Hypernuclear experiments at K1.1 in future Tohoku University H. Tamura
IX International Conference on Hypernuclear and Strange Particle Physics
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Transcript of IX International Conference on Hypernuclear and Strange Particle Physics
IX International Conference onHypernuclear and Strange Particle Physics
Johannes Gutenberg-UniversitätMainz, October 10 - 14, 2006
Marco MaggioraDipartimento di Fisica ``A. Avogadro'' and INFN - Torino, Italy
SPIN OBSERVABLES IN BARYON-BARYON INTERACTIONS
@ DISTO
DISTO @ Saturne: polarised proton beam up to T = 2.9 Gev
Acceptance:
• 2-cm thick unpolarised LH2 target• S170 magnet (<14.7 KGauss, = 120 , = 20)• semi-cylindrical 1mm-square scintillating fibers triplets inside magnet• MWPC planar triplets outside magnet• scintillator hodoscopes vertically and horizontally segmented• scintillator hodoscopes as polarimeter slabs• doped water Cerenkov counters
Á § :±
µ § ±
2.40
2.34
1.79
1.58
Detected Prongs Reaction p
sthr
~pp ! pK ~ pK p¼¡
pK p¼¡ ~pp ! pK ~
~pp ! pK ¤
~pp ! pK ¤
pK p¼¡ ¼ ¼
pK ¼ ¼¡ ¡ ¼
pK ¼¡ p ¼ ¼¡
pK ¼ ¼¡ ¡ ¼
pK p¼¡ ¼
pK ¼¡ por ¼ ¼¡
~ ° ! p¼¡ °
GOAL: first exclusive (kinematically complete) measurements with a polarised beam for
Hyperon production @ DISTO
Hyperon events’ topology – Data @ 2.94 , 3.31 and 3.67 GeV
complete reconstruction
missing
0 and/or missing
pK
pK
pK
pK
• DECAY VERTEX:
• REACTION VERTEX: pK
1 positive track1 negative track
2 positives tracks
~ ! p¼¡
Spin observables
n ~pB£ ~pj~pB£ ~p j
Depolarisation
Analysing power
d¾if d¾P BS¤
nB y
DY Y ¡d¾"" d¾##¢
¡¡d¾"# d¾#"¢
d¾"" d¾## d¾"# d¾#"
AY ¡d¾"" d¾"#¢
¡¡d¾#" d¾##¢
d¾"" d¾"# d¾#" d¾##
Y dependence on the spin of the proton from the beam~Sp
AY d¾SB "¡ d¾SB #
d¾SB " d¾SB #
transfer of the transverse component of to ~Sp ~SY
DY Y d¾N SF ¡ d¾SF
d¾N SF d¾SF
Spin observables: experimental asymmetries
NPB "¡ NPB #
NPB " N PB # ¡N "" N "#¢
¡¡N#" N ##¢
N "" N "# N#" N ## AY PB
Self-analysing weak decay:
® : § :N µ¤ N P ® µ¤
NN SF ¡ NSF
NN SF N SF ¡N "" N ##¢
¡¡N "# N #"¢
N "" N ## N "# N #" DY Y PBcosÁ
= 15.5
most of events are acquired at high cos()
n ² nB Á
pp elastic scattering: ping pong trigger
Elastic proton-proton scattering p" p ! pp
pp elastic scattering acquired for some spills every run beam polarisation continuos evaluation
data validation
" AY PB
rcross q rL
rR
" r¡ r
rL N
PB "L
NPB #L
rR N
PB "R
NPB #R
L and R on one side only free from L/R acceptance
PB↑and PB
↓ simultaneously acquired PB PB
" PB#
¾" »
Poor data from literatureIn particular @ 3.67 GeV/c
Errors for spin obsdo not include
contribution from
¾PB » : ¥
¾PB
Hyperon production : event reconstruction
Unrefitted M- p Reffitted MpK
.
DYY evaluation: accounting for hyperon contamination
1. select exclusive and ‘s from 0 decay through a MpK cut
2. evaluate separately and
3. estimate relative contaminations , the fraction of and 0 in each gate, evaluated throught fit functions integration in each gate.
Of course is
4. extract the corrected DYY values from the linear combinations:
1. no cos dependence ) direct evaluation of and 0 yealds
f ; ;
f i f i
DYY EVALUATION: 0.7 · |cos|· 1.
AY EVALUATION: 0.7 · |cos|· 1.
DY Y ~ ! ~ °DY Y
D Y Y f
DY Y f DY Y ~ ! ~ °
D Y Y f
DY Y f DY Y ~ ! ~ °
DYY @ 2.94 , 3.31 and 3.67 GeV/c – Exclusive Λ production
Exclusive Λ production:
1. DYY sizeable and negative2. smooth energy dependence
- 0.7 ≤ xF ≤ 0.9 ; 0. ≤ pT ≤ 750 Mev/c ; |cos φΛ| ≤ 0.7
Λ from decay:
1. DYY strongly different from the one of exclusive Λ
2. positive and negative values3. smooth energy dependence
DYY @ 2.94 , 3.31 and 3.67 GeV/c – Λ from Σ0 decay
~ ! ~ °
- 0.7 ≤ xF ≤ 0.9 ; 0. ≤ pT ≤ 750 Mev/c ; |cos φΛ| ≤ 0.7
AY @ 2.94 , 3.31 and 3.67 GeV/c – Exclusive Λ production
Exclusive Λ production:
1. effects less important vs DYY
2. smooth energy dependence
- 0.7 ≤ xF ≤ 0.9 ; 0. ≤ pT ≤ 750 Mev/c ; |cos φΛ| ≤ 0.7
Λ from decay:
1. differences from exclusive Λ AY
2. smooth energy dependence
AY @ 2.94 , 3.31 and 3.67 GeV/c – Λ from Σ0 decay
~ ! ~ °
- 0.7 ≤ xF ≤ 0.9 ; 0. ≤ pT ≤ 750 Mev/c ; |cos φΛ| ≤ 0.7
DYY @ 2.94 , 3.31 and 3.67 GeV/c – Exclusive Λ production
Inclusive Λ production:
• high energy ) DYY > 0
Exclusive Λ production:
• lower energy ) DYY < 0
Exclusive Λ from Σ0 decay:
• lower energy ) ≠ DYY
Different reaction mechanism?
