Pisa, INFN, October 21, 2003 Dmitry Naumov, LNP JINR [email protected] Spin Physics in NOMAD OUTLINE 1.Spin Problem of the Proton … for Pedestrians

Pisa, INFN, October 21, 2003

Dmitry Naumov, LNP JINR [email protected]

Spin Physics in NOMAD

OUTLINE

1. Spin Problem of the Proton …for Pedestrians How to attack the problem? Why strange hyperons? Strange Particles Production

2. Other Spin Phenomena

1. NOMAD: experimental Observations and Analysis Procedure

2. Theoretical Description and Open Questions

3. Conclusions

Introduction

Data analysis



Hyperon's Production and Polarization in Neutrino Nucleon Interactions

OUTLINE





3. Conclusions

Introduction

Data analysis



Spin Problem of the Proton … for Pedestrians

N

S

Spin being a relativistic object is qualitatively presented as a rotation of point-like particle…

…circular charge flow is equivalent to a current circuit, thus a particle should have a magnetic moment

Can we understand hadron’s magnetic moments which are bound states of u,d,s,… quarks?

Yes! 1. Let us build QM wave functions of

hadrons in terms of quarks2. Given magnetic moment of each

quark provides us an estimationof magnetic moment of a hadron

3. Compare to the data



Building SU(6)=SU(3)F x SU(2)S non relativisticwave functions of octet baryons:

p, n, +,0, -, 0, 0, -

Cyclic permutations…)



q = eq/2mq• eq is quark

charge• mq is quark

mass q is quark spin

operatorTaking mu = md = 336 MeV, ms = 510 MeV we can reasonable well describe the data:

SU(6) predictionMagnetic moment formula value experiment Exp/SU(6)

11.02810.910.0041.12 0.020.87 0.011.33 0.061.05 0.12

Magnetic moment of a baryon (B) can be computed as:

(B) = <B|B|B>

QM operator of the hadron’s magnetic moment reads: B = q q q,



Thus we can conclude that a non relativistic SU(6) model is adequate to describe the baryons magnetic moments through magnetic moments (proportional to the spin) of constituents quarks.

It is natural to ask: “what is the quark’s contribution to the Proton Spin?”



1. Evidence for point-like partons in the proton came from late 60s from SLAC e-p scattering.

2. R. Feynman formulated quark-parton model (QPM) of proton.

3. Gell-Mann created Quantum Color Dynamics (QCD) theory describing interactions between partons.

How proton is made? …quarks, kinematics and all that

k = (E,k) k’ = (E’,k’)Kinematic variables:

In QPM x is a fraction of the proton momentum



Deep inelastic cross-section is expressed via:

Proton structure function

Quark (gluon) distributions in QPMF1,F2 unpolarized

g1,g2 polarizedq(x), G(x) unpolarizedq(x),G(x), polarized

Longitudinally polarized leptons off longitudinally polarized nucleon are to probe spin structure of the nucleon:

g1(x,Q2) = ½ i e2i q(x)

Γ1

ep=∫0

1

dxg1ep

Experimentallymeasured: … known from hyperon decays

QCD corrections

= [1/12 (u-d) + 1/36(u+d-2s)]Cns

+ 1/9(u+d+s)Cs

…proton spin carried by quarks



Model independent Bjorken Sum Rule reads

Corrections:

QCD

Final target mass

Higher twist effects

Theory

Experiment 4% difference and well agrees within errors

Bjorken Sum Rule is OK!

Ellis-Jaffe Sum Rule (assuming s=0 and exact SU(3)) is violated…

Quark’s contribution to the Proton Spin

u+d+s = 0.27 0.04Naïve SU(6) gives:up = 4/3,

dp =-1/3, with u+d+s = 1sp = 0

Ellis-Jaffe expected: u+d+s = 0.579

Theory Experiment

…if G=0



A.Efremov, O.Teryaev.G.Altarelli, G.Ross. R.Carlitz,J.Collins,A.Mueller

showed that a possible gluon polarization gives:

q q - s/(2) G

Proton Spin Sum Rule:

½ = ½(u+d+s)+orbital momentum of partons+G

G=2 is enough to explain the datawith s=0 and u+d+s = 0.27…

Important questions:

1. Are gluons polarized?

1. Are strange (and sea) quarks polarized?

1. Is there a spin problem for hyperons?

“Prompt” measurement in (anti) neutrino (quasi)elastic scattering, strange hyperons polarization

Today COMPASS and HERMES attack G problem



s can be measured directly in (anti)neutrino(quasi) elastic scattering…

(by W.Alberico,S.Bilenky, C.Guinti)

This is challenging experimentally!

Strong force in 0- channel (,)

Negative proton strangeness should give a negative Lambda polarization in target fragmentation region

Polarization in DIS is sensitive indirect tool to probe s

Expected spin anti-correlation

J.Ellis, et al. suggested a qualitativemodel for negative strangeness in the proton



R.L.Jaffe suggested to measure polarization in the quark (current) fragmentation region.…if spin problem for proton then on the same foot spin problem for and other hyperons.

