Kinematics of  + n   p   0  p reaction Susumu Oda 2007/04/10-19

Motivation TAPS, PRL 94, (2005) –  A   X   0  X

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 (  + n   p) and decays (    0 ,  0  2  ) are assumed. ++ n p     00 More omega mesons might be produced at forward direction (high momentum in lab. frame). backwardforward

P lab  + =1100MeV/c Momentum of omega (MeV/c) Polar angle (rad) red: proton green: omega blue: pizero Gamma energy (MeV) black: from omega blue and red: from pizero green: lowest energy gamma Polar angle (rad) black: from omega blue 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) ForwardBackward

P lab  + =1200MeV/c Most interested region

P lab  + =1400MeV/c Most interested region

P lab  + =1600MeV/c Most interested region

P lab  + =1800MeV/c Most interested region

P lab  + =2000MeV/c Most interested region

Summary To detect all three photons from omega, calorimeter with large solid angle (0<  <~120deg) is necessary. –FOREST?? To detect recoil protons for background rejection, magnetic spectrometer 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 (LD 2, Nb, etc.). –Vertex determination. Mass resolution? Production cross section vs beam momentum? Final state interaction?   2  0  4  measurement at the same time??

Background and trigger There is huge  + n   0 p background. –3 gamma coincidence is necessary. >=3 gamma background. –2  0  4  (  +  0  p2  0,   2  0, no  partner for  0 mass in the acceptance?) –   3  0  6  (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, (2001) –Studying the omega mass in-medium in gamma+A  pi0gamma+X reactions PRL 94, (2005) –Observation of In-Medium Modifications of the omega Meson

JAM simulation Projectile : pi+ Target : neutron Impact parameter : b=0-1.5fm, b 2 type Number of events : 1 million Other parameters –mstc(8)=0 –mstc(156)=1 Events which have particles from omega mesons are recorded. omega  pi0gamma decay mode was very tiny fraction. (bug??)

P lab  + =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  + n   p reaction  cutoff ? 

P lab  + =1.1GeV/c Reaction in this region is possible with the beam energy. Bug??

P lab  + =1.2GeV/c Reaction in this region is possible with the beam energy. Bug??

P lab  + =1.3GeV/c Reaction in this region is possible with the beam energy. Bug??

P lab  + =1.4GeV/c Reaction in this region is possible with the beam energy. Bug??

P lab  + =1.45GeV/c Reaction in this region is possible with the beam energy. Bug??

P lab  + =1.5GeV/c Reaction in this region is possible with the beam energy. Bug??

P lab  + =1.55GeV/c Reaction in this region is possible with the beam energy. Bug??

P lab  + =1.6GeV/c Reaction in this region is possible with the beam energy. Bug??

P lab  + =1.65GeV/c

P lab  + =1.7GeV/c

P lab  + =1.75GeV/c

P lab  + =1.8GeV/c  n   n channel is opened.

P lab  + =1.85GeV/c

P lab  + =1.9GeV/c

P lab  + =2GeV/c

P lab  + =2.5GeV/c

P lab  + =3GeV/c

P lab  + =5GeV/c

Problem of angular distribution from JAM The behavior of the following resonance around plab= GeV/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- strange 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 target Proton momentum (GeV/c) Plab  +=1.4GeV/c Plab  +=1.7GeV/c Plab  +=1.6GeV/c Black: all Red: 92, string Green: 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 P lab  + =1.7GeV/c Proton momentum (GeV/c) Proton polar angle (rad)

2H target P lab  + =1.7GeV/c Proton momentum (GeV/c) Proton polar angle (rad)

2H target P lab  + =1.7GeV/c K4(i).EQ.0 (original proton) rejection Proton momentum (GeV/c) Proton polar angle (rad)

12C target P lab  + =1.7GeV/c Proton momentum (GeV/c) Proton polar angle (rad)

12C target P lab  + =1.7GeV/c K4(i).EQ.0 (original proton) rejection Proton momentum (GeV/c) Proton polar angle (rad)

High pT proton tag P lab  + =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 event pT>1.5GeV/c && theta<0.1rad

n 2H 12C 92Nb Red : high pT proton tagged event pT>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 md.htmlhttp://tonic.physics.sunysb.edu/program/rq md.html Target and projectile must be nuclei. For the UrQMD, target and projectile must also be nuclei.

Isospin symmetry Since isospins of  + n   p reaction and  - p   n reaction are symmetric, the cross sections should be almost the same. A reference of  - p   n reaction is PRD14, 28 (1975). –The angular distribution was isotropic in CM.

Calorimeter?? TAPS/CB ELSA? Tohoku-LNS FOREST? KEK E246, 768CsI, 75% of 4pi –Nucl.Instrum.Meth. A494 (2002)