My involvement in the Spin and Parity Programs at JLab, and beyond

Introduction — nucleon structure and electron scatteringThree types of Deep Inelastic Scattering (DIS) and some completed/future experiments at JLabResearch opportunitiesWhat does it take to achieve a Ph.D.?

Xiaochao ZhengOctober 1, 2010

d2

d dE '= Mott [F1Q

2 ,F 2 Q2 ,]

Exploring Nucleon Structure Using EM Probe

The cross section:

For point­like target

k=E,k

k '=E',k '

q= , q

W 2=P ' 2

Q 2=−q 2

P=M,0

➔ Elastic – the nucleus appears as a rigid body 

➔ Quasi­elastic – individual nucleon appears as a rigid body; nucleus = incoherent sum of nucleons

(quasi-) elastic — rigid body

Q2=2MT

Q2=2MN

Exploring Nucleon Structure Using EM Probe (cont.)

Nucleon form factors well measured

1W2GeV

1W2GeV

➔ Resonance region – quarks inside the nucleon react coherently

resonances — certain excitations of the internal structure

Exploring Nucleon Structure Using EM Probe (cont.)

For resonances, typically use phenomenological models to study N-N* transition amplitudes and polarizations.

Deep Inelastic Scattering (DIS):Quarks start to react incoherentlyStart to see constituents of the nucleon

Exploring Nucleon Structure Using EM Probe (cont.)

For DIS, perturbation theory starts to work, can test perturbative QCD.

Current Knowledge of Nucleon Unpolarized Structure                                                                      (after 40 years of study)     

● Phys. Rev. D 66, 010001 (2002)

d2

d dE '= Mott [F1Q

2 ,F 2 Q2 ,]

After 39 years of DIS experiments, the unpolarized structure of the nucleon is reasonably well understood (for moderate xBj region).

F1x =12 ei

2[qi x ] in the Quark­Parton Model and the 

infinite momentum frame (IMF)

(P  ∞)

Current Knowledge of Nucleon Unpolarized Structure                                                                      (after 40 years of study)     

Polarized DIS (1980~present)

Scattering cross section is spin­dependent  (imaging throwing two small magnets together)

Longitudinal

Transverse

d 2

d dE '−

d2

d dE '∝ point−like [ ' g1x , Q2

' g2 x , Q2]

d 2

d dE '−

d2

d dE '∝ point−like [ ' ' g1x ,Q2 ' ' g2 x , Q2]

N SN SS N N S vs.

Polarized Structure Function and the Nucleon Spin Structure

in QPM and the infinite momentum frame:

g1x = 12 ei

2[q i

x −qi

x] = 1

2 ei

2[ qi x ]

The integral of g1(x) over x describes how much of the nucleon's spin is carried by quarks' spin

But do we really understand strong interaction?

To do this, we must understand the nucleon structure from the theory of strong interaction (QCD).

SQ2

=4

11−2 n f /3ln Q2/ 2

Because strong interaction is highly non-perturbative, it is very difficult to predict the value of structure functions from QCD.

Data vs. Theory – How do we test QCD?For most cases, QCD cannot predict the value of structure functions because of their non­perturbative nature.However, the large x region provides a handful of exceptions:

F2p/F2

n and d/uA1

p, A1n , or u/u and d/d 

A1 =1/2− 3/2

1/2 3/2

2 =Q2

2=

4 M2 x2

Q2

Virtual photon asymmetry:

A1 =g1−

2 g2

F1

≈g1

F1.at large Q2

At large x, valence quarks dominate, a relatively clean/easy region to 

study/model the nucleon

The 6 GeV Hall A Measurement (21 PAC days, 2001)

HHC not valid,quark OAM?

(1) SU(6)(2)(2) CQMCQM(3) LSS(BBS)(4) BBS(5) Bag 

Model(6) Duality(7) LSS 2001(8) Statistical 

Model(9) Chiral 

Soliton

(1)CQM   (2)LSS(BBS):pQCD+HHC(3)Statistical Model     (4)LSS 2001

(Deutron data not shown: E143, E155, SMC)

X. Zheng et al., Phys. Rev. Lett. 92, 012004 (2004); Phys. Rev. C 70, 065207 (2004)

(1)

(9)

(8)

(7)

(2)

(6)

(4)(3)(6)(5) (1)

(1)

(2)

(2)

(3)

(3)

(4)

(4)

Polarized DIS and Nucleon Spin StructureH. Avakian, S. Brodsky, A. Deur, F. Yuan, 

Phys. Rev. Lett.99:082001(2007)Figure credit: A. Deur

Future Experiments after the 11 GeV JLab Upgrade

Fully approved in August 2010, rated A.There are in fact two experiments, one in Hall A, one in Hall C.

