recent results from the opera experiment
DESCRIPTION
Recent results from the OPERA experiment. Maximiliano Sioli (Bologna University and INFN) on behalf of the OPERA Collaboration SLAC Experimental Seminar - June 22, 2010. The OPERA Collaboration. Belgium IIHE Brussels Bulgaria Sofia Croatia IRB Zagreb - PowerPoint PPT PresentationTRANSCRIPT
Recent results from theOPERA experiment
Maximiliano Sioli (Bologna University and INFN)on behalf of the OPERA Collaboration
SLAC Experimental Seminar - June 22, 2010
The OPERA CollaborationBelgiumIIHE BrusselsBulgariaSofiaCroatiaIRB ZagrebFranceLAPP Annecy, IPNL Lyon, IRES StrasbourgGermanyHamburg, Münster, RostockIsraelTechnion HaifaItalyBari, Bologna, LNF Frascati, L’Aquila, LNGS, Naples, Padova, Rome La Sapienza, SalernoJapanAichi, Kobe, Nagoya, Toho, UtsunomiyaKoreaJinjuRussiaINR Moscow, NPI Moscow, ITEP Moscow, SINP MSU Moscow, JINR Dubna, ObninskSwitzerlandBern, ZurichTurkeyMETU Ankara
2M. Sioli - SLAC Experimental Seminar - June 22, 2010
Outline
• Introduction• The OPERA experiment
– The physics case– Detector description
• Experimental results– Oscillation physics
First nt candidate event
– Non-Oscillation physics Atmospheric muon charge ratio
• Conclusions
3M. Sioli - SLAC Experimental Seminar - June 22, 2010
Sub. to Physics Letters B (Acc 11/Jun/2010)arXiv:1006.1623
Published in EPJC 67 (2010) 25.arXiv:1003.1907
Introduction
• The OPERA experiment was mainly designed to unambiguously prove the oscillation phenomenon through direct nt appearance– Definitely close of the discovery phase of neutrino
oscillations• The detector - although optimized for beam
neutrino detection - can also be exploited for non-oscillation studies– Cosmic ray physics at the Gran Sasso Lab.
M. Sioli - SLAC Experimental Seminar - June 22, 2010 4
OPERAOscillation Project with Emulsion tRacking Apparatus
5
Long baseline neutrino oscillation experiment:search for tau neutrino appearance at Gran Sasso laboratory
in a quasi-pure muon neutrino beam produced at CERN (732 km)
First direct observation of nm ↔ nt oscillation
M. Sioli - SLAC Experimental Seminar - June 22, 2010
CNGSCERN Neutrino to Gran Sasso beam
• Protons from SPS: 400 GeV/c• Cycle length: 6 s• 2 extractions separated by 50 ms• Pulse length: 10.5 ms• Beam intensity: 2.4 1013
proton/extr.
732 km
6M. Sioli - SLAC Experimental Seminar - June 22, 2010
dEEEEPEMNN CCDA )()()()(
ttm
m nnnnt
CNGS beam optimized for nt appearance, i.e. optimized for the maximal number of nt charged current interactions: nm flux spectrum above t threshold. Taken into account the nt CC cross section.
nm flux “off peak” w.r.t the maximum oscillation probability.
“off peak”
CNGSCERN Neutrino to Gran Sasso beam
Beam main features
L 732 km<En> 17 GeV
(ne+ne)/nm 0.87%nm / nm 2.1%nt
promptnegligibl
e )E
LΔm.(θ)νtP(νm
2232
232 271sin)2(sin»
Limiting for nm ne searches
7M. Sioli - SLAC Experimental Seminar - June 22, 2010
CNGS PERFORMANCE
8
2006 0.076x1019 pot no bricks Commissioning
2007 0.082x1019 pot 38 ev. Commissioning
2008 1.78x1019 pot 1698 ev. First physics run
2009 3.52x1019 pot 3693 ev. Physics run
2010 0.60x1019 pot (23 May) 579 ev. Physics run2010
2009
2008
5970 events collected until 23 May 2010 (within 1 in agreement with expectations)
Improving features, high CNGS efficiency (97% in 2008-2009)
2010: close to nominal year; Multi Turn Extraction routinely running
Aim at high-intensity runs in 2011 and 2012
DaysM. Sioli - SLAC Experimental Seminar - June 22, 2010
9
Detection of the nt appearance signal
Two conflicting requirements:
Large mass ~O(kton) High granularity ~1mm resolution
The challenge is to discriminate nt interactions
from nm interactions:identify t leptons via their
decay topology
nm
nm
m-
Decay “kink”
nt
n
t-
~1 mm
nm oscillation
m-
m- nt nm
h- nt n(po)
e- nt ne
p+ p- p- nt n(po)
B. R. ~ 17%
B. R. ~ 50%
B. R. ~ 18%
B. R. ~ 14%
dEEEmEPEMNN CCDA )()(),()( 2
ttm
m nnnnt
signal selection background rejection
ECC concept adopted
M. Sioli - SLAC Experimental Seminar - June 22, 2010
10
Emulsion Cloud Chamber concept
8.3 Kg
The brick is the target basic component: 57 nuclear emulsion films interleaved by 1 mm thick lead plates
125.1 mm
99.8 mm Emulsion Resolution:dx = 1 µm dq = 2 mrad
ECC = sequence of emulsion-lead layers
High resolution and large mass in a modular way.
