Syllabus Introduction What is MASS ? How to measure particle mass in nuclear matter

１１-JAN-2000 @ RIKEN Winter School

Hideto En'yo, Kyoto University

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Nuclear Matter Probed with Meson

- exploring the lost symmetry-

Hideto En’yo Hideto En’yo Kyoto UniversityKyoto University

SyllabusSyllabus Introduction Introduction

What is MASS ?What is MASS ? How to measure particle mass in How to measure particle mass in

nuclear matternuclear matter

Related Experiments Related Experiments KEK-PS E325 experimentKEK-PS E325 experiment

PhysicsPhysics SpectrometerSpectrometer ResultsResults

SummarySummary 　　 EntertainmentEntertainment



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Mass in QCDMass in QCD• Particle Data Booklet

– mu = 1.5~5 MeV m = 140 MeV– md = 3~9 MeV m = 770 MeV– ms = 60~170 MeV m= 1020 MeV

0

1

2

3

4

0 1 2 3

p2 (GeV2)

E2 (G

eV2)

When Particle M decays M 2=ei

2pi2 invariant

massWhat happens in Media ?

In Free SpaceE2=M2+P2

Mass is effectively given, but the state is GROUND LEVEL

Can we restore the symmetry ?How we measure ?



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What Theorists Say ?What Theorists Say ?

•<qq> quark condensate : order parameter • to indicate how much the symmetry broken• but not an observable

→ 　 Mass of Vector Meson, Mv = 2 x Mq

eff + small interaction term



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Bound NucleonsBound Nucleons

• Imagine that a neutron ( or proton ) in Oxygen nuclei made GUT decay in Kamiokande. (assume that you have a perfect detector )

n → π+ + e

Mn2 → Eπ

+ Ee)2 Pπ + Pe)2

Mn = 939.6 MeV , Mn

= 938.3MeV ?????

• More precisely16O → π+ + e + 15O*

(Mn +M15O ) 2 → 15O + Eπ

+ Ee )2 P15o + Pπ

+ Pe )2

0

1

2

3

4

0 1 2 3

p2 (GeV2)

E2 (

GeV

2)

You measure 16O levels



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Moving Mesons in MediaMoving Mesons in Media

• In-media meson modification– Observed Mass is not Lorentz Invariant

• shift of resonance position

• resonance broadening/narrowing→ 　 DISPERSION

be smallbe small



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How to Measure Mass How to Measure Mass in Mediain Media

1: Search for a deeply bound meson sta1: Search for a deeply bound meson state, Measure the level. (possible only at te, Measure the level. (possible only at normal nucler density)normal nucler density)

2: Invariant Mass Spectroscopy, determ2: Invariant Mass Spectroscopy, determine the dispersion of mesons in nuclear ine the dispersion of mesons in nuclear media ( even in hot or dense mater)media ( even in hot or dense mater)

3: Compare Decay Branching Ratios to 3: Compare Decay Branching Ratios to different channels (decay Q value must different channels (decay Q value must be sensitive) be sensitive)

Meson spectroscopy ( in free space) can be considered as the mass spectroscopy for the valence quarks in normal vacuum, with which it is difficult to answer “what is the origin of the mass”.



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Hurdles

• Many Unknown ( theories exist but almost no experiments )

– Temperature & dependence of <qq>– Temperature & time evolution

→CERN/RHIC/LHC

– Density & dependence of <qq>– Density & time evolution

→BNL/JHF

– Dispersion & Broadening

A lot of inputs from experiments needed, even at the normal　 nuclear　matter density.



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Present and Future ExperimentsPresent and Future Experiments

CLUES

Experiment Measurements Interests

CERES/HELIOS-3 modification Temp. dep.

KEK-TANASHI ES modification Density dep.

GSI modification Density dep.

The efforts to be continued at RHIC and LHC (temperature dependence)

Present & future experiments to measure the mass of vector mesons at normal nuclear matter density.

