status and physics programme of lhcf experiment sergio ricciarini for the lhcf collaboration...

Status and Physics Programme of LHCf experiment

Sergio Ricciarini

for the LHCf collaboration

Istituto Nazionale di Fisica Nucleare (INFN)

Structure of Florence, Italy

Workshop on “Diffractive and electromagnetic processes at LHC”

ECT Trento - 5 January 2010

S. Ricciarini 2010-01-05

Summary

• 1. Physics motivations

• 2. LHCf experimental setup

• 3. LHCf physics performances

• 4. Preliminary results for 2009 operation

• 5. Future programme

1.Physics motivations


The LHCf Collaboration

USAUSALBNL Berkeley:LBNL Berkeley:W.C. TurnerW.C. Turner

FRANCEFRANCEEcole Polytechnique Paris:Ecole Polytechnique Paris:M. HaguenauerM. Haguenauer

SPAINSPAINIFIC Valencia:IFIC Valencia: A.Faus, J.VelascoA.Faus, J.Velasco

ITALYITALYFirenze University and INFN:Firenze University and INFN: O.Adriani, O.Adriani, L.Bonechi, M.Bongi, G.Castellini, L.Bonechi, M.Bongi, G.Castellini, R.D’Alessandro, H. Menjo, P.Papini, R.D’Alessandro, H. Menjo, P.Papini, S.Ricciarini, A.VicianiS.Ricciarini, A.VicianiCatania University and INFN:Catania University and INFN: A.Tricomi A.Tricomi

JAPANJAPANSTE Laboratory Nagoya University:STE Laboratory Nagoya University:K. Fukui, Y.Itow, T.Mase, K.Masuda, K. Fukui, Y.Itow, T.Mase, K.Masuda, Y.Matsubara, H.Matsumoto, T.Sako, K.TakiY.Matsubara, H.Matsumoto, T.Sako, K.TakiKonan University Kobe:Konan University Kobe: Y.Muraki Y.MurakiUniversity of Tokyo: University of Tokyo: Y.ShimizuY.ShimizuKanagawa University Yokohama: Kanagawa University Yokohama: T.TamuraT.TamuraWaseda University:Waseda University: K.Kasahara, M.Mizuishi, K.Kasahara, M.Mizuishi, S.ToriiS.ToriiShibaura Institute of Technology Saitama:Shibaura Institute of Technology Saitama: K.YoshidaK.Yoshida

CERN: CERN: D. Macina, A.L. PerrotD. Macina, A.L. Perrot


LHCf: LHC “forward” experiment

• The smallest of the six LHC experiments.

• LHCf is fully dedicated to High Energy Cosmic Rays (HECR) Physics.

• Experimental observation of HECR (E > 1014 eV) achieved only through Extensive Air Showers (EAS).

• LHCf will provide useful data to calibrate the hadronic interaction models used in Monte Carlo simulations of EAS.

LHCf:Calibration of hadronic Monte Carlo

used in HECR Physics with data collected at LHC


• Hadronic Monte Carlo codes need tuning with beam-test data.

• In this forward region the highest energy measurements of π0 production cross section were obtained by UA7 at SppS: Elab = 1014 eV.

• For LHCf: √s = 14 TeV → Elab = 1017eV

EAS: Extensive Air Showers

• Determination of E and M of HECR primary depends on comparison between Monte Carlo and experimental description of EAS.

• The dominant contribution to the energy flux is in the very forward region ( ≈ 0) and mainly depends on the first hadronic interaction.


Cosmic ray spectra at GZK cutoff

GZK cutoff (1020 eV) would limit energy to 1020eV for protons, due to Cosmic Microwave Backgroundp γ(2.7K) → Δ → N π

Different results between different experiments.Agasa points toward super-GZK events (and therefore exotic physics).

Based on data presented at the 30th ICRCMerida (Mexico).Figure prepared by Y. Tokanatsu


Importance of Monte Carlo tuning

Same data after arbitrarily scaling energy:

AGASA x 0.9HiRes x 1.2Yakutsk x 0.75Auger x 1.2

AGASA energy systematics 18% of which10% from hadron interaction model (QGSJET, SYBILL)

Berezinsky 2007 Berezinsky 2007


HECR composition

The depth of the shower maximum Xmax in the atmosphere depends on energy and type of primary particle.

Different hadronic interaction models give different answers about the composition of HECR.

Unger, ECRS 2008Unger, ECRS 2008

2.LHCf experimental setup


LHCf experimental setup• Two independent electromagnetic calorimeters equipped with different position sensitive layers,

on both sides of IP1.• Measure energy and impact point of γ from π0 decays and neutrons from pp interaction with “very-

forward” kinematics: pseudorapidity η > 8.4 or, equivalently, angle from beam axis θ < 450 μrad.

140 m 140 m

n π0

γ

γ

”Arm 1”:

W absorber + scintillator layers.

Scintillating fibers.

”Arm 2”:

W absorber + scintillator layers.