Total number of bricks: ~150000 (1350 tons)
M. Sioli - SLAC Experimental Seminar - June 22, 2010
11
Tracks in OPERA emulsions
Passing-through tracks rejection
Vertex reconstruction in the brick
Track segment: aligned clusters
44 mm
15 tomographic views
Track segments found in 8 consecutive plates
Automated emulsion scanning: based on the tomographic acquisition of emulsion layers.
44 mm
Scanning speed: 20 cm2/h
Field of view
390 μm × 310 μm
M. Sioli - SLAC Experimental Seminar - June 22, 2010
12
20m
10m
10m
nTarget sections (6.7 m2):29 brick walls (77500 bricks)31 Target Tracker walls (TT)
Magnetic spectrometers (6×10 m2):22 RPC planes 6 drift tube planesB = 1.55 T
Total target mass = 1.35 ktons
Brick selectionCalorimetry
Target SuperModule(side view)OPERA general structure
M. Sioli - SLAC Experimental Seminar - June 22, 2010
13
SM2
Veto plane (RPC)
High Precision Tracker(6 drift tube stations)
Bricks (lead + emulsions) and Target Tracker (plastic scintillators)
Instrumented dipole magnet (22 RPC planes in total)
The OPERA detector
M. Sioli - SLAC Experimental Seminar - June 22, 2010
14
Detector concept
0 max
p.h.
The brick is the solution to the requirements of high granularity and large mass.Need of electronic detectors in order to: trigger for a neutrino interaction locate the candidate brick muon identification and momentum/charge measurement
hybrid detector needed
n
On-line analysis of electronic data Brick finding algorithm Pb/Em. brick
8 cm
M. Sioli - SLAC Experimental Seminar - June 22, 2010
Selected brick is removed from the target and exposed to cosmic rays (alignment). Emulsions are developed and sent to scanning stations / labs
15
The first nt candidate
A. Ereditato - LNGS - 31 May 2010 16
OPERA nominal analysis flow applied to the hadronic kink candidates:
• kink occurring within 2 lead plates downstream
• kink angle larger than 20 mrad
• daughter momentum higher than 2 GeV
• decay Pt higher than 600 MeV, 300 MeV if ≥ 1 gamma pointing to the decay vertex
• missing Pt at primary vertex lower than 1 GeV
• Azimuthal angle between the resulting hadron momentum direction and the parent track direction larger than p/2 radians
ANALYSIS
A. Ereditato - LNGS - 31 May 2010 17
po mass r mass
1st g and 2nd g 90 ± 30 MeV 515 +110-60 MeV
(1stg+3rdg) and 2nd g
110 ± 40 MeV 560 +110-60 MeV
Invariant mass reconstruction
• The event passes all cuts, with the presence of at least one gamma pointing to the secondary vertex, and is therefore a candidate to the t -> 1-hadron decay mode.
• The presence of the charged prong and of two gammas pointing to the secondary vertex allows to attempt to the reconstruction of the r(770) invariant mass from the
t -> p- p0 nt decay mode
• According to the gammas assignment scheme shown before, we have then:
A. Ereditato - LNGS - 31 May 2010 18
We observe 1 event in the 1-prong hadron topology with a background expectation (assuming a conservative 50% error) of:
0.011±0.005 (syst) events 1-prong (hadron re-interaction) 0.007±0.003 (syst) events 1-prong (charm) 0.024±0.012 (syst) events 3-prongs, m and e decay channels
Considering all decay modes the probability to observe 1 event due to background fluctuations is 4.3%. This corresponds to a statistical significance of 2.03 on the measurement of a first t candidate event in OPERA.
