Elastic proton-proton scattering: Excitation functions from 0.45 to 2.5 GeV

Progress in Particle and Nuclear Physics PERGAMON

Progress in Particle and Nuclear Physics 50 (2003) 537-546 http://www.elscvier.com!locate/npe

Elastic Proton-Proton Scattering: Excitation Functions from 0.45 to 2.5 GeV F. HINTERBERGER’, F. BAUER*, J. BISPLINGHOFF’, K. BihER*, M. BUSCH’, T. COLBERG*, L. DEMIRijRS*, C. DAHL’, PD. EVERSHEIM’, 0. EYSER*, 0. FELDEN3, R. GEBEL’, J. GREIFF’, E. JONAS*, H. KRAUSE’, C. LEHMANN*, J. LINDLEIN*, R. MAIER3, A. MEINERZHAGEN’, C. PAULI*, D. PRASUHN3, H. ROHDJEO’, D. ROSENDAAL’, P. VON ROSSEN3, N. SCHIRM*, W. SCOBEL*, K. ULBRICH’, E. WEISE’, T. WOLF* and R. ZIEGLER’ ‘Helmhok-Insfifuf ftir Sfrahlen- und Kemphysik, UniversifGf Bonn, Nu_l?allee14-16, D-531 IS Bonn, Germany 21n.~fifufjIirExperimenfulphysik, Universifiir Humburg, Germany 31nsfifufj7irKemphysik, Forschungszenfmm Jiilich. Germany

Excitation

functions

of the differential

and spin correlation internal

targets

parameters

cross sections do/d&

ANN,

Ass

and deceleration

experimental angular

method

distributions

angles 30” 5 8,,

5 90”. Details of the

of high precision and internal

are found. Upper liits

elastic scattering

in the mass range fi

consistency.

functions

on the coupling of narrow resonances = 2.2..

and

No evidence for

.2.8 GeV are deduced.

to

The data

impact on phase shift solutions.

Introduction elastic scattering

Proton-proton

teraction.

experiments

At low energies a precise database

has been accumulated.

These data

[2, 3, 4, 5, 6, 71. Modern descriptions bation

beam for kinetic energies

The results provide excitation

narrow structures

have significant

1

are presented.

with

COSY. Data were taken continously

of the internal

between 450 and 2500 MeV and scattering

powers AN

and ASL have been measured

at the Cooler Synchrotron

during the acceleration

analyzing

phenomenological

should also be mentioned

In view of the repulsive

by energy

and meson-theoretical

in this context

potential

bombarding

energies

the short range part of the NN interaction

0146-6410/03/$ - see front matter 0 2003 Elsevicr PII: SOl46-6410(03)00048-6

Science

shift solutions

models provide excellent

the pp scattering

data at low

parts of the NN interaction.

are needed

in order

to reach small

at GeV energies is ideally suited to study

with high resolution.

is reached

phase

observables

work based on chiral pertur-

of the long- and medium-range

core higher

of up to 2.3 GeV/c

dependent

[9]. However,

of the NN in-

and polarization

[8]. Recent theoretical

(< 0.8 fm). It turns out that pp elastic scattering

transfer

to the understanding

cross sections

are well represented

energies provide only the understanding

momentum

of differential

of the data up to the pion threshold

theory

distances

[l] are fundamental

corresponding

At 2.5 GeV kinetic to spatial

BV. All rights reserved.

resolutions

energy a four of less than

538

E Hinterberger et al. /Prog. Parr. Nucl. Phys. 50 (2003) 537-546

0.15 fm. Elastic pp scattering

at those energies provides

other heavy meson exchanges. occur at small distances

involving

the nature of the repulsive Another

unsettled

nonexistence

energies

far [lo].

Excitation

i.e. cross sections

were inconsistencies

The available

resonant

of the Scattering The remaining

groups

Amplitudes ambiguities

Therefore,

central, spin-orbit, cross sections,

scattering

accuracy. spin-spin

Analysis

or

with cm.

has been observed

so

and spin correlation

of the two incoming

protons,

of data was

data base was rather poor and there

had been observed

measured in certain

at different discrete spin observables

(PSA) unambiguously

up to about

data of sufficient quality and density

[Ill. 1 GeV

were not available

waves, leading to serious discrepancies

by the Saclay-Geneva

experiment

of existence

1995 showed that the vast majority

between

phase-

Direct Reconstruction

group (121 has not solved this problem.

