Kinematics of +np0p reaction

Susumu Oda

2007/04/10-19

Motivation

• TAPS, PRL 94, 192303 (2005)– AX0X

Condition of kinematics in vacuum• + beam is assumed.

• Neutron is target.

• Beam momentum range is 1087(threshold) – 1800(?) MeV/c.– J-PARC K1.8 beam line.

• Isotropic production (+np) and decays (0, 02) are assumed.

+ np

0

More omega mesons might be produced at forward direction (high momentum in lab. frame).

backward forward

Plab+=1100MeV/c

Momentum of omega (MeV/c)

Polar angle (rad)red: protongreen: omegablue: pizero

Gamma energy (MeV)black: from omegablue and red: from pizero

green: lowest energy gamma

Polar angle (rad)black: from omegablue and red: from pizero

purple: most backward gamma

X: Momentum of omega (MeV/c)Y: Energy of lowest energy gamma (MeV)

X: Momentum of omega (MeV/c)Y: Polar angle of most backward gamma (rad)

X: Momentum of omega (MeV/c)Y: Polar angle of proton (rad)

Forward Backward

Plab+=1200MeV/c

Most interested region

Plab+=1400MeV/c

Most interested region

Plab+=1600MeV/c

Most interested region

Plab+=1800MeV/c

Most interested region

Plab+=2000MeV/c

Most interested region

Summary• To detect all three photons from omega, calorimeter with large

solid angle (0<<~120deg) is necessary. – FOREST??

• http://www.lns.tohoku.ac.jp/~hadron/• To detect recoil protons for background rejection, magnetic spe

ctrometer with large solid angle and good momentum resolution is necessary.– SKS? (aperture?)– 2D position detector is a substitute.

• 2MeV/c 1 mrad 300 m/30cm• GEM?

– Final state interaction of proton in nucleus.– Fermi motion of neutron target (LD2, Nb, etc.).– Vertex determination.

• Mass resolution?• Production cross section vs beam momentum?• Final state interaction?

• 204measurement at the same time??

Background and trigger

• There is huge +n0p background.– 3 gamma coincidence is necessary.

• >=3 gamma background.– 204(+0p20, 20, no partner for 0 mass in the

acceptance?)– 306(low mass in offline analysis, many hits online

rejection?).– etc.

• 1 charged track online (offline?) coincidence (+vertex extrapolation from XY-XY measurement?) – Multi charged track veto?

• Interaction rate?• Accidental coincidence rate?

– With large acceptance for final state interaction

Reference

• Eur. Phys. J. A 11, 95-103 (2001)– Studying the omega mass in-medium in gam

ma+Api0gamma+X reactions

• PRL 94, 192303 (2005)– Observation of In-Medium Modifications of the

omega Meson

JAM simulation

• http://quark.phy.bnl.gov/~ynara/jam/

• Projectile : pi+• Target : neutron• Impact parameter : b=0-1.5fm, b2 type• Number of events : 1 million• Other parameters

– mstc(8)=0– mstc(156)=1

• Events which have particles from omega mesons are recorded.

• omegapi0gamma decay mode was very tiny fraction. (bug??)

Plab+=1.8GeV/c

omega mass (GeV)

omega polar angle in lab frame (rad)

omega momentum in lab frame (GeV)

X: omega momentum in lab frame (GeV)Y: omega polar angle in lab frame (rad)

Red region is +np reaction

cutoff ?

Plab+=1.1GeV/c

Reaction in this region is possiblewith the beam energy. Bug??

Plab+=1.2GeV/c

Reaction in this region is possiblewith the beam energy. Bug??

Plab+=1.3GeV/c

Reaction in this region is possiblewith the beam energy. Bug??

Plab+=1.4GeV/c

Reaction in this region is possiblewith the beam energy. Bug??

Plab+=1.45GeV/c

Reaction in this region is possiblewith the beam energy. Bug??

Plab+=1.5GeV/c

Reaction in this region is possiblewith the beam energy. Bug??

Plab+=1.55GeV/c

Reaction in this region is possiblewith the beam energy. Bug??

Plab+=1.6GeV/c

Reaction in this region is possiblewith the beam energy. Bug??

Plab+=1.65GeV/c

Plab+=1.7GeV/c

Plab+=1.75GeV/c

Plab+=1.8GeV/c

nn channel is opened.

Plab+=1.85GeV/c

Plab+=1.9GeV/c

Plab+=2GeV/c

Plab+=2.5GeV/c

Plab+=3GeV/c

Plab+=5GeV/c

Problem of angular distribution from JAM

• The behavior of the following resonance around plab=1.4-1.7GeV/c is strange.– KF=32124 N(1720)+– KF=12128 N(1990)+

– Plab=1.5GeV/c is sqrt(s)=1.932GeV– Plab=1.55GeV/c is sqrt(s)=1.956GeV– Plab=1.642GeV/c is sqrt(s)=2.0GeV– parc(51) : (D=2.0GeV/c2) minimum mass of string for non-strang

e baryons.– parc(65) : (D=0.7GeV/c2) minimum value for the invariant mass

of the excited meson-like string system in a hadron-hadron interaction.

Neutron targetProton momentum (GeV/

c)

Plab+=1.4GeV/c

Plab+=1.7GeV/c

Plab+=1.6GeV/c

Black: allRed: 92, stringGreen: 2214, Delta+ 3/2+Blue: 12128, N(1990)+ 7/2+Yellow: 12212, N(1440)+ 1/2+Magenta: 32124, N(1720) 3/2+

Proton 2D plots

n target Plab+=1.7GeV/cP

roto

n m

om

entu

m (

GeV

/c)

Proton polar angle (rad)

2H target Plab+=1.7GeV/cP

roto

n m

om

entu

m (

GeV

/c)

Proton polar angle (rad)

2H target Plab+=1.7GeV/cK4(i).EQ.0 (original proton) rejection

Pro

ton

mo

men

tum

(G

eV/c

)

Proton polar angle (rad)

12C target Plab+=1.7GeV/cP

roto

n m

om

entu

m (

GeV

/c)

Proton polar angle (rad)

12C target Plab+=1.7GeV/cK4(i).EQ.0 (original proton) rejection

Pro

ton

mo

men

tum

(G

eV/c

)

Proton polar angle (rad)

High pT proton tag

• Plab+=1.7GeV/c

• omega event

• pT>1.5GeV/c && theta<0.1rad is used.– pT>1.3GeV/c && theta<0.5rad is better??

• Done by SKS??

n

2H

12C

92Nb

Red : high pT proton tagged eventpT>1.5GeV/c && theta<0.1rad

n

2H

12C

92Nb

Red : high pT proton tagged eventpT>1.3GeV/c && theta<0.5rad

Issue

• How to separate beam pions and recoil protons?

• 2pizero event rate??

• Cross section by other simulation codes.

• Mass resolution of calorimeter??

RQMD

• http://tonic.physics.sunysb.edu/program/rqmd.html

• Target and projectile must be nuclei.

• For the UrQMD, target and projectile must also be nuclei.

Isospin symmetry

• Since isospins of +np reaction and -pn reaction are symmetric, the cross sections should be almost the same.

• A reference of -pn reaction is PRD14, 28 (1975).– The angular distribution wa

s isotropic in CM.

Calorimeter??

• TAPS/CB ELSA?• Tohoku-LNS FORES

T?• KEK E246, 768CsI, 7

5% of 4pi– Nucl.Instrum.Meth. A4

94 (2002) 318-325