Considering the 1-prong channel only, the background fluctuation has a probability of 1.9%, for a significance of 2.35
OPERA as a cosmic ray detector
M. Sioli - SLAC Experimental Seminar - June 22, 2010 19
Gran Sasso underground lab: 1400 m of rock (3800 m.w.e) shielding, cosmic ray flux reduced by a factor 106 w.r.t. surface, very reduced environmental radioactivity.
OPERA vs previous and current underground experiments:a deep underground detector with charge and momentum reconstruction and excellent timing capabilities (~10 ns).Analyses under way:
Atmospheric neutrino induced muonsCoincidences among experiments (OPERA/LVD)Atmospheric muon charge ratio this talk
1400
m
Atmospheric muon charge ratio• The atmospheric muon charge ratio Rm ≡ Nm+/Nm-
is being studied and measured since many decades– Depends on the chemical composition and energy spectrum of the
primary cosmic rays– Depends on the hadronic interaction feautures– At high energy, depends on the prompt component
• It provides the possibility to check HE hadronic interaction models (E>1TeV) in the fragmentation region, where no data exists
• Since atmospheric muons are kinematically related to atmospheric neutrinos (same sources), Rm constitus a benchmark for atmospheric n computations (background for neutrino telescopes)
M. Sioli - SLAC Experimental Seminar - June 22, 2010 20
The physics of CR TeV muons
M. Sioli - SLAC Experimental Seminar - June 22, 2010 21
m
m
(ordinary) meson decay: dNm/d cosq ~ 1/ cosq
p
K
hadronic interaction: multiparticle production (A,E), dN/dx(A,E) extensive air shower
m
short-lifetimemeson production and prompt decay
(e.g. charmed mesons)Isotropic angular
distribution
detection: Nm(A,E), dNm/dr
transverse size of bundle PT(A,E)
TeV muon propagation in the rock: radiative processes andfluctuations
Primary C.R. proton/nucleus: A, E, isotropic
Analytic predictions• Naive prediction:
– Since charged multiplicity grows with the energy, the extra-charge of the primary proton is diluited and Rm 1 in the HE limit (WRONG!)
• A more elaborate model:– Suppose only primary protons with a spectrum dN/dE = N0E-(1+g)
– Suppose only pions and neglect decays (HE limit)– Consider the inclusive cross-section for pions
– The pion spectrum is then
M. Sioli - SLAC Experimental Seminar - June 22, 2010 22
p
pppp
Ed
dEEEf pinelpp
pp
),(
),()()( )1(pp
E
EEfdEEE
constE ppg
pp
p
p
-
p
p (primary)air
nucleus
– This expression can be simplified under the assumption
and becomes
– Finally we have
Analytic predictions (cont’d)
M. Sioli - SLAC Experimental Seminar - June 22, 2010 23
)(),(~
xfEd
dEEEf pEp
inelpp
pp
pp
pppp
Feynmanscaling
- p
gppp
pZEconstE )1()()( -
1
0
1~
)( dxxxfZ ppg
pp
SpectrumWeightedMoments
-
-
-
p
p
p
p
m
mm p
pmm
p
p
Z
Z
EE
EE
R)()(
)()(
Interpretation of the result• Interpretation of the result
– The result is valid only in the fragmentation region, since in the central region Feynman scaling is strongly violated
– But the steeply falling primary spectrum (g ~ 2.7) in the SWM suppresses the contribution of the central region in the secondary production scaling holds (at least for E < 1 TeV);In other words: each pion is likely to have an energy close tothe one of the projectile (primary CR proton) and comes fromits fragmentation (valence quarks) positive charge
– Rm does not depend on Ep (or Em) nor on the target nature– Rm depends on the primary spectrum g
M. Sioli - SLAC Experimental Seminar - June 22, 2010 24
Neutrons in the primary flux• Further refinements
– Introducing the neutron component in the primary flux (in heavy nuclei) and considering the isospin symmetries:
one obtains:
M. Sioli - SLAC Experimental Seminar - June 22, 2010 25
-- pppp npnp
ZZZZ ,
82.0)np/()np( 00000 »-d
)ZZ/()ZZ1()ZZ/()ZZ(
where
22.111R
pnpppnpp
pppp
0
0
--
-
»d-d
-- pppp
Proton excess
Kaon contribution• At higher energy (>100 GeV) the
contribution of K becomes important• In general, the contribution of each
component to the muon flux Npar = (p, K, charmed, etc.) depends on the relative contributionof decays and interaction probabilities:
where
M. Sioli - SLAC Experimental Seminar - June 22, 2010 26
-
parN
i ii
Nii
NN
N
bZa
Z 1 )(/11)(
qm
mm E
E
)1)(1()()1()(
1
--
gmg
g
i
iii r
iBrraa
)/log)(1)(1())(1)(2()( 2
1
Niii
Niiii r
rbbg
gg g
g
---
2)/( ii mmr m
i = i(q) is the “critical energy”, i.e. the energy above which interactions dominate over decays. Along the vertical (q = 0o) i(0)= mich/ti (h = 6.5 km)
p 115 GeV K 850 GeVX > 107 GeV
q = 0o
q = 60op K
Kaon contribution to Rm
• However, for kaons:
Because of their strangeness (S = +1), K+ and K0 can be yielded in association with a leading barion Λ o Σ. On the other hand, the production of K−,K0 requires the creation of a sea-quark pair s − s together with the leading nucleon and this is a superior order process.
• This leads to a larger Rm ratio at high energy
M. Sioli - SLAC Experimental Seminar - June 22, 2010 27
-- KKK»>> pnp ZZZ
General form for Rm
• Let us consider again the general form for the muon flux
where we have explicited the i(q) dependence on q
where q* is the zenith angle at the production point• The correct variable to describe the evolution of Rm is
therefore Emcosq*
• The Rm evolution as a function of Emcosq* spans over the different sourcesRm = wpRm
p + wKRmK + wcharmRm
charm +…
M. Sioli - SLAC Experimental Seminar - June 22, 2010 28
-
parNi
N
i ii
i
NN
N
bZa
Z 1* )0(/cos11
)(qm
mm E
E
*cos/)0()( qq ii Earth
q*q
POWERFUL HANDLE TODISCRIMINATE MODELS
OPERA (2009): Emcosq ≈ 2000 GeV The (magnetized) experiment withthe largest Emcosq
Cosmic-event reconstruction
• Cosmic-event tagging:– Outside the CNGS spill window
• Dedicated pattern recognition and track finding/fitting:– Cosmic events are passing-through– Cosmic events comes from all directions– Cosmic events may have multiple parallel tracks (in
OPERA 5% of the events are muon bundles)– Different reconstruction philosophy
M. Sioli - SLAC Experimental Seminar - June 22, 2010 29
Pattern recognition• Tracking philosophy
– we know a priori which is the target: single tracks or bundle of tracks almost parallel (RMS is ~1 deg, mainly due to MCS in the overburden)
• Hybrid strategy– global method (Hough Transform) to individuate the event direction– scan the Hough Space and select the slope corresponding to the
maximum used to set the qslice of the slice– local method (pivot points) on slices around the direction
“resolutions” < 1 degboth for zenith andazimuth directionreconstruction
M. Sioli - SLAC Experimental Seminar - June 22, 2010 30
q
Pattern recognition (cont’d)
Real double muon event
31M. Sioli - SLAC Experimental Seminar - June 22, 2010Z
original coordinate plane
q
r1
2
3
Y
ypeak
r
y
Track finding and fitting• Within each slice, build straight lines defined by all possible
couples of external points (pivot points), then search for points aligned with the previous two according to pre-defined tolerances
• Fit the selected points and iterate the procedure to merge or reject extra points
• “resolutions” < 1 deg both for zenith and azimuth direction reconstruction
• Merge the tracks inthe XZ and YZ views 3D track
M. Sioli - SLAC Experimental Seminar - June 22, 2010 32
q
PT track reconstruction
M. Sioli - SLAC Experimental Seminar - June 22, 2010 33