PSA solutions. at the cooler synchrotron

The aim of the experiment

COSY

was concieved

is to measure

excitation

to provide functions

of

over a wide energy range up to 2.5 GeV in fine energy steps and

Both for a phase shift analysis and spin-tensor

but also spin observables

as such and for its use in identifying

forces, it is mandatory

such as analyzing

of the energy.

Precise

to measure

not only spin-averaged

powers An and spin correlation and consistent

of PSA solutions

and the development

now, only a few relativistic

meson exchange

models have been extended

data are needed

of new theoretical

coefficients both for the

approaches.

Until

beyond the pion threshold

up

1 GeV [B].

In this paper the experimental In the discussion, functions

is

amplitudes.

and extension

to about

problem

resonances

powers

[7, 121 above 1.2 GeV. A model independent

allow different

ANN, Ass and Asr, as a function improvement

structures

of partial

data of sufficient quality and density. the elastic proton-proton

might

that may show up in the elastic channel

errors in the angular distributions

(DRSA)

the EDDA

with a high relative

resonances

and nonresonant

experimental

number

of different

analyzing

Above 1200 MeV, the experimental

energy dependent

the increased

dibaryonic

on the relative spin orientation

data allowed to do a Phase-Shift

shift solutions

A related

is the question

predict

cross sections,

test for dibaryonic

[2, 3, 4, 5, 71. At higher energies, to determine

new processes

constituents.

2.1 and 2.9 GcV. Not any resonance

of differential

and normalization

In addition,

genuinely

dynamics

models

of the world data set at about

below 800 MeV kinetic energy.

energies.

between

between

Closer inspection

QCD inspired

depending

sensitive

due to the interference

of the quark-gluon

to the quark-gluon

Various

functions

provide an especially

the dynamics

issue related

En ranging

resonance

from the true meson-exchange

core.

of dibaryons.

parameters,

Apart

a sharp focus on the role of the w-meson and

the impact

methods

and the results of the EDDA experiment

are presented.

of the new data on the PSA and the DRSA is shown.

The excitation

allow also to deduce upper limits on the coupling of narrow resonances

in the mass range fi

= 2.2.. .2.8 GeV.

to the elastic channel

539

E Hinterberger et al. / Prog. Pan. Nucl. Phys. 50 (2003) 537-546

2

Experimental Technique

The EDDA experiment proton

scattering

concieved proceeds

[13, 14, 151 is designed

with a high energy

as an internal

target

during synchrotron

is measured

This technique

requires

Using the internal

targets and 5 pm diameter

beam.

as a function

in a multi-pass

with a polarized

cross sections

In phase 3, the polarization

correlation

by (i) coplanarity

- both in triggering

The EDDA detector the elastic pp channel of scintillating multianode

(right).

benefit

over many cycles.

operation

of COSY.

that the luminosities

are high

[13]. using 4 pm x 5 pm CHz fiber In phase 2, the analyzing

atomic

beam target

and a polarized

events of a given kinematic

These conditions

powers

and a unpolarized

ANN, Ass and AS,, were measured

parameters

double

function

proton

beam.

signature.

geometry

and a

Elastic events are kinematics

are employed - with different degrees

during off-line analysis. layers covering

30” to 150” in @,,, for

85 % of the full solid angle. The inner layers HELIX are composed

fibers which are helically

The direction

by averaging

large solid angle coverage in a cylindrical

of two cylindrical

at backward

Figure 1: Scheme of the EDDA detector target

Data collection

so that a full excitation

subtraction.

and in event identification

consists

and about

photomultipliers

[16]:

with the beam (cpi - cpz = 180”) and (ii) the elastic scattering

imposing tan 81 .tan 02 = 2m,cz/(2m,cz+TP). of stringency

To this end EDDA was

COSY

were measured

atomic beam target

(Fig. 1) provides

of the elastic proton-

a very stable and reproducable

of energy using a polarized

of energy using a polarized

range.

is obtained

atomic beam target

fast and efficient trigger on low multiplicity identified

accuracy

C fiber targets for background

as a function

The EDDA detector

technique,

COSY beam has the additional

differential

functions

in the cooler synchrotron

cycle. Statistical

recirculating

In phase 1, unpolarized

proton

experiment

excitation

over a wide energy

(and has demonstrated)

enough for measurements

An were measured

resolution

acceleration

in each acceleration

to measure

normal

wound in opposing angles.

directions

They are not required

(left) and its combination

to the accelerator

and connected

to 16channel

for measuring

spin-averaged

with the polarized

plane is denoted

y.

atomic

beam

540

E Hintcrherger et al. /Frog. Part. Nucl. Phys. 50 (2003) 537-546

cross sections

with a CHz fiber target,

polarized atomic beam target, scintillator

scintillating

by scintillator

scintillating

granularity

fibers, this provides

electron

current

electron

scattering.

alone.

