0 polarization in pp → p 0 K + ( + - ) 5 at 27.5 GeV.
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Transcript of 0 polarization in pp → p 0 K + ( + - ) 5 at 27.5 GeV.
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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+}.