KEK-ES: +A →+A*(→+) (Published)

KEK-PS: p+A→+X(→K+K/e+e) (Running)

SPring-8: + →+A*(→ K+K) 　　　　 (Ready to run )

GSI: d +A→3He+A*(bound states) (Ready to run )

GSI-HADES: +A→ +A* (→e+e) (Preparation, 2001?)



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KEK-PS E325 KEK-PS E325 to measureto measure decays decays in nuclear matterin nuclear matter

is narrow resonance (is narrow resonance (=4.4MeV) =4.4MeV) Q=38MeVQ=38MeV = 4.4MeV sensitive to resonance-shape change = 4.4MeV sensitive to resonance-shape change Q= 38MeV sensitive to the decay branching ratiosQ= 38MeV sensitive to the decay branching ratios

→K+K (49%) →e+e (3x10-4))

KK Thresholdin Free Space

K modification ?

modification ?



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E325 PHYSICSE325 PHYSICS

Expected Signal(electron pairs)

• KEK-PS E325 to measure KEK-PS E325 to measure decays inside a nucleus

– In 12GeV p+A (C/CH_2/Cu/Pb)→ + X– Observables

– Invariant mass spectrum; →K+K and →e+e – Branching ratio; Br( →K+K )/Br( →e+e

– Less ambiguous data on the modification – Also Sensitive to the production and interaction of

in nucleus



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• Particle Production follows

A

for – Drell-Yan lepton pairs

– J/

– perturbative production

for - fragmentations

• production ?

Br( →K+K) / Br( →e+ePb Br( →K+K) / Br( →e+eC

to be free from

production mechanism

Mechanism of Mechanism of Production at 12 GeVProduction at 12 GeV

J/

Drell-Yan

2/3

2/3

XF

300GeV p+A →

120GeV p+A→→KK



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Some Tips of E325• Expected mass shift is 20~40 MeV ( Hatsuda-Lee).• Focus on slowly moving 's, p =~1GeV/c(lab). Abo

ut 10% of 's will decay inside a nucleus if nothing happens.

• Secondary peak may enhance when low 's are selected.

• The ratio (→K+K)/(→e+e) is sensitive to in-media modification of phi and/or K

• natural width of is narrow (4.4MeV), but some broadening can happen.. Estimations are:

= N 0 <20MeV {N} < $10mb, total cross section (from +A→) =0.7,0 =0.16/fm3

→+*K*(KN→X) 　 Klingle and Weise ~44MeV (at rest)

• 109/sec primary protons on thin (0.1%) nuclear target tosuppress conversions.



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Brief Mile Stones and Status

• 1994 March KEK-PS PAC conditionally 　 approved• 1995 March KEK-PS PAC approved • 1996 July- Construction started• 1996 November Engineering Run• 1997 June, First Physics Run with K+K. 17days

– Data accumulation mainly with K+K channel trigger– Beam Intensity 1~2 x108$ protons/spill– 0.6% interaction target (106 interaction/spill)– C/CH2/Pb 3 targets in-line– 165GByte Data (160M events) collected in 50 shifts

• 1998 March, Completion of Spectrometer, • 1998 April -May: Production Running of 29 days

– Parallel Trigger. K+K-/ e+e- – Beam Intensity 1~2 x 109 protons/spill– 0.1% interaction target (106$ interaction/spill)– $C/CH2/Cu 3 targets inline– 502GByte Data (180M events) collected in 85 shifts

• 1999 June 60 shifts Data Taking performed– Parallel Trigger. K+K-/ e+e- – Beam Intensity 1~2 x 109 protons/spill– 0.2% interaction target (106$ interaction/spill) – 360GByte Data (180M events) collected in 85 shifts

• 2000 May 80-100 shifts Data Taking Expected



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E325 collaboration

• Kyoto University– H.Enyo, H.Funahashi, T.Haseyama, M.Ish

ino, H.Kanda, M.Kitaguchi, S.Mihara, M.Miyabe, T.Miyashita, K.Miyazaki, T.Murakami, R.Muto, M.Naruki, K.Ozawa, H.D. Sato, T.Tabaru, S.Yamada, S.Yokkaichi, Y.Yoshimura

• T.I.T. – K.Hamada, Y.Sakemi, T.A.Shibata

• CNS, University of Tokyo – H.Hamagaki

• KEK– J.Chiba, M.Ieiri, O.Sasaki, M.Sekimoto, K.

