Introduction – pp2pp physics program; Description of the experiment; Engineering run in 2002;

First Result from the pp2pp Experiment Włodek Guryn

for pp2pp collaboration Brookhaven National Laboratory, Upton, NY, USA

•Introduction – pp2pp physics program;

•Description of the experiment;

•Engineering run in 2002;

•Data analysis and results;

•Summary and outlook.

RHIC/AGS Users MeetingBNL, May 15-16, 2003 Włodek Guryn

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Total and Differential Cross Sections, and Polarization Effects in pp Elastic Scattering at RHIC

S. Bueltmann, B. Chrien, A. Drees, R. Gill, W. Guryn*, I. H. Chiang, D. Lynn, C. Pearson, P. Pile, A. Rusek, M. Sakitt, S. Tepikian

Brookhaven National Laboratory, USA

J. Chwastowski, B. PawlikInstitute of Nuclear Physics, Cracow, Poland

M. HaguenauerEcole Polytechnique/IN2P3-CNRS, Palaiseau, France

A. A. Bogdanov, S.B. Nurushev, M.F RuntzoMoscow Engineering Physics Institute (MEPHI), Moscow, Russia

I. G. Alekseev, V. P. Kanavets, B. V. Morozov, D. N. SviridaITEP, Moscow, Russia

M. Rijssenbeek, C. Tang, S. YeungSUNY Stony Brook, USA

K. De, N. Guler, J. Li, N. OzturkUniversity of Texas at Arlington, USA

A. SandaczInstitute for Nuclear Studies, Warsaw, Poland

* spokesman


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Polarized Proton Collisions in RHIC

~12 10-6m after scraping

BRAHMS & PP2PP (p)

STAR (p)

PHENIX (p)

AGS

LINACBOOSTER

Pol. Proton Source500 A, 300 s

GeVs

cmsL

50050

onPolarizati%70

102 2132max

Spin Rotators

Partial Siberian Snake

Siberian Snakes

200 MeV Polarimeter AGS Internal Polarimeter

Rf Dipoles

RHIC pC PolarimetersAbsolute Polarimeter (H jet)

2 1011 Pol. Protons / Bunch = 20 mm mrad

AGS pC Polarimeters

Strong AGS Snake


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Proton - Proton Elastic Scattering Phenomenology

P, O -1Cor 1 C

Vacuum QM exchanged

p

pp

p

+p

pp

p

Pomeron(C=+1)

Odderon(C=1)+

Perturbative QCD PictureOP

OP

AAppppA

AAppppA

)(

)(

pp2pp experiment studies the dynamics and spin dependence of hadronic interaction through proton-proton elastic scattering

s = (p1 + p2 )2 = (C.M energy)2 t = (p1 – p3 )2 = - (four momentum transfer)2

s t 1 (GeV/c)2 – Non-pertutrbative regimeElastic scattering d/dt + optical theorem total cross section tot


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M

50 500

PP2PPHighest energy so far:

pp: 63 GeV (ISR)

pp: 1.8 TeV (Tevatron)

pp2pp energy range:

50 GeV s 500 GeV

pp2pp t-range:

(at s = 500 GeV)

4•10–4 GeV2 |t | 1.3 GeV2

Summary of Existing Data


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RHIC has the UNIQUE capability for colliding POLARIZED proton beams, further elucidating the exchange dynamics:

– Beam energy between 25 and 250 GeV;– Transverse polarization up to 70%;– Polarization can be chosen on a bunch-by-bunch basis (good for eliminating detection systematics!);

Allows to measure spin dependence of proton-proton elastic scattering

CNI region:

0.0004 < -t < 0.02 (GeV/c)2 √s = 200 GeV

0.0004 < -t < 0.13 (GeV/c)2 √s = 500 GeV

tot, , B, d/dt, AN(t), ANN(t)

ot = 300 barn (0.5%), = 0.005 (4%), AN(t), ANN(t) = 0.001

Medium |t| region:

0.02 < -t < 1.3 (GeV/c)2 √s = 500 GeV

diffractive minimum (peaks and bumps) and their spin dependence

PP2PP Physics program

Design parameters


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Spin Physics with pp2ppFive helicity amplitudes describe proton-proton elastic scattering

