Non-identified Two Particle Correlations from Run I

Understanding drift chamber tracking– Tracker and candidatory– Two particle efficiencies/ghosts

A first look. Momentum distributions, etc.

First correlation function

Gamow corrections

And from here…

The current status of DC tracking

As I understand it.– Tracker (old):

Assumes x wires parallel to beam. Works in nominal dc position, even with minor changes in geometry Large fraction of tracks with reconstructed UV wires

– Candidatory (new): Same pattern recognition philosophy as above. Built to withstand major changes in geometry (I.e. retracted arms) Better interface to the rest of dc software Cleaner separation of pattern recognition from hit association Most tracks are not reconstructed through UV wires (‘simple’ bug)

– currently bypasses this problem by boot-strapping with PC1 What we need to use in the long run – but unusable now. (?)

DC tracking variables:

Use bounded, natural variables for pattern recognition (I.e. not slope and intercept)

Two particle effects occur at low and with the x wires and and zed with the uv.

– Can see from this that two particle inefficiencies occur at low relative and => almost no two track inefficiency in opposite charged tracks.

3-momentum reconstructed from fit to associated hits in PHDchTrackModel

Ghosting in tracker:

Small (but measurable) fraction of tracks have a ghost pair at low and . (=> low q)

3 solutions:– 1. Fix tracker to remove ghosts

(in progress by DC group)– 2. Quantitatively understand 2-

particle in/over-efficiencies and correct for it

– 3. Cut it out You don’t have to think to hard to

know which choice I made here …

Cut in 2-dimensional space.

Real

Mixed

Ghosting in zed

A look at the raw (zed) distribution [top] also shows a clear ghosting problem.

After cutting on ||<.005 && ||<.005, however, the peak in zed disappears

I should probably make a full 3d cut, but this will do for this talk…

zed

zed

Real

Mixed

Real

Mixed

Motivation for studying correlation functions*

[A reminder or impetus for further personal study…]

Amplitude for detecting two bosons (pions in my case) in above configuration is:

Then the probability is the amplitude squared, and integrating over the source:

x

y

* This slide stolen almost completely from W. Zajc, Proc. Of 4th Intersections Conference (1991)

(r2,p2)

(r1,p1)

The 2 particle counting rate is related to the Fourier transform of the source. The normalization of requires C(q=0) -> 2.

Then for a simple Gaussian source:

Want to know more?

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Event characterization

Runs:– 9979, 9981, 9987, 9988, 9992– 20 files

Events: ~20k – <½ in pairs I’ll show today

Some naïve cuts just to get us started– |BBC zvtx| < 30cm (Track model works

out to +/- 45 cm– > 50 tracks reconstructed (~central)

=> Pairs: – 760K + +– 430K - -– 1.1M + -

Kinematic distributions

DC pattern recognition and track model built to work above 180 MeV.

– Cut out low pt part

– Unphysical Bug in track model (?)

And a kt distribution …

– <kt>~700 MeV for all tracks

– <kt>~400 MeV for all tracks with q<100MeV

kt(GeV/c)

q distributions

q=|p1-p2| Before the ghost tracks cut the real

distribution shows a strong peak at low q. After the ghosting cut in both the real and mixed the distributions are similar. (though we hope they’re not identical)

Now as experimentalists, we determine the probability of detecting pairs at relative momentum q by measuring the ratio: A(q)/B(q)

– A(q) => distribution of measured q from same event pairs

– B(q) => from different (uncorrelated) events

Real

Mixed

Real

Mixed

q (GeV/c)

q (GeV/c)

Raw correlation function

Recall: in ideal case, C(q)2

But we don’t have ideal bosons since they are charged

– leads to a depletion at low q due to the coulomb repulsion of the pair

++

--

Gamow Correction

First correction: Gamow correction for particles from point source:

Dependent on mass of particles in pair …

Ratios of particles from Min Bias hijing as a function of q

– = 87.6%– K = 9.3%– p = 2.5%– KK = .3%

212

2

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EEqQ

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inv

Gamow correcting opposites

In red:– raw correlation function for

opposite pairs

In blue:– corrected for Gamow assuming a

point source.

It appears to be an over correction

– not surprising since we don’t have a point source

or if we did we should call a CERN press conference.

+-

And Gamow Corrected…

Now same charge pairs corrected for Gamow.

Again, an over-correction at low q. (off scale)

Low statistics.

But, heck … let’s fit a Gaussian to that and see what we get.

--

++

Analysis Note #7

Simple study of PHENIX’s ability to resolve source size:

– Throw two tracks into acceptance.

– Impose artificial correlation on pair.

– Reconstruct R from correlation.

22 )(21 qR

RR

Questions: http://www.phenix.bnl.gov/p/info/an/007/

Comparisons

– Slight beam energy dependence– strong centrality and kt

dependence.– What’s shown here is for higher

<kt> than most previous experiments. In the end we’ll do it as a function of kt for direct comparison

The point:– First study– Correlation function is visible

with a small fraction of the data set

– Results of 1D fit are in the ballpark

<kt> Root-s RTside QM99

.35 4.7 4 Soltz et al.

.25 8.7 4.2 Ganz

.25 17.2 5.0 Ganz

.4 130 3.5-5.0 Us

Lots still to do:

Understand two particle ghosts/efficiencies/etc p/q resolutions PID!

– Requires working DC code, track model and TOF Multi-dimensional anaysis Full coulomb correction Centrality/kt dependence Etc, etc, etc.

Another postdoc at LLNL (Mike Heffner) has just begun additional studies on correlations

David Brown, source imaging guru, joining theory effort in October

Schedule to have publishable results by QM 2001