Combined

traversing

of the fractional

the outer

light output

(by a factor of 5) than would be polar and azimuthal

with the spatial

resolution

with a la resolution

FWHM

angle

of the 2.5 mm

of less than 1 mm in the

Details are given in [17, 181.

as a function emanating

cross section

of momentum

measurements

conducting.

thin windows in the beam pipe.

located

electron current

The &electron

from the elastic Aluminum

Rel-

proton-

film in order to

scales as the energy deposited

updown

symmetrical

rate scales as the Rosenbluth

to the angular distribution

arrangement

Absolute

measured

into

were measured

cross section.

within 3 % for all beam energies.

with reference

monitor.

(i) the secondary

energy loss rate. The &electrons

in a left-right,

give the same relative normalization at 1455 MeV/c

and (ii) the J-electrons

to the restricted

0 = 40” using four silicon detectors

by measuring

were covered by a 20 pg/cm2

The secondary

the target fiber. It is proportional

was the luminosity

was accomplished

from the fiber target

The CHa fiber targets

make them electrically

is established

Analysis

The resulting

a vertex reconstruction

A crucial point of the differential ative normalization

FR close to the target are made from

much more accurately

1” and 1.5”, respectively.

X-, y- and z-direction.

methods

R. The semi-rings

bars and rings.

the angles of incidence

with the

The outer layers consist of 32

cross sections are designed so that each particle

possible on the basis of detector is about

spin observables

to the beam axis and which are read out at both ends.

a signal in two neighbouring

is used to determine

resolution

parallel semi-rings

fibers. The scintillator

layers produces

for measuring

as they provide for vertex reconstruction.

bars B which are running

They are surrounded

but are essential

at

behind The two

normalization

by Simon et al. [19]

with 1% total uncertainty. The polarized polarized permanent

hydrogen

monitored

hyperfine

state

beam target

atoms are prepared

sextupole

tinuously

atoms/cm2.

atomic

magnets

using a Breit-Rabi

units.

polarimeter.

yields a peak polarization

In the beam dump Preparing

a polarized

of 85 %, and an effective

location

is ~12 mm (FWHM).

holding field (1 mT) which can be chosen arbitrarily

The analyzing

power excitation

functions

during the deceleration

of the COSY beam.

cycle to cycle between

*Z and fy

[21]. Since the polarization

on the right side of Fig. 1. The

using an atomic beam source with dissociator,

and d-transition

The width at the target

a weak magnetic

[20] is shown schematically

The direction

during

density

of about

2.10”

is provided

the acceleration

spin flip correction the acceleration

can be achieved provided

and target

was ideally fulfilled during

This condition

beam in a pure

by

from cycle to cycle.

beam (time period -20 s) a high relative accuracy can be kept constant.

is con-

atomic

of the target polarization

a proper

is constant

the polarization

The spin direction

were taken not only during

thus allowing

of the target

target

cooled nozzle,

but also

was changed

from

of false asymmetries and deceleration

of the

the overlap between beam the measurements.

The

I? Hinterherger et al. /Prog. Part. Nucl. Phys. 50 (2003) 537-546

COSY accelerator region stayed was centered established

was adjusted

constant

during

such that the vertical acceleration

to angular

The spin correlation

parameters

a polarized

target.

of six possible between

and deceleration

on the much wider polarized with reference

fy.

The direction

directions

&x, fy,

The spin correlation

section from the spin-averaged the beam (L) or normal spin combination

beam position

target

and beam width

and the COSY

beam (FWHM

distributions

measured

at 1458 MeV/c

and fz.

polarization

In addition

parameters

yields characteristic

modulations

the deviation

protons

oriented

angle.

range. We took data during acceleration

and at nine evenly spaced flattop-momenta

statistical

This allows to cover the low {acceleration) accuracy.

extracted

The spin correlation

either by calculating

The overall normalization

EDDA analyzing

3 3.1

of the target

rate for each

in the (1 - 5) . 10z7/(cm2s) between

polarizations

[21, 231 which cancel the influence techniques.

Both methods

and beam polarizations

2.1 and

energy region with sufficient

as well as beam and target

x2 minimization

arc

of detector

yield consistent

is fixed with reference

to the

power data [15].

