detailed study of parton energy loss via measurement of fractional momentum loss of high p t hadrons...

$: Detailed study of parton energy loss via measurement of fractional momentum loss of high p T hadrons in heavy ion collisions Takao Sakaguchi Brookhaven$
Detailed study of parton energy loss via measurement of fractional momentum loss of high pT hadrons in heavy ion collisions

Takao Sakaguchi

Brookhaven National Laboratory

for the PHENIX Collaboration

Hard scattering as densimeter Parton may change its momentum in the medium.

– Energy loss through Gluon radiation, etc..

Effect is path-length and parton density dependent ~a densimeter~.

Look at leading particles of jet as a measure of jet energy.

2014-09-12 T. Sakaguchi, HPT2014@Nantes, France2 X.-N., Wang, PRC 58 (1998)2321

Energy loss =Yield suppress

0 without energy loss

0 with energy loss

Yie

ld [

GeV

-1c]

pT [GeV/c]

p+p Au+Au

Cross section of A+B collisions AB p+p collisions

High pT hadron RAA

Measured in 200GeV Au+Au collisions.

p0 and h are very consistent.

Results have been solid over years.

2014-09-12 T. Sakaguchi, HPT2014@Nantes, France3

PRC82, 011902(R) (2010)

MinBias, Black: p0, Blue: h

RAA (1/Nevt

AA )(dN AA /dpT )

TAA (d pp /dpT )

Black: Year-2004, Red: Year-2007

PRC87, 034911 (2013)

MinBias

Black- 2004Red - 2007

0-10%

20-30% 40-50%

60-70% 80-93%

Collision energy dependence of RAA p0 in Cu+Cu @ 200, 62.4, 22.4GeV (RHIC Year-5)

– 200GeV and 62GeV show suppression, and 22.4GeV shows enhancement (Cronin)

p0 in Au+Au @ 200, 62.4, 39GeV (RHIC Year-4, 7, 10)– Similar suppression at higher pT


PRL 101, 162301(2008)PRL109, 152301 (2012)

Centrality dependence of RAA

Centrality dependence of integrated p0 RAA was investigated in Cu+Cu and Au+Au collisions

– As a function of cms energy

Top: Cu+Cu:– 2.5<pT<3.5GeV/c

Bottom: Au+Au– pT>6GeV/c

Indication of a switch of suppression and enhancement below 39GeV?


PRL 101, 162301(2008)

PRL109, 152301 (2012)

Similar suppression for RHIC and LHC?

RHIC data from PHENIX publication

– p0 in Au+Au @ 0.2TeV

LHC data from ALICE publication

– Charged hadrons in Pb+Pb @ 2.76TeV

Center-of-mass energies differ by a factor of 14!

Similar RAA doesn’t mean similar energy loss

– RAA is not a good quantity?– Power of the spectra is different

energy loss will be different


PRC87, 034911 (2013)

Looking at suppressions from a different angle


New quantity ~momentum loss~ Coming back to the original idea: measuring energy loss of partons

Statistically measure the fractional momentum loss (dpT/pT) of high pT hadrons instead of RAA.

2014-09-128 T. Sakaguchi, HPT2014@Nantes, France

pT

dpT)()(

)(:

AAppppp

pppp

TTT

TT

(p+p) denotes p+p yield scaled by number of binary nucleon-nucleon collisions (Ncoll).

In 2005, statistics was not enough, so.. We assumed that the spectra at high pT follows power-law function

With this assumption, we wrote a formula to obtain dpT/pT from RAA

– Fractional momentum shift: S(pT)/pT=S0


]/)(1[

'

)('/)()1(22

TT

T

TTTpp

AA

TTAAevtAA

dppdS

dydp

pSppd

T

dydppNdN

]/)(1[]/)(1[

]/)(1[)]([

)(

1

1

1

TTn

TT

TTnT

nTT

TAA

dppdSppS

dppdSp

pSppR

nTpdp

dE

3

3

0

)2/(1

20

1

1)(

,)1()(

SpR

SpR

nTAA

nTAA

)2/(1

0

)(1

)1/(11))(/()(

n

TAA

TTTloss

pR

SpSppSS

Note pT is pT in Au+Au PHENIX, PRC76, 034904 (2007)

