 200kThick Fe 5 GeV/c - 100k

Thin = 6 mm, Thick = 6 cm

Beampipe:

Supports:

Magnet:


Measurement of secondaries

PHOBOS: Very preliminary data. (May ‘97)

Beam thru hole: 50k pions @ 5GeV


Measurement of secondaries

PHOBOS: Very preliminarydata! (May ‘97)

Fe target No target

Beam hits detector:

Beam thru hole:

5 GeV beam:


Tracking Results

• Hough Transform Studies– Limited acceptance, non-GEANT

• Spectrometer design optimized and validated

• Efficiency & ghost rate acceptable

– Full acceptance GEANT studies• Validated above results

• Template Tracking Code– Limited acceptance, non-GEANT

• Fully integrated in ROOT/C++

• Results look good.


Hough Tracking Event Display

Placeholder only. Will use baker_sideways.ppt


Efficiency and Ghosts

• Full GEANT simulation– 100% efficient planes

• Hough Transform– Tight cuts

• Results:– 85% efficiency

– No p dependence

– Ghosts negligible


Momentum Resolution


Tracking vs. Plane Efficiency

• No major problem– 1% plane inefficiency 2% tracking inefficiency

– Probably improvable (better covariance matrices)


Track finding - very low Pt

deg

deg

deg

deg

7 planes, E>800 keV

7 planes, all hits

80

6020 40

20 40 60

80

0

0

-8

8

8

-8

Stopping Kaon


Particle ID by dE/dx

safe extended


Particle ID - very low Pt

2

1

dx

dE

2mEkin

mdx

dEEkin


Particle ID - very low Ptm

ass

para

met

er

mas

s pa

ram

eter

)(MeVEloss )(MeVEloss


Spectrometer Acceptance


HBT Acceptance

TruthResolution smeared


PHOBOS HBT Capabilities

• “Standard” Scenario– Extrapolate from low E

• Exotic Scenario I– Very large source


PHOBOS HBT Capabilities• “Standard” Scenario

– Extrapolate from low E

• Exotic Scenario II– Very rapid expansion


HBT Summary

• We can measure 20 fm sources accurately.– 10% systematics with simple analysis– Easily improved.

• We can distinguish interesting physics from a simple baseline extrapolation.


Phi Rates

• Assumptions:– 15 K K / central event– 100 Hz central events (15% central & vtx cut)– Yields: 9x10 K K /nominal week

• Reconstructed K K – 1 nominal week (15% central cut)

• Si-extended + TOF: 230,000

• Si-only conservative PID: 50,000

+

+

+


Phi Resolution

• Resolution: (Minv) = 1.6 MeV– Dominated by momentum resolution– Calculated 2 ways:

• Fast Simulation

• Analytic propagation of errors

• Error on Width (after 1 nominal week)– 0.7 MeV (extended-dE/dx + TOF)– 1.0 MeV (conservative-dE/dx only)


Phi Width Measurement

Placeholder only

see baker_sideways.ppt


Phi Width Measurement

Placeholder only

see baker_sideways.ppt


Computing Organization

R . V erd ie rD ep u ty H ead

D . M cL eodC . C on n er

C . H a lliwe llO n lin e M on ito rin g

A . Trzu p ekP ID & low P t

P . D ecow sk i B . W os iekm om . fit t in g

G . R o lan dS p ec t. R econ s tru c tion

R . G an zP rim ary V ertex

R . V erd ie rM u ltip lic ity R econ .

R . G an zTes tb eam A n a lys is

K . W ozn iakG E A N T M C

A . O lszewsk iF as t S im .

A . Trzu p ekG eom etry

E .G arc ia -S o lisG en era to rs

B . W os iekS im u la tion s & K rakow L iason

A . O lszewsk iP . D ecow sk i

TB A : (V erd ie r/R o lan d /G an z )O fflin e In fras tru c tu re

M . B akerH ead o f C om p u tin g ~9 FTEs total

• Mark Baker

• Chris Conner

• Patrick Decowski

• Rudi Ganz

• Edmundo Garcia-Solis

• Clive Halliwell

• Don McLeod

• Andrzej Olszewski

• Lou Remsberg

• Gunther Roland

• Ashutosh Sanzgiri

• George Stephans

• Cyrus Taylor

• Adam Trzupek

• Robin Verdier

• Frank Wolfs

• Barbara Wosiek

• Krzysztof Wozniak


Conclusions

• Physics capabilities look good!– N, dN/d– HBT – Phi mass

• Technical capabilities look good– Track Finding– Particle ID– Low p acceptanceT

Documents

JUNE 1997PHOBOS Review Mark D. Baker PHOBOS Review Physics Simulations Mark D. Baker Physics PHOBOS design is sound. –( & PHOBOS Computing Project is on