Systematic errors studies in the rhic ags proton carbon cni polarimeters
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Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters. Andrei Poblaguev Brookhaven National Laboratory The RHIC/AGS Polarimetry Group: I. Alekseev, E. Aschenauer, G. Atoian , A. Bazilevsky , A. Dion, H. Huang,

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Systematic errors studies in the rhic ags proton carbon cni polarimeters

Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Andrei Poblaguev

Brookhaven National Laboratory

The RHIC/AGS Polarimetry Group:

I. Alekseev, E. Aschenauer, G. Atoian, A. Bazilevsky, A. Dion, H. Huang,

Y. Makdisi, A.Poblaguev, W. Schmidke, D. Smirnov, D. Svirida, K. Yip, A. Zelenski

PSTP 2011, St. Petersburg


Systematic errors studies in the rhic ags proton carbon cni polarimeters

BRAHMS(p) Polarimeters

Absolute Polarimeter (H jet)

RHIC pC Polarimeters

Siberian Snakes

Spin flipper

PHENIX (p)

STAR (p)

Spin Rotators

(longitudinal polarization)

Spin Rotators

(longitudinal polarization)

Solenoid Partial Siberian Snake

LINAC

BOOSTER

Helical Partial

Siberian Snake

Pol. H- Source

AGS

200 MeV Polarimeter

AGS pC Polarimeter

Strong AGS Snake

Layout of the RHIC facility

  • H jet (pp) polarimeter provides absolute polarization measurements at RHIC

  • RHIC pCpolarimeters provide polarization monitoring including polarization profile measurements

  • AGS pCpolarimeter provides polarization monitoring (mainly used for technical control and special beam studies)

PSTP 2011, St. Petersburg


Proton carbon polarimeter kinematics
Proton-Carbon PolarimetersPolarimeter kinematics

Plan view

Event selection in RHIC/BNL

pC polarimeters:

PSTP 2011, St. Petersburg


Polarization measurement
Polarization Measurement Polarimeters

Spin dependent amplitude:

Rate in the detector:

1. Spin Flip (one detector):

A theoretical model for AN(t) (a fit to the BNL E950 data)

2. Left-right asymmetry

(two detectors)

Square-root formula:

Combining “spin flip” and “left/right asymmetry” methods allows us to strongly suppress systematic errors

PSTP 2011, St. Petersburg


Ags cni polarimeter 2011
AGS CNI Polarimeter 2011 Polarimeters

3 different detector types:

1,8 - Hamamatsu, slow preamplifiers

Larger length (50 cm)

2,3,6,7 - BNL, fast preamplifiers

Regular length (30 cm)

4,5 - Hamamatsu, fast preamplifiers

Silicon Strip Detectors:

Dead Layer

Strip orientation

90 degree detectors (2,3,6,7)

45 degree detectors (1,4,5,8)

PSTP 2011, St. Petersburg


Schema of mesurements
Schema of Mesurements Polarimeters

WFD

α-source measurements (241Am , 5.486 MeV)

“Banana fit”

t-t0 = tA(xDL,αA)

PSTP 2011, St. Petersburg


An example of data selection
An example of data selection Polarimeters

If t0 is known, a model independent calibration can be done

Wrong determination of mean time

It must be a vertical line if detector is properly calibrated

PSTP 2011, St. Petersburg


The ags pc polarimeter is succesfully used for the relative measurements
The AGS pC polarimeter is succesfully used for the relative measurements

Beam Intensity, I

Polarization profile measuremens

(jump quads study)

Study of Polarization dependence on beam intensity

PSTP 2011, St. Petersburg


Is absolute polarization measurement possible with a proton carbon polarimeter
Is absolute polarization measurement possible with a proton-Carbon polarimeter ?

  • A systematic errors study is necessary to answer this question.

  • Are results dependent on detector configuration ?

  • Do we know the Analyzing Power AN(t) ?

  • Could we properly calibrate detectors ?

  • Do we understand energy losses in the target ?

  • Can we control rate dependence of polarization measurements ?

PSTP 2011, St. Petersburg


Polarization vs beam intensity late cbm vertical target3 all 2011 runs

Polarization dependence on detector type proton-Carbon polarimeter ?

Polarization vs Beam Intensity (Late CBM),Vertical Target3, all 2011 runs

Polarization measured by all 3 types of detectors is consistent within 1-2% accuracy !

Can we explain slope difference for 90 and 45 degree detectors by rate effect ?

All 2011 data was included in the fit. Results of the fit should be used for comparison only

Polarization, P(1.2) , is given for intensity 1.2×1011

PSTP 2011, St. Petersburg


Hamamatsu 45 degree vs bnl 90 degree detectors

Polarization dependence on detector type proton-Carbon polarimeter ?

Hamamatsu (45 degree) vs. BNl (90 degree) detectors

No visible variations of the polarization ratio during 4-month Run 2011!

