World's first measurement of force of interaction between pairs of - - PowerPoint PPT Presentation

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World's first measurement of force of interaction between pairs of antiprotons

Yu-Gang Ma (⻢驭余刚)

Shanghai Institute of Applied Physics （SINAP), Chinese Academy of Sciences, China and STAR@RHIC Collaboration main collaborators: Zhengqiao Zhang, Aihong Tang et al.

The 9th Japan- China Joint Nuclear Physics Symposium (JCNP 2015), Nov. 7-12, 2015, Osaka Univ., Japan

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Outline

• Motivation
• Introduction of correlation and an example of RIB reaction
• RHIC-STAR Collaboration
• About Antimatter
• Analysis procedure & results
• Summary

Motivation

• So far the large body of knowledge on nuclear force was derived

from studies made on nucleons or nuclei. However, there is no quantitative information about the nuclear force between anti- nucleons.

• The knowledge of interaction among two anti-protons, the simplest

system of anti-nucleons(nuclei), is a fundamental ingredient for understanding the structure of more sophisticated anti-nuclei and their properties.

• With abundantly produced anti-nucleons, RHIC (and LHC) has the

excellent capability of conducting such kind of studies.

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pp correlation function—intensity interferometry

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• for pp

However, there is no any antiproton-antiproton measurement so far. If so , antiproton interaction parameter could be extracted.

singlet wave attractive

An example: p-p momentum correlation measurement 
 in RNB

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two-proton correlation from proton-rich nuclei-22Mg & 23Al

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Different 2p emission mechanism for 23Al and 22Mg: (1) 23Al —three body decay or cascade emission; (2) 22Mg - strong 2p emission component

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Effective emission source size extracted from 
 pp HBT correlation measurement

• Since p-p interaction

parameters are well known, so different p-p correlation strength indicates different effective source size

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R~4.7fm R~3.5fm R~2.5fm

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A minireview:

• Y. G. Ma, J. Chen, L. Xue, Front. Phys., 2012, 7(6): 637–646

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STAR Detectors

Full 2π coverage; Pseudorapidity coverage ~ ±1 unit

EEMC Magnet MTD BEMC TPC TOF BBC

TOF & MTD: Chinese contribution

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what Chinese contributes?

STAR-China groups: SINAP(CAS); USTC; CCNU; ThU; IMP (CAS); SDU; 2006-2009, China group contributed for a Full Time

• f Flight Detectors which are based on MRPC

techniques for STAR Alos, contributed to MTD & HLT for STAR Project Leader & Convenor : Yu-Gang Ma

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A real event in 200GeV/c Au+Au collision @ STAR A fake event with Suhzhou Embroidery

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Jinhui Chen (SINAP), 2012 APS George E. Valley Prize

L

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Liang Xue (SINAP), Quark Matter 2011 talk； 2013 Excellent CAS PhD Dissertation;

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Particle Identification

TPC (Time Projection Chamber)

We use TPC and TOF (Time of Flight) for the particle

• identification. The purity for anti-proton is over 99%.

m2 vs nσp: Negative Charge

p×q (GeV/c) dE/dx (keV/cm)

TOF

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Femtoscopy Analysis

Correlation Function(CF): A(k*) - real pair, B(k*) - pair from mixed event k* - half of relative momentum between two particles Purity correction:

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Formula to fit our data

where and

Inside our (anti)proton samples, there are secondary (anti)protons that are indistinguishable from primordial ones. In the residual protons, the Lambda decay channel gives the most contribution. We fit the data by the following equation

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Antiproton-antiproton Correlation Function

The theoretical correlation function can be obtained with Lednický and Lyuboshitz analytical model:

is the s-wave scattering amplitude renormalized by Coulomb interaction.

where

f0 & d0

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The scattering length f0 in quantum mechanics describes low-energy scattering. The elastic cross section, σe , at low energies is determined solely by the scattering length,

d0 is the effective range of strong interaction between two particles. It corresponds to the range of the potential in an extremely simplified scenario - the square well potential.

• f0 and d0 are two important parameters in characterizing the strong

interaction between two particles.

• The part in the equation we used to fit the data is

calculated based on f0 and d0.

Here k is the wave number.

The scattering length is a measurement of how particles deviate as they travel from source to destination

The effective range indicates how close particles need to be

for their charges to influence each other, like magnets.