Silicon microstrips.ATLAS interaction point (IP1)

8 cm 6 cm


LHCf experimental setup

• Each “arm” is installed in the “Total Absorber for Neutral particles” (TAN) 140 m away from IP 1.

• Here the beam pipe splits in 2 separate tubes.

• No background from charged particles, swept away by magnets (dipole D1).

Charged particles

Neutral particlesIP 1

Protons - Beam 2

Protons - Beam 1

Arm 1

TAN

Arm 1 (or 2)

9.6 cm


beam axis

4 cm

2 cm

“Arm 1” detector

2 towers stacked vertically with 5 mm gap.

Calorimeter:17 W layers (7 mm or 14 mm thick);16 scintillator layers (3 mm thick).

Total thickness 22 cm:44 X0

1.7 λI

Tracking: 4 X-Y double layers of scintillating fiber (SciFi, 1mm cross-section) at 6, 10, 30, 42 X0.


“Arm 2” detector

Tracking: 4 X-Y double layers of Si microstrips (read-out pitch 160 μm) positioned at 6, 12, 30, 42 X0.

beam axis

3.2 cm

2.5 cm

2 towers stacked on their edges and offset from one another.Same structure of calorimetric layers as Arm 1.


Arm 2 assembly

W layer

scintillatorand light guide

Si microstripsensor

fiberglass pitch adapter

front-end hybrid

Si X Si Y (on opposite side)


Arm 2 assembly

Si microstrip sensor scintillator layer (2 towers)


Assembled LHCf

9 cm29 cm

Arm 1 Arm 2

3.LHCf physics performances


Arm 2: maximization of the acceptance in R (distance from beam center)

Transverse projection in the TAN slot

Dimensions in mm

Arm 1: maximization of the acceptance for vertical beam crossing angle (it can be moved down by 2 cm)

Both detectors are kept at +12 cm (“garage”) when beam is not stable, to minimize radiation damage of scintillators


140

0

Detectable kinematics for γ (Arm 1)

detectable kinematics limited by the projection of dipole D1 vacuum pipe on the detector impact plane (first W layer)

kinematics depend on beam vertical crossing angle at IP1

expected background (beam-gas/pipe) < 1%


Detector acceptance vs. γ impact point

0 rad beam crossing angle

of the γ impact point

of the incoming γ

Effective geometrical acceptance depends on impact point on detector. Detectors can be moved up/down by few cm to efficiently cover the whole kinematic range allowed by D1 projection.

Arm 1

Arm 2

Fraction of showers fully contained in the fiducial acceptance volume (2 mm cut on lateral tower edge) for 0μrad beam vertical crossing angle.It does not depend on energy.


Position resolution for EM shower

σX = 40 μm σY = 64 μm

X position (mm) Y position (mm)

num

ber o

f eve

nts

num

ber o

f eve

nts

Position of shower centre on Arm 2 first Si module for 200 GeV electrons

Similar results for Arm 1 first module (SciFi): σ ≈ 170 μm (with a design requirement < 200 μm)

Measured at SPS beam test by using auxiliary tracking system (ADAMO) with few μm resolution


Position resolution for EM shower

Measured position resolution improves with energy

With impact point:- transverse momentum;- correction for lateral shower leakage (ρMol (W) = 9 mm).NOTE: correction is independent from energy.

Measured energy before and after correction (SPS beam test data)

Arm 2 (Si)

fiducial volume

MIP

equ

ival

ent

part

icle

sM

IP e

quiv

alen

t pa

rtic

les


Energy resolution for EM shower

Measured at SPS beam test with electrons.

Energy defined as sum of signals over all the scintillator layers, after applying fiducial volume cut and leakage correction.

Excellent agreement between simulation and beam-test data for two different PMT gain settings.

Resolution improves with energy.

Linearity of read-out for all scintillator layers and different PMT gains was characterized with laser light up to 2x105 MIP equivalent particles.


Expected energy resolution for γ

Simulation for Arm 1 inner (smaller) tower.Simulation validated with beam test as previously shown.

5 %

only physics

physics + PMT (L.G.)

physics + PMT (H.G.)

By using different PMT gains (to avoid saturation of read-out stages), resolution is better than 5%

region of interest


Expected gamma energy spectrum on Arm 1 inner tower at beam centre

par

ticl

es/b

in (

arb

itra

ry u

nit

s)Model discrimination with γ

Quantitative discrimination with the help of a properly defined χ2 discriminating variable based on the spectrum shape.

- Simulation of 106 LHC interactions (i.e. 1 minute exposure at 1029 cm-2s-1 luminosity) with 5% energy resolution (conservative).- Discrimination between various models is feasible.


Model discrimination with neutronsExpected neutron energy spectrum on Arm 1inner tower at beam center Original n spectrum

Given the limited depth (1.7 λI) only n interacting in the first half of the calorimeter can be efficiently characterized

After introducing energy resolution

part

icle

s/b

in (

arbi

trar

y un

its)

contaminationfrom K0


Model discrimination with π0

Detector segmentation in two towers specifically designed for π0 → γγ identification.