FIRST EXCLUSIVE DATA AVAILABLE,FIRST DATA IN THE TFR (xF < 0 )
DYY theoretical predictions – Exclusive Λ production
Polarisation transfer mechanism:
DIRECT FUSION MODEL[1]
DYY SIZEABLE AND POSITIVE
[1] C. Boros and Liang Zuo-tang, Phys. Rev. D53 (1996) 2279
.~Sp k ~S DY Y »
DYY theoretical predictions – Exclusive Λ production
LAGET’S OBE MODEL[1]
NEGATIVE DYY CAN BE INTERPRETED
[1] J. M. Laget, Phys. Lett. B259 (1991) 24.
xF << 0 (TFR):DNN = 0
xF >> 0 (BFR):kaon ) DNN = -1pion ) DNN = +1
Conclusions
• first exclusive data available• first data in the TFR (xF < 0 ) region• first data for the exclusive selection of the Λ from Σ0 decay
Exclusive Λ production:
1. DYY sizeable and negative2. smooth energy dependence3. DYY not easily interpreted in a
quark-model framework4. OBE approach can account
with FSI for DYY < 0
Λ from decay:
1. DYY strongly different from the one of exclusive Λ
2. positive and negative values3. smooth energy dependence
~ ! ~ °
Both Λ production:
1. effects less important vs DYY
2. smooth energy dependence
Question time
QUESTION TIME
4body event reconstruction @ DISTO
pattern reconstruction and track fitting iteration: pattern recognition provides candidate for the fitting stage; input is the 12D coordinates vector
track fitting: 5D parameter vector (x,y): coordinates of the intersection point with z = 0a: inclination of track at z = 0starting angle in (x-z) plane : inverse momentum perpendicolar to B
detector coordinated depend smootly on all parameters
pxz ppx pz
~p
~x
4body event reconstruction @ DISTO
track fitting by lookup table: goal is inverting in
look-up table:5D lattice that provide for tracks track coordinates
consist in linear interpolation of the lattice toobtain
2 minimisation:F inversion is performed minimizing:
iteration stops if do not change to nearest grid point
~p G~x
~p
~x F ~p
F ~p~x
Âmin
2
4 P
j 2fvalid coordsg
µxm
j ¡ xj ~p¾j
¶3
5
min ~p ~x
4body event reconstruction @ DISTO
kinematically constrained refit:
1. global 4 tracks – 2 vertices refit
2. same approach, inversion of
3. more complex parameter 18D • 3 (x12, y12, z12) for the reaction vertex• six (1, a1, pxz,1, 2, a2, pxz,2 to describe momenta of the
two track emerging from the reaction vertex• 3 (x12, y12, z12) for decay vertex• six (3, a3, pxz,3, 4, a4, pxz,4 to describe momenta of the
two track emerging from the decay vertex
4. 4 degrees of freedom are constrained kinematically
~x F ~p~p
Hyperon production: reconstruction @ DISTO
kinematic constrains:
1. reconstructed momentun parallel to the joiner of the reaction and decay verteces ) 2 parameters
2. reconstructed M- p at decay vertex is M 1.115 GeV/c2 ) 1 parameter
3. M4B= 0 ( or ) or M4B= M ( ) ) 1 parameter
14D
~pp ! pK ~ ~pp ! pK ~
~pp ! pK ~ ¤
~p
Âmin
2
4d ~vreac;~bzr eac¾
d
P
j 2valid coordsg
µxm
j ¡ xj ~pcon¾j
¶3
5
min“soft” constraint on reaction vertex along the beam
Hyperon production: event selection
One of the most effective cuts in event selection is the kinematically constrained refit itself!
1. M- p = M
2.
3. M4B = 0 or M4B = M
Additional cuts:
1. veto
2. |
| < 0.15 rad, decay proton momentun in LF
3. p ID for positive track from decay vertex
4. p
< 1 GeV/c ) missing a at most
5. |vz| < 3.5 cm ) Klegecell veto
~p k ~VRVD
Kinematic region restricted to:
-0.7 ≤ xF ≤ 0.9pT ≤ 750 MeV/c
|cos | < 0.7
Particle identification @ DISTO
particle identication: iterative process for tagging candidates
+ veto: pp+- is
major background
Particle identification @ DISTO
particle identication: combined Cerenkon and hodoscopes tagging
very small + contaminationin hyperon sample
Spin observables: inferring polarisation
Self-analysing weak decay:
NU R¡ N µ¤d µ¤
P ®
NU¡ NDNU ND
P ";#
sign of PB
® : § :N µ¤ N P ® µ¤
Geometrical interpretation of AN:
L ";L # R#;R"Á ! Á ¼N "
L N #R ;N #
L N "R
ALN
PB
N "L ¡ N#
LN "
L N#L
PB
N "L ¡ N "
RN "
L N "R
DYY theoretical predictions – Exclusive Λ production
LAGET’S OBE MODEL[1]
NEGATIVE DYY CAN BE INTERPRETED
[1] J. M. Laget, Phys. Lett. B259 (1991) 24.