3D tracks are used to “guide”track finding and fitting in the PTsystem: Find the line tangent to the
drift circles with the best c2
250 mm position resolution 0.15 (1) mrad angular resolution
for doublets (singlets) for = 0 (improve for > 0)
Residuals ~250 mm
• In each side of the magnet arm we can reconstruct an independent angle j, j=1,...,6.• Each j can be reconstructed with one station (singlets) or two stations (doublets)• We compute k = i – j , k=1,...,4, angle differences between adjacent station-pairs
– 55% of ’s comes from doublets– 9% from singlets– 36% are mixed
34
Momentum reconstruction
M. Sioli - SLAC Experimental Seminar - June 22, 2010
2
2
11
]/)/(exp[1)/(
xz
yzk s
sBedxdE
dxdElp
-
l
B ≡ Bd/l = effective magnetic field
B B
Charge reconstruction
• Charge is reconstructed according to the sign• If each track contributes to multiple angles, a
weighted average is computed– weights = angular experimental errors
M. Sioli - SLAC Experimental Seminar - June 22, 2010 35
4
1
4
1
kk
kkk p
p
4
1
4
1
kk
kkkq
q
k)(1
2 qd
where
• Consider the magnetic field bending and the total deflection spoiling (detector + MCS)
• Requiring />1 we obtain (for =0):– pmax(doublets) = 1.25 TeV
– pmax(singlets) = 190 TeV– pmax(mixed) = 260 TeV
Maximum Detectable Momentum
M. Sioli - SLAC Experimental Seminar - June 22, 2010 36
0
222 0136.021 X
dp
pBd
B3.0
Exact computation at all angles (MC) ~500 GeV/c
Charge mis-identification
M. Sioli - SLAC Experimental Seminar - June 22, 2010 37
Rm = (1.9 ± 0.9) %
Cross-check with beam data
pm
Monte Carlo simulation
• MC simulation used for different purposes:a) Calibrate and correct (unfold) experimental datab) Estimate surface muon energy and
primary-cosmic-ray related quantities• Two MCs used:
a) Parametrized generator- Fast but approximate
b) Full Monte Carlo simulation- Slow but reliable
M. Sioli - SLAC Experimental Seminar - June 22, 2010 38
Monte Carlo simulation (MC1)Generates multiple muon events at the level of the Underground Halls of the LNGS Laboratory
– each primary type and its energy are sampled according to the composition model (MACRO-fit model)
– the direction is sampled isotropically and the corresponding amount of rock overburden is computed (from Gran Sasso map)
– given the primary type, its energy, the direction and the rock, the probability to have nm muons at underground level is computedusing tables obtained from a full MC simulation, the same used to derive the primary composition model SELF-CONSISTENCY
– Then the residual energy for each muon is computed from a parameterized function [PRD 44 (1991) 3543]
– The lateral dispersion Rm of each muon w.r.t. the shower axis is again parameterized according to a full MC simulation
– The muon charge ratio is introduced by hand (Rm = 1.4)
M. Sioli - SLAC Experimental Seminar - June 22, 2010 39
Muon flux
)%3.09.95(1
MC
DATA
RateRate
Monte Carlo simulation (MC2)
M. Sioli - SLAC Experimental Seminar - June 22, 2010 40
• Based on the FLUKA code• Full simulation chain:
– Detailed geometry description (atmosphere, mountain)
– HE hadronic interactions (h-N and N-N) handled by DPMJET
– Primary composition model from APP 19 (2003) 193
– Predictive of the atmosperic muon charge ratio
• Usage:– Surface muon energy estimation– Link between underground variables and
primary cosmic ray parameter
Aknee
A2
Aknee
A1
EE,EKdEdN
EE,EKdEdN
A2
A1
>
g-
g-
EEcut
g~2.7÷3Ecut~3000 TeV
Data pre-selection• Data taken during 2008
CNGS physics run:– from June 18th until November
10th 2008
• The data acquisition was segmented in “extraction periods”of ~12 hours each.
