NARROW STRUCTURES OBSERVED IN THE p-p ANALYZING POWER AND NARROW RESONANCES

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NARROW STRUCTURES OBSERVED IN THE p-p ANALYZING POWER AND NARROW

RESONANCES

H. Shimizu, G. Glass, J. Hiebert, S. Hiramatsu, J. Holt, K. Imai, R. Kenefick, K. Kobayashi, Y. Kobayashi, Y. Mori, et al.

To cite this version:

H. Shimizu, G. Glass, J. Hiebert, S. Hiramatsu, J. Holt, et al.. NARROW STRUCTURES OB-

SERVED IN THE p-p ANALYZING POWER AND NARROW RESONANCES. Journal de Physique

Colloques, 1990, 51 (C6), pp.C6-367-C6-370. �10.1051/jphyscol:1990630�. �jpa-00230897�

Colloque C6, supplement au n022, Tome 51, 15 novembre 1990

NARROW STRUCTURES OBSERVED IN THE p-p ANALYZING POWER AND NARROW RESONANCES

H. SHIMIZU, G. GLASS*, J.C. HIEBERT* , S. HIRAMATSU*. , J.A. HOLT** , K. IMAI* * , R. A. KENEFICK* , K. KOBAYASHI* * , Y. KOBAYASHI* * * * ,

Y. MORI*", T. NAKAGAWA'***, S. N A T H * * * * * , L. C. NORTHCLIFFE* , H. OHNUMA***'** , H. SATO** A. SIMON*, A. TAKAGI*", T. TOYAMA* * , A. UENO* * and H. Y. YOSHIDA' * * * *

Cepartment of Physics, Yamagata University, Yamagata 990, Nippon Texas A and M University, College Station, Texas 77843, U.S.A.

* * National Laboratory for High Energy Physics (KEK), Tsukuba 305, flippon

Department of Physics, Kyoto University, Kyoto 606, Nippon

* * * * Department of Physics, Tohoku University, Sendai 980, Nippon

* * * * X

Los Alamos Natior-sl Laboratory, Los Alamos, NM 87545, U.S.A.

* i t * * *

Department of Physics, Tokyo Institute of Technology, Tokyo 152, Nippon

Rtsume

-

Nous avons obsewk les structures petites mais tr&s ttroites dans la dkpendance de moment des pouvoirs d'analyse dans la difhsion tlastique proton-proton autour 1 GeV/c. Nous traitons la possibilite d'une explication de ces structures en utilisant les rksonances de deux-protons ttroits.

Abstract

-

Small but rather narrow structures have been observed in the momentum dependence of the analyzing power in proton-proton elastic scattering around l GeV/c. A possible explanation for the structures using narrow two-proton resonances is discussed.

1

-

EXPERIMENTAL RESULTS

The experiment was performed at KEK using an internal string target while the polarized beam was accelerated from 1 to 3 GeV/c. A detailed description of the experimental procedure is given elsewhere/l/. The experimental results are shown in Fig. 1 of the proton-proton (p-p) elastic analyzing power at the laboratory backward angle of 68'. The beam polarizition was continuously measured in the main ring to be 0.46 at 1 GeV/c, just before the start of acceleration. The relative uncertainty of the analyzing power, AAy, is typically less than 0.0 1. Two prominent narrow peaks (-15 MeV FWHM) are observed at incident momenta of 1.23 and 1.32 GeV/c which correspond to p-p invariant mass values 2.16 and 2.19 GeV, respectively. Here we assume constant beam polarization over this momentum region. This assumption might be acceptable if there are no depolarizing resonances during polarized beam acceleration. However there exist 3 imperfection resonances capable of causing depolarization of the beam at yG=3,4, and 5 in this momentum region. The corresponding beam momenta are indicated with vertical dash-dotted lines in the figure. As far as these 3 imperfection resonances are concerned, fortunately, their strength is evaluated to be very weak (at most a few percents) and their widths are calculated to be much less than one momentum bin/2/. Thus, the beam polarization and consequently the measured asymmetry are expected to decrease like a step function at the momentum bin where depolarization occurs. No such step is seen in Fig. 1 at the beam momenta corresponding to yG=3 and 5, but a small step is apparent at 1.87 GeV/c corresponding to @=4. Similar evidence of depolarization at yG=4 is seen in the data taken with backward monitor counters placed at Blab' 75".

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990630

COLLOQUE DE PHYSIQUE

Here is, however, still a serious question on the experimental result: If there is a complicated polarization distribution in the beam spot, does it give rise to the structure since the beam moves over the internal string target during acceleration? To answer to the question we measured another analyzing power for the inclusive reactions at the same time when the p-p elastic analyzing power was measured, with the same beam, the same target, and the same detectors but using a different logic. We directly measure aspmetries instead of analyzing powers and assume constant beam polarization to get the analyzing powers. Therefore if the beam polarization changes during acceleration and consequently it makes the structure in the elastic analyzing power a similar effect should also be observed in the inclusive analyzing power. Fig. 2 shows the momentum dependence of the analyzing power in the inclusive reactions such as pp+pX, pp-rnx, pC-rpX, pC-rnX, and so forth, at the laboratory backward angle of 68". No structure is seen at around yG=3 and 5, and a small step is observed again

0.7

1.0 1.5 2.0 2.5

Incident proton momentum (GeV/c)

Fig. 1

-

The momentum dependence of the analyzing power for p-p elastic scattering at the laboratory backward angle of 68". No correction is made for the apparent depolarization of the beam at yG=4.