Tanaka

• RCNP– M.Nomachi

\250,000,000/5students/5years=\10,000,000



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E325 SETUP



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Trigger CountersTrigger Counters

TOF

ACGCs

Lead Glass Calorimeter

Karm Accceptance

Inside Magnet

AC vetos 99% of pion (P>0.55GeV/c)TOF t~200psec

2-Stage e-ID reject 99.9% pions



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Typical EventTypical Event



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Spectrometer Spectrometer PerformancePerformance→p→p

Invariant Mass SpectrumInvariant Mass Spectrum

M= 1115.1MeV/c2

(PDG 1115.7MeV/c2)

M= 2.2MeV/c2

→ M= 1.2MeV/c2



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→ →KK++KK Invariant Mass SpectrumInvariant Mass Spectrum

• 0.4<Mkk<0.6 GeV/c2 , Pk<1.2GeV/c

• Two kaons are in the same arm.

• Mixed event background is over-plotted (shaded area).

ALL CH2

C Pb



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Target Dependence of WidthTarget Dependence of Width

• Resonance positions & widths are consistent with those in free space (within the statistic of ‘97 data)

• Pb data looks wider though.



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Target Mass Dependence ofTarget Mass Dependence of →K→K++KK

=0.98 0.10

Absolute cross section is not well determined yet. is surprisingly large



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Comparison to other dataComparison to other data

• consistent with the high energy date (Einc > 100GeV) where the is produced somewhat perturbatively. Surprising that similar production mechanism even at 12GeV

• May suggest the perturbative production of even at 12 GeV



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‘99 data

• We now have enough data to identify decays outside and inside nuclei.

Very

Preliminary



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Summary and OutlookSummary and Outlook• Study of in-media modification of meson is very important a

nd interesting to understand the broken chiral symmetry in QCD.

• The experiment, E325, at KEK 12GeV PS measures 12GeV p + A → + X reactions in both →K+K and →e+e channels.

• To observe possible changes of the ratio, Br(

→K+K)/Br( →e+e), and of the shape of the invariant mass peak under the normal nuclear density ( and T = 0).

• Especially we put an emphasis on the detection of slowly moving mesons ~ 1-2GeV/c in lab., subject to thus decay in Nuclear Media.

• The ‘97 →K+Kdata have been analyzed so far (1/5 of the data already collected, 1/10 of data to be acquired). The results shows

– No statistical significance on the mass shape deformation (YET)

– Strong A dependence ( =0.97 0.10 ) in the production• No significant increase of with pT

• The ‘99 →K+Kdata are still preliminary, with some hint of in-media decay component in the mass shape.

• Many new experimental results including this experiment will be available soon, from GSI, Spring-8, and KEK.



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EntertainmentEntertainmentGeneral Physics QuestionsGeneral Physics QuestionsThink when you are on the liftThink when you are on the lift

Q1: You are freely in free space Q1: You are freely in free space (without gravity). Can you turn (without gravity). Can you turn right around ? (you can’t blow )right around ? (you can’t blow )

Q2: You have 1 Q2: You have 1 llitteritter of of hot red hot red water (100water (100ooC)C) and 1 and 1 llitteritter of of cold cold blue water (0blue water (0ooC)C). You want to . You want to warm up the warm up the blue waterblue water with the with the red waterred water. How high you can . How high you can warm it up ? (do not use extra warm it up ? (do not use extra energy from outside)energy from outside)

Syllabus Introduction What is MASS ? How to measure particle mass in nuclear matter

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