• Each “extraction” wasselected or rejected on the basis of:
– Run stability– Global distributions (see
figure)
• Livetime: 113.4 days• Total number of events:
403069
M. Sioli - SLAC Experimental Seminar - June 22, 2010 41
Data reduction
A set of progressive cuts applied in order to isolate a clean data sample:a) at least one reconstructed angle
(acceptance cut)b) Remove events with large number of PT hits (clean
PT cut)c) Remove events with bendings smaller than the
experimental resolution (deflection cut)c’) Remove events with very large bendings
(effective for pm<5 GeV/c)
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Clean PT cut
Remove events with a large number of PT tubes fired (d-rays, secondary interactions, electronic noise etc) can induce wrong matching
M. Sioli - SLAC Experimental Seminar - June 22, 2010 43
M = M() N’ = N - M()
Deflection cut
Tracks with a bending below the experimental resolution are removed:
/ > n, n=3
M. Sioli - SLAC Experimental Seminar - June 22, 2010 44
The robustness of the cut with respect to n was checked, i.e. the results do not depend on n, when n>2
Deflection cut: effects on and h
M. Sioli - SLAC Experimental Seminar - June 22, 2010 45
m+m-
m+m-
w/o deflection cut
with deflection cut
The charge mis-identification h is stronglyreduced.Possible differences between MC andreal h is a source of systematic uncertaintyon Rm will be reported later
h ~ 3%
Data reduction - statistics
M. Sioli - SLAC Experimental Seminar - June 22, 2010 46
DATA MC
evt/day f1 f2 evt/day f1 f2
Acceptance 992 100.0% - 1222 100.0% -
Clean PT 515 51.9% - 959 78.5% -
Deflection 391 39.4% 76.0% 708 58.0% 73.8%
Single m 379 38.2% 96.9% 673 55.1% 95.1%
Multiple m 12 1.2% 3.1% 35 2.9% 4.9%
Quality cuts vs reconstructed pm
M. Sioli - SLAC Experimental Seminar - June 22, 2010 47
No cuts Clean PT
<100 mrad / > 3
Alignment of the PT system• Rm strongly depends on the alignment precision of the PT system• Two stages of correction:
– Mechanical: gross corrections using a theodolite– Cosmic rays: finer corrections using HE muons
(with and w/o magnetic field)• Mis-alignment may have different contributions:
– Global: each PT station can be roto-translated as a whole w.r.t. the master reference frame
• Accounted for with the present statistics– Local: each PT station may have distortions which vary from point-to-
point• Not yet accounted for with the present statistics
M. Sioli - SLAC Experimental Seminar - June 22, 2010 48
Alignment of the PT systemPhase1: Align two stations of a doublet treating them as rigid bodies
- first shifts, in x, y and z- then rotation, in x, y and z
Phase2: Align two doublets on both sides of an iron arm using CR data w/o magnetic field
Phase3: Estimate bending effects
M. Sioli - SLAC Experimental Seminar - June 22, 2010 49
Underground muon charge ratio
• Rm computed separately for the three categories and then unfolded:
• Finally compute Rmunf as the weighted average of the 3 samples:
M. Sioli - SLAC Experimental Seminar - June 22, 2010 50
Nm+ Nm- Rmmeas h Rm
unf
Doublets 13595 9993 1.360 ± 0.018 0.0165 ± 0.0012 1.375 ± 0.019
Mixed 8951 6603 1.355 ± 0.022 0.0403 ± 0.0022 1.393 ± 0.025
Singlets 2181 1704 1.28 ± 0.06 0.064 ± 0.005 1.33 ± 0.05
Rm = 1.377 ± 0.014
)1()1(
hhhh
m
mm --
-- meas
measunf
RR
R 2
2222
)]1([)()1()()21(
hhdhdh
dm
mmm --
-- meas
measmeasunf
RRR
R
Rm computed separately for single and multiple muon events– check of the hypotheis of “diluition” of Rm when proton-Air and
neutron-Air interactions change their relative contributions– in practice: compute Rm when the 3D
multiplicity is > 1, independently on the number of measured charges in the event
Underground muon charge ratio
M. Sioli - SLAC Experimental Seminar - June 22, 2010 51
Nm ‹A› ‹E/A›primary[TeV]
H fraction Np/Nn Rmunf
(2008)= 1 3.35 ± 0.09 19.4 ± 0.1 0.667 ± 0.007 4.99 ± 0.05 1.377 ± 0.014
> 1 8.5 ± 0.3 77 ± 1 0.352 ± 0.012 2.09 ± 0.07 1.23 ± 0.06
Different at 2.4 level: first indication of a “diluition” effect
OK,nm=3
Systematic uncertainty on Rm
a) Mis-alignment of the PT system can be estimated with the “2-arm” test: consider tracks which cross
