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0 polarization in pp → p0K+(+- )5 at 27.5 GeV

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J. Félix1, D.C. Christian 3, M.D. Church 4, M. Forbush 5 , E.E. Gottschalk 3, G. Gutiérrez 3, E.P. Hartouni 2, S.D. Holmes 3,

F.R. Huson 5, D.A. Jensen 2, B.C. Knapp 4, M.N. Kreisler 2, J. Uribe 2, B.J. Stern 4, M.H.L.S. Wang 2, A. Wehmann 3 ,

L.R. Wrencke 4, J.T. White 5.

1 Universidad de Guanajuato, León, Gto.2 University of Massachusetts, Amherst, MA 01003 USA

3 Fermilab, Batavia, IL 60510, USA4 Columbia University, Nevis Lab. Irvington NY, 10533 USA

5 Department of Physics, Texas A&M University, College Station

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INTRODUCTIONINTRODUCTION

BNL 766 EXPERIMENTBNL 766 EXPERIMENT

DATA SELECTIONDATA SELECTION

00 POLARIZATION POLARIZATION

RESULTSRESULTS

CONCLUSIONSCONCLUSIONS

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Introduction 1. Elementary Concepts

pp → p0K+

1.1 xF

1.2 PT xF

C of M

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xF

xF

max

Transverse momentum

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1.3 n normal to the production plane

n

production plane

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1.4 Mx invariant mass of {0K+} system.

0K+

0

K+

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1.5 Hyperon polarization

0

0

-

+

0

B. Lundberg et al, PRD 40, 39 (1989)

K. Heller et al, PRL 51, 7025 (1983)

R. Rameika et al, PRD 33, 3172 (1986)

P. M. Ho et al, PRL 65, 1713 (1990)

A. Morelos et al, PRL 71, 2172 (1993)

J. Felix et al, PRL 82, 5213 (1999); 88, 061801 (2002); 76, 22 (1996)

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1.6 Models

Semiclassical ideas

Regge like

QCD

PQCD

Fragmentation functions

Gluon fusion

T. De Grand et al, PRD 24, 2419 (1981)

R. Barni et al, PLB 296 (1992) 251

G.L. Kane et al, PRL 41, 1689 (1978)

M. Anselmino et al, PRD 63, (2001) 054029

C. Boros et al, PRD 62 (2000) 014021

W.G.D. Dharmaratna and G.R. Goldstein,PRD 53, 1073 (1996)

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2. Typical results of 0 polarization as function of xF and PT .

xF < 0

xF > 0

(a)

(b)

circles, this Experimentsquares, reference 2

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

PT (GeV/c)

-0.3

-0.2

-0.1

0

-0.2

0.2

0

PO

LA

RIZ

AT

ION

PP

OL

AR

IZA

TIO

N P

PRL J. Felix 1996 Ref. 2 PRL, Heller 1978

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In inclusive and exclusive p-nucleus reactions 0 polarization, in some kinematical regions is described very well by

P(xF , PT) = +a xF PT

a depends on target nature, it is independent of the beam energy.

in pp → p0K+(+- )N, N= 1, 2, 3, 4 at 27.5 GeV

a = - 0.443 + 0.037 (GeV/c)-1 PRL J. Felix et al, (1999)

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Typical results of 0 polarization as function of Mx { 0K+}

J. Felix et al, PRL, (2002)

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BNL 766 ExperimentWas designed to study exclusive pp reactions up to 20 charged particles in the final state.

E766 Spectrometer

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collected ~ 320 million raw events

~ 3 million as exclusive events

pp → pp (+- )N, N= 1, 2, 3, 4, 5

or

pp → p0K+(+- )N, N= 1, 2, 3, 4, 5

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Data Selection

Kinematical constraints

1. momentum

2. electric charge

3. strangeness

4. baryon number

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additionally to select

1. Two vertices separated

2. 0 → p-

3. Fourteen charged particles

pp → p0K+(+- )5

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1973 events with small background

0 mass (GeV)

01.105 1.1075 1.11 1.1125 1.115 1.1175 1.12 1.1225 1.125 1.1275 1.13

225

200

175

150

125

100

75

50

25

0

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Mx (GeV)

Eve

nts

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typical reconstructed event

pp → p0K+(+- )5

0

p

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p

-

= 0.642 + 0.013 Polarization

0 polarization

0

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fitting to a straight line cos distribution

cos

2 dof = 0.68

1.61 < Mx < 1.70

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P = mb

P =P mm( )

2 bb

2( )

( )2

+ +

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Resultsas function of xF

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Resultsas function of PT

J. Felix et al, PRL 2002

This experiment

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Resultsas function of Mx

J. Felix et al, PRL 2002

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Conclusions

- 0 polarization from pp → p0K+(+- )5

at 27.5 GeV is akin to 0 polarization from pp → p0K+ at 800 GeV.

- 0 polarization depends on xF, PT and Mx {0 K+}.