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

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 9 th Japan- China Joint Nuclear Physics Symposium (JCNP 2015), Nov. 7-12, 2015, Osaka Univ., Japan 1

Outline • Motivation • Introduction of correlation and an example of RIB reaction • RHIC-STAR Collaboration • About Antimatter • Analysis procedure & results • Summary 2

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. 3

pp correlation function—intensity interferometry 4

singlet wave attractive -for pp However, there is no any antiproton-antiproton measurement so far. If so , antiproton interaction parameter could be extracted. 5

An example: p-p momentum correlation measurement 
 in RNB 6

two-proton correlation from proton-rich nuclei-22Mg & 23Al Different 2p emission mechanism for 23Al and 22Mg: (1) 23Al —three body decay or cascade emission; (2) 22Mg - strong 2p emission component 7

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Effective emission source size extracted from 
 pp HBT correlation measurement R~4.7fm R~3.5fm • Since p-p interaction parameters are well known, so different p-p correlation strength indicates different effective source size R~2.5fm 9

A minireview: 10 Y . G. Ma, J. Chen, L. Xue, Front. Phys., 2012, 7(6): 637–646

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STAR Detectors Magnet MTD EEMC BEMC TPC TOF BBC Full 2 π coverage; Pseudorapidity coverage ~ ±1 unit TOF & MTD: Chinese contribution 12

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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 of Flight Detectors which are based on MRPC techniques for STAR Alos, contributed to MTD & HLT for STAR Project Leader & Convenor : Yu-Gang Ma 15

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A real event in 200GeV/c Au+Au collision @ STAR A fake event with Suhzhou Embroidery 19

Jinhui Chen (SINAP), 2012 APS George E. Valley Prize 20

L Liang Xue (SINAP), Quark Matter 2011 talk ； 2013 Excellent CAS PhD Dissertation; 21

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Particle Identification TOF TPC (Time Projection Chamber) dE/dx (keV/cm) p × q (GeV/c) m 2 vs n σ p : Negative Charge We use TPC and TOF (Time of Flight) for the particle identification. The purity for anti-proton is over 99%. 23

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: 24

Formula to fit our data 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 where and 25

Antiproton-antiproton Correlation Function The theoretical correlation function can be obtained with Lednick ý and Lyuboshitz analytical model: where is the s-wave scattering amplitude renormalized by Coulomb interaction. 26

f 0 & d 0 The scattering length f 0 in quantum mechanics describes low-energy scattering. The elastic cross section, σ e , at low energies is determined solely by the T he scattering length is a measurement of how particles scattering length, deviate as they travel from source to destination Here k is the wave number. d 0 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. T he effective range indicates how close particles need to be for their charges to influence each other, like magnets. • f 0 and d 0 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 f 0 and d 0 . 27

Neha Saha (SINAP), PRL(2015) 28

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From k_pL to k_pp using Transformation matrix • 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. 30

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 , f 0 =7.41±0.19fm, d 0 =2.14±0.27fm; /NDF=1.61 STAR Preliminary /NDF contour, 1-sigma boundary in white 31

f 0 and d 0 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). STAR Preliminary • 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! 32

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. ¡T hese ¡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. ¡ ¡ 33

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), one of my PhD students, PhD Dissertation (2016) 34

a carton view on pbar-pbar correlation A schematic of the two-particle correlation process in a heavy-ion collision. 35

Summary • We report the result of antiproton-antiproton correlation function from 200GeV Au+Au collisions. Parameters f 0 & d 0 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. 36

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THANKS! 38