Sloss in 200GeV Au+Au collisions

Sloss (dpT/pT), where pT is pT at a Au+Au point

Lines: Sloss Npart2/3

– Sloss increases approximately like Npart2/3

– GLV and PQM model suggested 2/3

2014-09-12 T. Sakaguchi, HPT2014@Nantes, France10PHENIX, PRC76, 034904 (2007)

Path-length dependence of RAA

PHENIX measured the RAA as a function of emission angle with respect to event planes for several centralities

– Gives handle of path-length that partons traverse

Le is path from the center of ellipse to the edge


cyan, 60–70%mauve, 50–60%blue, 40–50%green, 30–40%red, 20–30%black, 0–10%

Path-length dependence of Sloss

Converted RAA to Sloss and plotted against Le

Data points nicely aligned for 5<pT<8GeV/c


cyan, 60–70%mauve, 50–60%blue, 40–50%green, 30–40%red, 20–30%black, 0–10%

ALICE recently performed similar study

Using Pb+Pb 2.76TeV data (ALICE). L should be equivalent to the Le in the previous slide

L is not very good at higher pT?


P. Christiansen, K. Tywoniuk, and V. Vislavicius, PRC 89, 034912 (2014)

With better statistics..


Direct calculation is possible

Direct calculation of fractional momentum loss (dpT/pT) became possible.

One doesn’t need to assume the function form of the spectra.


pT

dpT

Direct calculation is possible

Direct calculation of fractional momentum loss (dpT/pT) became possible.

One doesn’t need to assume the function form of the spectra.


p+p p0 spectra Au+Au p0 spectra

Fractional momentum loss (dpT/pT) of p0

Measured fractional momentum loss (dpT/pT) instead of RAA

– In Au+Au collisions

dpT/pT=0.2 in 0-10% centrality, =0.02 in 70-80% centrality


dp

T/p

T

PRC87, 034911 (2013)

MinBias 0-10%

20-30% 40-50%

60-70% 80-93%

Energy dependence of dpT/pT (I) dpT/pT decreases significantly going from 200 to 62, 39GeV.

Significantly different dpT/pT while the RAA is similar.


RA

A

PRL109, 152301 (2012)

Energy dependence of dpT/pT (II)

dpT/pT increase by a factor of 1.5 from 200GeV to 2.76TeV.

~0.2 for RHIC and ~0.3 for LHC


LHC

RHIC

PRC87, 034911 (2013)

Energy dependence of dpT/pT (III)

dpT/pT from 62GeV to 2.76TeV: by a factor of 6 change!

2014-09-1220 T. Sakaguchi, HPT2014@Nantes, FrancePRL109, 152301 (2012)

LHC

RHIC

PRC87, 034911 (2013)

Systematic studies across systems

We tried to plot dpT/pT against universal variables

Number of participant nucleons (Npart)

Number of quark participants (Nqp)

Charged multiplicity (dNch/dh), as a measure of the energy density


Number of quark participants (Nqp)? Number of quark participants, Nqp,

is estimated using a Glauber model.– Nucleons are distributed using a Woods-

Saxon distribution.– Quarks are distributed around the

nucleon centers following: r(r)= r0proton e-

ar, where a = 4.27 fm-1.

Quarks interact when their distance, d, satisfies the condition of:

Quark-quark inelastic cross section (qq

inel) is estimated by reproducing the n-n inelastic cross section of:


Ratios of Nqp/Npart as a function of Npart for 62, 130 and 200GeV Au+Au collisions

PHENIX, PRC89, 044905 (2014)

Is Nqp a good scaling variable? Recently, PHENIX found that the dET/dh scales better with Nqp than Npart

dET/dh affects the energy loss of partons


dET/dh/(0.5 Npart) dET/dh/(0.5 Nqp)

PHENIX, PRC89, 044905 (2014)

dpT/pT over collision systems (vs Npart)

Plotting against Npart

– Npart are obtained in given centrality at given cms energy.

– dpT/pT‘s at pT=7GeV/c of p+p are plotted.


dpT/pT over collision systems (vs Nqp)

Plotting against Nqp

– Nqp are obtained in given centrality at given cms energy.



dpT/pT over collision systems (vs dNch/dh)

Plotting against dNch/dh (as a measure of energy density)– dNch/dh are obtained in given centrality at given cms energy.



