qcd meeting july 23, 2004

QCD MeetingJuly 23, 2004

Is it due to the hard collision?

Is it due tofragmentation?

Strong polarization seenin fixed-target experimentswhere jet NOT observed.

PolarizationTom Devlin

Rutgers/CDF

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Asymmetry plots in beam- and beam-K system (ignores jets)Polarization allowed under parity conservation

is in the y-direction (second from top).

Solid lines: DataDashed lines: 20 hybrid MC-events/real-event scaled by 1/20

Fits Without and With Mass Constraints

How Do We Get Polarization From This?

These cos() plots contain:1. The Signal: and 2. Ks Background3. Background from random 2-track crossings.

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Monte Carlo Simulation

and and Ks are straightforward and in place

Now working on random 2-track crossings

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Work in Progress and Planned: Summer-Fall, 2004

11 Mass-constrained fits: 2-, 2-Ks, 1-ee.11 Sum of weights over solutions = 1.0 per event.3. Mix MC events for events with both K and solutions as in the data, weighted by relative P(2)*P(Decay).4. Further study of sailor-cowboy problem.11 Add fits with mass constraints displaced by 20 MeV.6. Background subtraction.7. Decide whether analysis is viable or not.8. If so, do polarization in the other two coordinate systems.

Additional Tasks

11 Use 2 = 2(MassConstraint) - 2(NoMassConstraint)10. Random 2-track crossings.

24 : Fit with mass-constraint – 4 deg. freedom

23 : Fit without mass-constraint – 3 deg. freedomIrrelevant Fluctuations in 2 e.g. deviations

from exact 3-D intersection at vertex tend to cancel.Strong deviations from correct mass DO NOT cancel in 2 .

Repeat for Mass Constraint = M 20 MeV(Note that p threshold is only 38 MeV below M)

Subtract sum of two sidebands from Signal+Background(Sideband normalization used here is from previous graphs.)

Problem:The backgrounds from sidebands populate

the cos plots at different values from real backgrounds.

Alternate Approach:Generate hybrid MC backgrounds

For each real event, generate 20 MC events• at same decay vertex as real event• parent mass from background mass distribution• random angles in CM system• apply standard acceptance cuts• apply tight cuts in 2

Fit with no Mass Constraint: Assume Daughters are pSubtract signal, Smooth Remainder (5-bins)

Normalize Probability Distribution P(M) to Unit Area.Numerically Integrate.

Find values of M(p) at intervals of 0.01 in the integraland form a table of its integral.

Choose a random number R(0:1)Table Lookup and Interpolate to get M(p)

Status and Plans

Three known contributions to dataset: -- Signal -- Ks Background -- Continuum 2-track background

MC code exists to generate first two.Coding in progress for the third.

Plan: Generate 20 MC of each type for each real event. Mix three MC samples, in appropriate proportions to produce 20 MC events for each real event. Adjust proportions of each and assumed polarization of MC ’s to fit data.