PSTP 2011, St. Petersburg


A n measurement for assumed 65 polarization

Analyzing Power A proton-Carbon polarimeter ?N(t)

AN measurement for assumed 65% polarization

  • Poor consistency between theory and measurements

  • Wrong energy calibration and energy losses in the

  • target may contribute to the discrepancy

  • Results depend on the target (rate ?, energy losses ?)

Potentially, analyzing power may be measured by the pC polarimeter (up to a normalization constant)

PSTP 2011, St. Petersburg


Dead layer corrections

Enrgy Calibration proton-Carbon polarimeter ?

Dead-Layer corrections

L0 is stopping range derived from MSTAR dE/dx (used in “standard” calibration)

Stopping range parametrization:

“standard parametrization”, p=1/d

constant energy loss, p=Eloss

polinomial

Carbon Energy from measured amplitude:

PSTP 2011, St. Petersburg


Systematic errors studies in the rhic ags proton carbon cni polarimeters

Enrgy Calibration proton-Carbon polarimeter ?

Inverse task:

If E(αA) is known then we can determine L(E) and dE/dx

If t0 is know then we can measure Carbon energy as a function of the amplitude αA

A model independent calibration of the amplitude

and thus we can measure dE/dx (in deadlayer length units)

WARNING: In such a way we measure effectivedE/dx which may be different from ionization lossesdE/dx.

If t0 is unknown we can make a fit, that is to try all possible t0and select one which provides best data consistency. It might provide us with value of t0 and calibration of the measured amplitude ECarbon = E(αA) .

WARNING: the fit may work incorrectly if parameterization of stopping range L(p, αA) can not approach well true effective dE/dx.

PSTP 2011, St. Petersburg


New calibration method vs standard one
New calibration method vs standard one proton-Carbon polarimeter ?

  • The function L(E) = p0L0(E) + p1L02(E) fits data much better then “standard” calibration function p0L0(E)

  • Significant difference in the value of t0

  • Significant difference (up to 15% ) in the energy scale

Better fit of data does not guarantee better calibration !

PSTP 2011, St. Petersburg


Comments about t 0 determination in the fit
Comments about proton-Carbon polarimeter ?t0 determination in the fit

Including t0 to the fit:

(τis time of flight for 1 MeV carbon )

If then (good calibration)

However, if may be approximated by variations of the

then result of the calibration is unpredictable

may be masked by faked correction

PSTP 2011, St. Petersburg


An estimate of the rate effect

Rate effect proton-Carbon polarimeter ?

An estimate of the rate effect

Simplified example

Only one carbon signal may be taken by the DAQ

Detection efficiency:

where r is average rate per bunch.

More realistic example

is rate of good events

is total DAQ rate

- is a strip pair number

- is average rate per strip (millions events per spill)

- is rate in strip i (events per bunch), n = 0.0528

- is relative rate in the strip I

assume factor k is the same for all strips

Rate contribution

Machine contribution

PSTP 2011, St. Petersburg


Vertical target3 all 2011 runs strip pairs

Rate effect proton-Carbon polarimeter ?

Vertical Target3, all 2011 runs: Strip Pairs

The measured value of the rate effect factor

agrees well with a pileup based estimate

Polarization dependence on beam intensity (averaged over all 2011 runs) :

PSTP 2011, St. Petersburg


Target dependence of the polarization measurements

Enrgy losses in the target proton-Carbon polarimeter ?

Target dependence of the Polarization measurements

Polarization vs intensity, Horiz. target #1, JQ-on

Polarization vs intensity, Vertical target#3, JQ-on

AGS pol., during H-jet meas. at injection

Intensity -1.5

  • Slope difference is consistent with our estimates

  • We can explain 4±1 % of polarization difference

  • by rate effect. Where the rest 4.6±1.7% come

  • from?

PSTP 2011, St. Petersburg


Energy losses in the target

Enrgy losses in the target proton-Carbon polarimeter ?

Energy losses in the target

125 μm target

Target

φ

Beam

(d ~ 30 nm)

Measured/True Polarization

dE/dx

Calculation

  • Effect of energy losses in the target

  • may be significant

  • may be unpredictable

AN(t)

Results are independent on target width !

Energy range 400-900 keV

PSTP 2011, St. Petersburg


Summary
Summary proton-Carbon polarimeter ?

  • Different types of detectors were tested in the Run 2011

  • Results of polarization measurements were consistent within 1-2% accuracy

  • No significant variation of the results of measurements were observed during the whole 4 month run.

  • The polarimeter has a capability to measure analyzing power up to the arbitrary normalization factor, but accurate study of the systematic errors is needed for that.

  • Standard energy calibration method was found to be unreliable, new method of calibration are suggested but more development is still needed.

  • Experimental evaluation of the rate effect is consistent with estimation of pileup contribution.

  • More accurate control of energy losses in the target is needed.

PSTP 2011, St. Petersburg