Differential Cross Sections functions

of the unpolarized

and the outer detector

differential

cross sections

were taken with CHz and C fiber

shell alone [14]. Four out of 28 excitation

functions

[14] are shown on

the left side of Fig. 2. On the basis of those new EDDA data and the data of the NN Program SATURNE

[24] Arndt

(2360 MeV/c) are solutions

3.2

to

Results

Excitation targets

parameters

count rate asymmetries

efficiencies to first order, or by standard results.

and high (flattop)

of the cross

With beam intensities

stored

we achieved luminosities

switched

longitudinal

The scattering

with the azimuthal

is

beam and

was regularly

ranging from 3 . IO9 to 1.5 . 10” protons

3.3 GeV/c.

calibration

from cycle to cycle to one

ANN, Ass and AWL describe

plane.

6 mm)

[22].

the beam polarization

(S) in the scattering

(FWHM

with a polarized

was switched

value for the spin of beam and target

(N) to or sideways

beam

in the target

12 mm). The absolute

ANN, Ass and A SL are measured

of the target

541

and coworkers

were able to extend

up to 2500 MeV (3300 MeV/c) from 1994. All excitation

their phase shift analysis

from 1600 MeV

which is shown as solid curves [6]. The dashed

functions

show a smooth

dependence

at

curves

on beam momentum.

Analyzing Powers

Analyzing

power excitation

functions

in the momentum

range 1.0 - 3.3 GeV/c

0.45 - 2.5 GeV) are shown on the right side of Fig. 2 and compared data are grouped

in (AQ = 4”, Ap = 30 MeV/c)

wide bins.

(kinetic

energy range

to recent phase shift solutions.

The dahed curves are calculated

The using

542

E Hinterberger r-“-‘-

-I-

et al. / Prog. Part. Nucl. Phys. 50 (2003) 537-546 1-

other experiments

1500

1000

2m

2500

3000

pbe, (McVW

Figure 2: Left: Differential 28 scattering

angles.

Right: Analyzing

cross section

The solid (dashed)

power excitation

- 2.5 GcV (pk,,=l.O

- 3.3 GeV/c).

the dashed curves are the solutions

the phase shift solution shift solution were included. solutions

3.3

excitation

functions

at four out of

curves are from the SM97 (SM94) phase shift analysis

functions

for elastic pp scattering

SAID SM97 from summer

trend of the excitations

but there arc still some systematic

SAID FAOO [7],

97 [S].

97. The solid curves represent

FAOO from fall 2000. In this analysis

[6].

in the kinetic energy range 0.45

The solid curves are recent phase shift solutions

SAID SM97 from summer

The general

for elastic pp scattering

a more recent phase

also the new analyzing

power data from EDDA

functions

by the recent phase shift

deviations

is reproduced

at higher momenta.

Spin-Correlation Parameters

The data analysis of phase 3 is almost finalixed.

Preliminary

ANN, Ass and Asr, arc shown in Fig. 3 in comparison solid) and the &clay-Geneva correlation

parameters

[12] (dashed

to phase shift predictions

line) analysis.

at SC,,, = 47.5” are shown.

data on the spin correlation

parameters

of SAID [7] (SMOO,

On the left excitation

Here, open and closed symbols

functions distinguish

of spin data

E Hinterberger et al. / Prog. Purt. Nucl. Phys. 50 (2003) 537-546

543

0.6

1

??

0.5 d

EDDA (prelimina

Jo.4 EDDA (preliminary)

$0

L I,,., ibo6’‘-’1500

0.2

,,,,I,

2ObO 2500 p (MeV/c)

Figure 3: Excitation

functions

(right) of spin correlation

parameters

distinguish

data points

during

angular distributions correlation

measured

at fixed energies

strikingly correlation

as observed

(DRSA)

80

, ,I 90

at Tp = 1800 McV of

On the left, closed (open)

acceleration)

of the COSY machine

of the COSY machine Previous

were mainly done at SATURNE

in the SATURNE

PSA solutions.

, ,

70

to phase shift predictions

line) analysis.

(during

and the flattop

cycle.

On the right

measurements

[24] (open symbols

at all energies.

of spin on the

However, we find values in the angular

data. before

above 800 MeV. The new data

It will be interesting

data on Ass will modify the PSA solutions.

amplitudes

60

[24] are shown as open symbols.

