systematic errors studies in the rhic/ags proton-carbon cni polarimeters

21
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 1 PSTP 2011, St. Petersburg 06/18/22

Upload: tarika

Post on 05-Jan-2016

23 views

Category:

Documents


0 download

DESCRIPTION

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, - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: 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

1PSTP 2011, St. Petersburg04/20/23

Page 2: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

PHENIX (p)

AGS

LINACBOOSTER

Pol. H- Source

Solenoid Partial Siberian Snake

200 MeV Polarimeter

Helical Partial Siberian Snake

Spin Rotators(longitudinal polarization)

Siberian Snakes

Spin Rotators(longitudinal polarization)

Strong AGS Snake

RHIC pC PolarimetersAbsolute Polarimeter (H jet)

STAR (p)

BRAHMS(p)

AGS pC Polarimeter

Spin flipper

Layout of the RHIC facility

• H jet (pp) polarimeter provides absolute polarization measurements at RHIC• RHIC pC polarimeters provide polarization monitoring including polarization profile measurements• AGS pC polarimeter provides polarization monitoring (mainly used for technical control and special beam studies)

2PSTP 2011, St. Petersburg04/20/23

Page 3: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Proton-Carbon Polarimeter kinematics

Plan view

Event selection in RHIC/BNL pC polarimeters:

3PSTP 2011, St. Petersburg04/20/23

Page 4: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Polarization MeasurementSpin dependent amplitude:

Rate in the detector:

1. Spin Flip (one detector):

2. Left-right asymmetry (two detectors)

Square-root formula:

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

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

4PSTP 2011, St. Petersburg04/20/23

Page 5: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

AGS CNI Polarimeter 2011

PSTP 2011, St. Petersburg 5

1,8 - Hamamatsu, slow preamplifiers

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

4,5 - Hamamatsu, fast preamplifiers

3 different detector types:

Larger length (50 cm)

Regular length (30 cm)

Silicon Strip Detectors:

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

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

Strip orientationDead Layer

04/20/23

Page 6: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Schema of Mesurements

PSTP 2011, St. Petersburg 6

WFD α-source measurements (241Am , 5.486 MeV)

“Banana fit” t-t0 = tA(xDL,αA)

04/20/23

Page 7: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

An example of data selection

PSTP 2011, St. Petersburg 7

Wrong determination of mean time

It must be a vertical line if detector is properly calibrated

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

04/20/23

Page 8: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

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

8PSTP 2011, St. Petersburg04/20/23

Page 9: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

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 ?• …

9PSTP 2011, St. Petersburg04/20/23

Page 10: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

10PSTP 2011, St. Petersburg

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

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

Polarization dependence on detector type

04/20/23

Page 11: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

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

PSTP 2011, St. Petersburg 11

Polarization dependence on detector type

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

04/20/23

Page 12: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

AN measurement for assumed 65% polarization

PSTP 2011, St. Petersburg 12

Analyzing Power AN(t)

• 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)

04/20/23

Page 13: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Dead-Layer corrections

Stopping range parametrization:

“standard parametrization”, p=1/dconstant energy loss, p=Eloss polinomial

Carbon Energy from measured amplitude:13PSTP 2011, St. Petersburg

Enrgy Calibration

04/20/23

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

Page 14: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

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

and thus we can measure dE/dx (in deadlayer length units)WARNING: In such a way we measure effective dE/dx which may be different from ionization losses dE/dx.

If t0 is unknown we can make a fit, that is to try all possible t0 and 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.

14PSTP 2011, St. Petersburg

A model independent calibration of the amplitude

Enrgy Calibration

04/20/23

Page 15: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

New calibration method vs standard one

• 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 !

15PSTP 2011, St. Petersburg04/20/23

Page 16: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Comments about t0 determination in the fit

Including t0 to the fit:

(τ is 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

16PSTP 2011, St. Petersburg04/20/23

Page 17: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

More realistic example is rate of good events is total DAQ rate

Simplified exampleOnly one carbon signal may be taken by the DAQDetection efficiency:

where r is average rate per bunch.

An estimate of the rate effectRate effect

- 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

17PSTP 2011, St. Petersburg04/20/23

Page 18: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

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

The measured value of the rate effect factor

agrees well with a pileup based estimate

Vertical Target3, all 2011 runs: Strip Pairs

18PSTP 2011, St. Petersburg

Rate effect

04/20/23

Page 19: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Target dependence of the Polarization measurements

PSTP 2011, St. Petersburg 19

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

Intensity -1.5

Polarization vs intensity, Horiz. target #1, JQ-on Polarization vs intensity, Vertical target#3, JQ-on

• 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?

Enrgy losses in the target

04/20/23

Page 20: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Energy losses in the target

20PSTP 2011, St. Petersburg

φ Target

Beam

Energy range 400-900 keV

Calculation

AngleTarget Thickness (μg/cm2)

4 8 16

0 0.991 0.982 0.965

45 0.987 0.975 0.951

80 0.950 0.903 0.825

85 0.903 0.802 0.610

0 - 360 0.970 0.948 0.911

Measured/True Polarization

Results are independent on target width !

125 μm target

Effect of energy losses in the target• may be significant• may be unpredictable

Enrgy losses in the target

04/20/23

dE/dx

AN(t)

(d ~ 30 nm)

Page 21: Systematic Errors Studies in the RHIC/AGS Proton-Carbon CNI Polarimeters

Summary

• 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.

21PSTP 2011, St. Petersburg04/20/23