Arm 1 in “normal”position Arm 1 moved

down by 1 cm

Detectable kinematics can be improved by moving down the towers.

gap betweentowers


Model discrimination with π0

Simulated reconstructed spectrum after 20 min at 1029 cm-2s-1 is in good agreement with original spectrum (using DPMJETIII).

Main systematic error comes from energy resolution (here assumed 5% conservatively).


Reconstructed π0 mass

Peak:134 ± 5 MeV

From simulation, expected mass resolution is better than 4%.

Performance verified at SPS beam test (350 GeV proton beam on C target) with worse conditions than LHC:- low γ energy (20 to 50 GeV);- direct protons in the towers;- multiple hits in the same tower.

π0 mass [MeV]

≈ 250 π0 events

Powerful tool:- absolute energy calibration;- reject background from randomly correlated γ pairs.

sigma: 8 MeVresolution: 6%

4.Preliminary resultsfor 2009 operation


LHCf 2009 operation

• From End of October 2009 LHC restarted operation.

• LHCf collected > 6000 shower events at 450+450 GeV in stable beam conditions with typically 4x4 or 5x5 bunch configuration.– effective running time ~ 1 day, peak luminosity at IP1 < 1027 cm-2s-1.

• To minimize radiation damage, LHCf is allowed to move to running position on beam axis from “garage” (+12 cm) only with stable beam.

• No stable beam at 1.2+1.2 TeV which means no data for LHCf at this energy for this year.


Arm 1 γ event in inner tower

lateral profileSciFi X

lateral profileSciFi Y

longitudinal profile(inner tower)

(outer tower)


Arm 2 γ event in inner tower


lateral profileSi microstrip X

lateral profileSi microstrip Y


Arm 2 neutron event in inner tower



γ/neutron discrimination

Discrimination achieved with longitudinal profile.

Here L(90%) and L(20%) expressed in X0.

L(90%) < 20 X0

for most γ.

photons

neutrons

Cut with 99%hadron rejection power(verified at beam test with protons)


Arm 1 preliminary γ plots

Collision data are identified by coincidence with signal of “bunch crossing” at IP1.“Single bunch” data are background from beam-gas or beam-pipe interactions.

Dipole D1 shadow affects only particles coming from IP1

dN/(d

E*B

C)


Arm 2 preliminary γ plots

dN/(d

E*B

C)

Different profiles of two data samples point out their different origin (IP1 collision or beam background).

5.Future programme


LHCf future running scenario

• After LHC restarts in February 2010, LHCf will take data for 1.2+1.2 TeV and 3.5+3.5 TeV collisions.

• LHCf will be removed when luminosity becomes too high (>1031 cm-2s-1, with integrated luminosity 2 pb-1).

• LHCf will be reinstalled when beam energy reaches 5+5 TeV (end 2010).

• A second removal and a subsequent third installation are foreseen for 7+7 TeV collisions.

• Why remove LHCf? Its scintillator and SciFi layers are designed to run during beam commissioning (low luminosity).


Study of scintillator radiation damage

scintillators andSciFi used in LHCf

at 1 kGy light outputis reduced by 20%


Luminosity and radiation damage

• Initial LHC schedule implied a fast, low-luminosity energy ramp up to 7+7 TeV, but now long high-luminosity runs at lower energies are scheduled.

• 1 kGy total absorbed dose is reached, with detectors in running position, with an integrated luminosity of 2 pb-1 for 3.5+3.5 TeV collisions.

• At 1030 cm-2s-1 this means ~ 1 month effective running time (but: with such luminosity, few hours are already sufficient to collect enough statistics).

• Garage position is used when beam not stable (dose is reduced by 103).

• Light output and transparency is continuously calibrated by sending laser pulses from ATLAS underground counting room (USA15) to the scintillator layers.


Improve LHCf radiation hardness

• A new detector concept is being prepared for the second LHCf installation.

• Plastic scintillator will be replaced by GSO (rad-hard).

• The order and number of silicon X-Y double layers will be changed to improve the energy measurement with the Si system and use it as cross-check for scintillator measurement.

• The new detector will be precisely calibrated with a dedicated beam test before installation.


(whole calorimeter)

γ energy measurement with Si layers

Showers from γ mostly develop in the first half of the detector, where currently there are 2 Si double layers (at 6 and 12 X0).


Conclusions

• LHCf is an interesting link between High Energy Cosmic Rays and accelerator physics.

• LHCf is working very fine and already got its first data at LHC.

• With more statistics and increase of beam energy, as foreseen for the first months of 2010, it will be possible to publish the first spectra and begin discriminating among different Monte Carlo models.

status and physics programme of lhcf experiment sergio ricciarini for the lhcf collaboration...

Documents

lhcf physics performances4

lhcf experimental setup3

measure energy

energy flux

hadronic monte carlo

hecr primary

exotic physics

physics motivations2