Expected ResultsCombined results from Hall C (neutron) and B (proton) 11 GeV experiments

EM observables — σ, A... (polarized beam + polarized target)

hadron structure, strong interaction and its standard model (QCD);   

Weak observables — parity violating asymmetries (APV)(polarized beam + unpolarized target)

study hadron structure elastic scattering: strange form factors     A4, G0, HAPPEX, SAMPLEDIS: non­perturbative effects, CSV etc...                                    PVDIS 

test the standard model of electro­weak interaction       Qweak 

Parity Violating DIS 

ALR≡

r−

l

r

l≈

Q2

M Z2≈120 ppm

at Q2=1GeV /c2

N SS N vs.

 From Ad can extract C1,2q and sin2W.

For a deuterium target

In the SM, tree level

Ad = 540 ppmQ2 2C1u [1RC x ]−C1d [1RS x ]Y 2 C2u−C2dRV x

5RS x4RC x

C1d=gAe gV

d=

12−

23

sin2W

C1u=gAe gV

u=−

12

43

sin2W

C2d=gVe gA

d=

12−2 sin2

W

C2u=gVe gA

u=−

122sin2

W

Test of EW Standard Model Using PVDIS

1970's, result from SLAC E122 consistent with sin2W=1/4, confirmed the Standard Model prediction;Development in experimental technique allows to search for new physics

JLab 6 GeV Experiment 08­011

E08­011 ran Oct­Dec 2009

Used 105A, 6 GeV, 85% polarized beam on a 20­cm LD2 target;

Two Hall A High Resolution Spectrometers detect scattered electrons;

Customerized DAQ built by UVa group 

Measure Ad at Q2=1.10 and 1.90 GeV2 to about 3­4% (stat.);

Co­spokesperson & contact:   X. ZhengCo­spokesperson: P.E. Reimer, R. Michaels

Students: Diancheng Wang, Xiaoyan Deng, Huaibo Ding, Kai Panpostdoc: Ramesh Subedi

●ANL, Calstate, FIU, Jlab, Kentucky, U. of Ljubljana (Slovenia), MIT, UMD, UMass, UNH, Universidad Nacional Autonoma de Mexico, Rutgers, Smith C., Syracuse, UVa, W&M

Current Knowledge on C1,2q

MIT/ Bates

SLAC/Prescott

R. Young (PVES)

R. Young (combined)

PDG best fit

Cs APV

PDG best fit

SAMPLE

SLAC/ Prescott

all are 1  limit

Best: (2C2u­C2d) = 0.24

C2u

+C2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2u­C2d

- 0.25 0.50.250- 0.5

0.10

0.125

0.15

0.175

C1u­C1d

- 0.4- 0.6- 0.8

C1u

+C1d

Tl APV

Qweak (expected)

MIT/ Bates

SLAC/Prescott

R. Young (PVES)

R. Young (combined)

PDG best fit

Cs APV

SAMPLE

SLAC/ Prescott

all are 1  limit

Best: (2C2u­C2d) = 0.24

C2u

+C2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2u­C2d

- 0.25 0.50.250- 0.5

0.10

0.125

0.15

0.175

C1u­C1d

- 0.4- 0.6- 0.8

C1u

+C1d

Tl APV

The 6 GeV E08­011

PDG best fit

Expected: JLab 6 GeV PV­DIS E08­011 (assuming small hadronic effects and a 4% stat error on Ad)

Qweak (expected)

Hall A large acceptance “solenoid” device: PR09­012

Measure Ad to 1% for a wide range of (x,Q2,y), clean separation of     New Physics (via  C2q and sin2W), HT and CSV possible;

Extract d/u at large x from PVDIS on a proton target, free of nuclear effects;Other hadronic physics study possible: A1

n at large x, Semi­inclusive DIS.

Two approaches:

Hall C “baseline” SHMS+HMS: PR12­07­102 (P.E. Reimer, X­C. Z, K. Paschke,

1% on Ad, extraction of C2q, sin2W (if higher­twists and CSV are negligible);

PVDIS Program at JLab 12 GeV

(conditionally approved)

Hall A large acceptance “solenoid” device: PR10­007 fully approved

Measure Ad to 1% for a wide range of (x,Q2,y), clean separation of     New Physics (via  C2q and sin2W), HT and CSV possible;

Extract d/u at large x from PVDIS on a proton target, free of nuclear effects;Other hadronic physics study possible: A1

n at large x, Semi­inclusive DIS.

Two approaches:

Hall C “baseline” SHMS+HMS: PR12­07­102 (P.E. Reimer, X­C. Z, K. Paschke)

1% on Ad, extraction of C2q, sin2W (if higher­twist and CSV are negligible);

PVDIS Program at JLab 11 GeV

Projected PVDIS Measurement with SOLID@11 GeV

figure from K. Kumar, Seattle 2009 EIC Workshop EW talks

Projected PVDIS Measurement with SOLID@11 GeV

figure from K. Kumar, Seattle 2009 EIC Workshop EW talks

Ongoing 6 GeV Physics Program

Measurement of neutron asymmetry A1n in the valence quark 

region at JLab 12 GeV

Flagship experimentMay be one of the first experiments to run (~2014?)