Φ1(s,t ) <++|M|++>

Φ2(s,t ) <++|M|-->

Φ3(s,t ) <+-|M|+->

Φ4(s,t ) <+-|M|-+>

Φ5(s,t ) <++|M|+->

σtot = Im [ Φ+(s,t ) ]t=0

8 π

sMeasure:

Φn(s,t ) <h3 h4 |M|h1 h2>

with hx = s-channel helicity

p1 = -p2 incoming protons

p3 = -p4 scattered protons

Φ+(s,t ) = ½ ( Φ1(s,t ) + Φ3(s,t ) )

dσdt = ( |Φ1|2 + |Φ2|2 + |Φ3|2 + |Φ4|2 | + 4|Φ5|2 )

2 πs 2

ΔσT = - Im [ Φ2(s,t ) ]t=0 = σ

- σ

8 π

s

ΔσL = Im [ Φ1(s,t ) - Φ3(s,t ) ]t=0 = σ

- σ

8 π

s


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Spin Physics with pp2pp

N.H. Buttimore, B.Z. Kopeliovich, E. Leader, J. Soffer, T.L. Trueman, “The Spin Dependence of High-Energy Proton Scattering”, PRD 59, 114010 (1999)

Single spin asymmetry AN arises in CNI region mainly from interference of hadronic non-flip amplitude with electromagnetic spin-flip amplitude

pp2pp will measure t- later also s-dependence of:

Data from E704 (1993)

2002 run pp2pp t-range

Statistical Precision with 2002 data set ΔAN 0.02

AN(t ) =N (t) + N(t) - N (t) - N(t) 1

Pbeam• cos N (t) + N(t) + N (t) + N(t)

N(t ) =

= Azimuth

Pblue = Beam Polarization

dN

dt

Im [ Φ5* Φ+ ]

dσ / dtfor small t


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Principle of Measurement

Elastically scattered protons have very small scattering angle θ, hence beam transport magnets determine trajectory scattered protons

The optimal position for the detectors is where scattered protons are well separated from beam protons

Need Roman Pot to measure scattered protons close to beam without breaking accelerator vacuum

Beam transport equations relate measured position at detector to scattering angle x = a11 x0 + Leff θx Optimize so that a11 small and Leff large

θx = a12 x0 + a22 θx x0 can be eliminated by measuring θx*

*

*

x : Position at Detector

θx : Angle at Detector

x0 : Position at Interaction Point

θx : Scattering Angle at IP*

Similar equations for y-coordinate

We found that because of the roll, misalignment, of the quadrupoles there is a mixing between x and y.

Bea

m T

rans

port

S.

Tep

ikia

n

pp

2p

p

RP P

osi

tion


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x

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Actual transport: (x0, y0) not known also coupled because of the quad roll

Yellow Blue


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pp2pp Experimental Setup in Enginnering run 2002Elastic and Inelastic Detectors

2×4 Scintillation Counter planes, 2.5|| 5.5

0. 100. m -100. m

D0

RP Stations

IR DX D0

RP Stations

-50. m 50. m


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Running Conditions in 2002Running conditions during a pp2pp, 14 hour dedicated run:

Beam momentum p = 100 GeV/c

Number of bunches per beam NB = 55 used 35 bunches

Beam scraped to emittance ε 12 π •10-6 m

and intensity I 5•1011 protons in each beam

Beam optics used β* = 10 m

Beam polarization (working #) Pb = 0.24 0.02

Closest approach of first detector strip to beam about

15 mm 15 beam tmin = -4•10-3 GeV2

Collected ~1 million triggers of which >30 % are elastic events

O. Jinnouchi


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Data Analysis: CollinearityCorrelation plots of x- and y-coordinates using elastic triggers with reconstructed tracks of scattered protons


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Hit Pattern and Transport CorrectionDistribution of y- vs. x-coordinate in sector 2 and θy vs. θx calculated using the beam transport, which includes the quadrupole roll