Naïve SU(6) predicts:u=d=0 s=1Spin Problem for predicts:u=d-0.2

Contributions from * and are of great importance:

Yields of strange hadrons andresonances has to be measured

polarization is being measured in:

1. e+e- at Z0 pole (LEP)2. Lepton nucleon DIS (E665,HERMES,COMPASS)3. (anti) neutrino nucleon DIS(old bubble chambers,

NOMAD)

Why ?p- weak decay provides information on polarization vector



Parity conservation forbids to produce longitudinallypolarized Lambda hyperons if beam or target areunpolarized. However Lambda hyperons can be transversally polarized(orthogonal to the production plane).

Unpolarized hadron hadron DIS Transverse polarization in HERMES

No transverse polarization found in old bubble chambers experiments No transverse polarization found in e+e- at Z0 pole




OUTLINE





3. Conclusions

Introduction

Data analysis




OUTLINE





3. Conclusions

Introduction

Data analysis



Why Neutrinos?

1. are naturally polarized particles2. interact with left handed quarks and right handed anti-quarks3. interact with quarks and anti-quarks of specific flavor

Neutrinos

Thus…Neutrino beams are clean and power tools for the Spin Physics



A (short) history of neutrino detectors

Anti-+p e++n

e++e-

15 s after: n+Cd+...

Reactor anti-Neutrino detection byReines and Cowan (1953)



A (short) history of neutrino detectorsNeutrinos come to CERN

CDHS

CHARM

CHARMII

BEBCCHORUS

NOMAD





NOMAD had wide neutrino beam mainly madeof muon neutrinos

NOMAD simulation chain



V0 Mass resolution

V0 yields (in %) Yields in data are 40-60% below than default JETSET



V0 integral yields in NOMAD compared to previous measurements



V0 differential yields in NOMAD

KsLambda Anti Lambda

xF = 2pL/W*



Strange resonances in NOMAD

Resonance/V0 in data anddefault JETSET:Factor 1.5–2 difference

Resume:Before doing a polarizationAnalysis tune JETSET

After JETSET tuning MCis well describing strangeparticles in NOMAD ready for polarization study!

K*+

K*-

*+

*-

-

… by Artyom Chukanov (see his PhD)



Polarization Analysis



General Results polarization

General Results polarization_



Lambda Polarization Vector in Targetand “Current” Fragmentation Regions



Strong dependence on W2

Controversial theoretical descriptions at xF>0 …



Longitudinal Lambda Polarization – Theoretical Description

d

d

uu

d

du

d

s

u

s

_q

q

q_

q_

J.Ellis et al. model

Current direction

Negatively polarized

d

d

u



Spin transfer from: a) quark fragmentation

In SU(6) model In Burkhardt-Jaffe model

b) Di-quark fragmentation J.Ellis et al. model SU(6) model

c) heavier strange hyperons decays

Simulation chain:JETSET7.4 with NOMAD tuned parameters LEPTO6.1 (a bug corrected): adequately describes all unpolarizeddistributions in the NOMAD data















qq q

Rank from diquark

Rank from quark

Tagging scheme for a hyperonWhich contains:

Rqq=1 (A)

Rqq1 & Rq1 (B)

Rq=1 (A)

Rq1 & Rqq1 (B)

Remnant diquark

Struck quark



Conclusion:

Current energies of all experiments in game today are too low to access quark fragmentation to hyperons…

The diquark fragmentation is dominant



Fixing free parameters of the model



Compare to NOMAD data: Absolute value OK Functional Dependencies OK Proton/neutron targets No



Compare to HERMES (ep @27.5 GeV)

Compare to E665 (p @470 GeV)

Small statistics yet…

…Waiting new data byCOMPAS, HERMES,NOMAD



Transverse Polarization



Transverse Polarization



d

d

ud

uud

u

ud

u

u

q_q

d

u

u

q_q

q

q_

d

u

u

q_

q q_

q

L

Sz

s

s_

PT

PT

A qualitative picture for polarization vs PT



Before my conclusions…

Starting from a hypothetical particle by Pauli, passing through an almost undetectable particle by Bethe and Pierls nowdays neutrinos provide a precise and powerful tool for Particle physics.

NOMAD worked on:1. Neutrino oscillation exclusion

region2. Strange particles production

and polarization3. Charm particles production,

mc measurement4. Diffractive physics5. Bose-Einstein Correlations 6. Many Others…

NOMAD is still working on:1. Sin W measurement2. Quasi Elastic cross

section and MA measurement

3. K* spin alignment

4. Strange Particles and Spin Physics in Neutral Currents (Z0 boson exchange)

5. Penta Quark Search

by Vladimir Lyubushkin

by Artyom Chukanov



Conclusions1. Measurement of hyperon’s and meson’s yields

is a milestone for Monte Carlo generators tuning…

2. Spin Problem of the Proton is still not resolved finally while much more better understood today. 1. COMPAS (CERN) and HERMES (DESY) attack

this problem 2. NOMAD data favors that s quarks in the

nucleon sea are negatively polarized… shadowing the valence quark spin of the nucleon

3. The transverse polarization of strange hyperons is clearly observed in NOMAD (for the first time in neutrino experiments).1. the polarization originates in the string

fragmentation2. There is no good theory of this polarization

4. Many other exciting and top level things can be done within neutrino detector like the NOMAD and some of them are under investigation

Documents

Pisa, INFN, October 21, 2003 Dmitry Naumov, LNP JINR [email protected] Spin Physics in NOMAD OUTLINE 1.Spin Problem of the Proton … for Pedestrians