Noise Analysis for PREx - Pb Radius Experiment

Presented by:

Luis Mercado

UMass - Amherst

6/20/2008

Overview

Part I: About the experiment– Introduction – What is PREX?– Motivation / Physics Background– Applications in nuclear and astrophysics.

Part II: My current work– Luminosity Monitors– Recent Results– Looking Forward

PART I

About the Experiment…

Introduction – What is PREx?

PREx is a Parity Violation experiment to be conducted in Hall A in 2010.

Will measure PV electroweak asymmetry in elastic scattering of polarized electrons from 208Lead.

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Motivation

Because the Z boson couples mainly to neutrons, ALR can provide a clean measurement of Rn by studying the ratio of proton and neutron form factors.

Proton form factor is well known, so we can extract the neutron density distribution from the neutron form factor.

The value of Rn is currently known to 5% accuracy. PREx aims to achieve an accuracy of 1% or less.

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Physics Background

Heavy nuclei such as 208Pb are believe to have a larger neutron-weak radius than its proton-charge radius.

This “neutron skin” is a result of a large neutron excess and a large Coulomb barrier.

Finding Rn will be a fundamental test of nuclear theory and provide clues about neutron-rich matter. (C. J. Horowitz)

Heavy Nuclei and Neutron Stars

The 208Pb nucleus is 18 orders smaller and 55 orders lighter than a neutron star.

Rn -> Sv -> E(np/nn) -> Pressure Lead’s neutron skin is similar to the crust of a

neutron star, made up of neutron-rich matter at similar densities.

To understand these systems, the equation of state of dense matter is essential.

Transition density between crust and outer core depends on the neutron skin of 208Pb.

PART II

My current work…

Luminosity Monitor Setup

Used as diagnostic for experimental setup (beam-line, instrumentation and target).

Located 7m from the target. Consists of eight symmetrically placed

detectors.

Luminosity Monitor Setup

Reason for Analysis

Lumis are sensitive to very small scattering angles (~0.5°), where any measured asymmetries should go to zero (sub-ppm levels).

Width of integrated signal gives an idea of the intrinsic noise of the experimental setup.

Want noise to be < 100ppm. Noise is defined as width of asymmetry distribution for 15Hz pulse pair.

January ’08 Test Run

Had week long test period for diagnosing several components of the experiment.

Used several beam energies/currents on Carbon and Lead targets.

Tested target stability up to 100uA successfully. New Lumi design was made to include a filter box. Some of the goals were to study backgrounds,

diagnose noise and understand linearity of Lumi setup (PMTs and ADCs).

Test Run Configuration

1, 3, 5 & 7 see full signal.

2 & 6 have 10% filters. 4 & 8 were ‘blinded’

with aluminum sheets. Bottom three were

shielded by Lead bricks.

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Analysis of ’08 Run #10296

Data acquired on 01/25/08 with beam current of 60uA on a Thin Lead target.

RMS values are regressed with respect to position and current.

Lumi ID Reg. RMS [ppm]

1 119.1

2 270.2

3 112.4

4 816.3

5 105.7

6 152

7 112.4

8 383.6

’08 RMS Values I (odd)

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’08 RMS Values II (even)

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’08 Combo Noise

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Analysis of ’08 Run (cont.)

Statistics for 4-Lumi combo is ~50 ppm

For each odd-numbered Lumi, noise should be ~100 ppm, but we get higher value.

When averaging Lumis, width does not scale like 1/sqrt(N).

Lumi ID Reg. RMS [ppm]

V 55.7

H 62.8

D1 149.6

D2 451.2

C 51.7

X 241.1

Sum 126.7

Ave 126.3

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D1VD2

What are the source of noise?

Blinded – Backgrounds. Electronics noise in BPM and BCM. Unaccounted Beam Noise. PMT pedestals. Correlated noise. Possible Higher order effects.

Summary

Lumi data is very useful for studying noise. Seems like we will be able to achieve

required noise levels. Can try to reduce it further by over-sampling

or by using a thicker target. Problem: thicker target introduces

nonlinearities in PMTs and ADCs. Need further tests and analysis.

Acknowledgements

Robert Michaels (JLab) Kent Pachke (UVA) Krishna Kumar (UMASS) Dustin McNulty (UMASS) Charles Horowitz (IU-Bloomington) The rest of the HAPPEx/PREx

Collaboration…