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Beam Angular Divergence

Good agreement between width of θx and θy distributions for measured and simulated events with emittance of:

ε = 12 π •10-6 m

And vertex size:

z = 70 cm

Δθx 150 μrad

Δθy 70 μrad

N. Öztürk

ΔθyΔθx

N. Öztürk


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Silicon Microstrip Detector Efficiency

First order efficiency calculated for

combination of two x- or y-planes

inside any given Roman Pot

14 out of 16 total silicon detectors

have an average efficiency > 0.98

Detection efficiency for elastic

arm A is almost 100%

RP1

RP3

x y x y y x y x

Arm A


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Event Reconstruction

Elastic event: good track in two “opposite” set of detectors

• SSD coordinate was calculated using energy weighted average of the position of the strips belonging to the isolated cluster of no more than three hits;

• Correlation between tracks in two Roman Pots:

require that (x2 + y2) be within “radius” : (x2 + y2) < 16 (x2 + y

2 );

• At least six out of eight hits belong to the track;

• No more than two planes with hits in “non” elastic arm;

• Select events within uniform t-acceptance tcut


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|t |--AcceptanceFind region in |t |- and -space with full acceptance coverage and high statistics

t = - ( pbeam •θ ) 2

= azimuthal angle

Event Sample 196,000 events:

159,250 events ( 0 < < 180º )

122,437 events ( 45º < < 135º )

58,511 events ( 45º < < 135º )

& 0.010 GeV2 |t | 0.019 GeV2 )


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Extracting B from dN/dt-Distribution

ddt

= GE

t2

tot2

e+Bt

GE tot

e+½Bt t

+

+

[

]

C

Fit |t |-distribution with

fixing tot51.6 mb and 0.13 and keeping B as a free parameter in range 0.010 GeV2 |t | 0.019 GeV2results in

B = ( 16.3 1.6 ) GeV-2

Depends on detector position

Depends on beam transport element positions

B = ( 16.3 1.6 ) GeV-2


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Systematic and Correlation Errors

Sytematic Errors were evaluated using Monte Carlo simulations:

1. Beam emmitence;

2. Vertex position spread in x, y, z;

3. Incoming beam angels – major source;

4. Beam transport uncertainty;

Total Systematic Error 0.9 (Gev/c)-2

Correlation between fitted parameter B and values of and :

±4 mb => ±0.07 (Gev/c)-2

±0.02 => ±0.32 (Gev/c)-2


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RESULT

Arm A

B = 16.3 ± 1.6 (stat.) ± 0.9 (syst.) (Gev/c)-2

Analysis described here was done by S. Bültmann (BNL)

An independent analysis by ITEP group agrees with result of S.B.


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pp2pp Experimental Setup in 2003Two RP stations on each side

2×4 Scintillation Counter planes, 2.5|| 5.5

0. 100. m -100. m

D0

RP Stations

IR DX D0

RP Stations

-50. m 50. m

Measurement of angle and position at RP to solve for x0, y0 and scatt. angles will reduce systematic errors.

=yD

D

xD

D

y

x

*0

*0

y

x

y

x

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y

x

y

x

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Actual transport: (x0, y0) not known also coupled because of the quad roll

Yellow Blue


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PP2PP Future Plans

•Equip two more Roman pot stations not to depend on vertex position ( in x0 and

y0 ) in calculation of scattering angles;

•Measure beam tune under pp2pp running conditions to reduce systematic

uncertainty in beam transport calculation;

•Include Van der Meer beam scans for luminosity determination;

•Run longer to improve statistics in view of physics goals (and also systematic

uncertainties)

pp2pp will measure spin-dependent elastic proton-proton scattering in a new kinematic

region probing large distance QCD (Pomeron, Odderon)

2003 – at √s = 200 GeV: tot, B, d/dt, AN(t), ANN(t)

2004 – at √s = 500 GeV: tot, B, d/dt, AN(t), ANN(t)

2005 – at √s = 500 GeV: B(t), d/dt, diffractive minimum

Exciting opportunities at RHIC for pp2pp over the next few years

Documents

Introduction – pp2pp physics program; Description of the experiment; Engineering run in 2002;