Consistency with previous studies

PHENIX studied fractional momentum loss in two publications– PRC76, 034904 (2007), PRL101, 232301 (2008)– Assuming the spectra shape is power-law with the power “n”, we can write:

If we assume dNch/dh Npart1.16, found in PRC71, 034908(2005), we can

write the relationship as follows:

2014-09-12 T. Sakaguchi, HPT2014@Nantes, France27PRL101, 232301 (2008)





k=0.55,b=6.010-3

k=0.35,b=2.510-2

Review the money plot


Summary

Looking at fractional momentum loss gives more insight on actual energy loss of partons– Similar RAA does not give similar energy loss

Centrality, system, and energy dependence of fractional momentum loss is studied.– A trend is seen from 200GeV Au+Au to 2.76TeV Pb+Pb

dpT/pT vs dNch/dh for 200GeV Au+Au and Cu+Cu collisions tend to merge into the one for 2.76TeV Pb+Pb collisions at larger dNch/dh, independent of √sNN.

Within same √sNN, both Npart and Nqp scaling work very well.


Backup


Hard scattering as densimeter Parton may change its momentum in the medium.

– Energy loss through Gluon radiation, etc..

Effect is path-length and system dependent ~a densimeter~.

Look at leading particles of jet as a measure of jet energy.

2014-09-12 T. Sakaguchi, HPT2014@Nantes, France32 X.-N., Wang, PRC 58 (1998)2321

Energy loss =Yield suppress

0 without energy loss

0 with energy loss

Yie

ld [

GeV

-1c]

pT [GeV/c] PHENIX, p0 in Au+Au, PRL. 91, 072301 (2003)





a=0.55,b=6.010-3

a=0.35,b=2.510-2

Consistency with previous studies

PHENIX studied fractional momentum loss in two publications– PRC76, 034904 (2007), PRL101, 232301 (2008)– Assuming the spectra shape is power-law with the power “n”, we can write:

In this study, if we assume dNch/dh Npart, we can write the relationship as follows:


cGeVpT /[email protected] cGeVpT /[email protected]

PRL101, 232301 (2008)

d+Au and Au+Au system similarity?

Au+Au 60-92% and d+Au 0-20% have similar Npart, Ncoll

Ratios of all ID’ed hadron spectra are on the same curve

Common production mechanism?

If all CNM scales with Npart, ratios may mean Eloss in the medium in peripheral Au+Au

Low pT increase may rise from rapidity shift in d+Au


arXiv:1304.3410

Setup for measurement Event triggered by a coincidence

of BBC South and BBC North.– Sitting in 3.1<|h|<3.9

p0 and h measurement– EMCal(PbSc, PbGl): Energy

measurement and identification of real photons.

– Tracking(DC, PC): Veto to Charged particles.


View From Beam

View From Side

Results presented here are obtained from 0.813 nb-1 Au+Au 200GeV events recorded by PHENIX in 2007.

p0 h

EMCal

How we measure p0, h? Reconstruct hadrons via 2g invariant mass in EMCal (example is in Au+Au)

Subtract Combinatorial background– Compute Mass using gs from different events. (mixed-event technique)


PRC87, 034911 (2013) PRC82, 011902(R) (2010)

)cos1(2)()( 212

212

212 EEEEM pp

p0

h

p0 h

p0, h spectra in Au+Au


p0 h

Spectra reached to ~20GeV/c for p0 and ~22GeV/c for h

Systematic errors

Type A: point-by-point fluctuating errors

Type B: pT-correlated errors

Type C: overall normalization errors


source type 5GeV 10GeV 15GeV 20GeV

peak extraction B 2 2 2 2

acceptance C 2.5 2.5 2.5 2.5

PID efficiency B 7 8 8.5 9

energy scale B 7.5 8 8 8

photon conversion C 2 2 2 2

cluster merging B 0 0 8 18

total 11 12 15 22

source type 5GeV 10GeV 15GeV

peak extraction B 4 3.5 3

acceptance C 2.5 2.5 2.5

PID efficiency B 7 8 8.5

energy scale B 11 12 12

photon conversion C 2 2 2

total 12 15 15

p0 systematic errors

h systematic errors

detailed study of parton energy loss via measurement of fractional momentum loss of high p t hadrons...

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