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Neha Saha (SINAP), PRL(2015)

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From k_pL to k_pp using Transformation matrix

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• The transformation matrix is derived from THERMINATOR2 to

transform .

• Particle cuts for the transformation matrix: |eta|<0.7,0.4<rigidity<2.5,

0.4GeV/c<pt<2.5GeV/c.

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Correlations and the ratio

Fit results: For proton-proton CF, R=2.75±0.01fm; /NDF = 1.66; For pbar-pbar CF, R=2.80±0.02fm , f0=7.41±0.19fm, d0=2.14±0.27fm; /NDF=1.61

/NDF contour, 1-sigma boundary in white

STAR Preliminary

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f0 and d0 for antiproton-antiproton

• Within errors, the f0 and d0 for the

antiproton-antiproton interaction are consistent with the ones for the proton-proton interaction.

• Our measurements provide input for

descriptions of the interaction among antiprotons, one of the simplest systems of anti-nucleons(nuclei).

• The result provides a quantitative

verification of matter-antimatter symmetry in the context of the forces responsible for the binding of (anti)nuclei. CPT symmetry still works!

STAR Preliminary

Nature Referees’ comments

Referee ¡1: ¡ ¡ This ¡is ¡the ¡first ¡direct ¡measurement ¡of ¡pbar ¡pbar ¡interactions ¡ever! ¡ The ¡paper ¡announces ¡an ¡important ¡discovery: ¡antiprotons ¡interact ¡with ¡each ¡other ¡with ¡high ¡accuracy ¡ like ¡protons ¡interact ¡with ¡each ¡other. ¡These ¡Measurement ¡offers ¡important ¡original ¡contribution ¡to ¡the ¡ forces ¡in ¡antimatter ¡! ¡ Referee ¡2: ¡ Presented ¡in ¡this ¡paper ¡is ¡the ¡first ¡experimental ¡results ¡to ¡determine ¡directly ¡the ¡interaction ¡ parameters ¡between ¡anti-­‑protons ¡utilizing ¡the ¡high-­‑energy ¡heavy-­‑ion ¡collisions. ¡ ¡ Referee ¡3: ¡ The ¡manuscript ¡contains ¡exciting ¡new ¡results ¡on ¡the ¡interaction ¡between ¡antiprotons. ¡The ¡interactions ¡ between ¡nucleons ¡are ¡of ¡fundamental ¡interest ¡for ¡the ¡whole ¡nuclear ¡physics ¡community ¡and ¡possibly ¡ even ¡beyond ¡for ¡atomic ¡physics ¡applications ¡or ¡condensed ¡matter ¡physicists. ¡The ¡first ¡measurement ¡of ¡ the ¡scattering ¡length ¡and ¡the ¡effective ¡range ¡of ¡the ¡interaction ¡between ¡antiprotons ¡is ¡presented ¡and ¡ confirmed ¡to ¡be ¡equal ¡within ¡errors ¡to ¡the ¡values ¡that ¡are ¡known ¡for ¡the ¡proton ¡proton ¡interaction. ¡This ¡ equality ¡is ¡crucial ¡to ¡understand ¡the ¡CPT ¡invariance ¡of ¡the ¡strong ¡interaction. ¡Therefore, ¡I ¡think ¡that ¡this ¡ paper ¡is ¡most ¡likely ¡one ¡of ¡the ¡five ¡most ¡significant ¡papers ¡published ¡in ¡the ¡discipline ¡this ¡year. ¡ ¡

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Manuscript published online in Nature

• Nov. 4, (2015) online

Principal authors

• Y. G. Ma, Q. Y. Shou, A. Tang,

K.F. Xin, Z.Q. Zhang， M. Lisa et al.,

This work is a part of Mr. Zhenqqiao Zhang (SINAP),

• ne of my PhD students, PhD

Dissertation (2016)

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a carton view on pbar-pbar correlation

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A schematic of the two-particle correlation process in a heavy-ion collision.

Summary

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• We report the result of antiproton-antiproton correlation function

from 200GeV Au+Au collisions. Parameters f0 & d0 are, for the first time, extracted from the correlation function and the interaction between the two anti-protons is found to be attractive.

• This direct information on the interaction between two anti-

protons, one of the simplest systems of anti-nucleons, provides a fundamental ingredient for understanding the structure of more complex anti-nuclei and their properties.

• Within the current errors, antiproton-antiproton interaction is the

same as proton-proton interaction, it indicates the CPT symmetry still works for interaction.

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THANKS!