SOLID program (2015 or later)

PVDIS at 11 GeV — ultimate goal: clean separation of New Physics and CSV

A1n, d/u measurements, SIDIS, etc.

Research Opportunities

Frontiers of Nuclear Science“Building  on  the  foundation  of  the  recent past,  nuclear  science  is  focused  on  three broad  but  highly  related  research  frontiers: (1) QCD and its implications and predictions (1) QCD and its implications and predictions for the state of matter  in the early universe, for the state of matter  in the early universe, quark  confinement,  the  role  of  gluons,  and quark  confinement,  the  role  of  gluons,  and the  structure  of  the proton and neutron;the  structure  of  the proton and neutron;  (2) the  structure  of  atomic  nuclei  and  nuclear astrophysics,  which  addresses  the  origin  of the  elements,  the  structure  and  limits  of nuclei, and the evolution of the cosmos; and (3)  developing  a  New  Standard  Model  of (3)  developing  a  New  Standard  Model  of nature's  fundamental  interactions,  and nature's  fundamental  interactions,  and understanding its  implications for the origin understanding its  implications for the origin of matter and the properties of neutrinos and of matter and the properties of neutrinos and nuclei.nuclei.”

A few words (slides) beyond the exact research topic

How a life towards your Ph.D. will feel like?

It's not like course work, there is no homework, no scheduled assignments, no TA/instructor to tell you what to do everyday.There is no midterm or final

It's not like course work, there is no homework, no scheduled assignments, no TA/instructor to tell you what to do everyday.There is no midterm or final

If you want to solve a problem, you need to go out and ask! Most of time, you have to define the problem yourself.If you want to know if what you are doing is leading towards your Ph.D., you need to sit down and think!There is no “after-midterm” or “after-final” vacation time to look forward to. You are facing years of hard work.Could be more complicated if you are also bothered by other questions, such as ... ...

How a life towards your Ph.D. will feel like?How a life towards your Ph.D. will feel like?

It's not like course work, there is no homework, no scheduled assignments, no TA/instructor to tell you what to do everyday.There is no midterm or final

If you want to solve a problem, you need to go out and ask! Most of time, you have to define the problem yourself.If you want to know if what you are doing is leading towards your Ph.D., you need to sit down and think!There is no “after-midterm” or “after-final” vacation time to look forward to. You are facing years of hard work.Could be more complicated if you are also bothered by other questions, such as ... ...

No wonder most of people I know said the few years leading to their Ph.D are the “darkest time” of their life.

How a life towards your Ph.D. will feel like?How a life towards your Ph.D. will feel like?

The Basics

A Doctor of Philosophy degree, abbreviated Ph.D., is the highest academic degree anyone can earn. Because earning a Ph.D. requires extended study and intense intellectual effort, less than one percent of the population attains the degree. Society shows respect for a person who holds a Ph.D. by addressing them with the title ``Doctor''.

To earn a Ph.D., one must accomplish two things. First, one must master a specific subject completely. Second, one must extend the body of knowledge about that subject.

A Few Questions To Ask

1. Do you want a research career?

even if you are planning a industrial/financial position, keep in mind what the people there are looking for?

2. Do you want an academic position?

3. Do you have what it takes?

It is difficult for an individual to assess their own capabilities. The following guidelines and questions may be of help.

Intelligence;

Time;

Creativity;

Intense curiosity;

Adaptability;

Problem-solving skills;

Self-Motivation;

Competitiveness;

Maturity.

A few warnings:Students sometimes enroll in a Ph.D. program for the wrong reasons. After a while, such students find that the requirements overwhelm them. Before starting one should realize that a Ph.D. is not:

Prestigious in itselfA guarantee of respect for all your opinions

A goal in itselfA job guarantee

A practical way to impress your family or friendsSomething you can “try” to find out how smart you are

The only research topic you will ever pursueEasier than entering the work force

Better than the alternativesA way to make more money

The good news:

Despite all our warnings, we are proud that we earned Ph.D. degrees and proud of our research accomplishments. If you have the capability and interest, a research career can bring rewards unequaled in any other profession. You will meet and work with some of the brightest people on the planet. You will reach for ideas beyond your grasp, and in so doing extend your intellectual capabilities. You will solve problems that have not been solved before. You will explore concepts that have not been explored. Working on research will become sheer joy (without saying it loud). You may enjoy your work so much that you look forward to every day ahead of you, and you may not want to retire, ever.