both arms of a spectrometer. Neglecting energy losses, the two deflections should be the same:
M. Sioli - SLAC Experimental Seminar - June 22, 2010 52
d() 1 - 2 = 0
d() 0.08 mrad
dRm 0.015
Systematic uncertainty on Rm
Consistency checks:• The 4 Rm values, computed separately for each magnet arm,
fluctuates around the average of 0.017, which is below their statistical accuracy (0.03)
• Run with inverted polarity (9 days): Rminverted = 1.39 ± 0.04
b) Charge mis-identification h• estimate dh = hdata – hMC for a subsample of events again with
the “2-arm” test, then extrapolate to the whole sample• the probability that 1 and 2 have opposite sign is related to h
through a function h = h(p), computed via MCdh = 0.007 dRm = 0.007
M. Sioli - SLAC Experimental Seminar - June 22, 2010 53
The total systematic uncertainty is dRmunf(syst) = +0.017, -0.015
Rm as a function of pm
• Rm was computed in bins of pm (underground momentum) and unfolded (bin migrations taken into account with the Bayes method)
• Evolution with pm is compatible with a constant
M. Sioli - SLAC Experimental Seminar - June 22, 2010 54
Rm = a0 + a1 log10 pm
a0 = 1.29 ± 0.06a1 = 0.05 ± 0.03
Rm = c0
c0 = 1.379 ± 0.015
c2/dof = 2.47/1(compatible with a constant)
• The resolution on Em is dominated by fluctuations in the stochastic of the energy loss
• Different attempts to retrieve Em
– Use of the standard (approximate) formula:
– Back-propagation algorithm• Start from pm and back-propagate the track up to the surface, up
– Use of “crude” MC2• Build a table Em = f(h,pm)
Rm as a function of Emcosq*
M. Sioli - SLAC Experimental Seminar - June 22, 2010 55
EEEdhdE )()( -
mm /)/( - heEE (E) (E)
BEST PERFORMANCE
Rm as a function of Emcosq*
M. Sioli - SLAC Experimental Seminar - June 22, 2010 56
Fixing RKp = 0.149 (Gaisser):Rp = ZNp+/ZNp-= 1.229 ± 0.001RK = ZNK+/ZNK-= 2.12 ± 0.03
Analysis update
Further investigatio on the HE point:-Inclusion of 2009 run data-New estimation of the “surface muon energy”-New estimation of charge mis-identification h
Update with 2009 data (preliminary)
• From June 1st until November 23rd 2009: livetime 2009 = 123.2 days
M. Sioli - SLAC Experimental Seminar - June 22, 2010 58
nm ‹A› ‹E/A›primary[TeV]
H fraction Np/Nn Rmunf
(2008)Rm
unf
(2009)Rm
unf
(2008+2009)
= 1 3.35 ± 0.09 19.4 ± 0.1 0.667 ± 0.007 4.99 ± 0.05 1.377 ± 0.014 1.402 ± 0.014 1.392 ± 0.010
> 1 8.5 ± 0.3 77 ± 1 0.352 ± 0.012 2.09 ± 0.07 1.23 ± 0.06 1.20 ± 0.05 1.22 ± 0.04
Discrepancy now at 4.2 level
2008 data 2009 data
New estimation of the “surface muon energy”
• Same as before, but take the MPV of the Landau distribution instead of the mean better resolution and residuals well centered
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h (bin 2)
pm (bin 3)
Emsurface
MPV
Log10(h)
Emsurface(GeV)
Log10(pm/GeV)
New estimation of the “surface muon energy”
• Using MC2 the proper binning was computed:
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5 bin in log10(Emcosq*) : 2.9 – 4.2(bin width = 2*RMS = 0.26)
New estimation of charge mis-identification h
• Due to the increased statistics, it is now possible to use only doublet data, for which the charge mis-identification can be extracted directly from data (2-arm test)
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Re-evaluation of muon Rm vs Emcosq*
• The anomaly in the HE point still present.
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Independenton pm
max!
New fit with world survey
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Fixing RKp = 0.149 (Gaisser):Rp = ZNp+/ZNp-= 1.219 ± 0.001RK = ZNK+/ZNK-= 2.43 ± 0.04
Conclusions
• First…
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Spares
Brick Assembling Machine
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Alignment: phase 1
67
Alignment: phase 1, results
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Alignment: phase 2 (rotations)
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Alignment: bendings
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CR stability as a function of data taking
Event number 71M. Sioli - SLAC Experimental Seminar - June 22, 2010