0.25

0.00

1.0 1.5 2.0 2.5

Incident proton momentum (GeV/c)

I " ' ! ' I " " I " -

! e4'"b=68.0 (deg) f Backward Single

!

l !

I I

I I

-

I

-

^{7 G = 3}

yG = 4

I -Q

! !

1 , , * , : 1 , , -

Fig. 2

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The momentum dependence of the analyzing power for the inclusive reactions of pp+pX, pp-rnX, pC-rpX, pC+nX, etc. No correction is made for the apparent depolarization of the beam at yG=4.

GeV/c in the elastic analyzing power is real.

2

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DISCUSSION

We tried to reproduce the structure in the elastic analyzing power by introducing narrow resonances in the 3P waves since the triplet waves give the main contribution to the analyzing power and the P waves are dominant in this energy region. We employ the energy dependent amplitudes deduced from Arndt's PSA (SM88) to describe the smooth background. Narrow resonances will not show up due to the coarse steps which are between 50 and 100 MeV in this energy region. At this level of the discussion, the previously existing data are still sparse, with the exception of the energy dependent differential cross section data, at 0 ~ ~ = 9 0 O , taken at LNS, which show no narrow structure/3/and are already taken into account in the SM88 analysis. Therefore we cannot improve the situation in reproducingthe differential cross section by adding a narrow resonance term to the SM88 amplitudes. The question is whether we can reproduce the structure observed in the analyzing power by introducing the resonance term without having any big influence on the energy dependence of the differential cross section.

pp Elastic Analyzing Power pp Elastic Analping Power

. . , > l a . , , , 8 . , , b . . ,

. . . . , I . . I . I . . I L

a,

-

^{68.0 lard} a,

-

^{sa.0 (deg)}

1 " ' 1 " " 1 ' ' , ' 1 1 , ' '

2.1 2.15 2.2 2.25 2.3

M,, (QV)

(b)

pp Elastic Differential Cross Section pp Elastic Differential Cross Section

Fig. 3

-

The analyzing power (upper).and the differential cross section (lower) versus two-proton invariant mass.

The dash-dotted lines show predictions of SM88. The solid curves correspond to predictions of SM88 + a resonance in the 3P0 wave with the resonance parameters, ER=2.160 GeV, T=15 MeV, and q=0.2 (a); in the 3Pl wave with E~=2.160 GeV, T= 15 MeV, and q=0.1 (b); in the 3 ~ 2 wave with

ER=^.

^{170 GeV, T= 15 MeV,}

and y 0 . 0 3 (c); and 2 resonances in the 3p2 wave with E~=2.170 and 2.200 GeV, r=15 MeV, and q=0.03 (d).

COLLOQUE DE PHYSIQUE

pp Elasiic Analping Power

' I I ' ' l " l " ' -

s , = 66.0 (&g) 0.60

O.==

L'

^-

pp Elastic -4nalyzing Power

" ' I " " . a,

-

^{eaa (*S)}

0.60

pp Elastic Differential Cross Section pp Elastic Differential Cross Section

. . "

^{1 . . . . 1 . , . . I . . . ,}

2.1 2.15 2.2 2.25 2.3 2.1 2.15 2.2 2.25 2.3

M,, M,, (GeV)

Figs. 3a show the results when we input a narrow resonance in the 3Po partial wave at 2.160 GeV.

When a narrow resonance is introduced in the 3p1 wave at 2.160 GeV with a width of 15 MeV there is very good reproduction of the first peak at 1.23 GeV/c as shown in the upper part of Figs. 3b. This resonance, however, gives a very big effect on the elastic differential cross section (lower part of Figs. 3b), and no such structure is seen in the existing data. A resonance in the 3 ~ 2 wave at 2.170 GeV with a width of 15 MeV reproduces the structure well and gives no large effects on the cross section (Figs. 3c). The elasticity q of this resonance is 0.03. Of course we can obtain better results with one additional resonance (Figs. 3d). In the present analysis we find the elasticity of the resonance, if it exists in the 3~ waves, must be very small (q ^;*

0.03). This might be the reason why narrow structures have not been observed previously in the N-N channel.

In this case the resonance structure is really enhanced in the analyzing power by interference terms of the amplitudes. Since the elasticities are very small in the case of the 3~ resonances we have also examined the effects of a resonance in other partial waves up to the F waves. A 3~~ resonance gives the same contribution as the 3pl resonance at around the first peak in the analyzing power with a slight larger elasticity (q = 0.05) and shows opposite behavior in the differential cross section. It seems that there is no partial wave in which a resonance can reproduce the second peak at 1.32 GeV/c other than the 3 ~ 2 wave.

REFERENCES

/V H. Shimizu, Proc. 5th French-Japanese Symposium on Nuclear Physics, Dogdshima, Japan, Sept. 1989, p. 33 1; H. Shimizu et al., to be published in Phys. Rev. C.

N H. Sato, Jpn. J. Appl. Phys. 27 (1988) 1022 ; H. Sato et al., Nucl. Instr.& Meth. A272 (1988) 617.

N M. Garqon et al., Nucl. Phys. A445 (1985) 669.