Ass has not been measured

with different

, ,, ,,,

with zero at all angles and do not confirm excursions

of our data to the world database scattering

[12] (dashed

our new data on ANN is consistent

for AsL more or less compatible

, 50

distributions

at the fixed energy Tp = 1800 MeV arc shown.

parameters

The observable

40

e,,. (deg)

at the flattop

the acceleration

right side). In comparison,

distributions

30

ANN, Ass , and AWL in comparison

cycle. On the right, data from SATURNE

points measured

20

= 47.5” (left) and angular

SAID [7] (SMOO, solid) and the Saclay-Geneva symbols

j,,

'3000

at &,.

,,, , ,

-0.41,

I ,

to see to what extent

the new spin

As a first step we found [25] that the addition

removes some of the ambiguities

found in [12].

disagree

in the direct reconstruction

of the

544

4

E Hinterberger et al. / Prog Part. Nucl. Phys. 50 (2003) 537-546

Upper Limits on Resonance Contributions

The excitation

functions

of the differential

dence for narrow resonances. resonances

Therefore,

have been deduced

is introduced

cross sections

matrix

s,,J

Here, rlL_resr6LJis the nonresonant

excitation

element

77LJc2i6u _

=

functions.

of a resonating

narrow

To this end a Breit-Wigner

partial

term

wave (L, J),

(1)

r E - ER + iI’/2’

amplitude,

Fe1 the partial

r-

elastic

width,

F the total

-1

“-IL 2500

Fer/F of hypothetical

r iC2i@Rt)L,re’

background

0.5

powers have shown no evi-

upper limits for the elasticities

from the smooth

into the scattering

and analyzing

2600

2700

2800

2900

3000

3100

p (MeV/c)

Figure 4: Differential

cross sections

The best fit, with (without) excluded

a ‘So resonance

with 99% CL by the data

nonresonant width,

at two out of 28 scattering

background

resonant functions.

energy

and nonresonant The elasticity

continuum.

determines

The dotted

PSA analysis background

has been tested

quantitatively

a null-hypothesis

excursion

in the PSA is slowly varying the resonance

data

and the compatibility

of a narrow

with energy parameters

as compared

to the resonance

width

in a partial

wave was tested

increasing

the partial

with the data

dependence to be tested.

ER, r and 4~ were varied systematically

by gradually

by a special

have been used for

ER = 2200.. .2800 MeV, I? = 10.. . 100 MeV and & = 0”. . . 360”. The hypothesis of a resonance

the

and the nonresonant

resonance

[26]. This can be done as long as the energy

between

in the excitation

have been fitted

along Ref. [6]. The fitted phase shift parameters

amplitudes

line shows the

The interference

the size of a resonance

the EDDA

= 0.043,

of the resonance.

Fd/I’ is a measure of the coupling between the resonance

the nonresonant

test calculations

line.

and 4~ the phase of the resonance.

In order to establish

energy dependent

by the PSA in the presence

amplitudes

to PSA solutions.

at E R = 2.7 GeV, I? = 50 MeV and I’&’

is shown as the solid (dashed)

as described

ER the resonance

angles in comparison

assumed In the

in the range of the existence

elastic width Id until

E Hinterberger et al. / Prog. Part. Nucl. Phys. SO (2003) 537-546

the resonance

was excluded

For the unknown corresponding Iel/I

withh 99% confidence

phase 4s the value giving the largest

to a ‘So-resonance

predicted

for the five lowest uncoupled

partial

3P1 and 0.05 for 3F3. The EDDA data, exclude a sizeablc coupling parameter

5

level (CL) by a x*-test I&

excluded

based on the EDDA data. was chosen.

An example

in Ref. [27] - is shown in Fig. 4. Typical

-.

upper limits of

waves are 0.08 for ‘So, 0.04 for *Dz, 0.10 for 3Ps, 0.03 for i.e. the differential

of resonances,

like dibaryons,

cross section

and analyzing

to the elastic proton-proton

power data, channel

in the

space covered.

Summary

and Conclusions

The principle of measuring

excitation

functions

with internal

targets

tion works well. On the basis of the new EDDA data on du/dR have been extended polarization

from 1600 to 2500 MeV. The analyzing

standard

with existing excitation

545

in the GeV region.

PSA solutions

functions

the energy dependent power excitation

The spin correlation

will have a major

impact

during acceleration

and decelera-

PSA solutions

functions

provide a new

data on Ass which disagree

on forthcoming

allow to deduce sharp upper limits for the occurence

[6]

PSA solutions.

strikingly

The smooth

of narrow resonances

in the

elastic channel. The excellent to Prof. R. Arndt

support

by the COSY accelerator

for providing

team is warmly acknowledged.

We are indebted

us and helping with the PSA-software.

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